/**
 * vis.js
 * https://github.com/almende/vis
 *
 * A dynamic, browser-based visualization library.
 *
 * @version @@version
 * @date    @@date
 *
 * @license
 * Copyright (C) 2011-2014 Almende B.V, http://almende.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy
 * of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
!function(e){if("object"==typeof exports)module.exports=e();else if("function"==typeof define&&define.amd)define(e);else{var f;"undefined"!=typeof window?f=window:"undefined"!=typeof global?f=global:"undefined"!=typeof self&&(f=self),f.vis=e()}}(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);throw new Error("Cannot find module '"+o+"'")}var f=n[o]={exports:{}};t[o][0].call(f.exports,function(e){var n=t[o][1][e];return s(n?n:e)},f,f.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
/**
 * vis.js module imports
 */

// Try to load dependencies from the global window object.
// If not available there, load via require.

var moment = (typeof window !== 'undefined') && window['moment'] || require('moment');

var Hammer;
if (typeof window !== 'undefined') {
  // load hammer.js only when running in a browser (where window is available)
  Hammer = window['Hammer'] || require('hammerjs');
}
else {
  Hammer = function () {
    throw Error('hammer.js is only available in a browser, not in node.js.');
  }
}

var mousetrap;
if (typeof window !== 'undefined') {
  // load mousetrap.js only when running in a browser (where window is available)
  mousetrap = window['mousetrap'] || require('mousetrap');
}
else {
  mousetrap = function () {
    throw Error('mouseTrap is only available in a browser, not in node.js.');
  }
}




// Internet Explorer 8 and older does not support Array.indexOf, so we define
// it here in that case.
// http://soledadpenades.com/2007/05/17/arrayindexof-in-internet-explorer/
if(!Array.prototype.indexOf) {
  Array.prototype.indexOf = function(obj){
    for(var i = 0; i < this.length; i++){
      if(this[i] == obj){
        return i;
      }
    }
    return -1;
  };

  try {
    console.log("Warning: Ancient browser detected. Please update your browser");
  }
  catch (err) {
  }
}

// Internet Explorer 8 and older does not support Array.forEach, so we define
// it here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/forEach
if (!Array.prototype.forEach) {
  Array.prototype.forEach = function(fn, scope) {
    for(var i = 0, len = this.length; i < len; ++i) {
      fn.call(scope || this, this[i], i, this);
    }
  }
}

// Internet Explorer 8 and older does not support Array.map, so we define it
// here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/map
// Production steps of ECMA-262, Edition 5, 15.4.4.19
// Reference: http://es5.github.com/#x15.4.4.19
if (!Array.prototype.map) {
  Array.prototype.map = function(callback, thisArg) {

    var T, A, k;

    if (this == null) {
      throw new TypeError(" this is null or not defined");
    }

    // 1. Let O be the result of calling ToObject passing the |this| value as the argument.
    var O = Object(this);

    // 2. Let lenValue be the result of calling the Get internal method of O with the argument "length".
    // 3. Let len be ToUint32(lenValue).
    var len = O.length >>> 0;

    // 4. If IsCallable(callback) is false, throw a TypeError exception.
    // See: http://es5.github.com/#x9.11
    if (typeof callback !== "function") {
      throw new TypeError(callback + " is not a function");
    }

    // 5. If thisArg was supplied, let T be thisArg; else let T be undefined.
    if (thisArg) {
      T = thisArg;
    }

    // 6. Let A be a new array created as if by the expression new Array(len) where Array is
    // the standard built-in constructor with that name and len is the value of len.
    A = new Array(len);

    // 7. Let k be 0
    k = 0;

    // 8. Repeat, while k < len
    while(k < len) {

      var kValue, mappedValue;

      // a. Let Pk be ToString(k).
      //   This is implicit for LHS operands of the in operator
      // b. Let kPresent be the result of calling the HasProperty internal method of O with argument Pk.
      //   This step can be combined with c
      // c. If kPresent is true, then
      if (k in O) {

        // i. Let kValue be the result of calling the Get internal method of O with argument Pk.
        kValue = O[ k ];

        // ii. Let mappedValue be the result of calling the Call internal method of callback
        // with T as the this value and argument list containing kValue, k, and O.
        mappedValue = callback.call(T, kValue, k, O);

        // iii. Call the DefineOwnProperty internal method of A with arguments
        // Pk, Property Descriptor {Value: mappedValue, : true, Enumerable: true, Configurable: true},
        // and false.

        // In browsers that support Object.defineProperty, use the following:
        // Object.defineProperty(A, Pk, { value: mappedValue, writable: true, enumerable: true, configurable: true });

        // For best browser support, use the following:
        A[ k ] = mappedValue;
      }
      // d. Increase k by 1.
      k++;
    }

    // 9. return A
    return A;
  };
}

// Internet Explorer 8 and older does not support Array.filter, so we define it
// here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/filter
if (!Array.prototype.filter) {
  Array.prototype.filter = function(fun /*, thisp */) {
    "use strict";

    if (this == null) {
      throw new TypeError();
    }

    var t = Object(this);
    var len = t.length >>> 0;
    if (typeof fun != "function") {
      throw new TypeError();
    }

    var res = [];
    var thisp = arguments[1];
    for (var i = 0; i < len; i++) {
      if (i in t) {
        var val = t[i]; // in case fun mutates this
        if (fun.call(thisp, val, i, t))
          res.push(val);
      }
    }

    return res;
  };
}


// Internet Explorer 8 and older does not support Object.keys, so we define it
// here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Object/keys
if (!Object.keys) {
  Object.keys = (function () {
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length;

    return function (obj) {
      if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) {
        throw new TypeError('Object.keys called on non-object');
      }

      var result = [];

      for (var prop in obj) {
        if (hasOwnProperty.call(obj, prop)) result.push(prop);
      }

      if (hasDontEnumBug) {
        for (var i=0; i < dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i]);
        }
      }
      return result;
    }
  })()
}

// Internet Explorer 8 and older does not support Array.isArray,
// so we define it here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/isArray
if(!Array.isArray) {
  Array.isArray = function (vArg) {
    return Object.prototype.toString.call(vArg) === "[object Array]";
  };
}

// Internet Explorer 8 and older does not support Function.bind,
// so we define it here in that case.
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind
if (!Function.prototype.bind) {
  Function.prototype.bind = function (oThis) {
    if (typeof this !== "function") {
      // closest thing possible to the ECMAScript 5 internal IsCallable function
      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
    }

    var aArgs = Array.prototype.slice.call(arguments, 1),
        fToBind = this,
        fNOP = function () {},
        fBound = function () {
          return fToBind.apply(this instanceof fNOP && oThis
              ? this
              : oThis,
              aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
  };
}

// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Object/create
if (!Object.create) {
  Object.create = function (o) {
    if (arguments.length > 1) {
      throw new Error('Object.create implementation only accepts the first parameter.');
    }
    function F() {}
    F.prototype = o;
    return new F();
  };
}

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
if (!Function.prototype.bind) {
  Function.prototype.bind = function (oThis) {
    if (typeof this !== "function") {
      // closest thing possible to the ECMAScript 5 internal IsCallable function
      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
    }

    var aArgs = Array.prototype.slice.call(arguments, 1),
        fToBind = this,
        fNOP = function () {},
        fBound = function () {
          return fToBind.apply(this instanceof fNOP && oThis
              ? this
              : oThis,
              aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
  };
}

/**
 * utility functions
 */
var util = {};

/**
 * Test whether given object is a number
 * @param {*} object
 * @return {Boolean} isNumber
 */
util.isNumber = function isNumber(object) {
  return (object instanceof Number || typeof object == 'number');
};

/**
 * Test whether given object is a string
 * @param {*} object
 * @return {Boolean} isString
 */
util.isString = function isString(object) {
  return (object instanceof String || typeof object == 'string');
};

/**
 * Test whether given object is a Date, or a String containing a Date
 * @param {Date | String} object
 * @return {Boolean} isDate
 */
util.isDate = function isDate(object) {
  if (object instanceof Date) {
    return true;
  }
  else if (util.isString(object)) {
    // test whether this string contains a date
    var match = ASPDateRegex.exec(object);
    if (match) {
      return true;
    }
    else if (!isNaN(Date.parse(object))) {
      return true;
    }
  }

  return false;
};

/**
 * Test whether given object is an instance of google.visualization.DataTable
 * @param {*} object
 * @return {Boolean} isDataTable
 */
util.isDataTable = function isDataTable(object) {
  return (typeof (google) !== 'undefined') &&
      (google.visualization) &&
      (google.visualization.DataTable) &&
      (object instanceof google.visualization.DataTable);
};

/**
 * Create a semi UUID
 * source: http://stackoverflow.com/a/105074/1262753
 * @return {String} uuid
 */
util.randomUUID = function randomUUID () {
  var S4 = function () {
    return Math.floor(
        Math.random() * 0x10000 /* 65536 */
    ).toString(16);
  };

  return (
      S4() + S4() + '-' +
          S4() + '-' +
          S4() + '-' +
          S4() + '-' +
          S4() + S4() + S4()
      );
};

/**
 * Extend object a with the properties of object b or a series of objects
 * Only properties with defined values are copied
 * @param {Object} a
 * @param {... Object} b
 * @return {Object} a
 */
util.extend = function (a, b) {
  for (var i = 1, len = arguments.length; i < len; i++) {
    var other = arguments[i];
    for (var prop in other) {
      if (other.hasOwnProperty(prop) && other[prop] !== undefined) {
        a[prop] = other[prop];
      }
    }
  }

  return a;
};

/**
 * Convert an object to another type
 * @param {Boolean | Number | String | Date | Moment | Null | undefined} object
 * @param {String | undefined} type   Name of the type. Available types:
 *                                    'Boolean', 'Number', 'String',
 *                                    'Date', 'Moment', ISODate', 'ASPDate'.
 * @return {*} object
 * @throws Error
 */
util.convert = function convert(object, type) {
  var match;

  if (object === undefined) {
    return undefined;
  }
  if (object === null) {
    return null;
  }

  if (!type) {
    return object;
  }
  if (!(typeof type === 'string') && !(type instanceof String)) {
    throw new Error('Type must be a string');
  }

  //noinspection FallthroughInSwitchStatementJS
  switch (type) {
    case 'boolean':
    case 'Boolean':
      return Boolean(object);

    case 'number':
    case 'Number':
      return Number(object.valueOf());

    case 'string':
    case 'String':
      return String(object);

    case 'Date':
      if (util.isNumber(object)) {
        return new Date(object);
      }
      if (object instanceof Date) {
        return new Date(object.valueOf());
      }
      else if (moment.isMoment(object)) {
        return new Date(object.valueOf());
      }
      if (util.isString(object)) {
        match = ASPDateRegex.exec(object);
        if (match) {
          // object is an ASP date
          return new Date(Number(match[1])); // parse number
        }
        else {
          return moment(object).toDate(); // parse string
        }
      }
      else {
        throw new Error(
            'Cannot convert object of type ' + util.getType(object) +
                ' to type Date');
      }

    case 'Moment':
      if (util.isNumber(object)) {
        return moment(object);
      }
      if (object instanceof Date) {
        return moment(object.valueOf());
      }
      else if (moment.isMoment(object)) {
        return moment(object);
      }
      if (util.isString(object)) {
        match = ASPDateRegex.exec(object);
        if (match) {
          // object is an ASP date
          return moment(Number(match[1])); // parse number
        }
        else {
          return moment(object); // parse string
        }
      }
      else {
        throw new Error(
            'Cannot convert object of type ' + util.getType(object) +
                ' to type Date');
      }

    case 'ISODate':
      if (util.isNumber(object)) {
        return new Date(object);
      }
      else if (object instanceof Date) {
        return object.toISOString();
      }
      else if (moment.isMoment(object)) {
        return object.toDate().toISOString();
      }
      else if (util.isString(object)) {
        match = ASPDateRegex.exec(object);
        if (match) {
          // object is an ASP date
          return new Date(Number(match[1])).toISOString(); // parse number
        }
        else {
          return new Date(object).toISOString(); // parse string
        }
      }
      else {
        throw new Error(
            'Cannot convert object of type ' + util.getType(object) +
                ' to type ISODate');
      }

    case 'ASPDate':
      if (util.isNumber(object)) {
        return '/Date(' + object + ')/';
      }
      else if (object instanceof Date) {
        return '/Date(' + object.valueOf() + ')/';
      }
      else if (util.isString(object)) {
        match = ASPDateRegex.exec(object);
        var value;
        if (match) {
          // object is an ASP date
          value = new Date(Number(match[1])).valueOf(); // parse number
        }
        else {
          value = new Date(object).valueOf(); // parse string
        }
        return '/Date(' + value + ')/';
      }
      else {
        throw new Error(
            'Cannot convert object of type ' + util.getType(object) +
                ' to type ASPDate');
      }

    default:
      throw new Error('Cannot convert object of type ' + util.getType(object) +
          ' to type "' + type + '"');
  }
};

// parse ASP.Net Date pattern,
// for example '/Date(1198908717056)/' or '/Date(1198908717056-0700)/'
// code from http://momentjs.com/
var ASPDateRegex = /^\/?Date\((\-?\d+)/i;

/**
 * Get the type of an object, for example util.getType([]) returns 'Array'
 * @param {*} object
 * @return {String} type
 */
util.getType = function getType(object) {
  var type = typeof object;

  if (type == 'object') {
    if (object == null) {
      return 'null';
    }
    if (object instanceof Boolean) {
      return 'Boolean';
    }
    if (object instanceof Number) {
      return 'Number';
    }
    if (object instanceof String) {
      return 'String';
    }
    if (object instanceof Array) {
      return 'Array';
    }
    if (object instanceof Date) {
      return 'Date';
    }
    return 'Object';
  }
  else if (type == 'number') {
    return 'Number';
  }
  else if (type == 'boolean') {
    return 'Boolean';
  }
  else if (type == 'string') {
    return 'String';
  }

  return type;
};

/**
 * Retrieve the absolute left value of a DOM element
 * @param {Element} elem        A dom element, for example a div
 * @return {number} left        The absolute left position of this element
 *                              in the browser page.
 */
util.getAbsoluteLeft = function getAbsoluteLeft (elem) {
  var doc = document.documentElement;
  var body = document.body;

  var left = elem.offsetLeft;
  var e = elem.offsetParent;
  while (e != null && e != body && e != doc) {
    left += e.offsetLeft;
    left -= e.scrollLeft;
    e = e.offsetParent;
  }
  return left;
};

/**
 * Retrieve the absolute top value of a DOM element
 * @param {Element} elem        A dom element, for example a div
 * @return {number} top        The absolute top position of this element
 *                              in the browser page.
 */
util.getAbsoluteTop = function getAbsoluteTop (elem) {
  var doc = document.documentElement;
  var body = document.body;

  var top = elem.offsetTop;
  var e = elem.offsetParent;
  while (e != null && e != body && e != doc) {
    top += e.offsetTop;
    top -= e.scrollTop;
    e = e.offsetParent;
  }
  return top;
};

/**
 * Get the absolute, vertical mouse position from an event.
 * @param {Event} event
 * @return {Number} pageY
 */
util.getPageY = function getPageY (event) {
  if ('pageY' in event) {
    return event.pageY;
  }
  else {
    var clientY;
    if (('targetTouches' in event) && event.targetTouches.length) {
      clientY = event.targetTouches[0].clientY;
    }
    else {
      clientY = event.clientY;
    }

    var doc = document.documentElement;
    var body = document.body;
    return clientY +
        ( doc && doc.scrollTop || body && body.scrollTop || 0 ) -
        ( doc && doc.clientTop || body && body.clientTop || 0 );
  }
};

/**
 * Get the absolute, horizontal mouse position from an event.
 * @param {Event} event
 * @return {Number} pageX
 */
util.getPageX = function getPageX (event) {
  if ('pageY' in event) {
    return event.pageX;
  }
  else {
    var clientX;
    if (('targetTouches' in event) && event.targetTouches.length) {
      clientX = event.targetTouches[0].clientX;
    }
    else {
      clientX = event.clientX;
    }

    var doc = document.documentElement;
    var body = document.body;
    return clientX +
        ( doc && doc.scrollLeft || body && body.scrollLeft || 0 ) -
        ( doc && doc.clientLeft || body && body.clientLeft || 0 );
  }
};

/**
 * add a className to the given elements style
 * @param {Element} elem
 * @param {String} className
 */
util.addClassName = function addClassName(elem, className) {
  var classes = elem.className.split(' ');
  if (classes.indexOf(className) == -1) {
    classes.push(className); // add the class to the array
    elem.className = classes.join(' ');
  }
};

/**
 * add a className to the given elements style
 * @param {Element} elem
 * @param {String} className
 */
util.removeClassName = function removeClassname(elem, className) {
  var classes = elem.className.split(' ');
  var index = classes.indexOf(className);
  if (index != -1) {
    classes.splice(index, 1); // remove the class from the array
    elem.className = classes.join(' ');
  }
};

/**
 * For each method for both arrays and objects.
 * In case of an array, the built-in Array.forEach() is applied.
 * In case of an Object, the method loops over all properties of the object.
 * @param {Object | Array} object   An Object or Array
 * @param {function} callback       Callback method, called for each item in
 *                                  the object or array with three parameters:
 *                                  callback(value, index, object)
 */
util.forEach = function forEach (object, callback) {
  var i,
      len;
  if (object instanceof Array) {
    // array
    for (i = 0, len = object.length; i < len; i++) {
      callback(object[i], i, object);
    }
  }
  else {
    // object
    for (i in object) {
      if (object.hasOwnProperty(i)) {
        callback(object[i], i, object);
      }
    }
  }
};

/**
 * Update a property in an object
 * @param {Object} object
 * @param {String} key
 * @param {*} value
 * @return {Boolean} changed
 */
util.updateProperty = function updateProp (object, key, value) {
  if (object[key] !== value) {
    object[key] = value;
    return true;
  }
  else {
    return false;
  }
};

/**
 * Add and event listener. Works for all browsers
 * @param {Element}     element    An html element
 * @param {string}      action     The action, for example "click",
 *                                 without the prefix "on"
 * @param {function}    listener   The callback function to be executed
 * @param {boolean}     [useCapture]
 */
util.addEventListener = function addEventListener(element, action, listener, useCapture) {
  if (element.addEventListener) {
    if (useCapture === undefined)
      useCapture = false;

    if (action === "mousewheel" && navigator.userAgent.indexOf("Firefox") >= 0) {
      action = "DOMMouseScroll";  // For Firefox
    }

    element.addEventListener(action, listener, useCapture);
  } else {
    element.attachEvent("on" + action, listener);  // IE browsers
  }
};

/**
 * Remove an event listener from an element
 * @param {Element}     element         An html dom element
 * @param {string}      action          The name of the event, for example "mousedown"
 * @param {function}    listener        The listener function
 * @param {boolean}     [useCapture]
 */
util.removeEventListener = function removeEventListener(element, action, listener, useCapture) {
  if (element.removeEventListener) {
    // non-IE browsers
    if (useCapture === undefined)
      useCapture = false;

    if (action === "mousewheel" && navigator.userAgent.indexOf("Firefox") >= 0) {
      action = "DOMMouseScroll";  // For Firefox
    }

    element.removeEventListener(action, listener, useCapture);
  } else {
    // IE browsers
    element.detachEvent("on" + action, listener);
  }
};


/**
 * Get HTML element which is the target of the event
 * @param {Event} event
 * @return {Element} target element
 */
util.getTarget = function getTarget(event) {
  // code from http://www.quirksmode.org/js/events_properties.html
  if (!event) {
    event = window.event;
  }

  var target;

  if (event.target) {
    target = event.target;
  }
  else if (event.srcElement) {
    target = event.srcElement;
  }

  if (target.nodeType != undefined && target.nodeType == 3) {
    // defeat Safari bug
    target = target.parentNode;
  }

  return target;
};

/**
 * Stop event propagation
 */
util.stopPropagation = function stopPropagation(event) {
  if (!event)
    event = window.event;

  if (event.stopPropagation) {
    event.stopPropagation();  // non-IE browsers
  }
  else {
    event.cancelBubble = true;  // IE browsers
  }
};

/**
 * Fake a hammer.js gesture. Event can be a ScrollEvent or MouseMoveEvent
 * @param {Element} element
 * @param {Event} event
 */
util.fakeGesture = function fakeGesture (element, event) {
  var eventType = null;

  // for hammer.js 1.0.5
  return Hammer.event.collectEventData(this, eventType, event);

  // for hammer.js 1.0.6
  //var touches = Hammer.event.getTouchList(event, eventType);
  //return Hammer.event.collectEventData(this, eventType, touches, event);
};

/**
 * Cancels the event if it is cancelable, without stopping further propagation of the event.
 */
util.preventDefault = function preventDefault (event) {
  if (!event)
    event = window.event;

  if (event.preventDefault) {
    event.preventDefault();  // non-IE browsers
  }
  else {
    event.returnValue = false;  // IE browsers
  }
};


util.option = {};

/**
 * Convert a value into a boolean
 * @param {Boolean | function | undefined} value
 * @param {Boolean} [defaultValue]
 * @returns {Boolean} bool
 */
util.option.asBoolean = function (value, defaultValue) {
  if (typeof value == 'function') {
    value = value();
  }

  if (value != null) {
    return (value != false);
  }

  return defaultValue || null;
};

/**
 * Convert a value into a number
 * @param {Boolean | function | undefined} value
 * @param {Number} [defaultValue]
 * @returns {Number} number
 */
util.option.asNumber = function (value, defaultValue) {
  if (typeof value == 'function') {
    value = value();
  }

  if (value != null) {
    return Number(value) || defaultValue || null;
  }

  return defaultValue || null;
};

/**
 * Convert a value into a string
 * @param {String | function | undefined} value
 * @param {String} [defaultValue]
 * @returns {String} str
 */
util.option.asString = function (value, defaultValue) {
  if (typeof value == 'function') {
    value = value();
  }

  if (value != null) {
    return String(value);
  }

  return defaultValue || null;
};

/**
 * Convert a size or location into a string with pixels or a percentage
 * @param {String | Number | function | undefined} value
 * @param {String} [defaultValue]
 * @returns {String} size
 */
util.option.asSize = function (value, defaultValue) {
  if (typeof value == 'function') {
    value = value();
  }

  if (util.isString(value)) {
    return value;
  }
  else if (util.isNumber(value)) {
    return value + 'px';
  }
  else {
    return defaultValue || null;
  }
};

/**
 * Convert a value into a DOM element
 * @param {HTMLElement | function | undefined} value
 * @param {HTMLElement} [defaultValue]
 * @returns {HTMLElement | null} dom
 */
util.option.asElement = function (value, defaultValue) {
  if (typeof value == 'function') {
    value = value();
  }

  return value || defaultValue || null;
};


/**
 * Compare two numbers and return the lowest, non-negative number.
 *
 * @param {number} number1
 * @param {number} number2
 * @returns {number}        | number1 or number2, the lowest positive number. If both negative, return -1
 * @private
 */
util._getLowestPositiveNumber = function(number1,number2) {
  if (number1 >= 0) {
    if (number2 >= 0) {
      return (number1 < number2) ? number1 : number2;
    }
    else {
      return number1;
    }
  }
  else {
    if (number2 >= 0) {
      return number2;
    }
    else {
      return -1;
    }
  }
}

/**
 * Event listener (singleton)
 */
// TODO: replace usage of the event listener for the EventBus
var events = {
  'listeners': [],

  /**
   * Find a single listener by its object
   * @param {Object} object
   * @return {Number} index  -1 when not found
   */
  'indexOf': function (object) {
    var listeners = this.listeners;
    for (var i = 0, iMax = this.listeners.length; i < iMax; i++) {
      var listener = listeners[i];
      if (listener && listener.object == object) {
        return i;
      }
    }
    return -1;
  },

  /**
   * Add an event listener
   * @param {Object} object
   * @param {String} event       The name of an event, for example 'select'
   * @param {function} callback  The callback method, called when the
   *                             event takes place
   */
  'addListener': function (object, event, callback) {
    var index = this.indexOf(object);
    var listener = this.listeners[index];
    if (!listener) {
      listener = {
        'object': object,
        'events': {}
      };
      this.listeners.push(listener);
    }

    var callbacks = listener.events[event];
    if (!callbacks) {
      callbacks = [];
      listener.events[event] = callbacks;
    }

    // add the callback if it does not yet exist
    if (callbacks.indexOf(callback) == -1) {
      callbacks.push(callback);
    }
  },

  /**
   * Remove an event listener
   * @param {Object} object
   * @param {String} event       The name of an event, for example 'select'
   * @param {function} callback  The registered callback method
   */
  'removeListener': function (object, event, callback) {
    var index = this.indexOf(object);
    var listener = this.listeners[index];
    if (listener) {
      var callbacks = listener.events[event];
      if (callbacks) {
        index = callbacks.indexOf(callback);
        if (index != -1) {
          callbacks.splice(index, 1);
        }

        // remove the array when empty
        if (callbacks.length == 0) {
          delete listener.events[event];
        }
      }

      // count the number of registered events. remove listener when empty
      var count = 0;
      var events = listener.events;
      for (var e in events) {
        if (events.hasOwnProperty(e)) {
          count++;
        }
      }
      if (count == 0) {
        delete this.listeners[index];
      }
    }
  },

  /**
   * Remove all registered event listeners
   */
  'removeAllListeners': function () {
    this.listeners = [];
  },

  /**
   * Trigger an event. All registered event handlers will be called
   * @param {Object} object
   * @param {String} event
   * @param {Object} properties (optional)
   */
  'trigger': function (object, event, properties) {
    var index = this.indexOf(object);
    var listener = this.listeners[index];
    if (listener) {
      var callbacks = listener.events[event];
      if (callbacks) {
        for (var i = 0, iMax = callbacks.length; i < iMax; i++) {
          callbacks[i](properties);
        }
      }
    }
  }
};

/**
 * An event bus can be used to emit events, and to subscribe to events
 * @constructor EventBus
 */
function EventBus() {
  this.subscriptions = [];
}

/**
 * Subscribe to an event
 * @param {String | RegExp} event   The event can be a regular expression, or
 *                                  a string with wildcards, like 'server.*'.
 * @param {function} callback.      Callback are called with three parameters:
 *                                  {String} event, {*} [data], {*} [source]
 * @param {*} [target]
 * @returns {String} id    A subscription id
 */
EventBus.prototype.on = function (event, callback, target) {
  var regexp = (event instanceof RegExp) ?
      event :
      new RegExp(event.replace('*', '\\w+'));

  var subscription = {
    id:       util.randomUUID(),
    event:    event,
    regexp:   regexp,
    callback: (typeof callback === 'function') ? callback : null,
    target:   target
  };

  this.subscriptions.push(subscription);

  return subscription.id;
};

/**
 * Unsubscribe from an event
 * @param {String | Object} filter   Filter for subscriptions to be removed
 *                                   Filter can be a string containing a
 *                                   subscription id, or an object containing
 *                                   one or more of the fields id, event,
 *                                   callback, and target.
 */
EventBus.prototype.off = function (filter) {
  var i = 0;
  while (i < this.subscriptions.length) {
    var subscription = this.subscriptions[i];

    var match = true;
    if (filter instanceof Object) {
      // filter is an object. All fields must match
      for (var prop in filter) {
        if (filter.hasOwnProperty(prop)) {
          if (filter[prop] !== subscription[prop]) {
            match = false;
          }
        }
      }
    }
    else {
      // filter is a string, filter on id
      match = (subscription.id == filter);
    }

    if (match) {
      this.subscriptions.splice(i, 1);
    }
    else {
      i++;
    }
  }
};

/**
 * Emit an event
 * @param {String} event
 * @param {*} [data]
 * @param {*} [source]
 */
EventBus.prototype.emit = function (event, data, source) {
  for (var i =0; i < this.subscriptions.length; i++) {
    var subscription = this.subscriptions[i];
    if (subscription.regexp.test(event)) {
      if (subscription.callback) {
        subscription.callback(event, data, source);
      }
    }
  }
};

/**
 * DataSet
 *
 * Usage:
 *     var dataSet = new DataSet({
 *         fieldId: '_id',
 *         convert: {
 *             // ...
 *         }
 *     });
 *
 *     dataSet.add(item);
 *     dataSet.add(data);
 *     dataSet.update(item);
 *     dataSet.update(data);
 *     dataSet.remove(id);
 *     dataSet.remove(ids);
 *     var data = dataSet.get();
 *     var data = dataSet.get(id);
 *     var data = dataSet.get(ids);
 *     var data = dataSet.get(ids, options, data);
 *     dataSet.clear();
 *
 * A data set can:
 * - add/remove/update data
 * - gives triggers upon changes in the data
 * - can  import/export data in various data formats
 *
 * @param {Object} [options]   Available options:
 *                             {String} fieldId Field name of the id in the
 *                                              items, 'id' by default.
 *                             {Object.<String, String} convert
 *                                              A map with field names as key,
 *                                              and the field type as value.
 * @constructor DataSet
 */
// TODO: add a DataSet constructor DataSet(data, options)
function DataSet (options) {
  this.id = util.randomUUID();

  this.options = options || {};
  this.data = {};                                 // map with data indexed by id
  this.fieldId = this.options.fieldId || 'id';    // name of the field containing id
  this.convert = {};                              // field types by field name
  this.showInternalIds = this.options.showInternalIds || false; // show internal ids with the get function

  if (this.options.convert) {
    for (var field in this.options.convert) {
      if (this.options.convert.hasOwnProperty(field)) {
        var value = this.options.convert[field];
        if (value == 'Date' || value == 'ISODate' || value == 'ASPDate') {
          this.convert[field] = 'Date';
        }
        else {
          this.convert[field] = value;
        }
      }
    }
  }

  // event subscribers
  this.subscribers = {};

  this.internalIds = {};            // internally generated id's
}

/**
 * Subscribe to an event, add an event listener
 * @param {String} event        Event name. Available events: 'put', 'update',
 *                              'remove'
 * @param {function} callback   Callback method. Called with three parameters:
 *                                  {String} event
 *                                  {Object | null} params
 *                                  {String | Number} senderId
 */
DataSet.prototype.subscribe = function (event, callback) {
  var subscribers = this.subscribers[event];
  if (!subscribers) {
    subscribers = [];
    this.subscribers[event] = subscribers;
  }

  subscribers.push({
    callback: callback
  });
};

/**
 * Unsubscribe from an event, remove an event listener
 * @param {String} event
 * @param {function} callback
 */
DataSet.prototype.unsubscribe = function (event, callback) {
  var subscribers = this.subscribers[event];
  if (subscribers) {
    this.subscribers[event] = subscribers.filter(function (listener) {
      return (listener.callback != callback);
    });
  }
};

/**
 * Trigger an event
 * @param {String} event
 * @param {Object | null} params
 * @param {String} [senderId]       Optional id of the sender.
 * @private
 */
DataSet.prototype._trigger = function (event, params, senderId) {
  if (event == '*') {
    throw new Error('Cannot trigger event *');
  }

  var subscribers = [];
  if (event in this.subscribers) {
    subscribers = subscribers.concat(this.subscribers[event]);
  }
  if ('*' in this.subscribers) {
    subscribers = subscribers.concat(this.subscribers['*']);
  }

  for (var i = 0; i < subscribers.length; i++) {
    var subscriber = subscribers[i];
    if (subscriber.callback) {
      subscriber.callback(event, params, senderId || null);
    }
  }
};

/**
 * Add data.
 * Adding an item will fail when there already is an item with the same id.
 * @param {Object | Array | DataTable} data
 * @param {String} [senderId] Optional sender id
 * @return {Array} addedIds      Array with the ids of the added items
 */
DataSet.prototype.add = function (data, senderId) {
  var addedIds = [],
      id,
      me = this;

  if (data instanceof Array) {
    // Array
    for (var i = 0, len = data.length; i < len; i++) {
      id = me._addItem(data[i]);
      addedIds.push(id);
    }
  }
  else if (util.isDataTable(data)) {
    // Google DataTable
    var columns = this._getColumnNames(data);
    for (var row = 0, rows = data.getNumberOfRows(); row < rows; row++) {
      var item = {};
      for (var col = 0, cols = columns.length; col < cols; col++) {
        var field = columns[col];
        item[field] = data.getValue(row, col);
      }

      id = me._addItem(item);
      addedIds.push(id);
    }
  }
  else if (data instanceof Object) {
    // Single item
    id = me._addItem(data);
    addedIds.push(id);
  }
  else {
    throw new Error('Unknown dataType');
  }

  if (addedIds.length) {
    this._trigger('add', {items: addedIds}, senderId);
  }

  return addedIds;
};

/**
 * Update existing items. When an item does not exist, it will be created
 * @param {Object | Array | DataTable} data
 * @param {String} [senderId] Optional sender id
 * @return {Array} updatedIds     The ids of the added or updated items
 */
DataSet.prototype.update = function (data, senderId) {
  var addedIds = [],
      updatedIds = [],
      me = this,
      fieldId = me.fieldId;

  var addOrUpdate = function (item) {
    var id = item[fieldId];
    if (me.data[id]) {
      // update item
      id = me._updateItem(item);
      updatedIds.push(id);
    }
    else {
      // add new item
      id = me._addItem(item);
      addedIds.push(id);
    }
  };

  if (data instanceof Array) {
    // Array
    for (var i = 0, len = data.length; i < len; i++) {
      addOrUpdate(data[i]);
    }
  }
  else if (util.isDataTable(data)) {
    // Google DataTable
    var columns = this._getColumnNames(data);
    for (var row = 0, rows = data.getNumberOfRows(); row < rows; row++) {
      var item = {};
      for (var col = 0, cols = columns.length; col < cols; col++) {
        var field = columns[col];
        item[field] = data.getValue(row, col);
      }

      addOrUpdate(item);
    }
  }
  else if (data instanceof Object) {
    // Single item
    addOrUpdate(data);
  }
  else {
    throw new Error('Unknown dataType');
  }

  if (addedIds.length) {
    this._trigger('add', {items: addedIds}, senderId);
  }
  if (updatedIds.length) {
    this._trigger('update', {items: updatedIds}, senderId);
  }

  return addedIds.concat(updatedIds);
};

/**
 * Get a data item or multiple items.
 *
 * Usage:
 *
 *     get()
 *     get(options: Object)
 *     get(options: Object, data: Array | DataTable)
 *
 *     get(id: Number | String)
 *     get(id: Number | String, options: Object)
 *     get(id: Number | String, options: Object, data: Array | DataTable)
 *
 *     get(ids: Number[] | String[])
 *     get(ids: Number[] | String[], options: Object)
 *     get(ids: Number[] | String[], options: Object, data: Array | DataTable)
 *
 * Where:
 *
 * {Number | String} id         The id of an item
 * {Number[] | String{}} ids    An array with ids of items
 * {Object} options             An Object with options. Available options:
 *                              {String} [type] Type of data to be returned. Can
 *                                              be 'DataTable' or 'Array' (default)
 *                              {Object.<String, String>} [convert]
 *                              {String[]} [fields] field names to be returned
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 * {Array | DataTable} [data]   If provided, items will be appended to this
 *                              array or table. Required in case of Google
 *                              DataTable.
 *
 * @throws Error
 */
DataSet.prototype.get = function (args) {
  var me = this;
  var globalShowInternalIds = this.showInternalIds;

  // parse the arguments
  var id, ids, options, data;
  var firstType = util.getType(arguments[0]);
  if (firstType == 'String' || firstType == 'Number') {
    // get(id [, options] [, data])
    id = arguments[0];
    options = arguments[1];
    data = arguments[2];
  }
  else if (firstType == 'Array') {
    // get(ids [, options] [, data])
    ids = arguments[0];
    options = arguments[1];
    data = arguments[2];
  }
  else {
    // get([, options] [, data])
    options = arguments[0];
    data = arguments[1];
  }

  // determine the return type
  var type;
  if (options && options.type) {
    type = (options.type == 'DataTable') ? 'DataTable' : 'Array';

    if (data && (type != util.getType(data))) {
      throw new Error('Type of parameter "data" (' + util.getType(data) + ') ' +
          'does not correspond with specified options.type (' + options.type + ')');
    }
    if (type == 'DataTable' && !util.isDataTable(data)) {
      throw new Error('Parameter "data" must be a DataTable ' +
          'when options.type is "DataTable"');
    }
  }
  else if (data) {
    type = (util.getType(data) == 'DataTable') ? 'DataTable' : 'Array';
  }
  else {
    type = 'Array';
  }

  // we allow the setting of this value for a single get request.
  if (options != undefined) {
    if (options.showInternalIds != undefined) {
      this.showInternalIds = options.showInternalIds;
    }
  }

  // build options
  var convert = options && options.convert || this.options.convert;
  var filter = options && options.filter;
  var items = [], item, itemId, i, len;

  // convert items
  if (id != undefined) {
    // return a single item
    item = me._getItem(id, convert);
    if (filter && !filter(item)) {
      item = null;
    }
  }
  else if (ids != undefined) {
    // return a subset of items
    for (i = 0, len = ids.length; i < len; i++) {
      item = me._getItem(ids[i], convert);
      if (!filter || filter(item)) {
        items.push(item);
      }
    }
  }
  else {
    // return all items
    for (itemId in this.data) {
      if (this.data.hasOwnProperty(itemId)) {
        item = me._getItem(itemId, convert);
        if (!filter || filter(item)) {
          items.push(item);
        }
      }
    }
  }

  // restore the global value of showInternalIds
  this.showInternalIds = globalShowInternalIds;

  // order the results
  if (options && options.order && id == undefined) {
    this._sort(items, options.order);
  }

  // filter fields of the items
  if (options && options.fields) {
    var fields = options.fields;
    if (id != undefined) {
      item = this._filterFields(item, fields);
    }
    else {
      for (i = 0, len = items.length; i < len; i++) {
        items[i] = this._filterFields(items[i], fields);
      }
    }
  }

  // return the results
  if (type == 'DataTable') {
    var columns = this._getColumnNames(data);
    if (id != undefined) {
      // append a single item to the data table
      me._appendRow(data, columns, item);
    }
    else {
      // copy the items to the provided data table
      for (i = 0, len = items.length; i < len; i++) {
        me._appendRow(data, columns, items[i]);
      }
    }
    return data;
  }
  else {
    // return an array
    if (id != undefined) {
      // a single item
      return item;
    }
    else {
      // multiple items
      if (data) {
        // copy the items to the provided array
        for (i = 0, len = items.length; i < len; i++) {
          data.push(items[i]);
        }
        return data;
      }
      else {
        // just return our array
        return items;
      }
    }
  }
};

/**
 * Get ids of all items or from a filtered set of items.
 * @param {Object} [options]    An Object with options. Available options:
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 * @return {Array} ids
 */
DataSet.prototype.getIds = function (options) {
  var data = this.data,
      filter = options && options.filter,
      order = options && options.order,
      convert = options && options.convert || this.options.convert,
      i,
      len,
      id,
      item,
      items,
      ids = [];

  if (filter) {
    // get filtered items
    if (order) {
      // create ordered list
      items = [];
      for (id in data) {
        if (data.hasOwnProperty(id)) {
          item = this._getItem(id, convert);
          if (filter(item)) {
            items.push(item);
          }
        }
      }

      this._sort(items, order);

      for (i = 0, len = items.length; i < len; i++) {
        ids[i] = items[i][this.fieldId];
      }
    }
    else {
      // create unordered list
      for (id in data) {
        if (data.hasOwnProperty(id)) {
          item = this._getItem(id, convert);
          if (filter(item)) {
            ids.push(item[this.fieldId]);
          }
        }
      }
    }
  }
  else {
    // get all items
    if (order) {
      // create an ordered list
      items = [];
      for (id in data) {
        if (data.hasOwnProperty(id)) {
          items.push(data[id]);
        }
      }

      this._sort(items, order);

      for (i = 0, len = items.length; i < len; i++) {
        ids[i] = items[i][this.fieldId];
      }
    }
    else {
      // create unordered list
      for (id in data) {
        if (data.hasOwnProperty(id)) {
          item = data[id];
          ids.push(item[this.fieldId]);
        }
      }
    }
  }

  return ids;
};

/**
 * Execute a callback function for every item in the dataset.
 * The order of the items is not determined.
 * @param {function} callback
 * @param {Object} [options]    Available options:
 *                              {Object.<String, String>} [convert]
 *                              {String[]} [fields] filter fields
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 */
DataSet.prototype.forEach = function (callback, options) {
  var filter = options && options.filter,
      convert = options && options.convert || this.options.convert,
      data = this.data,
      item,
      id;

  if (options && options.order) {
    // execute forEach on ordered list
    var items = this.get(options);

    for (var i = 0, len = items.length; i < len; i++) {
      item = items[i];
      id = item[this.fieldId];
      callback(item, id);
    }
  }
  else {
    // unordered
    for (id in data) {
      if (data.hasOwnProperty(id)) {
        item = this._getItem(id, convert);
        if (!filter || filter(item)) {
          callback(item, id);
        }
      }
    }
  }
};

/**
 * Map every item in the dataset.
 * @param {function} callback
 * @param {Object} [options]    Available options:
 *                              {Object.<String, String>} [convert]
 *                              {String[]} [fields] filter fields
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 * @return {Object[]} mappedItems
 */
DataSet.prototype.map = function (callback, options) {
  var filter = options && options.filter,
      convert = options && options.convert || this.options.convert,
      mappedItems = [],
      data = this.data,
      item;

  // convert and filter items
  for (var id in data) {
    if (data.hasOwnProperty(id)) {
      item = this._getItem(id, convert);
      if (!filter || filter(item)) {
        mappedItems.push(callback(item, id));
      }
    }
  }

  // order items
  if (options && options.order) {
    this._sort(mappedItems, options.order);
  }

  return mappedItems;
};

/**
 * Filter the fields of an item
 * @param {Object} item
 * @param {String[]} fields     Field names
 * @return {Object} filteredItem
 * @private
 */
DataSet.prototype._filterFields = function (item, fields) {
  var filteredItem = {};

  for (var field in item) {
    if (item.hasOwnProperty(field) && (fields.indexOf(field) != -1)) {
      filteredItem[field] = item[field];
    }
  }

  return filteredItem;
};

/**
 * Sort the provided array with items
 * @param {Object[]} items
 * @param {String | function} order      A field name or custom sort function.
 * @private
 */
DataSet.prototype._sort = function (items, order) {
  if (util.isString(order)) {
    // order by provided field name
    var name = order; // field name
    items.sort(function (a, b) {
      var av = a[name];
      var bv = b[name];
      return (av > bv) ? 1 : ((av < bv) ? -1 : 0);
    });
  }
  else if (typeof order === 'function') {
    // order by sort function
    items.sort(order);
  }
  // TODO: extend order by an Object {field:String, direction:String}
  //       where direction can be 'asc' or 'desc'
  else {
    throw new TypeError('Order must be a function or a string');
  }
};

/**
 * Remove an object by pointer or by id
 * @param {String | Number | Object | Array} id Object or id, or an array with
 *                                              objects or ids to be removed
 * @param {String} [senderId] Optional sender id
 * @return {Array} removedIds
 */
DataSet.prototype.remove = function (id, senderId) {
  var removedIds = [],
      i, len, removedId;

  if (id instanceof Array) {
    for (i = 0, len = id.length; i < len; i++) {
      removedId = this._remove(id[i]);
      if (removedId != null) {
        removedIds.push(removedId);
      }
    }
  }
  else {
    removedId = this._remove(id);
    if (removedId != null) {
      removedIds.push(removedId);
    }
  }

  if (removedIds.length) {
    this._trigger('remove', {items: removedIds}, senderId);
  }

  return removedIds;
};

/**
 * Remove an item by its id
 * @param {Number | String | Object} id   id or item
 * @returns {Number | String | null} id
 * @private
 */
DataSet.prototype._remove = function (id) {
  if (util.isNumber(id) || util.isString(id)) {
    if (this.data[id]) {
      delete this.data[id];
      delete this.internalIds[id];
      return id;
    }
  }
  else if (id instanceof Object) {
    var itemId = id[this.fieldId];
    if (itemId && this.data[itemId]) {
      delete this.data[itemId];
      delete this.internalIds[itemId];
      return itemId;
    }
  }
  return null;
};

/**
 * Clear the data
 * @param {String} [senderId] Optional sender id
 * @return {Array} removedIds    The ids of all removed items
 */
DataSet.prototype.clear = function (senderId) {
  var ids = Object.keys(this.data);

  this.data = {};
  this.internalIds = {};

  this._trigger('remove', {items: ids}, senderId);

  return ids;
};

/**
 * Find the item with maximum value of a specified field
 * @param {String} field
 * @return {Object | null} item  Item containing max value, or null if no items
 */
DataSet.prototype.max = function (field) {
  var data = this.data,
      max = null,
      maxField = null;

  for (var id in data) {
    if (data.hasOwnProperty(id)) {
      var item = data[id];
      var itemField = item[field];
      if (itemField != null && (!max || itemField > maxField)) {
        max = item;
        maxField = itemField;
      }
    }
  }

  return max;
};

/**
 * Find the item with minimum value of a specified field
 * @param {String} field
 * @return {Object | null} item  Item containing max value, or null if no items
 */
DataSet.prototype.min = function (field) {
  var data = this.data,
      min = null,
      minField = null;

  for (var id in data) {
    if (data.hasOwnProperty(id)) {
      var item = data[id];
      var itemField = item[field];
      if (itemField != null && (!min || itemField < minField)) {
        min = item;
        minField = itemField;
      }
    }
  }

  return min;
};

/**
 * Find all distinct values of a specified field
 * @param {String} field
 * @return {Array} values  Array containing all distinct values. If the data
 *                         items do not contain the specified field, an array
 *                         containing a single value undefined is returned.
 *                         The returned array is unordered.
 */
DataSet.prototype.distinct = function (field) {
  var data = this.data,
      values = [],
      fieldType = this.options.convert[field],
      count = 0;

  for (var prop in data) {
    if (data.hasOwnProperty(prop)) {
      var item = data[prop];
      var value = util.convert(item[field], fieldType);
      var exists = false;
      for (var i = 0; i < count; i++) {
        if (values[i] == value) {
          exists = true;
          break;
        }
      }
      if (!exists) {
        values[count] = value;
        count++;
      }
    }
  }

  return values;
};

/**
 * Add a single item. Will fail when an item with the same id already exists.
 * @param {Object} item
 * @return {String} id
 * @private
 */
DataSet.prototype._addItem = function (item) {
  var id = item[this.fieldId];

  if (id != undefined) {
    // check whether this id is already taken
    if (this.data[id]) {
      // item already exists
      throw new Error('Cannot add item: item with id ' + id + ' already exists');
    }
  }
  else {
    // generate an id
    id = util.randomUUID();
    item[this.fieldId] = id;
    this.internalIds[id] = item;
  }

  var d = {};
  for (var field in item) {
    if (item.hasOwnProperty(field)) {
      var fieldType = this.convert[field];  // type may be undefined
      d[field] = util.convert(item[field], fieldType);
    }
  }
  this.data[id] = d;

  return id;
};

/**
 * Get an item. Fields can be converted to a specific type
 * @param {String} id
 * @param {Object.<String, String>} [convert]  field types to convert
 * @return {Object | null} item
 * @private
 */
DataSet.prototype._getItem = function (id, convert) {
  var field, value;

  // get the item from the dataset
  var raw = this.data[id];
  if (!raw) {
    return null;
  }

  // convert the items field types
  var converted = {},
      fieldId = this.fieldId,
      internalIds = this.internalIds;
  if (convert) {
    for (field in raw) {
      if (raw.hasOwnProperty(field)) {
        value = raw[field];
        // output all fields, except internal ids
        if ((field != fieldId) || (!(value in internalIds) || this.showInternalIds)) {
          converted[field] = util.convert(value, convert[field]);
        }
      }
    }
  }
  else {
    // no field types specified, no converting needed
    for (field in raw) {
      if (raw.hasOwnProperty(field)) {
        value = raw[field];
        // output all fields, except internal ids
        if ((field != fieldId) || (!(value in internalIds) || this.showInternalIds)) {
          converted[field] = value;
        }
      }
    }
  }
  return converted;
};

/**
 * Update a single item: merge with existing item.
 * Will fail when the item has no id, or when there does not exist an item
 * with the same id.
 * @param {Object} item
 * @return {String} id
 * @private
 */
DataSet.prototype._updateItem = function (item) {
  var id = item[this.fieldId];
  if (id == undefined) {
    throw new Error('Cannot update item: item has no id (item: ' + JSON.stringify(item) + ')');
  }
  var d = this.data[id];
  if (!d) {
    // item doesn't exist
    throw new Error('Cannot update item: no item with id ' + id + ' found');
  }

  // merge with current item
  for (var field in item) {
    if (item.hasOwnProperty(field)) {
      var fieldType = this.convert[field];  // type may be undefined
      d[field] = util.convert(item[field], fieldType);
    }
  }

  return id;
};

/**
 * check if an id is an internal or external id
 * @param id
 * @returns {boolean}
 * @private
 */
DataSet.prototype.isInternalId = function(id) {
  return (id in this.internalIds);
};


/**
 * Get an array with the column names of a Google DataTable
 * @param {DataTable} dataTable
 * @return {String[]} columnNames
 * @private
 */
DataSet.prototype._getColumnNames = function (dataTable) {
  var columns = [];
  for (var col = 0, cols = dataTable.getNumberOfColumns(); col < cols; col++) {
    columns[col] = dataTable.getColumnId(col) || dataTable.getColumnLabel(col);
  }
  return columns;
};

/**
 * Append an item as a row to the dataTable
 * @param dataTable
 * @param columns
 * @param item
 * @private
 */
DataSet.prototype._appendRow = function (dataTable, columns, item) {
  var row = dataTable.addRow();

  for (var col = 0, cols = columns.length; col < cols; col++) {
    var field = columns[col];
    dataTable.setValue(row, col, item[field]);
  }
};

/**
 * DataView
 *
 * a dataview offers a filtered view on a dataset or an other dataview.
 *
 * @param {DataSet | DataView} data
 * @param {Object} [options]   Available options: see method get
 *
 * @constructor DataView
 */
function DataView (data, options) {
  this.id = util.randomUUID();

  this.data = null;
  this.ids = {}; // ids of the items currently in memory (just contains a boolean true)
  this.options = options || {};
  this.fieldId = 'id'; // name of the field containing id
  this.subscribers = {}; // event subscribers

  var me = this;
  this.listener = function () {
    me._onEvent.apply(me, arguments);
  };

  this.setData(data);
}

// TODO: implement a function .config() to dynamically update things like configured filter
// and trigger changes accordingly

/**
 * Set a data source for the view
 * @param {DataSet | DataView} data
 */
DataView.prototype.setData = function (data) {
  var ids, dataItems, i, len;

  if (this.data) {
    // unsubscribe from current dataset
    if (this.data.unsubscribe) {
      this.data.unsubscribe('*', this.listener);
    }

    // trigger a remove of all items in memory
    ids = [];
    for (var id in this.ids) {
      if (this.ids.hasOwnProperty(id)) {
        ids.push(id);
      }
    }
    this.ids = {};
    this._trigger('remove', {items: ids});
  }

  this.data = data;

  if (this.data) {
    // update fieldId
    this.fieldId = this.options.fieldId ||
        (this.data && this.data.options && this.data.options.fieldId) ||
        'id';

    // trigger an add of all added items
    ids = this.data.getIds({filter: this.options && this.options.filter});
    for (i = 0, len = ids.length; i < len; i++) {
      id = ids[i];
      this.ids[id] = true;
    }
    this._trigger('add', {items: ids});

    // subscribe to new dataset
    if (this.data.subscribe) {
      this.data.subscribe('*', this.listener);
    }
  }
};

/**
 * Get data from the data view
 *
 * Usage:
 *
 *     get()
 *     get(options: Object)
 *     get(options: Object, data: Array | DataTable)
 *
 *     get(id: Number)
 *     get(id: Number, options: Object)
 *     get(id: Number, options: Object, data: Array | DataTable)
 *
 *     get(ids: Number[])
 *     get(ids: Number[], options: Object)
 *     get(ids: Number[], options: Object, data: Array | DataTable)
 *
 * Where:
 *
 * {Number | String} id         The id of an item
 * {Number[] | String{}} ids    An array with ids of items
 * {Object} options             An Object with options. Available options:
 *                              {String} [type] Type of data to be returned. Can
 *                                              be 'DataTable' or 'Array' (default)
 *                              {Object.<String, String>} [convert]
 *                              {String[]} [fields] field names to be returned
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 * {Array | DataTable} [data]   If provided, items will be appended to this
 *                              array or table. Required in case of Google
 *                              DataTable.
 * @param args
 */
DataView.prototype.get = function (args) {
  var me = this;

  // parse the arguments
  var ids, options, data;
  var firstType = util.getType(arguments[0]);
  if (firstType == 'String' || firstType == 'Number' || firstType == 'Array') {
    // get(id(s) [, options] [, data])
    ids = arguments[0];  // can be a single id or an array with ids
    options = arguments[1];
    data = arguments[2];
  }
  else {
    // get([, options] [, data])
    options = arguments[0];
    data = arguments[1];
  }

  // extend the options with the default options and provided options
  var viewOptions = util.extend({}, this.options, options);

  // create a combined filter method when needed
  if (this.options.filter && options && options.filter) {
    viewOptions.filter = function (item) {
      return me.options.filter(item) && options.filter(item);
    }
  }

  // build up the call to the linked data set
  var getArguments = [];
  if (ids != undefined) {
    getArguments.push(ids);
  }
  getArguments.push(viewOptions);
  getArguments.push(data);

  return this.data && this.data.get.apply(this.data, getArguments);
};

/**
 * Get ids of all items or from a filtered set of items.
 * @param {Object} [options]    An Object with options. Available options:
 *                              {function} [filter] filter items
 *                              {String | function} [order] Order the items by
 *                                  a field name or custom sort function.
 * @return {Array} ids
 */
DataView.prototype.getIds = function (options) {
  var ids;

  if (this.data) {
    var defaultFilter = this.options.filter;
    var filter;

    if (options && options.filter) {
      if (defaultFilter) {
        filter = function (item) {
          return defaultFilter(item) && options.filter(item);
        }
      }
      else {
        filter = options.filter;
      }
    }
    else {
      filter = defaultFilter;
    }

    ids = this.data.getIds({
      filter: filter,
      order: options && options.order
    });
  }
  else {
    ids = [];
  }

  return ids;
};

/**
 * Event listener. Will propagate all events from the connected data set to
 * the subscribers of the DataView, but will filter the items and only trigger
 * when there are changes in the filtered data set.
 * @param {String} event
 * @param {Object | null} params
 * @param {String} senderId
 * @private
 */
DataView.prototype._onEvent = function (event, params, senderId) {
  var i, len, id, item,
      ids = params && params.items,
      data = this.data,
      added = [],
      updated = [],
      removed = [];

  if (ids && data) {
    switch (event) {
      case 'add':
        // filter the ids of the added items
        for (i = 0, len = ids.length; i < len; i++) {
          id = ids[i];
          item = this.get(id);
          if (item) {
            this.ids[id] = true;
            added.push(id);
          }
        }

        break;

      case 'update':
        // determine the event from the views viewpoint: an updated
        // item can be added, updated, or removed from this view.
        for (i = 0, len = ids.length; i < len; i++) {
          id = ids[i];
          item = this.get(id);

          if (item) {
            if (this.ids[id]) {
              updated.push(id);
            }
            else {
              this.ids[id] = true;
              added.push(id);
            }
          }
          else {
            if (this.ids[id]) {
              delete this.ids[id];
              removed.push(id);
            }
            else {
              // nothing interesting for me :-(
            }
          }
        }

        break;

      case 'remove':
        // filter the ids of the removed items
        for (i = 0, len = ids.length; i < len; i++) {
          id = ids[i];
          if (this.ids[id]) {
            delete this.ids[id];
            removed.push(id);
          }
        }

        break;
    }

    if (added.length) {
      this._trigger('add', {items: added}, senderId);
    }
    if (updated.length) {
      this._trigger('update', {items: updated}, senderId);
    }
    if (removed.length) {
      this._trigger('remove', {items: removed}, senderId);
    }
  }
};

// copy subscription functionality from DataSet
DataView.prototype.subscribe = DataSet.prototype.subscribe;
DataView.prototype.unsubscribe = DataSet.prototype.unsubscribe;
DataView.prototype._trigger = DataSet.prototype._trigger;

/**
 * @constructor  TimeStep
 * The class TimeStep is an iterator for dates. You provide a start date and an
 * end date. The class itself determines the best scale (step size) based on the
 * provided start Date, end Date, and minimumStep.
 *
 * If minimumStep is provided, the step size is chosen as close as possible
 * to the minimumStep but larger than minimumStep. If minimumStep is not
 * provided, the scale is set to 1 DAY.
 * The minimumStep should correspond with the onscreen size of about 6 characters
 *
 * Alternatively, you can set a scale by hand.
 * After creation, you can initialize the class by executing first(). Then you
 * can iterate from the start date to the end date via next(). You can check if
 * the end date is reached with the function hasNext(). After each step, you can
 * retrieve the current date via getCurrent().
 * The TimeStep has scales ranging from milliseconds, seconds, minutes, hours,
 * days, to years.
 *
 * Version: 1.2
 *
 * @param {Date} [start]         The start date, for example new Date(2010, 9, 21)
 *                               or new Date(2010, 9, 21, 23, 45, 00)
 * @param {Date} [end]           The end date
 * @param {Number} [minimumStep] Optional. Minimum step size in milliseconds
 */
TimeStep = function(start, end, minimumStep) {
  // variables
  this.current = new Date();
  this._start = new Date();
  this._end = new Date();

  this.autoScale  = true;
  this.scale = TimeStep.SCALE.DAY;
  this.step = 1;

  // initialize the range
  this.setRange(start, end, minimumStep);
};

/// enum scale
TimeStep.SCALE = {
  MILLISECOND: 1,
  SECOND: 2,
  MINUTE: 3,
  HOUR: 4,
  DAY: 5,
  WEEKDAY: 6,
  MONTH: 7,
  YEAR: 8
};


/**
 * Set a new range
 * If minimumStep is provided, the step size is chosen as close as possible
 * to the minimumStep but larger than minimumStep. If minimumStep is not
 * provided, the scale is set to 1 DAY.
 * The minimumStep should correspond with the onscreen size of about 6 characters
 * @param {Date} [start]      The start date and time.
 * @param {Date} [end]        The end date and time.
 * @param {int} [minimumStep] Optional. Minimum step size in milliseconds
 */
TimeStep.prototype.setRange = function(start, end, minimumStep) {
  if (!(start instanceof Date) || !(end instanceof Date)) {
    throw  "No legal start or end date in method setRange";
  }

  this._start = (start != undefined) ? new Date(start.valueOf()) : new Date();
  this._end = (end != undefined) ? new Date(end.valueOf()) : new Date();

  if (this.autoScale) {
    this.setMinimumStep(minimumStep);
  }
};

/**
 * Set the range iterator to the start date.
 */
TimeStep.prototype.first = function() {
  this.current = new Date(this._start.valueOf());
  this.roundToMinor();
};

/**
 * Round the current date to the first minor date value
 * This must be executed once when the current date is set to start Date
 */
TimeStep.prototype.roundToMinor = function() {
  // round to floor
  // IMPORTANT: we have no breaks in this switch! (this is no bug)
  //noinspection FallthroughInSwitchStatementJS
  switch (this.scale) {
    case TimeStep.SCALE.YEAR:
      this.current.setFullYear(this.step * Math.floor(this.current.getFullYear() / this.step));
      this.current.setMonth(0);
    case TimeStep.SCALE.MONTH:        this.current.setDate(1);
    case TimeStep.SCALE.DAY:          // intentional fall through
    case TimeStep.SCALE.WEEKDAY:      this.current.setHours(0);
    case TimeStep.SCALE.HOUR:         this.current.setMinutes(0);
    case TimeStep.SCALE.MINUTE:       this.current.setSeconds(0);
    case TimeStep.SCALE.SECOND:       this.current.setMilliseconds(0);
    //case TimeStep.SCALE.MILLISECOND: // nothing to do for milliseconds
  }

  if (this.step != 1) {
    // round down to the first minor value that is a multiple of the current step size
    switch (this.scale) {
      case TimeStep.SCALE.MILLISECOND:  this.current.setMilliseconds(this.current.getMilliseconds() - this.current.getMilliseconds() % this.step);  break;
      case TimeStep.SCALE.SECOND:       this.current.setSeconds(this.current.getSeconds() - this.current.getSeconds() % this.step); break;
      case TimeStep.SCALE.MINUTE:       this.current.setMinutes(this.current.getMinutes() - this.current.getMinutes() % this.step); break;
      case TimeStep.SCALE.HOUR:         this.current.setHours(this.current.getHours() - this.current.getHours() % this.step); break;
      case TimeStep.SCALE.WEEKDAY:      // intentional fall through
      case TimeStep.SCALE.DAY:          this.current.setDate((this.current.getDate()-1) - (this.current.getDate()-1) % this.step + 1); break;
      case TimeStep.SCALE.MONTH:        this.current.setMonth(this.current.getMonth() - this.current.getMonth() % this.step);  break;
      case TimeStep.SCALE.YEAR:         this.current.setFullYear(this.current.getFullYear() - this.current.getFullYear() % this.step); break;
      default: break;
    }
  }
};

/**
 * Check if the there is a next step
 * @return {boolean}  true if the current date has not passed the end date
 */
TimeStep.prototype.hasNext = function () {
  return (this.current.valueOf() <= this._end.valueOf());
};

/**
 * Do the next step
 */
TimeStep.prototype.next = function() {
  var prev = this.current.valueOf();

  // Two cases, needed to prevent issues with switching daylight savings
  // (end of March and end of October)
  if (this.current.getMonth() < 6)   {
    switch (this.scale) {
      case TimeStep.SCALE.MILLISECOND:

        this.current = new Date(this.current.valueOf() + this.step); break;
      case TimeStep.SCALE.SECOND:       this.current = new Date(this.current.valueOf() + this.step * 1000); break;
      case TimeStep.SCALE.MINUTE:       this.current = new Date(this.current.valueOf() + this.step * 1000 * 60); break;
      case TimeStep.SCALE.HOUR:
        this.current = new Date(this.current.valueOf() + this.step * 1000 * 60 * 60);
        // in case of skipping an hour for daylight savings, adjust the hour again (else you get: 0h 5h 9h ... instead of 0h 4h 8h ...)
        var h = this.current.getHours();
        this.current.setHours(h - (h % this.step));
        break;
      case TimeStep.SCALE.WEEKDAY:      // intentional fall through
      case TimeStep.SCALE.DAY:          this.current.setDate(this.current.getDate() + this.step); break;
      case TimeStep.SCALE.MONTH:        this.current.setMonth(this.current.getMonth() + this.step); break;
      case TimeStep.SCALE.YEAR:         this.current.setFullYear(this.current.getFullYear() + this.step); break;
      default:                      break;
    }
  }
  else {
    switch (this.scale) {
      case TimeStep.SCALE.MILLISECOND:  this.current = new Date(this.current.valueOf() + this.step); break;
      case TimeStep.SCALE.SECOND:       this.current.setSeconds(this.current.getSeconds() + this.step); break;
      case TimeStep.SCALE.MINUTE:       this.current.setMinutes(this.current.getMinutes() + this.step); break;
      case TimeStep.SCALE.HOUR:         this.current.setHours(this.current.getHours() + this.step); break;
      case TimeStep.SCALE.WEEKDAY:      // intentional fall through
      case TimeStep.SCALE.DAY:          this.current.setDate(this.current.getDate() + this.step); break;
      case TimeStep.SCALE.MONTH:        this.current.setMonth(this.current.getMonth() + this.step); break;
      case TimeStep.SCALE.YEAR:         this.current.setFullYear(this.current.getFullYear() + this.step); break;
      default:                      break;
    }
  }

  if (this.step != 1) {
    // round down to the correct major value
    switch (this.scale) {
      case TimeStep.SCALE.MILLISECOND:  if(this.current.getMilliseconds() < this.step) this.current.setMilliseconds(0);  break;
      case TimeStep.SCALE.SECOND:       if(this.current.getSeconds() < this.step) this.current.setSeconds(0);  break;
      case TimeStep.SCALE.MINUTE:       if(this.current.getMinutes() < this.step) this.current.setMinutes(0);  break;
      case TimeStep.SCALE.HOUR:         if(this.current.getHours() < this.step) this.current.setHours(0);  break;
      case TimeStep.SCALE.WEEKDAY:      // intentional fall through
      case TimeStep.SCALE.DAY:          if(this.current.getDate() < this.step+1) this.current.setDate(1); break;
      case TimeStep.SCALE.MONTH:        if(this.current.getMonth() < this.step) this.current.setMonth(0);  break;
      case TimeStep.SCALE.YEAR:         break; // nothing to do for year
      default:                break;
    }
  }

  // safety mechanism: if current time is still unchanged, move to the end
  if (this.current.valueOf() == prev) {
    this.current = new Date(this._end.valueOf());
  }
};


/**
 * Get the current datetime
 * @return {Date}  current The current date
 */
TimeStep.prototype.getCurrent = function() {
  return this.current;
};

/**
 * Set a custom scale. Autoscaling will be disabled.
 * For example setScale(SCALE.MINUTES, 5) will result
 * in minor steps of 5 minutes, and major steps of an hour.
 *
 * @param {TimeStep.SCALE} newScale
 *                               A scale. Choose from SCALE.MILLISECOND,
 *                               SCALE.SECOND, SCALE.MINUTE, SCALE.HOUR,
 *                               SCALE.WEEKDAY, SCALE.DAY, SCALE.MONTH,
 *                               SCALE.YEAR.
 * @param {Number}     newStep   A step size, by default 1. Choose for
 *                               example 1, 2, 5, or 10.
 */
TimeStep.prototype.setScale = function(newScale, newStep) {
  this.scale = newScale;

  if (newStep > 0) {
    this.step = newStep;
  }

  this.autoScale = false;
};

/**
 * Enable or disable autoscaling
 * @param {boolean} enable  If true, autoascaling is set true
 */
TimeStep.prototype.setAutoScale = function (enable) {
  this.autoScale = enable;
};


/**
 * Automatically determine the scale that bests fits the provided minimum step
 * @param {Number} [minimumStep]  The minimum step size in milliseconds
 */
TimeStep.prototype.setMinimumStep = function(minimumStep) {
  if (minimumStep == undefined) {
    return;
  }

  var stepYear       = (1000 * 60 * 60 * 24 * 30 * 12);
  var stepMonth      = (1000 * 60 * 60 * 24 * 30);
  var stepDay        = (1000 * 60 * 60 * 24);
  var stepHour       = (1000 * 60 * 60);
  var stepMinute     = (1000 * 60);
  var stepSecond     = (1000);
  var stepMillisecond= (1);

  // find the smallest step that is larger than the provided minimumStep
  if (stepYear*1000 > minimumStep)        {this.scale = TimeStep.SCALE.YEAR;        this.step = 1000;}
  if (stepYear*500 > minimumStep)         {this.scale = TimeStep.SCALE.YEAR;        this.step = 500;}
  if (stepYear*100 > minimumStep)         {this.scale = TimeStep.SCALE.YEAR;        this.step = 100;}
  if (stepYear*50 > minimumStep)          {this.scale = TimeStep.SCALE.YEAR;        this.step = 50;}
  if (stepYear*10 > minimumStep)          {this.scale = TimeStep.SCALE.YEAR;        this.step = 10;}
  if (stepYear*5 > minimumStep)           {this.scale = TimeStep.SCALE.YEAR;        this.step = 5;}
  if (stepYear > minimumStep)             {this.scale = TimeStep.SCALE.YEAR;        this.step = 1;}
  if (stepMonth*3 > minimumStep)          {this.scale = TimeStep.SCALE.MONTH;       this.step = 3;}
  if (stepMonth > minimumStep)            {this.scale = TimeStep.SCALE.MONTH;       this.step = 1;}
  if (stepDay*5 > minimumStep)            {this.scale = TimeStep.SCALE.DAY;         this.step = 5;}
  if (stepDay*2 > minimumStep)            {this.scale = TimeStep.SCALE.DAY;         this.step = 2;}
  if (stepDay > minimumStep)              {this.scale = TimeStep.SCALE.DAY;         this.step = 1;}
  if (stepDay/2 > minimumStep)            {this.scale = TimeStep.SCALE.WEEKDAY;     this.step = 1;}
  if (stepHour*4 > minimumStep)           {this.scale = TimeStep.SCALE.HOUR;        this.step = 4;}
  if (stepHour > minimumStep)             {this.scale = TimeStep.SCALE.HOUR;        this.step = 1;}
  if (stepMinute*15 > minimumStep)        {this.scale = TimeStep.SCALE.MINUTE;      this.step = 15;}
  if (stepMinute*10 > minimumStep)        {this.scale = TimeStep.SCALE.MINUTE;      this.step = 10;}
  if (stepMinute*5 > minimumStep)         {this.scale = TimeStep.SCALE.MINUTE;      this.step = 5;}
  if (stepMinute > minimumStep)           {this.scale = TimeStep.SCALE.MINUTE;      this.step = 1;}
  if (stepSecond*15 > minimumStep)        {this.scale = TimeStep.SCALE.SECOND;      this.step = 15;}
  if (stepSecond*10 > minimumStep)        {this.scale = TimeStep.SCALE.SECOND;      this.step = 10;}
  if (stepSecond*5 > minimumStep)         {this.scale = TimeStep.SCALE.SECOND;      this.step = 5;}
  if (stepSecond > minimumStep)           {this.scale = TimeStep.SCALE.SECOND;      this.step = 1;}
  if (stepMillisecond*200 > minimumStep)  {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 200;}
  if (stepMillisecond*100 > minimumStep)  {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 100;}
  if (stepMillisecond*50 > minimumStep)   {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 50;}
  if (stepMillisecond*10 > minimumStep)   {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 10;}
  if (stepMillisecond*5 > minimumStep)    {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 5;}
  if (stepMillisecond > minimumStep)      {this.scale = TimeStep.SCALE.MILLISECOND; this.step = 1;}
};

/**
 * Snap a date to a rounded value. The snap intervals are dependent on the
 * current scale and step.
 * @param {Date} date   the date to be snapped
 */
TimeStep.prototype.snap = function(date) {
  if (this.scale == TimeStep.SCALE.YEAR) {
    var year = date.getFullYear() + Math.round(date.getMonth() / 12);
    date.setFullYear(Math.round(year / this.step) * this.step);
    date.setMonth(0);
    date.setDate(0);
    date.setHours(0);
    date.setMinutes(0);
    date.setSeconds(0);
    date.setMilliseconds(0);
  }
  else if (this.scale == TimeStep.SCALE.MONTH) {
    if (date.getDate() > 15) {
      date.setDate(1);
      date.setMonth(date.getMonth() + 1);
      // important: first set Date to 1, after that change the month.
    }
    else {
      date.setDate(1);
    }

    date.setHours(0);
    date.setMinutes(0);
    date.setSeconds(0);
    date.setMilliseconds(0);
  }
  else if (this.scale == TimeStep.SCALE.DAY ||
      this.scale == TimeStep.SCALE.WEEKDAY) {
    //noinspection FallthroughInSwitchStatementJS
    switch (this.step) {
      case 5:
      case 2:
        date.setHours(Math.round(date.getHours() / 24) * 24); break;
      default:
        date.setHours(Math.round(date.getHours() / 12) * 12); break;
    }
    date.setMinutes(0);
    date.setSeconds(0);
    date.setMilliseconds(0);
  }
  else if (this.scale == TimeStep.SCALE.HOUR) {
    switch (this.step) {
      case 4:
        date.setMinutes(Math.round(date.getMinutes() / 60) * 60); break;
      default:
        date.setMinutes(Math.round(date.getMinutes() / 30) * 30); break;
    }
    date.setSeconds(0);
    date.setMilliseconds(0);
  } else if (this.scale == TimeStep.SCALE.MINUTE) {
    //noinspection FallthroughInSwitchStatementJS
    switch (this.step) {
      case 15:
      case 10:
        date.setMinutes(Math.round(date.getMinutes() / 5) * 5);
        date.setSeconds(0);
        break;
      case 5:
        date.setSeconds(Math.round(date.getSeconds() / 60) * 60); break;
      default:
        date.setSeconds(Math.round(date.getSeconds() / 30) * 30); break;
    }
    date.setMilliseconds(0);
  }
  else if (this.scale == TimeStep.SCALE.SECOND) {
    //noinspection FallthroughInSwitchStatementJS
    switch (this.step) {
      case 15:
      case 10:
        date.setSeconds(Math.round(date.getSeconds() / 5) * 5);
        date.setMilliseconds(0);
        break;
      case 5:
        date.setMilliseconds(Math.round(date.getMilliseconds() / 1000) * 1000); break;
      default:
        date.setMilliseconds(Math.round(date.getMilliseconds() / 500) * 500); break;
    }
  }
  else if (this.scale == TimeStep.SCALE.MILLISECOND) {
    var step = this.step > 5 ? this.step / 2 : 1;
    date.setMilliseconds(Math.round(date.getMilliseconds() / step) * step);
  }
};

/**
 * Check if the current value is a major value (for example when the step
 * is DAY, a major value is each first day of the MONTH)
 * @return {boolean} true if current date is major, else false.
 */
TimeStep.prototype.isMajor = function() {
  switch (this.scale) {
    case TimeStep.SCALE.MILLISECOND:
      return (this.current.getMilliseconds() == 0);
    case TimeStep.SCALE.SECOND:
      return (this.current.getSeconds() == 0);
    case TimeStep.SCALE.MINUTE:
      return (this.current.getHours() == 0) && (this.current.getMinutes() == 0);
    // Note: this is no bug. Major label is equal for both minute and hour scale
    case TimeStep.SCALE.HOUR:
      return (this.current.getHours() == 0);
    case TimeStep.SCALE.WEEKDAY: // intentional fall through
    case TimeStep.SCALE.DAY:
      return (this.current.getDate() == 1);
    case TimeStep.SCALE.MONTH:
      return (this.current.getMonth() == 0);
    case TimeStep.SCALE.YEAR:
      return false;
    default:
      return false;
  }
};


/**
 * Returns formatted text for the minor axislabel, depending on the current
 * date and the scale. For example when scale is MINUTE, the current time is
 * formatted as "hh:mm".
 * @param {Date} [date] custom date. if not provided, current date is taken
 */
TimeStep.prototype.getLabelMinor = function(date) {
  if (date == undefined) {
    date = this.current;
  }

  switch (this.scale) {
    case TimeStep.SCALE.MILLISECOND:  return moment(date).format('SSS');
    case TimeStep.SCALE.SECOND:       return moment(date).format('s');
    case TimeStep.SCALE.MINUTE:       return moment(date).format('HH:mm');
    case TimeStep.SCALE.HOUR:         return moment(date).format('HH:mm');
    case TimeStep.SCALE.WEEKDAY:      return moment(date).format('ddd D');
    case TimeStep.SCALE.DAY:          return moment(date).format('D');
    case TimeStep.SCALE.MONTH:        return moment(date).format('MMM');
    case TimeStep.SCALE.YEAR:         return moment(date).format('YYYY');
    default:                          return '';
  }
};


/**
 * Returns formatted text for the major axis label, depending on the current
 * date and the scale. For example when scale is MINUTE, the major scale is
 * hours, and the hour will be formatted as "hh".
 * @param {Date} [date] custom date. if not provided, current date is taken
 */
TimeStep.prototype.getLabelMajor = function(date) {
  if (date == undefined) {
    date = this.current;
  }

  //noinspection FallthroughInSwitchStatementJS
  switch (this.scale) {
    case TimeStep.SCALE.MILLISECOND:return moment(date).format('HH:mm:ss');
    case TimeStep.SCALE.SECOND:     return moment(date).format('D MMMM HH:mm');
    case TimeStep.SCALE.MINUTE:
    case TimeStep.SCALE.HOUR:       return moment(date).format('ddd D MMMM');
    case TimeStep.SCALE.WEEKDAY:
    case TimeStep.SCALE.DAY:        return moment(date).format('MMMM YYYY');
    case TimeStep.SCALE.MONTH:      return moment(date).format('YYYY');
    case TimeStep.SCALE.YEAR:       return '';
    default:                        return '';
  }
};

/**
 * @constructor Stack
 * Stacks items on top of each other.
 * @param {ItemSet} parent
 * @param {Object} [options]
 */
function Stack (parent, options) {
  this.parent = parent;

  this.options = options || {};
  this.defaultOptions = {
    order: function (a, b) {
      //return (b.width - a.width) || (a.left - b.left);  // TODO: cleanup
      // Order: ranges over non-ranges, ranged ordered by width, and
      // lastly ordered by start.
      if (a instanceof ItemRange) {
        if (b instanceof ItemRange) {
          var aInt = (a.data.end - a.data.start);
          var bInt = (b.data.end - b.data.start);
          return (aInt - bInt) || (a.data.start - b.data.start);
        }
        else {
          return -1;
        }
      }
      else {
        if (b instanceof ItemRange) {
          return 1;
        }
        else {
          return (a.data.start - b.data.start);
        }
      }
    },
    margin: {
      item: 10
    }
  };

  this.ordered = [];  // ordered items
}

/**
 * Set options for the stack
 * @param {Object} options  Available options:
 *                          {ItemSet} parent
 *                          {Number} margin
 *                          {function} order  Stacking order
 */
Stack.prototype.setOptions = function setOptions (options) {
  util.extend(this.options, options);

  // TODO: register on data changes at the connected parent itemset, and update the changed part only and immediately
};

/**
 * Stack the items such that they don't overlap. The items will have a minimal
 * distance equal to options.margin.item.
 */
Stack.prototype.update = function update() {
  this._order();
  this._stack();
};

/**
 * Order the items. The items are ordered by width first, and by left position
 * second.
 * If a custom order function has been provided via the options, then this will
 * be used.
 * @private
 */
Stack.prototype._order = function _order () {
  var items = this.parent.items;
  if (!items) {
    throw new Error('Cannot stack items: parent does not contain items');
  }

  // TODO: store the sorted items, to have less work later on
  var ordered = [];
  var index = 0;
  // items is a map (no array)
  util.forEach(items, function (item) {
    if (item.visible) {
      ordered[index] = item;
      index++;
    }
  });

  //if a customer stack order function exists, use it.
  var order = this.options.order || this.defaultOptions.order;
  if (!(typeof order === 'function')) {
    throw new Error('Option order must be a function');
  }

  ordered.sort(order);

  this.ordered = ordered;
};

/**
 * Adjust vertical positions of the events such that they don't overlap each
 * other.
 * @private
 */
Stack.prototype._stack = function _stack () {
  var i,
      iMax,
      ordered = this.ordered,
      options = this.options,
      orientation = options.orientation || this.defaultOptions.orientation,
      axisOnTop = (orientation == 'top'),
      margin;

  if (options.margin && options.margin.item !== undefined) {
    margin = options.margin.item;
  }
  else {
    margin = this.defaultOptions.margin.item
  }

  // calculate new, non-overlapping positions
  for (i = 0, iMax = ordered.length; i < iMax; i++) {
    var item = ordered[i];
    var collidingItem = null;
    do {
      // TODO: optimize checking for overlap. when there is a gap without items,
      //  you only need to check for items from the next item on, not from zero
      collidingItem = this.checkOverlap(ordered, i, 0, i - 1, margin);
      if (collidingItem != null) {
        // There is a collision. Reposition the event above the colliding element
        if (axisOnTop) {
          item.top = collidingItem.top + collidingItem.height + margin;
        }
        else {
          item.top = collidingItem.top - item.height - margin;
        }
      }
    } while (collidingItem);
  }
};

/**
 * Check if the destiny position of given item overlaps with any
 * of the other items from index itemStart to itemEnd.
 * @param {Array} items     Array with items
 * @param {int}  itemIndex  Number of the item to be checked for overlap
 * @param {int}  itemStart  First item to be checked.
 * @param {int}  itemEnd    Last item to be checked.
 * @return {Object | null}  colliding item, or undefined when no collisions
 * @param {Number} margin   A minimum required margin.
 *                          If margin is provided, the two items will be
 *                          marked colliding when they overlap or
 *                          when the margin between the two is smaller than
 *                          the requested margin.
 */
Stack.prototype.checkOverlap = function checkOverlap (items, itemIndex,
                                                      itemStart, itemEnd, margin) {
  var collision = this.collision;

  // we loop from end to start, as we suppose that the chance of a
  // collision is larger for items at the end, so check these first.
  var a = items[itemIndex];
  for (var i = itemEnd; i >= itemStart; i--) {
    var b = items[i];
    if (collision(a, b, margin)) {
      if (i != itemIndex) {
        return b;
      }
    }
  }

  return null;
};

/**
 * Test if the two provided items collide
 * The items must have parameters left, width, top, and height.
 * @param {Component} a     The first item
 * @param {Component} b     The second item
 * @param {Number} margin   A minimum required margin.
 *                          If margin is provided, the two items will be
 *                          marked colliding when they overlap or
 *                          when the margin between the two is smaller than
 *                          the requested margin.
 * @return {boolean}        true if a and b collide, else false
 */
Stack.prototype.collision = function collision (a, b, margin) {
  return ((a.left - margin) < (b.left + b.getWidth()) &&
      (a.left + a.getWidth() + margin) > b.left &&
      (a.top - margin) < (b.top + b.height) &&
      (a.top + a.height + margin) > b.top);
};

/**
 * @constructor Range
 * A Range controls a numeric range with a start and end value.
 * The Range adjusts the range based on mouse events or programmatic changes,
 * and triggers events when the range is changing or has been changed.
 * @param {Object} [options]   See description at Range.setOptions
 * @extends Controller
 */
function Range(options) {
  this.id = util.randomUUID();
  this.start = null; // Number
  this.end = null;   // Number

  this.options = options || {};

  this.setOptions(options);
}

/**
 * Set options for the range controller
 * @param {Object} options      Available options:
 *                              {Number} min    Minimum value for start
 *                              {Number} max    Maximum value for end
 *                              {Number} zoomMin    Set a minimum value for
 *                                                  (end - start).
 *                              {Number} zoomMax    Set a maximum value for
 *                                                  (end - start).
 */
Range.prototype.setOptions = function (options) {
  util.extend(this.options, options);

  // re-apply range with new limitations
  if (this.start !== null && this.end !== null) {
    this.setRange(this.start, this.end);
  }
};

/**
 * Test whether direction has a valid value
 * @param {String} direction    'horizontal' or 'vertical'
 */
function validateDirection (direction) {
  if (direction != 'horizontal' && direction != 'vertical') {
    throw new TypeError('Unknown direction "' + direction + '". ' +
        'Choose "horizontal" or "vertical".');
  }
}

/**
 * Add listeners for mouse and touch events to the component
 * @param {Component} component
 * @param {String} event        Available events: 'move', 'zoom'
 * @param {String} direction    Available directions: 'horizontal', 'vertical'
 */
Range.prototype.subscribe = function (component, event, direction) {
  var me = this;

  if (event == 'move') {
    // drag start listener
    component.on('dragstart', function (event) {
      me._onDragStart(event, component);
    });

    // drag listener
    component.on('drag', function (event) {
      me._onDrag(event, component, direction);
    });

    // drag end listener
    component.on('dragend', function (event) {
      me._onDragEnd(event, component);
    });
  }
  else if (event == 'zoom') {
    // mouse wheel
    function mousewheel (event) {
      me._onMouseWheel(event, component, direction);
    }
    component.on('mousewheel', mousewheel);
    component.on('DOMMouseScroll', mousewheel); // For FF

    // pinch
    component.on('touch', function (event) {
      me._onTouch();
    });
    component.on('pinch', function (event) {
      me._onPinch(event, component, direction);
    });
  }
  else {
    throw new TypeError('Unknown event "' + event + '". ' +
        'Choose "move" or "zoom".');
  }
};

/**
 * Event handler
 * @param {String} event       name of the event, for example 'click', 'mousemove'
 * @param {function} callback  callback handler, invoked with the raw HTML Event
 *                             as parameter.
 */
Range.prototype.on = function (event, callback) {
  events.addListener(this, event, callback);
};

/**
 * Trigger an event
 * @param {String} event    name of the event, available events: 'rangechange',
 *                          'rangechanged'
 * @private
 */
Range.prototype._trigger = function (event) {
  events.trigger(this, event, {
    start: this.start,
    end: this.end
  });
};

/**
 * Set a new start and end range
 * @param {Number} [start]
 * @param {Number} [end]
 */
Range.prototype.setRange = function(start, end) {
  var changed = this._applyRange(start, end);
  if (changed) {
    this._trigger('rangechange');
    this._trigger('rangechanged');
  }
};

/**
 * Set a new start and end range. This method is the same as setRange, but
 * does not trigger a range change and range changed event, and it returns
 * true when the range is changed
 * @param {Number} [start]
 * @param {Number} [end]
 * @return {Boolean} changed
 * @private
 */
Range.prototype._applyRange = function(start, end) {
  var newStart = (start != null) ? util.convert(start, 'Number') : this.start,
      newEnd   = (end != null)   ? util.convert(end, 'Number')   : this.end,
      max = (this.options.max != null) ? util.convert(this.options.max, 'Date').valueOf() : null,
      min = (this.options.min != null) ? util.convert(this.options.min, 'Date').valueOf() : null,
      diff;

  // check for valid number
  if (isNaN(newStart) || newStart === null) {
    throw new Error('Invalid start "' + start + '"');
  }
  if (isNaN(newEnd) || newEnd === null) {
    throw new Error('Invalid end "' + end + '"');
  }

  // prevent start < end
  if (newEnd < newStart) {
    newEnd = newStart;
  }

  // prevent start < min
  if (min !== null) {
    if (newStart < min) {
      diff = (min - newStart);
      newStart += diff;
      newEnd += diff;

      // prevent end > max
      if (max != null) {
        if (newEnd > max) {
          newEnd = max;
        }
      }
    }
  }

  // prevent end > max
  if (max !== null) {
    if (newEnd > max) {
      diff = (newEnd - max);
      newStart -= diff;
      newEnd -= diff;

      // prevent start < min
      if (min != null) {
        if (newStart < min) {
          newStart = min;
        }
      }
    }
  }

  // prevent (end-start) < zoomMin
  if (this.options.zoomMin !== null) {
    var zoomMin = parseFloat(this.options.zoomMin);
    if (zoomMin < 0) {
      zoomMin = 0;
    }
    if ((newEnd - newStart) < zoomMin) {
      if ((this.end - this.start) === zoomMin) {
        // ignore this action, we are already zoomed to the minimum
        newStart = this.start;
        newEnd = this.end;
      }
      else {
        // zoom to the minimum
        diff = (zoomMin - (newEnd - newStart));
        newStart -= diff / 2;
        newEnd += diff / 2;
      }
    }
  }

  // prevent (end-start) > zoomMax
  if (this.options.zoomMax !== null) {
    var zoomMax = parseFloat(this.options.zoomMax);
    if (zoomMax < 0) {
      zoomMax = 0;
    }
    if ((newEnd - newStart) > zoomMax) {
      if ((this.end - this.start) === zoomMax) {
        // ignore this action, we are already zoomed to the maximum
        newStart = this.start;
        newEnd = this.end;
      }
      else {
        // zoom to the maximum
        diff = ((newEnd - newStart) - zoomMax);
        newStart += diff / 2;
        newEnd -= diff / 2;
      }
    }
  }

  var changed = (this.start != newStart || this.end != newEnd);

  this.start = newStart;
  this.end = newEnd;

  return changed;
};

/**
 * Retrieve the current range.
 * @return {Object} An object with start and end properties
 */
Range.prototype.getRange = function() {
  return {
    start: this.start,
    end: this.end
  };
};

/**
 * Calculate the conversion offset and scale for current range, based on
 * the provided width
 * @param {Number} width
 * @returns {{offset: number, scale: number}} conversion
 */
Range.prototype.conversion = function (width) {
  return Range.conversion(this.start, this.end, width);
};

/**
 * Static method to calculate the conversion offset and scale for a range,
 * based on the provided start, end, and width
 * @param {Number} start
 * @param {Number} end
 * @param {Number} width
 * @returns {{offset: number, scale: number}} conversion
 */
Range.conversion = function (start, end, width) {
  if (width != 0 && (end - start != 0)) {
    return {
      offset: start,
      scale: width / (end - start)
    }
  }
  else {
    return {
      offset: 0,
      scale: 1
    };
  }
};

// global (private) object to store drag params
var touchParams = {};

/**
 * Start dragging horizontally or vertically
 * @param {Event} event
 * @param {Object} component
 * @private
 */
Range.prototype._onDragStart = function(event, component) {
  // refuse to drag when we where pinching to prevent the timeline make a jump
  // when releasing the fingers in opposite order from the touch screen
  if (touchParams.pinching) return;

  touchParams.start = this.start;
  touchParams.end = this.end;

  var frame = component.frame;
  if (frame) {
    frame.style.cursor = 'move';
  }
};

/**
 * Perform dragging operating.
 * @param {Event} event
 * @param {Component} component
 * @param {String} direction    'horizontal' or 'vertical'
 * @private
 */
Range.prototype._onDrag = function (event, component, direction) {
  validateDirection(direction);

  // refuse to drag when we where pinching to prevent the timeline make a jump
  // when releasing the fingers in opposite order from the touch screen
  if (touchParams.pinching) return;

  var delta = (direction == 'horizontal') ? event.gesture.deltaX : event.gesture.deltaY,
      interval = (touchParams.end - touchParams.start),
      width = (direction == 'horizontal') ? component.width : component.height,
      diffRange = -delta / width * interval;

  this._applyRange(touchParams.start + diffRange, touchParams.end + diffRange);

  // fire a rangechange event
  this._trigger('rangechange');
};

/**
 * Stop dragging operating.
 * @param {event} event
 * @param {Component} component
 * @private
 */
Range.prototype._onDragEnd = function (event, component) {
  // refuse to drag when we where pinching to prevent the timeline make a jump
  // when releasing the fingers in opposite order from the touch screen
  if (touchParams.pinching) return;

  if (component.frame) {
    component.frame.style.cursor = 'auto';
  }

  // fire a rangechanged event
  this._trigger('rangechanged');
};

/**
 * Event handler for mouse wheel event, used to zoom
 * Code from http://adomas.org/javascript-mouse-wheel/
 * @param {Event} event
 * @param {Component} component
 * @param {String} direction    'horizontal' or 'vertical'
 * @private
 */
Range.prototype._onMouseWheel = function(event, component, direction) {
  validateDirection(direction);

  // retrieve delta
  var delta = 0;
  if (event.wheelDelta) { /* IE/Opera. */
    delta = event.wheelDelta / 120;
  } else if (event.detail) { /* Mozilla case. */
    // In Mozilla, sign of delta is different than in IE.
    // Also, delta is multiple of 3.
    delta = -event.detail / 3;
  }

  // If delta is nonzero, handle it.
  // Basically, delta is now positive if wheel was scrolled up,
  // and negative, if wheel was scrolled down.
  if (delta) {
    // perform the zoom action. Delta is normally 1 or -1

    // adjust a negative delta such that zooming in with delta 0.1
    // equals zooming out with a delta -0.1
    var scale;
    if (delta < 0) {
      scale = 1 - (delta / 5);
    }
    else {
      scale = 1 / (1 + (delta / 5)) ;
    }

    // calculate center, the date to zoom around
    var gesture = util.fakeGesture(this, event),
        pointer = getPointer(gesture.touches[0], component.frame),
        pointerDate = this._pointerToDate(component, direction, pointer);

    this.zoom(scale, pointerDate);
  }

  // Prevent default actions caused by mouse wheel
  // (else the page and timeline both zoom and scroll)
  util.preventDefault(event);
};

/**
 * On start of a touch gesture, initialize scale to 1
 * @private
 */
Range.prototype._onTouch = function () {
  touchParams.start = this.start;
  touchParams.end = this.end;
  touchParams.pinching = false;
  touchParams.center = null;
};

/**
 * Handle pinch event
 * @param {Event} event
 * @param {Component} component
 * @param {String} direction    'horizontal' or 'vertical'
 * @private
 */
Range.prototype._onPinch = function (event, component, direction) {
  touchParams.pinching = true;

  if (event.gesture.touches.length > 1) {
    if (!touchParams.center) {
      touchParams.center = getPointer(event.gesture.center, component.frame);
    }

    var scale = 1 / event.gesture.scale,
        initDate = this._pointerToDate(component, direction, touchParams.center),
        center = getPointer(event.gesture.center, component.frame),
        date = this._pointerToDate(component, direction, center),
        delta = date - initDate; // TODO: utilize delta

    // calculate new start and end
    var newStart = parseInt(initDate + (touchParams.start - initDate) * scale);
    var newEnd = parseInt(initDate + (touchParams.end - initDate) * scale);

    // apply new range
    this.setRange(newStart, newEnd);
  }
};

/**
 * Helper function to calculate the center date for zooming
 * @param {Component} component
 * @param {{x: Number, y: Number}} pointer
 * @param {String} direction    'horizontal' or 'vertical'
 * @return {number} date
 * @private
 */
Range.prototype._pointerToDate = function (component, direction, pointer) {
  var conversion;
  if (direction == 'horizontal') {
    var width = component.width;
    conversion = this.conversion(width);
    return pointer.x / conversion.scale + conversion.offset;
  }
  else {
    var height = component.height;
    conversion = this.conversion(height);
    return pointer.y / conversion.scale + conversion.offset;
  }
};

/**
 * Get the pointer location relative to the location of the dom element
 * @param {{pageX: Number, pageY: Number}} touch
 * @param {Element} element   HTML DOM element
 * @return {{x: Number, y: Number}} pointer
 * @private
 */
function getPointer (touch, element) {
  return {
    x: touch.pageX - vis.util.getAbsoluteLeft(element),
    y: touch.pageY - vis.util.getAbsoluteTop(element)
  };
}

/**
 * Zoom the range the given scale in or out. Start and end date will
 * be adjusted, and the timeline will be redrawn. You can optionally give a
 * date around which to zoom.
 * For example, try scale = 0.9 or 1.1
 * @param {Number} scale      Scaling factor. Values above 1 will zoom out,
 *                            values below 1 will zoom in.
 * @param {Number} [center]   Value representing a date around which will
 *                            be zoomed.
 */
Range.prototype.zoom = function(scale, center) {
  // if centerDate is not provided, take it half between start Date and end Date
  if (center == null) {
    center = (this.start + this.end) / 2;
  }

  // calculate new start and end
  var newStart = center + (this.start - center) * scale;
  var newEnd = center + (this.end - center) * scale;

  this.setRange(newStart, newEnd);
};

/**
 * Move the range with a given delta to the left or right. Start and end
 * value will be adjusted. For example, try delta = 0.1 or -0.1
 * @param {Number}  delta     Moving amount. Positive value will move right,
 *                            negative value will move left
 */
Range.prototype.move = function(delta) {
  // zoom start Date and end Date relative to the centerDate
  var diff = (this.end - this.start);

  // apply new values
  var newStart = this.start + diff * delta;
  var newEnd = this.end + diff * delta;

  // TODO: reckon with min and max range

  this.start = newStart;
  this.end = newEnd;
};

/**
 * Move the range to a new center point
 * @param {Number} moveTo      New center point of the range
 */
Range.prototype.moveTo = function(moveTo) {
  var center = (this.start + this.end) / 2;

  var diff = center - moveTo;

  // calculate new start and end
  var newStart = this.start - diff;
  var newEnd = this.end - diff;

  this.setRange(newStart, newEnd);
};

/**
 * @constructor Controller
 *
 * A Controller controls the reflows and repaints of all visual components
 */
function Controller () {
  this.id = util.randomUUID();
  this.components = {};

  this.repaintTimer = undefined;
  this.reflowTimer = undefined;
}

/**
 * Add a component to the controller
 * @param {Component} component
 */
Controller.prototype.add = function add(component) {
  // validate the component
  if (component.id == undefined) {
    throw new Error('Component has no field id');
  }
  if (!(component instanceof Component) && !(component instanceof Controller)) {
    throw new TypeError('Component must be an instance of ' +
        'prototype Component or Controller');
  }

  // add the component
  component.controller = this;
  this.components[component.id] = component;
};

/**
 * Remove a component from the controller
 * @param {Component | String} component
 */
Controller.prototype.remove = function remove(component) {
  var id;
  for (id in this.components) {
    if (this.components.hasOwnProperty(id)) {
      if (id == component || this.components[id] == component) {
        break;
      }
    }
  }

  if (id) {
    delete this.components[id];
  }
};

/**
 * Request a reflow. The controller will schedule a reflow
 * @param {Boolean} [force]     If true, an immediate reflow is forced. Default
 *                              is false.
 */
Controller.prototype.requestReflow = function requestReflow(force) {
  if (force) {
    this.reflow();
  }
  else {
    if (!this.reflowTimer) {
      var me = this;
      this.reflowTimer = setTimeout(function () {
        me.reflowTimer = undefined;
        me.reflow();
      }, 0);
    }
  }
};

/**
 * Request a repaint. The controller will schedule a repaint
 * @param {Boolean} [force]    If true, an immediate repaint is forced. Default
 *                             is false.
 */
Controller.prototype.requestRepaint = function requestRepaint(force) {
  if (force) {
    this.repaint();
  }
  else {
    if (!this.repaintTimer) {
      var me = this;
      this.repaintTimer = setTimeout(function () {
        me.repaintTimer = undefined;
        me.repaint();
      }, 0);
    }
  }
};

/**
 * Repaint all components
 */
Controller.prototype.repaint = function repaint() {
  var changed = false;

  // cancel any running repaint request
  if (this.repaintTimer) {
    clearTimeout(this.repaintTimer);
    this.repaintTimer = undefined;
  }

  var done = {};

  function repaint(component, id) {
    if (!(id in done)) {
      // first repaint the components on which this component is dependent
      if (component.depends) {
        component.depends.forEach(function (dep) {
          repaint(dep, dep.id);
        });
      }
      if (component.parent) {
        repaint(component.parent, component.parent.id);
      }

      // repaint the component itself and mark as done
      changed = component.repaint() || changed;
      done[id] = true;
    }
  }

  util.forEach(this.components, repaint);

  // immediately reflow when needed
  if (changed) {
    this.reflow();
  }
  // TODO: limit the number of nested reflows/repaints, prevent loop
};

/**
 * Reflow all components
 */
Controller.prototype.reflow = function reflow() {
  var resized = false;

  // cancel any running repaint request
  if (this.reflowTimer) {
    clearTimeout(this.reflowTimer);
    this.reflowTimer = undefined;
  }

  var done = {};

  function reflow(component, id) {
    if (!(id in done)) {
      // first reflow the components on which this component is dependent
      if (component.depends) {
        component.depends.forEach(function (dep) {
          reflow(dep, dep.id);
        });
      }
      if (component.parent) {
        reflow(component.parent, component.parent.id);
      }

      // reflow the component itself and mark as done
      resized = component.reflow() || resized;
      done[id] = true;
    }
  }

  util.forEach(this.components, reflow);

  // immediately repaint when needed
  if (resized) {
    this.repaint();
  }
  // TODO: limit the number of nested reflows/repaints, prevent loop
};

/**
 * Prototype for visual components
 */
function Component () {
  this.id = null;
  this.parent = null;
  this.depends = null;
  this.controller = null;
  this.options = null;

  this.frame = null; // main DOM element
  this.top = 0;
  this.left = 0;
  this.width = 0;
  this.height = 0;
}

/**
 * Set parameters for the frame. Parameters will be merged in current parameter
 * set.
 * @param {Object} options  Available parameters:
 *                          {String | function} [className]
 *                          {EventBus} [eventBus]
 *                          {String | Number | function} [left]
 *                          {String | Number | function} [top]
 *                          {String | Number | function} [width]
 *                          {String | Number | function} [height]
 */
Component.prototype.setOptions = function setOptions(options) {
  if (options) {
    util.extend(this.options, options);

    if (this.controller) {
      this.requestRepaint();
      this.requestReflow();
    }
  }
};

/**
 * Get an option value by name
 * The function will first check this.options object, and else will check
 * this.defaultOptions.
 * @param {String} name
 * @return {*} value
 */
Component.prototype.getOption = function getOption(name) {
  var value;
  if (this.options) {
    value = this.options[name];
  }
  if (value === undefined && this.defaultOptions) {
    value = this.defaultOptions[name];
  }
  return value;
};

/**
 * Get the container element of the component, which can be used by a child to
 * add its own widgets. Not all components do have a container for childs, in
 * that case null is returned.
 * @returns {HTMLElement | null} container
 */
// TODO: get rid of the getContainer and getFrame methods, provide these via the options
Component.prototype.getContainer = function getContainer() {
  // should be implemented by the component
  return null;
};

/**
 * Get the frame element of the component, the outer HTML DOM element.
 * @returns {HTMLElement | null} frame
 */
Component.prototype.getFrame = function getFrame() {
  return this.frame;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
Component.prototype.repaint = function repaint() {
  // should be implemented by the component
  return false;
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
Component.prototype.reflow = function reflow() {
  // should be implemented by the component
  return false;
};

/**
 * Hide the component from the DOM
 * @return {Boolean} changed
 */
Component.prototype.hide = function hide() {
  if (this.frame && this.frame.parentNode) {
    this.frame.parentNode.removeChild(this.frame);
    return true;
  }
  else {
    return false;
  }
};

/**
 * Show the component in the DOM (when not already visible).
 * A repaint will be executed when the component is not visible
 * @return {Boolean} changed
 */
Component.prototype.show = function show() {
  if (!this.frame || !this.frame.parentNode) {
    return this.repaint();
  }
  else {
    return false;
  }
};

/**
 * Request a repaint. The controller will schedule a repaint
 */
Component.prototype.requestRepaint = function requestRepaint() {
  if (this.controller) {
    this.controller.requestRepaint();
  }
  else {
    throw new Error('Cannot request a repaint: no controller configured');
    // TODO: just do a repaint when no parent is configured?
  }
};

/**
 * Request a reflow. The controller will schedule a reflow
 */
Component.prototype.requestReflow = function requestReflow() {
  if (this.controller) {
    this.controller.requestReflow();
  }
  else {
    throw new Error('Cannot request a reflow: no controller configured');
    // TODO: just do a reflow when no parent is configured?
  }
};

/**
 * A panel can contain components
 * @param {Component} [parent]
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]    Available parameters:
 *                              {String | Number | function} [left]
 *                              {String | Number | function} [top]
 *                              {String | Number | function} [width]
 *                              {String | Number | function} [height]
 *                              {String | function} [className]
 * @constructor Panel
 * @extends Component
 */
function Panel(parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  this.options = options || {};
}

Panel.prototype = new Component();

/**
 * Set options. Will extend the current options.
 * @param {Object} [options]    Available parameters:
 *                              {String | function} [className]
 *                              {String | Number | function} [left]
 *                              {String | Number | function} [top]
 *                              {String | Number | function} [width]
 *                              {String | Number | function} [height]
 */
Panel.prototype.setOptions = Component.prototype.setOptions;

/**
 * Get the container element of the panel, which can be used by a child to
 * add its own widgets.
 * @returns {HTMLElement} container
 */
Panel.prototype.getContainer = function () {
  return this.frame;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
Panel.prototype.repaint = function () {
  var changed = 0,
      update = util.updateProperty,
      asSize = util.option.asSize,
      options = this.options,
      frame = this.frame;
  if (!frame) {
    frame = document.createElement('div');
    frame.className = 'panel';

    var className = options.className;
    if (className) {
      if (typeof className == 'function') {
        util.addClassName(frame, String(className()));
      }
      else {
        util.addClassName(frame, String(className));
      }
    }

    this.frame = frame;
    changed += 1;
  }
  if (!frame.parentNode) {
    if (!this.parent) {
      throw new Error('Cannot repaint panel: no parent attached');
    }
    var parentContainer = this.parent.getContainer();
    if (!parentContainer) {
      throw new Error('Cannot repaint panel: parent has no container element');
    }
    parentContainer.appendChild(frame);
    changed += 1;
  }

  changed += update(frame.style, 'top',    asSize(options.top, '0px'));
  changed += update(frame.style, 'left',   asSize(options.left, '0px'));
  changed += update(frame.style, 'width',  asSize(options.width, '100%'));
  changed += update(frame.style, 'height', asSize(options.height, '100%'));

  return (changed > 0);
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
Panel.prototype.reflow = function () {
  var changed = 0,
      update = util.updateProperty,
      frame = this.frame;

  if (frame) {
    changed += update(this, 'top', frame.offsetTop);
    changed += update(this, 'left', frame.offsetLeft);
    changed += update(this, 'width', frame.offsetWidth);
    changed += update(this, 'height', frame.offsetHeight);
  }
  else {
    changed += 1;
  }

  return (changed > 0);
};

/**
 * A root panel can hold components. The root panel must be initialized with
 * a DOM element as container.
 * @param {HTMLElement} container
 * @param {Object} [options]    Available parameters: see RootPanel.setOptions.
 * @constructor RootPanel
 * @extends Panel
 */
function RootPanel(container, options) {
  this.id = util.randomUUID();
  this.container = container;

  this.options = options || {};
  this.defaultOptions = {
    autoResize: true
  };

  this.listeners = {}; // event listeners
}

RootPanel.prototype = new Panel();

/**
 * Set options. Will extend the current options.
 * @param {Object} [options]    Available parameters:
 *                              {String | function} [className]
 *                              {String | Number | function} [left]
 *                              {String | Number | function} [top]
 *                              {String | Number | function} [width]
 *                              {String | Number | function} [height]
 *                              {Boolean | function} [autoResize]
 */
RootPanel.prototype.setOptions = Component.prototype.setOptions;

/**
 * Repaint the component
 * @return {Boolean} changed
 */
RootPanel.prototype.repaint = function () {
  var changed = 0,
      update = util.updateProperty,
      asSize = util.option.asSize,
      options = this.options,
      frame = this.frame;

  if (!frame) {
    frame = document.createElement('div');

    this.frame = frame;

    changed += 1;
  }
  if (!frame.parentNode) {
    if (!this.container) {
      throw new Error('Cannot repaint root panel: no container attached');
    }
    this.container.appendChild(frame);
    changed += 1;
  }

  frame.className = 'vis timeline rootpanel ' + options.orientation;
  var className = options.className;
  if (className) {
    util.addClassName(frame, util.option.asString(className));
  }

  changed += update(frame.style, 'top',    asSize(options.top, '0px'));
  changed += update(frame.style, 'left',   asSize(options.left, '0px'));
  changed += update(frame.style, 'width',  asSize(options.width, '100%'));
  changed += update(frame.style, 'height', asSize(options.height, '100%'));

  this._updateEventEmitters();
  this._updateWatch();

  return (changed > 0);
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
RootPanel.prototype.reflow = function () {
  var changed = 0,
      update = util.updateProperty,
      frame = this.frame;

  if (frame) {
    changed += update(this, 'top', frame.offsetTop);
    changed += update(this, 'left', frame.offsetLeft);
    changed += update(this, 'width', frame.offsetWidth);
    changed += update(this, 'height', frame.offsetHeight);
  }
  else {
    changed += 1;
  }

  return (changed > 0);
};

/**
 * Update watching for resize, depending on the current option
 * @private
 */
RootPanel.prototype._updateWatch = function () {
  var autoResize = this.getOption('autoResize');
  if (autoResize) {
    this._watch();
  }
  else {
    this._unwatch();
  }
};

/**
 * Watch for changes in the size of the frame. On resize, the Panel will
 * automatically redraw itself.
 * @private
 */
RootPanel.prototype._watch = function () {
  var me = this;

  this._unwatch();

  var checkSize = function () {
    var autoResize = me.getOption('autoResize');
    if (!autoResize) {
      // stop watching when the option autoResize is changed to false
      me._unwatch();
      return;
    }

    if (me.frame) {
      // check whether the frame is resized
      if ((me.frame.clientWidth != me.width) ||
          (me.frame.clientHeight != me.height)) {
        me.requestReflow();
      }
    }
  };

  // TODO: automatically cleanup the event listener when the frame is deleted
  util.addEventListener(window, 'resize', checkSize);

  this.watchTimer = setInterval(checkSize, 1000);
};

/**
 * Stop watching for a resize of the frame.
 * @private
 */
RootPanel.prototype._unwatch = function () {
  if (this.watchTimer) {
    clearInterval(this.watchTimer);
    this.watchTimer = undefined;
  }

  // TODO: remove event listener on window.resize
};

/**
 * Event handler
 * @param {String} event       name of the event, for example 'click', 'mousemove'
 * @param {function} callback  callback handler, invoked with the raw HTML Event
 *                             as parameter.
 */
RootPanel.prototype.on = function (event, callback) {
  // register the listener at this component
  var arr = this.listeners[event];
  if (!arr) {
    arr = [];
    this.listeners[event] = arr;
  }
  arr.push(callback);

  this._updateEventEmitters();
};

/**
 * Update the event listeners for all event emitters
 * @private
 */
RootPanel.prototype._updateEventEmitters = function () {
  if (this.listeners) {
    var me = this;
    util.forEach(this.listeners, function (listeners, event) {
      if (!me.emitters) {
        me.emitters = {};
      }
      if (!(event in me.emitters)) {
        // create event
        var frame = me.frame;
        if (frame) {
          //console.log('Created a listener for event ' + event + ' on component ' + me.id); // TODO: cleanup logging
          var callback = function(event) {
            listeners.forEach(function (listener) {
              // TODO: filter on event target!
              listener(event);
            });
          };
          me.emitters[event] = callback;

          if (!me.hammer) {
            me.hammer = Hammer(frame, {
              prevent_default: true
            });
          }
          me.hammer.on(event, callback);
        }
      }
    });

    // TODO: be able to delete event listeners
    // TODO: be able to move event listeners to a parent when available
  }
};

/**
 * A horizontal time axis
 * @param {Component} parent
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]        See TimeAxis.setOptions for the available
 *                                  options.
 * @constructor TimeAxis
 * @extends Component
 */
function TimeAxis (parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  this.dom = {
    majorLines: [],
    majorTexts: [],
    minorLines: [],
    minorTexts: [],
    redundant: {
      majorLines: [],
      majorTexts: [],
      minorLines: [],
      minorTexts: []
    }
  };
  this.props = {
    range: {
      start: 0,
      end: 0,
      minimumStep: 0
    },
    lineTop: 0
  };

  this.options = options || {};
  this.defaultOptions = {
    orientation: 'bottom',  // supported: 'top', 'bottom'
    // TODO: implement timeaxis orientations 'left' and 'right'
    showMinorLabels: true,
    showMajorLabels: true
  };

  this.conversion = null;
  this.range = null;
}

TimeAxis.prototype = new Component();

// TODO: comment options
TimeAxis.prototype.setOptions = Component.prototype.setOptions;

/**
 * Set a range (start and end)
 * @param {Range | Object} range  A Range or an object containing start and end.
 */
TimeAxis.prototype.setRange = function (range) {
  if (!(range instanceof Range) && (!range || !range.start || !range.end)) {
    throw new TypeError('Range must be an instance of Range, ' +
        'or an object containing start and end.');
  }
  this.range = range;
};

/**
 * Convert a position on screen (pixels) to a datetime
 * @param {int}     x    Position on the screen in pixels
 * @return {Date}   time The datetime the corresponds with given position x
 */
TimeAxis.prototype.toTime = function(x) {
  var conversion = this.conversion;
  return new Date(x / conversion.scale + conversion.offset);
};

/**
 * Convert a datetime (Date object) into a position on the screen
 * @param {Date}   time A date
 * @return {int}   x    The position on the screen in pixels which corresponds
 *                      with the given date.
 * @private
 */
TimeAxis.prototype.toScreen = function(time) {
  var conversion = this.conversion;
  return (time.valueOf() - conversion.offset) * conversion.scale;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
TimeAxis.prototype.repaint = function () {
  var changed = 0,
      update = util.updateProperty,
      asSize = util.option.asSize,
      options = this.options,
      orientation = this.getOption('orientation'),
      props = this.props,
      step = this.step;

  var frame = this.frame;
  if (!frame) {
    frame = document.createElement('div');
    this.frame = frame;
    changed += 1;
  }
  frame.className = 'axis';
  // TODO: custom className?

  if (!frame.parentNode) {
    if (!this.parent) {
      throw new Error('Cannot repaint time axis: no parent attached');
    }
    var parentContainer = this.parent.getContainer();
    if (!parentContainer) {
      throw new Error('Cannot repaint time axis: parent has no container element');
    }
    parentContainer.appendChild(frame);

    changed += 1;
  }

  var parent = frame.parentNode;
  if (parent) {
    var beforeChild = frame.nextSibling;
    parent.removeChild(frame); //  take frame offline while updating (is almost twice as fast)

    var defaultTop = (orientation == 'bottom' && this.props.parentHeight && this.height) ?
        (this.props.parentHeight - this.height) + 'px' :
        '0px';
    changed += update(frame.style, 'top', asSize(options.top, defaultTop));
    changed += update(frame.style, 'left', asSize(options.left, '0px'));
    changed += update(frame.style, 'width', asSize(options.width, '100%'));
    changed += update(frame.style, 'height', asSize(options.height, this.height + 'px'));

    // get characters width and height
    this._repaintMeasureChars();

    if (this.step) {
      this._repaintStart();

      step.first();
      var xFirstMajorLabel = undefined;
      var max = 0;
      while (step.hasNext() && max < 1000) {
        max++;
        var cur = step.getCurrent(),
            x = this.toScreen(cur),
            isMajor = step.isMajor();

        // TODO: lines must have a width, such that we can create css backgrounds

        if (this.getOption('showMinorLabels')) {
          this._repaintMinorText(x, step.getLabelMinor());
        }

        if (isMajor && this.getOption('showMajorLabels')) {
          if (x > 0) {
            if (xFirstMajorLabel == undefined) {
              xFirstMajorLabel = x;
            }
            this._repaintMajorText(x, step.getLabelMajor());
          }
          this._repaintMajorLine(x);
        }
        else {
          this._repaintMinorLine(x);
        }

        step.next();
      }

      // create a major label on the left when needed
      if (this.getOption('showMajorLabels')) {
        var leftTime = this.toTime(0),
            leftText = step.getLabelMajor(leftTime),
            widthText = leftText.length * (props.majorCharWidth || 10) + 10; // upper bound estimation

        if (xFirstMajorLabel == undefined || widthText < xFirstMajorLabel) {
          this._repaintMajorText(0, leftText);
        }
      }

      this._repaintEnd();
    }

    this._repaintLine();

    // put frame online again
    if (beforeChild) {
      parent.insertBefore(frame, beforeChild);
    }
    else {
      parent.appendChild(frame)
    }
  }

  return (changed > 0);
};

/**
 * Start a repaint. Move all DOM elements to a redundant list, where they
 * can be picked for re-use, or can be cleaned up in the end
 * @private
 */
TimeAxis.prototype._repaintStart = function () {
  var dom = this.dom,
      redundant = dom.redundant;

  redundant.majorLines = dom.majorLines;
  redundant.majorTexts = dom.majorTexts;
  redundant.minorLines = dom.minorLines;
  redundant.minorTexts = dom.minorTexts;

  dom.majorLines = [];
  dom.majorTexts = [];
  dom.minorLines = [];
  dom.minorTexts = [];
};

/**
 * End a repaint. Cleanup leftover DOM elements in the redundant list
 * @private
 */
TimeAxis.prototype._repaintEnd = function () {
  util.forEach(this.dom.redundant, function (arr) {
    while (arr.length) {
      var elem = arr.pop();
      if (elem && elem.parentNode) {
        elem.parentNode.removeChild(elem);
      }
    }
  });
};


/**
 * Create a minor label for the axis at position x
 * @param {Number} x
 * @param {String} text
 * @private
 */
TimeAxis.prototype._repaintMinorText = function (x, text) {
  // reuse redundant label
  var label = this.dom.redundant.minorTexts.shift();

  if (!label) {
    // create new label
    var content = document.createTextNode('');
    label = document.createElement('div');
    label.appendChild(content);
    label.className = 'text minor';
    this.frame.appendChild(label);
  }
  this.dom.minorTexts.push(label);

  label.childNodes[0].nodeValue = text;
  label.style.left = x + 'px';
  label.style.top  = this.props.minorLabelTop + 'px';
  //label.title = title;  // TODO: this is a heavy operation
};

/**
 * Create a Major label for the axis at position x
 * @param {Number} x
 * @param {String} text
 * @private
 */
TimeAxis.prototype._repaintMajorText = function (x, text) {
  // reuse redundant label
  var label = this.dom.redundant.majorTexts.shift();

  if (!label) {
    // create label
    var content = document.createTextNode(text);
    label = document.createElement('div');
    label.className = 'text major';
    label.appendChild(content);
    this.frame.appendChild(label);
  }
  this.dom.majorTexts.push(label);

  label.childNodes[0].nodeValue = text;
  label.style.top = this.props.majorLabelTop + 'px';
  label.style.left = x + 'px';
  //label.title = title; // TODO: this is a heavy operation
};

/**
 * Create a minor line for the axis at position x
 * @param {Number} x
 * @private
 */
TimeAxis.prototype._repaintMinorLine = function (x) {
  // reuse redundant line
  var line = this.dom.redundant.minorLines.shift();

  if (!line) {
    // create vertical line
    line = document.createElement('div');
    line.className = 'grid vertical minor';
    this.frame.appendChild(line);
  }
  this.dom.minorLines.push(line);

  var props = this.props;
  line.style.top = props.minorLineTop + 'px';
  line.style.height = props.minorLineHeight + 'px';
  line.style.left = (x - props.minorLineWidth / 2) + 'px';
};

/**
 * Create a Major line for the axis at position x
 * @param {Number} x
 * @private
 */
TimeAxis.prototype._repaintMajorLine = function (x) {
  // reuse redundant line
  var line = this.dom.redundant.majorLines.shift();

  if (!line) {
    // create vertical line
    line = document.createElement('DIV');
    line.className = 'grid vertical major';
    this.frame.appendChild(line);
  }
  this.dom.majorLines.push(line);

  var props = this.props;
  line.style.top = props.majorLineTop + 'px';
  line.style.left = (x - props.majorLineWidth / 2) + 'px';
  line.style.height = props.majorLineHeight + 'px';
};


/**
 * Repaint the horizontal line for the axis
 * @private
 */
TimeAxis.prototype._repaintLine = function() {
  var line = this.dom.line,
      frame = this.frame,
      options = this.options;

  // line before all axis elements
  if (this.getOption('showMinorLabels') || this.getOption('showMajorLabels')) {
    if (line) {
      // put this line at the end of all childs
      frame.removeChild(line);
      frame.appendChild(line);
    }
    else {
      // create the axis line
      line = document.createElement('div');
      line.className = 'grid horizontal major';
      frame.appendChild(line);
      this.dom.line = line;
    }

    line.style.top = this.props.lineTop + 'px';
  }
  else {
    if (line && line.parentElement) {
      frame.removeChild(line.line);
      delete this.dom.line;
    }
  }
};

/**
 * Create characters used to determine the size of text on the axis
 * @private
 */
TimeAxis.prototype._repaintMeasureChars = function () {
  // calculate the width and height of a single character
  // this is used to calculate the step size, and also the positioning of the
  // axis
  var dom = this.dom,
      text;

  if (!dom.measureCharMinor) {
    text = document.createTextNode('0');
    var measureCharMinor = document.createElement('DIV');
    measureCharMinor.className = 'text minor measure';
    measureCharMinor.appendChild(text);
    this.frame.appendChild(measureCharMinor);

    dom.measureCharMinor = measureCharMinor;
  }

  if (!dom.measureCharMajor) {
    text = document.createTextNode('0');
    var measureCharMajor = document.createElement('DIV');
    measureCharMajor.className = 'text major measure';
    measureCharMajor.appendChild(text);
    this.frame.appendChild(measureCharMajor);

    dom.measureCharMajor = measureCharMajor;
  }
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
TimeAxis.prototype.reflow = function () {
  var changed = 0,
      update = util.updateProperty,
      frame = this.frame,
      range = this.range;

  if (!range) {
    throw new Error('Cannot repaint time axis: no range configured');
  }

  if (frame) {
    changed += update(this, 'top', frame.offsetTop);
    changed += update(this, 'left', frame.offsetLeft);

    // calculate size of a character
    var props = this.props,
        showMinorLabels = this.getOption('showMinorLabels'),
        showMajorLabels = this.getOption('showMajorLabels'),
        measureCharMinor = this.dom.measureCharMinor,
        measureCharMajor = this.dom.measureCharMajor;
    if (measureCharMinor) {
      props.minorCharHeight = measureCharMinor.clientHeight;
      props.minorCharWidth = measureCharMinor.clientWidth;
    }
    if (measureCharMajor) {
      props.majorCharHeight = measureCharMajor.clientHeight;
      props.majorCharWidth = measureCharMajor.clientWidth;
    }

    var parentHeight = frame.parentNode ? frame.parentNode.offsetHeight : 0;
    if (parentHeight != props.parentHeight) {
      props.parentHeight = parentHeight;
      changed += 1;
    }
    switch (this.getOption('orientation')) {
      case 'bottom':
        props.minorLabelHeight = showMinorLabels ? props.minorCharHeight : 0;
        props.majorLabelHeight = showMajorLabels ? props.majorCharHeight : 0;

        props.minorLabelTop = 0;
        props.majorLabelTop = props.minorLabelTop + props.minorLabelHeight;

        props.minorLineTop = -this.top;
        props.minorLineHeight = Math.max(this.top + props.majorLabelHeight, 0);
        props.minorLineWidth = 1; // TODO: really calculate width

        props.majorLineTop = -this.top;
        props.majorLineHeight = Math.max(this.top + props.minorLabelHeight + props.majorLabelHeight, 0);
        props.majorLineWidth = 1; // TODO: really calculate width

        props.lineTop = 0;

        break;

      case 'top':
        props.minorLabelHeight = showMinorLabels ? props.minorCharHeight : 0;
        props.majorLabelHeight = showMajorLabels ? props.majorCharHeight : 0;

        props.majorLabelTop = 0;
        props.minorLabelTop = props.majorLabelTop + props.majorLabelHeight;

        props.minorLineTop = props.minorLabelTop;
        props.minorLineHeight = Math.max(parentHeight - props.majorLabelHeight - this.top);
        props.minorLineWidth = 1; // TODO: really calculate width

        props.majorLineTop = 0;
        props.majorLineHeight = Math.max(parentHeight - this.top);
        props.majorLineWidth = 1; // TODO: really calculate width

        props.lineTop = props.majorLabelHeight +  props.minorLabelHeight;

        break;

      default:
        throw new Error('Unkown orientation "' + this.getOption('orientation') + '"');
    }

    var height = props.minorLabelHeight + props.majorLabelHeight;
    changed += update(this, 'width', frame.offsetWidth);
    changed += update(this, 'height', height);

    // calculate range and step
    this._updateConversion();

    var start = util.convert(range.start, 'Number'),
        end = util.convert(range.end, 'Number'),
        minimumStep = this.toTime((props.minorCharWidth || 10) * 5).valueOf()
            -this.toTime(0).valueOf();
    this.step = new TimeStep(new Date(start), new Date(end), minimumStep);
    changed += update(props.range, 'start', start);
    changed += update(props.range, 'end', end);
    changed += update(props.range, 'minimumStep', minimumStep.valueOf());
  }

  return (changed > 0);
};

/**
 * Calculate the scale and offset to convert a position on screen to the
 * corresponding date and vice versa.
 * After the method _updateConversion is executed once, the methods toTime
 * and toScreen can be used.
 * @private
 */
TimeAxis.prototype._updateConversion = function() {
  var range = this.range;
  if (!range) {
    throw new Error('No range configured');
  }

  if (range.conversion) {
    this.conversion = range.conversion(this.width);
  }
  else {
    this.conversion = Range.conversion(range.start, range.end, this.width);
  }
};

/**
 * A current time bar
 * @param {Component} parent
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]        Available parameters:
 *                                  {Boolean} [showCurrentTime]
 * @constructor CurrentTime
 * @extends Component
 */

function CurrentTime (parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  this.options = options || {};
  this.defaultOptions = {
    showCurrentTime: false
  };
}

CurrentTime.prototype = new Component();

CurrentTime.prototype.setOptions = Component.prototype.setOptions;

/**
 * Get the container element of the bar, which can be used by a child to
 * add its own widgets.
 * @returns {HTMLElement} container
 */
CurrentTime.prototype.getContainer = function () {
  return this.frame;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
CurrentTime.prototype.repaint = function () {
  var bar = this.frame,
      parent = this.parent,
      parentContainer = parent.parent.getContainer();

  if (!parent) {
    throw new Error('Cannot repaint bar: no parent attached');
  }

  if (!parentContainer) {
    throw new Error('Cannot repaint bar: parent has no container element');
  }

  if (!this.getOption('showCurrentTime')) {
    if (bar) {
      parentContainer.removeChild(bar);
      delete this.frame;
    }

    return;
  }

  if (!bar) {
    bar = document.createElement('div');
    bar.className = 'currenttime';
    bar.style.position = 'absolute';
    bar.style.top = '0px';
    bar.style.height = '100%';

    parentContainer.appendChild(bar);
    this.frame = bar;
  }

  if (!parent.conversion) {
    parent._updateConversion();
  }

  var now = new Date();
  var x = parent.toScreen(now);

  bar.style.left = x + 'px';
  bar.title = 'Current time: ' + now;

  // start a timer to adjust for the new time
  if (this.currentTimeTimer !== undefined) {
    clearTimeout(this.currentTimeTimer);
    delete this.currentTimeTimer;
  }

  var timeline = this;
  var interval = 1 / parent.conversion.scale / 2;

  if (interval < 30) {
    interval = 30;
  }

  this.currentTimeTimer = setTimeout(function() {
    timeline.repaint();
  }, interval);

  return false;
};

/**
 * A custom time bar
 * @param {Component} parent
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]        Available parameters:
 *                                  {Boolean} [showCustomTime]
 * @constructor CustomTime
 * @extends Component
 */

function CustomTime (parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  this.options = options || {};
  this.defaultOptions = {
    showCustomTime: false
  };

  this.listeners = [];
  this.customTime = new Date();
}

CustomTime.prototype = new Component();

CustomTime.prototype.setOptions = Component.prototype.setOptions;

/**
 * Get the container element of the bar, which can be used by a child to
 * add its own widgets.
 * @returns {HTMLElement} container
 */
CustomTime.prototype.getContainer = function () {
  return this.frame;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
CustomTime.prototype.repaint = function () {
  var bar = this.frame,
      parent = this.parent,
      parentContainer = parent.parent.getContainer();

  if (!parent) {
    throw new Error('Cannot repaint bar: no parent attached');
  }

  if (!parentContainer) {
    throw new Error('Cannot repaint bar: parent has no container element');
  }

  if (!this.getOption('showCustomTime')) {
    if (bar) {
      parentContainer.removeChild(bar);
      delete this.frame;
    }

    return;
  }

  if (!bar) {
    bar = document.createElement('div');
    bar.className = 'customtime';
    bar.style.position = 'absolute';
    bar.style.top = '0px';
    bar.style.height = '100%';

    parentContainer.appendChild(bar);

    var drag = document.createElement('div');
    drag.style.position = 'relative';
    drag.style.top = '0px';
    drag.style.left = '-10px';
    drag.style.height = '100%';
    drag.style.width = '20px';
    bar.appendChild(drag);

    this.frame = bar;

    this.subscribe(this, 'movetime');
  }

  if (!parent.conversion) {
    parent._updateConversion();
  }

  var x = parent.toScreen(this.customTime);

  bar.style.left = x + 'px';
  bar.title = 'Time: ' + this.customTime;

  return false;
};

/**
 * Set custom time.
 * @param {Date} time
 */
CustomTime.prototype._setCustomTime = function(time) {
  this.customTime = new Date(time.valueOf());
  this.repaint();
};

/**
 * Retrieve the current custom time.
 * @return {Date} customTime
 */
CustomTime.prototype._getCustomTime = function() {
  return new Date(this.customTime.valueOf());
};

/**
 * Add listeners for mouse and touch events to the component
 * @param {Component} component
 */
CustomTime.prototype.subscribe = function (component, event) {
  var me = this;
  var listener = {
    component: component,
    event: event,
    callback: function (event) {
      me._onMouseDown(event, listener);
    },
    params: {}
  };

  component.on('mousedown', listener.callback);
  me.listeners.push(listener);

};

/**
 * Event handler
 * @param {String} event       name of the event, for example 'click', 'mousemove'
 * @param {function} callback  callback handler, invoked with the raw HTML Event
 *                             as parameter.
 */
CustomTime.prototype.on = function (event, callback) {
  var bar = this.frame;
  if (!bar) {
    throw new Error('Cannot add event listener: no parent attached');
  }

  events.addListener(this, event, callback);
  util.addEventListener(bar, event, callback);
};

/**
 * Start moving horizontally
 * @param {Event} event
 * @param {Object} listener   Listener containing the component and params
 * @private
 */
CustomTime.prototype._onMouseDown = function(event, listener) {
  event = event || window.event;
  var params = listener.params;

  // only react on left mouse button down
  var leftButtonDown = event.which ? (event.which == 1) : (event.button == 1);
  if (!leftButtonDown) {
    return;
  }

  // get mouse position
  params.mouseX = util.getPageX(event);
  params.moved = false;

  params.customTime = this.customTime;

  // add event listeners to handle moving the custom time bar
  var me = this;
  if (!params.onMouseMove) {
    params.onMouseMove = function (event) {
      me._onMouseMove(event, listener);
    };
    util.addEventListener(document, 'mousemove', params.onMouseMove);
  }
  if (!params.onMouseUp) {
    params.onMouseUp = function (event) {
      me._onMouseUp(event, listener);
    };
    util.addEventListener(document, 'mouseup', params.onMouseUp);
  }

  util.stopPropagation(event);
  util.preventDefault(event);
};

/**
 * Perform moving operating.
 * This function activated from within the funcion CustomTime._onMouseDown().
 * @param {Event} event
 * @param {Object} listener
 * @private
 */
CustomTime.prototype._onMouseMove = function (event, listener) {
  event = event || window.event;
  var params = listener.params;
  var parent = this.parent;

  // calculate change in mouse position
  var mouseX = util.getPageX(event);

  if (params.mouseX === undefined) {
    params.mouseX = mouseX;
  }

  var diff = mouseX - params.mouseX;

  // if mouse movement is big enough, register it as a "moved" event
  if (Math.abs(diff) >= 1) {
    params.moved = true;
  }

  var x = parent.toScreen(params.customTime);
  var xnew = x + diff;
  var time = parent.toTime(xnew);
  this._setCustomTime(time);

  // fire a timechange event
  events.trigger(this, 'timechange', {customTime: this.customTime});

  util.preventDefault(event);
};

/**
 * Stop moving operating.
 * This function activated from within the function CustomTime._onMouseDown().
 * @param {event} event
 * @param {Object} listener
 * @private
 */
CustomTime.prototype._onMouseUp = function (event, listener) {
  event = event || window.event;
  var params = listener.params;

  // remove event listeners here, important for Safari
  if (params.onMouseMove) {
    util.removeEventListener(document, 'mousemove', params.onMouseMove);
    params.onMouseMove = null;
  }
  if (params.onMouseUp) {
    util.removeEventListener(document, 'mouseup', params.onMouseUp);
    params.onMouseUp = null;
  }

  if (params.moved) {
    // fire a timechanged event
    events.trigger(this, 'timechanged', {customTime: this.customTime});
  }
};

/**
 * An ItemSet holds a set of items and ranges which can be displayed in a
 * range. The width is determined by the parent of the ItemSet, and the height
 * is determined by the size of the items.
 * @param {Component} parent
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]        See ItemSet.setOptions for the available
 *                                  options.
 * @constructor ItemSet
 * @extends Panel
 */
// TODO: improve performance by replacing all Array.forEach with a for loop
function ItemSet(parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  // one options object is shared by this itemset and all its items
  this.options = options || {};
  this.defaultOptions = {
    type: 'box',
    align: 'center',
    orientation: 'bottom',
    margin: {
      axis: 20,
      item: 10
    },
    padding: 5
  };

  this.dom = {};

  var me = this;
  this.itemsData = null;  // DataSet
  this.range = null;      // Range or Object {start: number, end: number}

  this.listeners = {
    'add': function (event, params, senderId) {
      if (senderId != me.id) {
        me._onAdd(params.items);
      }
    },
    'update': function (event, params, senderId) {
      if (senderId != me.id) {
        me._onUpdate(params.items);
      }
    },
    'remove': function (event, params, senderId) {
      if (senderId != me.id) {
        me._onRemove(params.items);
      }
    }
  };

  this.items = {};      // object with an Item for every data item
  this.selection = [];  // list with the ids of all selected nodes
  this.queue = {};      // queue with id/actions: 'add', 'update', 'delete'
  this.stack = new Stack(this, Object.create(this.options));
  this.conversion = null;

  // TODO: ItemSet should also attach event listeners for rangechange and rangechanged, like timeaxis
}

ItemSet.prototype = new Panel();

// available item types will be registered here
ItemSet.types = {
  box: ItemBox,
  range: ItemRange,
  rangeoverflow: ItemRangeOverflow,
  point: ItemPoint
};

/**
 * Set options for the ItemSet. Existing options will be extended/overwritten.
 * @param {Object} [options] The following options are available:
 *                           {String | function} [className]
 *                              class name for the itemset
 *                           {String} [type]
 *                              Default type for the items. Choose from 'box'
 *                              (default), 'point', or 'range'. The default
 *                              Style can be overwritten by individual items.
 *                           {String} align
 *                              Alignment for the items, only applicable for
 *                              ItemBox. Choose 'center' (default), 'left', or
 *                              'right'.
 *                           {String} orientation
 *                              Orientation of the item set. Choose 'top' or
 *                              'bottom' (default).
 *                           {Number} margin.axis
 *                              Margin between the axis and the items in pixels.
 *                              Default is 20.
 *                           {Number} margin.item
 *                              Margin between items in pixels. Default is 10.
 *                           {Number} padding
 *                              Padding of the contents of an item in pixels.
 *                              Must correspond with the items css. Default is 5.
 */
ItemSet.prototype.setOptions = Component.prototype.setOptions;

/**
 * Set range (start and end).
 * @param {Range | Object} range  A Range or an object containing start and end.
 */
ItemSet.prototype.setRange = function setRange(range) {
  if (!(range instanceof Range) && (!range || !range.start || !range.end)) {
    throw new TypeError('Range must be an instance of Range, ' +
        'or an object containing start and end.');
  }
  this.range = range;
};

/**
 * Change the item selection, and/or get currently selected items
 * @param {Array} [ids] An array with zero or more ids of the items to be selected.
 * @return {Array} ids  The ids of the selected items
 */
ItemSet.prototype.select = function select(ids) {
  var i, ii, id, item, selection;

  if (ids) {
    if (!Array.isArray(ids)) {
      throw new TypeError('Array expected');
    }

    // unselect currently selected items
    for (i = 0, ii = this.selection.length; i < ii; i++) {
      id = this.selection[i];
      item = this.items[id];
      if (item) item.unselect();
    }

    // select items
    this.selection = [];
    for (i = 0, ii = ids.length; i < ii; i++) {
      id = ids[i];
      item = this.items[id];
      if (item) {
        this.selection.push(id);
        item.select();
      }
    }

    // trigger a select event
    selection = this.selection.concat([]);
    events.trigger(this, 'select', {
      ids: selection
    });

    if (this.controller) {
      this.requestRepaint();
    }
  }
  else {
    selection = this.selection.concat([]);
  }

  return selection;
};

/**
 * Deselect a selected item
 * @param {String | Number} id
 * @private
 */
ItemSet.prototype._deselect = function _deselect(id) {
  var selection = this.selection;
  for (var i = 0, ii = selection.length; i < ii; i++) {
    if (selection[i] == id) { // non-strict comparison!
      selection.splice(i, 1);
      break;
    }
  }
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
ItemSet.prototype.repaint = function repaint() {
  var changed = 0,
      update = util.updateProperty,
      asSize = util.option.asSize,
      options = this.options,
      orientation = this.getOption('orientation'),
      defaultOptions = this.defaultOptions,
      frame = this.frame;

  if (!frame) {
    frame = document.createElement('div');
    frame.className = 'itemset';

    var className = options.className;
    if (className) {
      util.addClassName(frame, util.option.asString(className));
    }

    // create background panel
    var background = document.createElement('div');
    background.className = 'background';
    frame.appendChild(background);
    this.dom.background = background;

    // create foreground panel
    var foreground = document.createElement('div');
    foreground.className = 'foreground';
    frame.appendChild(foreground);
    this.dom.foreground = foreground;

    // create axis panel
    var axis = document.createElement('div');
    axis.className = 'itemset-axis';
    //frame.appendChild(axis);
    this.dom.axis = axis;

    this.frame = frame;
    changed += 1;
  }

  if (!this.parent) {
    throw new Error('Cannot repaint itemset: no parent attached');
  }
  var parentContainer = this.parent.getContainer();
  if (!parentContainer) {
    throw new Error('Cannot repaint itemset: parent has no container element');
  }
  if (!frame.parentNode) {
    parentContainer.appendChild(frame);
    changed += 1;
  }
  if (!this.dom.axis.parentNode) {
    parentContainer.appendChild(this.dom.axis);
    changed += 1;
  }

  // reposition frame
  changed += update(frame.style, 'left',   asSize(options.left, '0px'));
  changed += update(frame.style, 'top',    asSize(options.top, '0px'));
  changed += update(frame.style, 'width',  asSize(options.width, '100%'));
  changed += update(frame.style, 'height', asSize(options.height, this.height + 'px'));

  // reposition axis
  changed += update(this.dom.axis.style, 'left', asSize(options.left, '0px'));
  changed += update(this.dom.axis.style, 'width',  asSize(options.width, '100%'));
  if (orientation == 'bottom') {
    changed += update(this.dom.axis.style, 'top',  (this.height + this.top) + 'px');
  }
  else { // orientation == 'top'
    changed += update(this.dom.axis.style, 'top', this.top + 'px');
  }

  this._updateConversion();

  var me = this,
      queue = this.queue,
      itemsData = this.itemsData,
      items = this.items,
      dataOptions = {
        // TODO: cleanup
        // fields: [(itemsData && itemsData.fieldId || 'id'), 'start', 'end', 'content', 'type', 'className']
      };

  // show/hide added/changed/removed items
  Object.keys(queue).forEach(function (id) {
    //var entry = queue[id];
    var action = queue[id];
    var item = items[id];
    //var item = entry.item;
    //noinspection FallthroughInSwitchStatementJS
    switch (action) {
      case 'add':
      case 'update':
        var itemData = itemsData && itemsData.get(id, dataOptions);

        if (itemData) {
          var type = itemData.type ||
              (itemData.start && itemData.end && 'range') ||
              options.type ||
              'box';
          var constructor = ItemSet.types[type];

          // TODO: how to handle items with invalid data? hide them and give a warning? or throw an error?
          if (item) {
            // update item
            if (!constructor || !(item instanceof constructor)) {
              // item type has changed, hide and delete the item
              changed += item.hide();
              item = null;
            }
            else {
              item.data = itemData; // TODO: create a method item.setData ?
              changed++;
            }
          }

          if (!item) {
            // create item
            if (constructor) {
              item = new constructor(me, itemData, options, defaultOptions);
              item.id = id;
              changed++;
            }
            else {
              throw new TypeError('Unknown item type "' + type + '"');
            }
          }

          // force a repaint (not only a reposition)
          item.repaint();

          items[id] = item;
        }

        // update queue
        delete queue[id];
        break;

      case 'remove':
        if (item) {
          // remove the item from the set selected items
          if (item.selected) {
            me._deselect(id);
          }

          // remove DOM of the item
          changed += item.hide();
        }

        // update lists
        delete items[id];
        delete queue[id];
        break;

      default:
        console.log('Error: unknown action "' + action + '"');
    }
  });

  // reposition all items. Show items only when in the visible area
  util.forEach(this.items, function (item) {
    if (item.visible) {
      changed += item.show();
      item.reposition();
    }
    else {
      changed += item.hide();
    }
  });

  return (changed > 0);
};

/**
 * Get the foreground container element
 * @return {HTMLElement} foreground
 */
ItemSet.prototype.getForeground = function getForeground() {
  return this.dom.foreground;
};

/**
 * Get the background container element
 * @return {HTMLElement} background
 */
ItemSet.prototype.getBackground = function getBackground() {
  return this.dom.background;
};

/**
 * Get the axis container element
 * @return {HTMLElement} axis
 */
ItemSet.prototype.getAxis = function getAxis() {
  return this.dom.axis;
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
ItemSet.prototype.reflow = function reflow () {
  var changed = 0,
      options = this.options,
      marginAxis = options.margin && options.margin.axis || this.defaultOptions.margin.axis,
      marginItem = options.margin && options.margin.item || this.defaultOptions.margin.item,
      update = util.updateProperty,
      asNumber = util.option.asNumber,
      asSize = util.option.asSize,
      frame = this.frame;

  if (frame) {
    this._updateConversion();

    util.forEach(this.items, function (item) {
      changed += item.reflow();
    });

    // TODO: stack.update should be triggered via an event, in stack itself
    // TODO: only update the stack when there are changed items
    this.stack.update();

    var maxHeight = asNumber(options.maxHeight);
    var fixedHeight = (asSize(options.height) != null);
    var height;
    if (fixedHeight) {
      height = frame.offsetHeight;
    }
    else {
      // height is not specified, determine the height from the height and positioned items
      var visibleItems = this.stack.ordered; // TODO: not so nice way to get the filtered items
      if (visibleItems.length) {
        var min = visibleItems[0].top;
        var max = visibleItems[0].top + visibleItems[0].height;
        util.forEach(visibleItems, function (item) {
          min = Math.min(min, item.top);
          max = Math.max(max, (item.top + item.height));
        });
        height = (max - min) + marginAxis + marginItem;
      }
      else {
        height = marginAxis + marginItem;
      }
    }
    if (maxHeight != null) {
      height = Math.min(height, maxHeight);
    }
    changed += update(this, 'height', height);

    // calculate height from items
    changed += update(this, 'top', frame.offsetTop);
    changed += update(this, 'left', frame.offsetLeft);
    changed += update(this, 'width', frame.offsetWidth);
  }
  else {
    changed += 1;
  }

  return (changed > 0);
};

/**
 * Hide this component from the DOM
 * @return {Boolean} changed
 */
ItemSet.prototype.hide = function hide() {
  var changed = false;

  // remove the DOM
  if (this.frame && this.frame.parentNode) {
    this.frame.parentNode.removeChild(this.frame);
    changed = true;
  }
  if (this.dom.axis && this.dom.axis.parentNode) {
    this.dom.axis.parentNode.removeChild(this.dom.axis);
    changed = true;
  }

  return changed;
};

/**
 * Set items
 * @param {vis.DataSet | null} items
 */
ItemSet.prototype.setItems = function setItems(items) {
  var me = this,
      ids,
      oldItemsData = this.itemsData;

  // replace the dataset
  if (!items) {
    this.itemsData = null;
  }
  else if (items instanceof DataSet || items instanceof DataView) {
    this.itemsData = items;
  }
  else {
    throw new TypeError('Data must be an instance of DataSet');
  }

  if (oldItemsData) {
    // unsubscribe from old dataset
    util.forEach(this.listeners, function (callback, event) {
      oldItemsData.unsubscribe(event, callback);
    });

    // remove all drawn items
    ids = oldItemsData.getIds();
    this._onRemove(ids);
  }

  if (this.itemsData) {
    // subscribe to new dataset
    var id = this.id;
    util.forEach(this.listeners, function (callback, event) {
      me.itemsData.subscribe(event, callback, id);
    });

    // draw all new items
    ids = this.itemsData.getIds();
    this._onAdd(ids);
  }
};

/**
 * Get the current items items
 * @returns {vis.DataSet | null}
 */
ItemSet.prototype.getItems = function getItems() {
  return this.itemsData;
};

/**
 * Handle updated items
 * @param {Number[]} ids
 * @private
 */
ItemSet.prototype._onUpdate = function _onUpdate(ids) {
  this._toQueue('update', ids);
};

/**
 * Handle changed items
 * @param {Number[]} ids
 * @private
 */
ItemSet.prototype._onAdd = function _onAdd(ids) {
  this._toQueue('add', ids);
};

/**
 * Handle removed items
 * @param {Number[]} ids
 * @private
 */
ItemSet.prototype._onRemove = function _onRemove(ids) {
  this._toQueue('remove', ids);
};

/**
 * Put items in the queue to be added/updated/remove
 * @param {String} action     can be 'add', 'update', 'remove'
 * @param {Number[]} ids
 */
ItemSet.prototype._toQueue = function _toQueue(action, ids) {
  var queue = this.queue;
  ids.forEach(function (id) {
    queue[id] = action;
  });

  if (this.controller) {
    //this.requestReflow();
    this.requestRepaint();
  }
};

/**
 * Calculate the scale and offset to convert a position on screen to the
 * corresponding date and vice versa.
 * After the method _updateConversion is executed once, the methods toTime
 * and toScreen can be used.
 * @private
 */
ItemSet.prototype._updateConversion = function _updateConversion() {
  var range = this.range;
  if (!range) {
    throw new Error('No range configured');
  }

  if (range.conversion) {
    this.conversion = range.conversion(this.width);
  }
  else {
    this.conversion = Range.conversion(range.start, range.end, this.width);
  }
};

/**
 * Convert a position on screen (pixels) to a datetime
 * Before this method can be used, the method _updateConversion must be
 * executed once.
 * @param {int}     x    Position on the screen in pixels
 * @return {Date}   time The datetime the corresponds with given position x
 */
ItemSet.prototype.toTime = function toTime(x) {
  var conversion = this.conversion;
  return new Date(x / conversion.scale + conversion.offset);
};

/**
 * Convert a datetime (Date object) into a position on the screen
 * Before this method can be used, the method _updateConversion must be
 * executed once.
 * @param {Date}   time A date
 * @return {int}   x    The position on the screen in pixels which corresponds
 *                      with the given date.
 */
ItemSet.prototype.toScreen = function toScreen(time) {
  var conversion = this.conversion;
  return (time.valueOf() - conversion.offset) * conversion.scale;
};

/**
 * @constructor Item
 * @param {ItemSet} parent
 * @param {Object} data             Object containing (optional) parameters type,
 *                                  start, end, content, group, className.
 * @param {Object} [options]        Options to set initial property values
 * @param {Object} [defaultOptions] default options
 *                                  // TODO: describe available options
 */
function Item (parent, data, options, defaultOptions) {
  this.parent = parent;
  this.data = data;
  this.dom = null;
  this.options = options || {};
  this.defaultOptions = defaultOptions || {};

  this.selected = false;
  this.visible = false;
  this.top = 0;
  this.left = 0;
  this.width = 0;
  this.height = 0;
}

/**
 * Select current item
 */
Item.prototype.select = function select() {
  this.selected = true;
  if (this.visible) this.repaint();
};

/**
 * Unselect current item
 */
Item.prototype.unselect = function unselect() {
  this.selected = false;
  if (this.visible) this.repaint();
};

/**
 * Show the Item in the DOM (when not already visible)
 * @return {Boolean} changed
 */
Item.prototype.show = function show() {
  return false;
};

/**
 * Hide the Item from the DOM (when visible)
 * @return {Boolean} changed
 */
Item.prototype.hide = function hide() {
  return false;
};

/**
 * Repaint the item
 * @return {Boolean} changed
 */
Item.prototype.repaint = function repaint() {
  // should be implemented by the item
  return false;
};

/**
 * Reflow the item
 * @return {Boolean} resized
 */
Item.prototype.reflow = function reflow() {
  // should be implemented by the item
  return false;
};

/**
 * Return the items width
 * @return {Integer} width
 */
Item.prototype.getWidth = function getWidth() {
  return this.width;
}

/**
 * @constructor ItemBox
 * @extends Item
 * @param {ItemSet} parent
 * @param {Object} data             Object containing parameters start
 *                                  content, className.
 * @param {Object} [options]        Options to set initial property values
 * @param {Object} [defaultOptions] default options
 *                                  // TODO: describe available options
 */
function ItemBox (parent, data, options, defaultOptions) {
  this.props = {
    dot: {
      left: 0,
      top: 0,
      width: 0,
      height: 0
    },
    line: {
      top: 0,
      left: 0,
      width: 0,
      height: 0
    }
  };

  Item.call(this, parent, data, options, defaultOptions);
}

ItemBox.prototype = new Item (null, null);

/**
 * Repaint the item
 * @return {Boolean} changed
 */
ItemBox.prototype.repaint = function repaint() {
  // TODO: make an efficient repaint
  var changed = false;
  var dom = this.dom;

  if (!dom) {
    this._create();
    dom = this.dom;
    changed = true;
  }

  if (dom) {
    if (!this.parent) {
      throw new Error('Cannot repaint item: no parent attached');
    }

    if (!dom.box.parentNode) {
      var foreground = this.parent.getForeground();
      if (!foreground) {
        throw new Error('Cannot repaint time axis: ' +
            'parent has no foreground container element');
      }
      foreground.appendChild(dom.box);
      changed = true;
    }

    if (!dom.line.parentNode) {
      var background = this.parent.getBackground();
      if (!background) {
        throw new Error('Cannot repaint time axis: ' +
            'parent has no background container element');
      }
      background.appendChild(dom.line);
      changed = true;
    }

    if (!dom.dot.parentNode) {
      var axis = this.parent.getAxis();
      if (!background) {
        throw new Error('Cannot repaint time axis: ' +
            'parent has no axis container element');
      }
      axis.appendChild(dom.dot);
      changed = true;
    }

    // update contents
    if (this.data.content != this.content) {
      this.content = this.data.content;
      if (this.content instanceof Element) {
        dom.content.innerHTML = '';
        dom.content.appendChild(this.content);
      }
      else if (this.data.content != undefined) {
        dom.content.innerHTML = this.content;
      }
      else {
        throw new Error('Property "content" missing in item ' + this.data.id);
      }
      changed = true;
    }

    // update class
    var className = (this.data.className? ' ' + this.data.className : '') +
        (this.selected ? ' selected' : '');
    if (this.className != className) {
      this.className = className;
      dom.box.className = 'item box' + className;
      dom.line.className = 'item line' + className;
      dom.dot.className  = 'item dot' + className;
      changed = true;
    }
  }

  return changed;
};

/**
 * Show the item in the DOM (when not already visible). The items DOM will
 * be created when needed.
 * @return {Boolean} changed
 */
ItemBox.prototype.show = function show() {
  if (!this.dom || !this.dom.box.parentNode) {
    return this.repaint();
  }
  else {
    return false;
  }
};

/**
 * Hide the item from the DOM (when visible)
 * @return {Boolean} changed
 */
ItemBox.prototype.hide = function hide() {
  var changed = false,
      dom = this.dom;
  if (dom) {
    if (dom.box.parentNode) {
      dom.box.parentNode.removeChild(dom.box);
      changed = true;
    }
    if (dom.line.parentNode) {
      dom.line.parentNode.removeChild(dom.line);
    }
    if (dom.dot.parentNode) {
      dom.dot.parentNode.removeChild(dom.dot);
    }
  }
  return changed;
};

/**
 * Reflow the item: calculate its actual size and position from the DOM
 * @return {boolean} resized    returns true if the axis is resized
 * @override
 */
ItemBox.prototype.reflow = function reflow() {
  var changed = 0,
      update,
      dom,
      props,
      options,
      margin,
      start,
      align,
      orientation,
      top,
      left,
      data,
      range;

  if (this.data.start == undefined) {
    throw new Error('Property "start" missing in item ' + this.data.id);
  }

  data = this.data;
  range = this.parent && this.parent.range;
  if (data && range) {
    // TODO: account for the width of the item
    var interval = (range.end - range.start);
    this.visible = (data.start > range.start - interval) && (data.start < range.end + interval);
  }
  else {
    this.visible = false;
  }

  if (this.visible) {
    dom = this.dom;
    if (dom) {
      update = util.updateProperty;
      props = this.props;
      options = this.options;
      start = this.parent.toScreen(this.data.start);
      align = options.align || this.defaultOptions.align;
      margin = options.margin && options.margin.axis || this.defaultOptions.margin.axis;
      orientation = options.orientation || this.defaultOptions.orientation;

      changed += update(props.dot, 'height', dom.dot.offsetHeight);
      changed += update(props.dot, 'width', dom.dot.offsetWidth);
      changed += update(props.line, 'width', dom.line.offsetWidth);
      changed += update(props.line, 'height', dom.line.offsetHeight);
      changed += update(props.line, 'top', dom.line.offsetTop);
      changed += update(this, 'width', dom.box.offsetWidth);
      changed += update(this, 'height', dom.box.offsetHeight);
      if (align == 'right') {
        left = start - this.width;
      }
      else if (align == 'left') {
        left = start;
      }
      else {
        // default or 'center'
        left = start - this.width / 2;
      }
      changed += update(this, 'left', left);

      changed += update(props.line, 'left', start - props.line.width / 2);
      changed += update(props.dot, 'left', start - props.dot.width / 2);
      changed += update(props.dot, 'top', -props.dot.height / 2);
      if (orientation == 'top') {
        top = margin;

        changed += update(this, 'top', top);
      }
      else {
        // default or 'bottom'
        var parentHeight = this.parent.height;
        top = parentHeight - this.height - margin;

        changed += update(this, 'top', top);
      }
    }
    else {
      changed += 1;
    }
  }

  return (changed > 0);
};

/**
 * Create an items DOM
 * @private
 */
ItemBox.prototype._create = function _create() {
  var dom = this.dom;
  if (!dom) {
    this.dom = dom = {};

    // create the box
    dom.box = document.createElement('DIV');
    // className is updated in repaint()

    // contents box (inside the background box). used for making margins
    dom.content = document.createElement('DIV');
    dom.content.className = 'content';
    dom.box.appendChild(dom.content);

    // line to axis
    dom.line = document.createElement('DIV');
    dom.line.className = 'line';

    // dot on axis
    dom.dot = document.createElement('DIV');
    dom.dot.className = 'dot';
  }
};

/**
 * Reposition the item, recalculate its left, top, and width, using the current
 * range and size of the items itemset
 * @override
 */
ItemBox.prototype.reposition = function reposition() {
  var dom = this.dom,
      props = this.props,
      orientation = this.options.orientation || this.defaultOptions.orientation;

  if (dom) {
    var box = dom.box,
        line = dom.line,
        dot = dom.dot;

    box.style.left = this.left + 'px';
    box.style.top = this.top + 'px';

    line.style.left = props.line.left + 'px';
    if (orientation == 'top') {
      line.style.top = 0 + 'px';
      line.style.height = this.top + 'px';
    }
    else {
      // orientation 'bottom'
      line.style.top = (this.top + this.height) + 'px';
      line.style.height = Math.max(this.parent.height - this.top - this.height +
          this.props.dot.height / 2, 0) + 'px';
    }

    dot.style.left = props.dot.left + 'px';
    dot.style.top = props.dot.top + 'px';
  }
};

/**
 * @constructor ItemPoint
 * @extends Item
 * @param {ItemSet} parent
 * @param {Object} data             Object containing parameters start
 *                                  content, className.
 * @param {Object} [options]        Options to set initial property values
 * @param {Object} [defaultOptions] default options
 *                                  // TODO: describe available options
 */
function ItemPoint (parent, data, options, defaultOptions) {
  this.props = {
    dot: {
      top: 0,
      width: 0,
      height: 0
    },
    content: {
      height: 0,
      marginLeft: 0
    }
  };

  Item.call(this, parent, data, options, defaultOptions);
}

ItemPoint.prototype = new Item (null, null);

/**
 * Repaint the item
 * @return {Boolean} changed
 */
ItemPoint.prototype.repaint = function repaint() {
  // TODO: make an efficient repaint
  var changed = false;
  var dom = this.dom;

  if (!dom) {
    this._create();
    dom = this.dom;
    changed = true;
  }

  if (dom) {
    if (!this.parent) {
      throw new Error('Cannot repaint item: no parent attached');
    }
    var foreground = this.parent.getForeground();
    if (!foreground) {
      throw new Error('Cannot repaint time axis: ' +
          'parent has no foreground container element');
    }

    if (!dom.point.parentNode) {
      foreground.appendChild(dom.point);
      foreground.appendChild(dom.point);
      changed = true;
    }

    // update contents
    if (this.data.content != this.content) {
      this.content = this.data.content;
      if (this.content instanceof Element) {
        dom.content.innerHTML = '';
        dom.content.appendChild(this.content);
      }
      else if (this.data.content != undefined) {
        dom.content.innerHTML = this.content;
      }
      else {
        throw new Error('Property "content" missing in item ' + this.data.id);
      }
      changed = true;
    }

    // update class
    var className = (this.data.className? ' ' + this.data.className : '') +
        (this.selected ? ' selected' : '');
    if (this.className != className) {
      this.className = className;
      dom.point.className  = 'item point' + className;
      changed = true;
    }
  }

  return changed;
};

/**
 * Show the item in the DOM (when not already visible). The items DOM will
 * be created when needed.
 * @return {Boolean} changed
 */
ItemPoint.prototype.show = function show() {
  if (!this.dom || !this.dom.point.parentNode) {
    return this.repaint();
  }
  else {
    return false;
  }
};

/**
 * Hide the item from the DOM (when visible)
 * @return {Boolean} changed
 */
ItemPoint.prototype.hide = function hide() {
  var changed = false,
      dom = this.dom;
  if (dom) {
    if (dom.point.parentNode) {
      dom.point.parentNode.removeChild(dom.point);
      changed = true;
    }
  }
  return changed;
};

/**
 * Reflow the item: calculate its actual size from the DOM
 * @return {boolean} resized    returns true if the axis is resized
 * @override
 */
ItemPoint.prototype.reflow = function reflow() {
  var changed = 0,
      update,
      dom,
      props,
      options,
      margin,
      orientation,
      start,
      top,
      data,
      range;

  if (this.data.start == undefined) {
    throw new Error('Property "start" missing in item ' + this.data.id);
  }

  data = this.data;
  range = this.parent && this.parent.range;
  if (data && range) {
    // TODO: account for the width of the item
    var interval = (range.end - range.start);
    this.visible = (data.start > range.start - interval) && (data.start < range.end);
  }
  else {
    this.visible = false;
  }

  if (this.visible) {
    dom = this.dom;
    if (dom) {
      update = util.updateProperty;
      props = this.props;
      options = this.options;
      orientation = options.orientation || this.defaultOptions.orientation;
      margin = options.margin && options.margin.axis || this.defaultOptions.margin.axis;
      start = this.parent.toScreen(this.data.start);

      changed += update(this, 'width', dom.point.offsetWidth);
      changed += update(this, 'height', dom.point.offsetHeight);
      changed += update(props.dot, 'width', dom.dot.offsetWidth);
      changed += update(props.dot, 'height', dom.dot.offsetHeight);
      changed += update(props.content, 'height', dom.content.offsetHeight);

      if (orientation == 'top') {
        top = margin;
      }
      else {
        // default or 'bottom'
        var parentHeight = this.parent.height;
        top = Math.max(parentHeight - this.height - margin, 0);
      }
      changed += update(this, 'top', top);
      changed += update(this, 'left', start - props.dot.width / 2);
      changed += update(props.content, 'marginLeft', 1.5 * props.dot.width);
      //changed += update(props.content, 'marginRight', 0.5 * props.dot.width); // TODO

      changed += update(props.dot, 'top', (this.height - props.dot.height) / 2);
    }
    else {
      changed += 1;
    }
  }

  return (changed > 0);
};

/**
 * Create an items DOM
 * @private
 */
ItemPoint.prototype._create = function _create() {
  var dom = this.dom;
  if (!dom) {
    this.dom = dom = {};

    // background box
    dom.point = document.createElement('div');
    // className is updated in repaint()

    // contents box, right from the dot
    dom.content = document.createElement('div');
    dom.content.className = 'content';
    dom.point.appendChild(dom.content);

    // dot at start
    dom.dot = document.createElement('div');
    dom.dot.className  = 'dot';
    dom.point.appendChild(dom.dot);
  }
};

/**
 * Reposition the item, recalculate its left, top, and width, using the current
 * range and size of the items itemset
 * @override
 */
ItemPoint.prototype.reposition = function reposition() {
  var dom = this.dom,
      props = this.props;

  if (dom) {
    dom.point.style.top = this.top + 'px';
    dom.point.style.left = this.left + 'px';

    dom.content.style.marginLeft = props.content.marginLeft + 'px';
    //dom.content.style.marginRight = props.content.marginRight + 'px'; // TODO

    dom.dot.style.top = props.dot.top + 'px';
  }
};

/**
 * @constructor ItemRange
 * @extends Item
 * @param {ItemSet} parent
 * @param {Object} data             Object containing parameters start, end
 *                                  content, className.
 * @param {Object} [options]        Options to set initial property values
 * @param {Object} [defaultOptions] default options
 *                                  // TODO: describe available options
 */
function ItemRange (parent, data, options, defaultOptions) {
  this.props = {
    content: {
      left: 0,
      width: 0
    }
  };

  Item.call(this, parent, data, options, defaultOptions);
}

ItemRange.prototype = new Item (null, null);

/**
 * Repaint the item
 * @return {Boolean} changed
 */
ItemRange.prototype.repaint = function repaint() {
  // TODO: make an efficient repaint
  var changed = false;
  var dom = this.dom;

  if (!dom) {
    this._create();
    dom = this.dom;
    changed = true;
  }

  if (dom) {
    if (!this.parent) {
      throw new Error('Cannot repaint item: no parent attached');
    }
    var foreground = this.parent.getForeground();
    if (!foreground) {
      throw new Error('Cannot repaint time axis: ' +
          'parent has no foreground container element');
    }

    if (!dom.box.parentNode) {
      foreground.appendChild(dom.box);
      changed = true;
    }

    // update content
    if (this.data.content != this.content) {
      this.content = this.data.content;
      if (this.content instanceof Element) {
        dom.content.innerHTML = '';
        dom.content.appendChild(this.content);
      }
      else if (this.data.content != undefined) {
        dom.content.innerHTML = this.content;
      }
      else {
        throw new Error('Property "content" missing in item ' + this.data.id);
      }
      changed = true;
    }

    // update class
    var className = (this.data.className? ' ' + this.data.className : '') +
        (this.selected ? ' selected' : '');
    if (this.className != className) {
      this.className = className;
      dom.box.className = 'item range' + className;
      changed = true;
    }
  }

  return changed;
};

/**
 * Show the item in the DOM (when not already visible). The items DOM will
 * be created when needed.
 * @return {Boolean} changed
 */
ItemRange.prototype.show = function show() {
  if (!this.dom || !this.dom.box.parentNode) {
    return this.repaint();
  }
  else {
    return false;
  }
};

/**
 * Hide the item from the DOM (when visible)
 * @return {Boolean} changed
 */
ItemRange.prototype.hide = function hide() {
  var changed = false,
      dom = this.dom;
  if (dom) {
    if (dom.box.parentNode) {
      dom.box.parentNode.removeChild(dom.box);
      changed = true;
    }
  }
  return changed;
};

/**
 * Reflow the item: calculate its actual size from the DOM
 * @return {boolean} resized    returns true if the axis is resized
 * @override
 */
ItemRange.prototype.reflow = function reflow() {
  var changed = 0,
      dom,
      props,
      options,
      margin,
      padding,
      parent,
      start,
      end,
      data,
      range,
      update,
      box,
      parentWidth,
      contentLeft,
      orientation,
      top;

  if (this.data.start == undefined) {
    throw new Error('Property "start" missing in item ' + this.data.id);
  }
  if (this.data.end == undefined) {
    throw new Error('Property "end" missing in item ' + this.data.id);
  }

  data = this.data;
  range = this.parent && this.parent.range;
  if (data && range) {
    // TODO: account for the width of the item. Take some margin
    this.visible = (data.start < range.end) && (data.end > range.start);
  }
  else {
    this.visible = false;
  }

  if (this.visible) {
    dom = this.dom;
    if (dom) {
      props = this.props;
      options = this.options;
      parent = this.parent;
      start = parent.toScreen(this.data.start);
      end = parent.toScreen(this.data.end);
      update = util.updateProperty;
      box = dom.box;
      parentWidth = parent.width;
      orientation = options.orientation || this.defaultOptions.orientation;
      margin = options.margin && options.margin.axis || this.defaultOptions.margin.axis;
      padding = options.padding || this.defaultOptions.padding;

      changed += update(props.content, 'width', dom.content.offsetWidth);

      changed += update(this, 'height', box.offsetHeight);

      // limit the width of the this, as browsers cannot draw very wide divs
      if (start < -parentWidth) {
        start = -parentWidth;
      }
      if (end > 2 * parentWidth) {
        end = 2 * parentWidth;
      }

      // when range exceeds left of the window, position the contents at the left of the visible area
      if (start < 0) {
        contentLeft = Math.min(-start,
            (end - start - props.content.width - 2 * padding));
        // TODO: remove the need for options.padding. it's terrible.
      }
      else {
        contentLeft = 0;
      }
      changed += update(props.content, 'left', contentLeft);

      if (orientation == 'top') {
        top = margin;
        changed += update(this, 'top', top);
      }
      else {
        // default or 'bottom'
        top = parent.height - this.height - margin;
        changed += update(this, 'top', top);
      }

      changed += update(this, 'left', start);
      changed += update(this, 'width', Math.max(end - start, 1)); // TODO: reckon with border width;
    }
    else {
      changed += 1;
    }
  }

  return (changed > 0);
};

/**
 * Create an items DOM
 * @private
 */
ItemRange.prototype._create = function _create() {
  var dom = this.dom;
  if (!dom) {
    this.dom = dom = {};
    // background box
    dom.box = document.createElement('div');
    // className is updated in repaint()

    // contents box
    dom.content = document.createElement('div');
    dom.content.className = 'content';
    dom.box.appendChild(dom.content);
  }
};

/**
 * Reposition the item, recalculate its left, top, and width, using the current
 * range and size of the items itemset
 * @override
 */
ItemRange.prototype.reposition = function reposition() {
  var dom = this.dom,
      props = this.props;

  if (dom) {
    dom.box.style.top = this.top + 'px';
    dom.box.style.left = this.left + 'px';
    dom.box.style.width = this.width + 'px';

    dom.content.style.left = props.content.left + 'px';
  }
};

/**
 * @constructor ItemRangeOverflow
 * @extends ItemRange
 * @param {ItemSet} parent
 * @param {Object} data             Object containing parameters start, end
 *                                  content, className.
 * @param {Object} [options]        Options to set initial property values
 * @param {Object} [defaultOptions] default options
 *                                  // TODO: describe available options
 */
function ItemRangeOverflow (parent, data, options, defaultOptions) {
  this.props = {
    content: {
      left: 0,
      width: 0
    }
  };

  ItemRange.call(this, parent, data, options, defaultOptions);
}

ItemRangeOverflow.prototype = new ItemRange (null, null);

/**
 * Repaint the item
 * @return {Boolean} changed
 */
ItemRangeOverflow.prototype.repaint = function repaint() {
  // TODO: make an efficient repaint
  var changed = false;
  var dom = this.dom;

  if (!dom) {
    this._create();
    dom = this.dom;
    changed = true;
  }

  if (dom) {
    if (!this.parent) {
      throw new Error('Cannot repaint item: no parent attached');
    }
    var foreground = this.parent.getForeground();
    if (!foreground) {
      throw new Error('Cannot repaint time axis: ' +
          'parent has no foreground container element');
    }

    if (!dom.box.parentNode) {
      foreground.appendChild(dom.box);
      changed = true;
    }

    // update content
    if (this.data.content != this.content) {
      this.content = this.data.content;
      if (this.content instanceof Element) {
        dom.content.innerHTML = '';
        dom.content.appendChild(this.content);
      }
      else if (this.data.content != undefined) {
        dom.content.innerHTML = this.content;
      }
      else {
        throw new Error('Property "content" missing in item ' + this.data.id);
      }
      changed = true;
    }

    // update class
    var className = this.data.className ? (' ' + this.data.className) : '';
    if (this.className != className) {
      this.className = className;
      dom.box.className = 'item rangeoverflow' + className;
      changed = true;
    }
  }

  return changed;
};

/**
 * Return the items width
 * @return {Number} width
 */
ItemRangeOverflow.prototype.getWidth = function getWidth() {
  if (this.props.content !== undefined && this.width < this.props.content.width)
    return this.props.content.width;
  else
    return this.width;
};

/**
 * @constructor Group
 * @param {GroupSet} parent
 * @param {Number | String} groupId
 * @param {Object} [options]  Options to set initial property values
 *                            // TODO: describe available options
 * @extends Component
 */
function Group (parent, groupId, options) {
  this.id = util.randomUUID();
  this.parent = parent;

  this.groupId = groupId;
  this.itemset = null;    // ItemSet
  this.options = options || {};
  this.options.top = 0;

  this.props = {
    label: {
      width: 0,
      height: 0
    }
  };

  this.top = 0;
  this.left = 0;
  this.width = 0;
  this.height = 0;
}

Group.prototype = new Component();

// TODO: comment
Group.prototype.setOptions = Component.prototype.setOptions;

/**
 * Get the container element of the panel, which can be used by a child to
 * add its own widgets.
 * @returns {HTMLElement} container
 */
Group.prototype.getContainer = function () {
  return this.parent.getContainer();
};

/**
 * Set item set for the group. The group will create a view on the itemset,
 * filtered by the groups id.
 * @param {DataSet | DataView} items
 */
Group.prototype.setItems = function setItems(items) {
  if (this.itemset) {
    // remove current item set
    this.itemset.hide();
    this.itemset.setItems();

    this.parent.controller.remove(this.itemset);
    this.itemset = null;
  }

  if (items) {
    var groupId = this.groupId;

    var itemsetOptions = Object.create(this.options);
    this.itemset = new ItemSet(this, null, itemsetOptions);
    this.itemset.setRange(this.parent.range);

    this.view = new DataView(items, {
      filter: function (item) {
        return item.group == groupId;
      }
    });
    this.itemset.setItems(this.view);

    this.parent.controller.add(this.itemset);
  }
};

/**
 * Change the item selection, and/or get currently selected items
 * @param {Array} [ids] An array with zero or more ids of the items to be selected.
 * @return {Array} ids  The ids of the selected items
 */
Group.prototype.select = function select(ids) {
  return this.itemset ? this.itemset.select(ids) : [];
};

/**
 * Repaint the item
 * @return {Boolean} changed
 */
Group.prototype.repaint = function repaint() {
  return false;
};

/**
 * Reflow the item
 * @return {Boolean} resized
 */
Group.prototype.reflow = function reflow() {
  var changed = 0,
      update = util.updateProperty;

  changed += update(this, 'top',    this.itemset ? this.itemset.top : 0);
  changed += update(this, 'height', this.itemset ? this.itemset.height : 0);

  // TODO: reckon with the height of the group label

  if (this.label) {
    var inner = this.label.firstChild;
    changed += update(this.props.label, 'width', inner.clientWidth);
    changed += update(this.props.label, 'height', inner.clientHeight);
  }
  else {
    changed += update(this.props.label, 'width', 0);
    changed += update(this.props.label, 'height', 0);
  }

  return (changed > 0);
};

/**
 * An GroupSet holds a set of groups
 * @param {Component} parent
 * @param {Component[]} [depends]   Components on which this components depends
 *                                  (except for the parent)
 * @param {Object} [options]        See GroupSet.setOptions for the available
 *                                  options.
 * @constructor GroupSet
 * @extends Panel
 */
function GroupSet(parent, depends, options) {
  this.id = util.randomUUID();
  this.parent = parent;
  this.depends = depends;

  this.options = options || {};

  this.range = null;      // Range or Object {start: number, end: number}
  this.itemsData = null;  // DataSet with items
  this.groupsData = null; // DataSet with groups

  this.groups = {};       // map with groups

  this.dom = {};
  this.props = {
    labels: {
      width: 0
    }
  };

  // TODO: implement right orientation of the labels

  // changes in groups are queued  key/value map containing id/action
  this.queue = {};

  var me = this;
  this.listeners = {
    'add': function (event, params) {
      me._onAdd(params.items);
    },
    'update': function (event, params) {
      me._onUpdate(params.items);
    },
    'remove': function (event, params) {
      me._onRemove(params.items);
    }
  };
}

GroupSet.prototype = new Panel();

/**
 * Set options for the GroupSet. Existing options will be extended/overwritten.
 * @param {Object} [options] The following options are available:
 *                           {String | function} groupsOrder
 *                           TODO: describe options
 */
GroupSet.prototype.setOptions = Component.prototype.setOptions;

GroupSet.prototype.setRange = function (range) {
  // TODO: implement setRange
};

/**
 * Set items
 * @param {vis.DataSet | null} items
 */
GroupSet.prototype.setItems = function setItems(items) {
  this.itemsData = items;

  for (var id in this.groups) {
    if (this.groups.hasOwnProperty(id)) {
      var group = this.groups[id];
      group.setItems(items);
    }
  }
};

/**
 * Get items
 * @return {vis.DataSet | null} items
 */
GroupSet.prototype.getItems = function getItems() {
  return this.itemsData;
};

/**
 * Set range (start and end).
 * @param {Range | Object} range  A Range or an object containing start and end.
 */
GroupSet.prototype.setRange = function setRange(range) {
  this.range = range;
};

/**
 * Set groups
 * @param {vis.DataSet} groups
 */
GroupSet.prototype.setGroups = function setGroups(groups) {
  var me = this,
      ids;

  // unsubscribe from current dataset
  if (this.groupsData) {
    util.forEach(this.listeners, function (callback, event) {
      me.groupsData.unsubscribe(event, callback);
    });

    // remove all drawn groups
    ids = this.groupsData.getIds();
    this._onRemove(ids);
  }

  // replace the dataset
  if (!groups) {
    this.groupsData = null;
  }
  else if (groups instanceof DataSet) {
    this.groupsData = groups;
  }
  else {
    this.groupsData = new DataSet({
      convert: {
        start: 'Date',
        end: 'Date'
      }
    });
    this.groupsData.add(groups);
  }

  if (this.groupsData) {
    // subscribe to new dataset
    var id = this.id;
    util.forEach(this.listeners, function (callback, event) {
      me.groupsData.subscribe(event, callback, id);
    });

    // draw all new groups
    ids = this.groupsData.getIds();
    this._onAdd(ids);
  }
};

/**
 * Get groups
 * @return {vis.DataSet | null} groups
 */
GroupSet.prototype.getGroups = function getGroups() {
  return this.groupsData;
};

/**
 * Change the item selection, and/or get currently selected items
 * @param {Array} [ids] An array with zero or more ids of the items to be selected.
 * @return {Array} ids  The ids of the selected items
 */
GroupSet.prototype.select = function select(ids) {
  var selection = [],
      groups = this.groups;

  // iterate over each of the groups
  for (var id in groups) {
    if (groups.hasOwnProperty(id)) {
      var group = groups[id];
      selection = selection.concat(group.select(ids));
    }
  }

  return selection;
};

/**
 * Repaint the component
 * @return {Boolean} changed
 */
GroupSet.prototype.repaint = function repaint() {
  var changed = 0,
      i, id, group, label,
      update = util.updateProperty,
      asSize = util.option.asSize,
      asElement = util.option.asElement,
      options = this.options,
      frame = this.dom.frame,
      labels = this.dom.labels,
      labelSet = this.dom.labelSet;

  // create frame
  if (!this.parent) {
    throw new Error('Cannot repaint groupset: no parent attached');
  }
  var parentContainer = this.parent.getContainer();
  if (!parentContainer) {
    throw new Error('Cannot repaint groupset: parent has no container element');
  }
  if (!frame) {
    frame = document.createElement('div');
    frame.className = 'groupset';
    this.dom.frame = frame;

    var className = options.className;
    if (className) {
      util.addClassName(frame, util.option.asString(className));
    }

    changed += 1;
  }
  if (!frame.parentNode) {
    parentContainer.appendChild(frame);
    changed += 1;
  }

  // create labels
  var labelContainer = asElement(options.labelContainer);
  if (!labelContainer) {
    throw new Error('Cannot repaint groupset: option "labelContainer" not defined');
  }
  if (!labels) {
    labels = document.createElement('div');
    labels.className = 'labels';
    this.dom.labels = labels;
  }
  if (!labelSet) {
    labelSet = document.createElement('div');
    labelSet.className = 'label-set';
    labels.appendChild(labelSet);
    this.dom.labelSet = labelSet;
  }
  if (!labels.parentNode || labels.parentNode != labelContainer) {
    if (labels.parentNode) {
      labels.parentNode.removeChild(labels.parentNode);
    }
    labelContainer.appendChild(labels);
  }

  // reposition frame
  changed += update(frame.style, 'height', asSize(options.height, this.height + 'px'));
  changed += update(frame.style, 'top',    asSize(options.top, '0px'));
  changed += update(frame.style, 'left',   asSize(options.left, '0px'));
  changed += update(frame.style, 'width',  asSize(options.width, '100%'));

  // reposition labels
  changed += update(labelSet.style, 'top',    asSize(options.top, '0px'));
  changed += update(labelSet.style, 'height', asSize(options.height, this.height + 'px'));

  var me = this,
      queue = this.queue,
      groups = this.groups,
      groupsData = this.groupsData;

  // show/hide added/changed/removed groups
  var ids = Object.keys(queue);
  if (ids.length) {
    ids.forEach(function (id) {
      var action = queue[id];
      var group = groups[id];

      //noinspection FallthroughInSwitchStatementJS
      switch (action) {
        case 'add':
        case 'update':
          if (!group) {
            var groupOptions = Object.create(me.options);
            util.extend(groupOptions, {
              height: null,
              maxHeight: null
            });

            group = new Group(me, id, groupOptions);
            group.setItems(me.itemsData); // attach items data
            groups[id] = group;

            me.controller.add(group);
          }

          // TODO: update group data
          group.data = groupsData.get(id);

          delete queue[id];
          break;

        case 'remove':
          if (group) {
            group.setItems(); // detach items data
            delete groups[id];

            me.controller.remove(group);
          }

          // update lists
          delete queue[id];
          break;

        default:
          console.log('Error: unknown action "' + action + '"');
      }
    });

    // the groupset depends on each of the groups
    //this.depends = this.groups; // TODO: gives a circular reference through the parent

    // TODO: apply dependencies of the groupset

    // update the top positions of the groups in the correct order
    var orderedGroups = this.groupsData.getIds({
      order: this.options.groupOrder
    });
    for (i = 0; i < orderedGroups.length; i++) {
      (function (group, prevGroup) {
        var top = 0;
        if (prevGroup) {
          top = function () {
            // TODO: top must reckon with options.maxHeight
            return prevGroup.top + prevGroup.height;
          }
        }
        group.setOptions({
          top: top
        });
      })(groups[orderedGroups[i]], groups[orderedGroups[i - 1]]);
    }

    // (re)create the labels
    while (labelSet.firstChild) {
      labelSet.removeChild(labelSet.firstChild);
    }
    for (i = 0; i < orderedGroups.length; i++) {
      id = orderedGroups[i];
      label = this._createLabel(id);
      labelSet.appendChild(label);
    }

    changed++;
  }

  // reposition the labels
  // TODO: labels are not displayed correctly when orientation=='top'
  // TODO: width of labelPanel is not immediately updated on a change in groups
  for (id in groups) {
    if (groups.hasOwnProperty(id)) {
      group = groups[id];
      label = group.label;
      if (label) {
        label.style.top = group.top + 'px';
        label.style.height = group.height + 'px';
      }
    }
  }

  return (changed > 0);
};

/**
 * Create a label for group with given id
 * @param {Number} id
 * @return {Element} label
 * @private
 */
GroupSet.prototype._createLabel = function(id) {
  var group = this.groups[id];
  var label = document.createElement('div');
  label.className = 'label';
  var inner = document.createElement('div');
  inner.className = 'inner';
  label.appendChild(inner);

  var content = group.data && group.data.content;
  if (content instanceof Element) {
    inner.appendChild(content);
  }
  else if (content != undefined) {
    inner.innerHTML = content;
  }

  var className = group.data && group.data.className;
  if (className) {
    util.addClassName(label, className);
  }

  group.label = label; // TODO: not so nice, parking labels in the group this way!!!

  return label;
};

/**
 * Get container element
 * @return {HTMLElement} container
 */
GroupSet.prototype.getContainer = function getContainer() {
  return this.dom.frame;
};

/**
 * Get the width of the group labels
 * @return {Number} width
 */
GroupSet.prototype.getLabelsWidth = function getContainer() {
  return this.props.labels.width;
};

/**
 * Reflow the component
 * @return {Boolean} resized
 */
GroupSet.prototype.reflow = function reflow() {
  var changed = 0,
      id, group,
      options = this.options,
      update = util.updateProperty,
      asNumber = util.option.asNumber,
      asSize = util.option.asSize,
      frame = this.dom.frame;

  if (frame) {
    var maxHeight = asNumber(options.maxHeight);
    var fixedHeight = (asSize(options.height) != null);
    var height;
    if (fixedHeight) {
      height = frame.offsetHeight;
    }
    else {
      // height is not specified, calculate the sum of the height of all groups
      height = 0;

      for (id in this.groups) {
        if (this.groups.hasOwnProperty(id)) {
          group = this.groups[id];
          height += group.height;
        }
      }
    }
    if (maxHeight != null) {
      height = Math.min(height, maxHeight);
    }
    changed += update(this, 'height', height);

    changed += update(this, 'top', frame.offsetTop);
    changed += update(this, 'left', frame.offsetLeft);
    changed += update(this, 'width', frame.offsetWidth);
  }

  // calculate the maximum width of the labels
  var width = 0;
  for (id in this.groups) {
    if (this.groups.hasOwnProperty(id)) {
      group = this.groups[id];
      var labelWidth = group.props && group.props.label && group.props.label.width || 0;
      width = Math.max(width, labelWidth);
    }
  }
  changed += update(this.props.labels, 'width', width);

  return (changed > 0);
};

/**
 * Hide the component from the DOM
 * @return {Boolean} changed
 */
GroupSet.prototype.hide = function hide() {
  if (this.dom.frame && this.dom.frame.parentNode) {
    this.dom.frame.parentNode.removeChild(this.dom.frame);
    return true;
  }
  else {
    return false;
  }
};

/**
 * Show the component in the DOM (when not already visible).
 * A repaint will be executed when the component is not visible
 * @return {Boolean} changed
 */
GroupSet.prototype.show = function show() {
  if (!this.dom.frame || !this.dom.frame.parentNode) {
    return this.repaint();
  }
  else {
    return false;
  }
};

/**
 * Handle updated groups
 * @param {Number[]} ids
 * @private
 */
GroupSet.prototype._onUpdate = function _onUpdate(ids) {
  this._toQueue(ids, 'update');
};

/**
 * Handle changed groups
 * @param {Number[]} ids
 * @private
 */
GroupSet.prototype._onAdd = function _onAdd(ids) {
  this._toQueue(ids, 'add');
};

/**
 * Handle removed groups
 * @param {Number[]} ids
 * @private
 */
GroupSet.prototype._onRemove = function _onRemove(ids) {
  this._toQueue(ids, 'remove');
};

/**
 * Put groups in the queue to be added/updated/remove
 * @param {Number[]} ids
 * @param {String} action     can be 'add', 'update', 'remove'
 */
GroupSet.prototype._toQueue = function _toQueue(ids, action) {
  var queue = this.queue;
  ids.forEach(function (id) {
    queue[id] = action;
  });

  if (this.controller) {
    //this.requestReflow();
    this.requestRepaint();
  }
};

/**
 * Create a timeline visualization
 * @param {HTMLElement} container
 * @param {vis.DataSet | Array | DataTable} [items]
 * @param {Object} [options]  See Timeline.setOptions for the available options.
 * @constructor
 */
function Timeline (container, items, options) {
  var me = this;
  var now = moment().hours(0).minutes(0).seconds(0).milliseconds(0);
  this.options = {
    orientation: 'bottom',
    min: null,
    max: null,
    zoomMin: 10,                                // milliseconds
    zoomMax: 1000 * 60 * 60 * 24 * 365 * 10000, // milliseconds
    // moveable: true, // TODO: option moveable
    // zoomable: true, // TODO: option zoomable
    showMinorLabels: true,
    showMajorLabels: true,
    showCurrentTime: false,
    showCustomTime: false,
    autoResize: false
  };

  // controller
  this.controller = new Controller();

  // root panel
  if (!container) {
    throw new Error('No container element provided');
  }
  var rootOptions = Object.create(this.options);
  rootOptions.height = function () {
    // TODO: change to height
    if (me.options.height) {
      // fixed height
      return me.options.height;
    }
    else {
      // auto height
      return (me.timeaxis.height + me.content.height) + 'px';
    }
  };
  this.rootPanel = new RootPanel(container, rootOptions);
  this.controller.add(this.rootPanel);

  // item panel
  var itemOptions = Object.create(this.options);
  itemOptions.left = function () {
    return me.labelPanel.width;
  };
  itemOptions.width = function () {
    return me.rootPanel.width - me.labelPanel.width;
  };
  itemOptions.top = null;
  itemOptions.height = null;
  this.itemPanel = new Panel(this.rootPanel, [], itemOptions);
  this.controller.add(this.itemPanel);

  // label panel
  var labelOptions = Object.create(this.options);
  labelOptions.top = null;
  labelOptions.left = null;
  labelOptions.height = null;
  labelOptions.width = function () {
    if (me.content && typeof me.content.getLabelsWidth === 'function') {
      return me.content.getLabelsWidth();
    }
    else {
      return 0;
    }
  };
  this.labelPanel = new Panel(this.rootPanel, [], labelOptions);
  this.controller.add(this.labelPanel);

  // range
  var rangeOptions = Object.create(this.options);
  this.range = new Range(rangeOptions);
  this.range.setRange(
      now.clone().add('days', -3).valueOf(),
      now.clone().add('days', 4).valueOf()
  );

  // TODO: reckon with options moveable and zoomable
  this.range.subscribe(this.rootPanel, 'move', 'horizontal');
  this.range.subscribe(this.rootPanel, 'zoom', 'horizontal');
  this.range.on('rangechange', function () {
    var force = true;
    me.controller.requestReflow(force);
  });
  this.range.on('rangechanged', function () {
    var force = true;
    me.controller.requestReflow(force);
  });

  // TODO: put the listeners in setOptions, be able to dynamically change with options moveable and zoomable

  // time axis
  var timeaxisOptions = Object.create(rootOptions);
  timeaxisOptions.range = this.range;
  timeaxisOptions.left = null;
  timeaxisOptions.top = null;
  timeaxisOptions.width = '100%';
  timeaxisOptions.height = null;
  this.timeaxis = new TimeAxis(this.itemPanel, [], timeaxisOptions);
  this.timeaxis.setRange(this.range);
  this.controller.add(this.timeaxis);

  // current time bar
  this.currenttime = new CurrentTime(this.timeaxis, [], rootOptions);
  this.controller.add(this.currenttime);

  // custom time bar
  this.customtime = new CustomTime(this.timeaxis, [], rootOptions);
  this.controller.add(this.customtime);

  // create groupset
  this.setGroups(null);

  this.itemsData = null;      // DataSet
  this.groupsData = null;     // DataSet

  // apply options
  if (options) {
    this.setOptions(options);
  }

  // create itemset and groupset
  if (items) {
    this.setItems(items);
  }
}

/**
 * Set options
 * @param {Object} options  TODO: describe the available options
 */
Timeline.prototype.setOptions = function (options) {
  util.extend(this.options, options);

  // force update of range
  // options.start and options.end can be undefined
  //this.range.setRange(options.start, options.end);
  this.range.setRange();

  this.controller.reflow();
  this.controller.repaint();
};

/**
 * Set a custom time bar
 * @param {Date} time
 */
Timeline.prototype.setCustomTime = function (time) {
  this.customtime._setCustomTime(time);
};

/**
 * Retrieve the current custom time.
 * @return {Date} customTime
 */
Timeline.prototype.getCustomTime = function() {
  return new Date(this.customtime.customTime.valueOf());
};

/**
 * Set items
 * @param {vis.DataSet | Array | DataTable | null} items
 */
Timeline.prototype.setItems = function(items) {
  var initialLoad = (this.itemsData == null);

  // convert to type DataSet when needed
  var newItemSet;
  if (!items) {
    newItemSet = null;
  }
  else if (items instanceof DataSet) {
    newItemSet = items;
  }
  if (!(items instanceof DataSet)) {
    newItemSet = new DataSet({
      convert: {
        start: 'Date',
        end: 'Date'
      }
    });
    newItemSet.add(items);
  }

  // set items
  this.itemsData = newItemSet;
  this.content.setItems(newItemSet);

  if (initialLoad && (this.options.start == undefined || this.options.end == undefined)) {
    // apply the data range as range
    var dataRange = this.getItemRange();

    // add 5% space on both sides
    var min = dataRange.min;
    var max = dataRange.max;
    if (min != null && max != null) {
      var interval = (max.valueOf() - min.valueOf());
      if (interval <= 0) {
        // prevent an empty interval
        interval = 24 * 60 * 60 * 1000; // 1 day
      }
      min = new Date(min.valueOf() - interval * 0.05);
      max = new Date(max.valueOf() + interval * 0.05);
    }

    // override specified start and/or end date
    if (this.options.start != undefined) {
      min = util.convert(this.options.start, 'Date');
    }
    if (this.options.end != undefined) {
      max = util.convert(this.options.end, 'Date');
    }

    // apply range if there is a min or max available
    if (min != null || max != null) {
      this.range.setRange(min, max);
    }
  }
};

/**
 * Set groups
 * @param {vis.DataSet | Array | DataTable} groups
 */
Timeline.prototype.setGroups = function(groups) {
  var me = this;
  this.groupsData = groups;

  // switch content type between ItemSet or GroupSet when needed
  var Type = this.groupsData ? GroupSet : ItemSet;
  if (!(this.content instanceof Type)) {
    // remove old content set
    if (this.content) {
      this.content.hide();
      if (this.content.setItems) {
        this.content.setItems(); // disconnect from items
      }
      if (this.content.setGroups) {
        this.content.setGroups(); // disconnect from groups
      }
      this.controller.remove(this.content);
    }

    // create new content set
    var options = Object.create(this.options);
    util.extend(options, {
      top: function () {
        if (me.options.orientation == 'top') {
          return me.timeaxis.height;
        }
        else {
          return me.itemPanel.height - me.timeaxis.height - me.content.height;
        }
      },
      left: null,
      width: '100%',
      height: function () {
        if (me.options.height) {
          // fixed height
          return me.itemPanel.height - me.timeaxis.height;
        }
        else {
          // auto height
          return null;
        }
      },
      maxHeight: function () {
        // TODO: change maxHeight to be a css string like '100%' or '300px'
        if (me.options.maxHeight) {
          if (!util.isNumber(me.options.maxHeight)) {
            throw new TypeError('Number expected for property maxHeight');
          }
          return me.options.maxHeight - me.timeaxis.height;
        }
        else {
          return null;
        }
      },
      labelContainer: function () {
        return me.labelPanel.getContainer();
      }
    });

    this.content = new Type(this.itemPanel, [this.timeaxis], options);
    if (this.content.setRange) {
      this.content.setRange(this.range);
    }
    if (this.content.setItems) {
      this.content.setItems(this.itemsData);
    }
    if (this.content.setGroups) {
      this.content.setGroups(this.groupsData);
    }
    this.controller.add(this.content);
  }
};

/**
 * Get the data range of the item set.
 * @returns {{min: Date, max: Date}} range  A range with a start and end Date.
 *                                          When no minimum is found, min==null
 *                                          When no maximum is found, max==null
 */
Timeline.prototype.getItemRange = function getItemRange() {
  // calculate min from start filed
  var itemsData = this.itemsData,
      min = null,
      max = null;

  if (itemsData) {
    // calculate the minimum value of the field 'start'
    var minItem = itemsData.min('start');
    min = minItem ? minItem.start.valueOf() : null;

    // calculate maximum value of fields 'start' and 'end'
    var maxStartItem = itemsData.max('start');
    if (maxStartItem) {
      max = maxStartItem.start.valueOf();
    }
    var maxEndItem = itemsData.max('end');
    if (maxEndItem) {
      if (max == null) {
        max = maxEndItem.end.valueOf();
      }
      else {
        max = Math.max(max, maxEndItem.end.valueOf());
      }
    }
  }

  return {
    min: (min != null) ? new Date(min) : null,
    max: (max != null) ? new Date(max) : null
  };
};

/**
 * Change the item selection, and/or get currently selected items
 * @param {Array} [ids] An array with zero or more ids of the items to be selected.
 * @return {Array} ids  The ids of the selected items
 */
Timeline.prototype.select = function select(ids) {
  return this.content ? this.content.select(ids) : [];
};

(function(exports) {
  /**
   * Parse a text source containing data in DOT language into a JSON object.
   * The object contains two lists: one with nodes and one with edges.
   *
   * DOT language reference: http://www.graphviz.org/doc/info/lang.html
   *
   * @param {String} data     Text containing a graph in DOT-notation
   * @return {Object} graph   An object containing two parameters:
   *                          {Object[]} nodes
   *                          {Object[]} edges
   */
  function parseDOT (data) {
    dot = data;
    return parseGraph();
  }

  // token types enumeration
  var TOKENTYPE = {
    NULL : 0,
    DELIMITER : 1,
    IDENTIFIER: 2,
    UNKNOWN : 3
  };

  // map with all delimiters
  var DELIMITERS = {
    '{': true,
    '}': true,
    '[': true,
    ']': true,
    ';': true,
    '=': true,
    ',': true,

    '->': true,
    '--': true
  };

  var dot = '';                   // current dot file
  var index = 0;                  // current index in dot file
  var c = '';                     // current token character in expr
  var token = '';                 // current token
  var tokenType = TOKENTYPE.NULL; // type of the token

  /**
   * Get the first character from the dot file.
   * The character is stored into the char c. If the end of the dot file is
   * reached, the function puts an empty string in c.
   */
  function first() {
    index = 0;
    c = dot.charAt(0);
  }

  /**
   * Get the next character from the dot file.
   * The character is stored into the char c. If the end of the dot file is
   * reached, the function puts an empty string in c.
   */
  function next() {
    index++;
    c = dot.charAt(index);
  }

  /**
   * Preview the next character from the dot file.
   * @return {String} cNext
   */
  function nextPreview() {
    return dot.charAt(index + 1);
  }

  /**
   * Test whether given character is alphabetic or numeric
   * @param {String} c
   * @return {Boolean} isAlphaNumeric
   */
  var regexAlphaNumeric = /[a-zA-Z_0-9.:#]/;
  function isAlphaNumeric(c) {
    return regexAlphaNumeric.test(c);
  }

  /**
   * Merge all properties of object b into object b
   * @param {Object} a
   * @param {Object} b
   * @return {Object} a
   */
  function merge (a, b) {
    if (!a) {
      a = {};
    }

    if (b) {
      for (var name in b) {
        if (b.hasOwnProperty(name)) {
          a[name] = b[name];
        }
      }
    }
    return a;
  }

  /**
   * Set a value in an object, where the provided parameter name can be a
   * path with nested parameters. For example:
   *
   *     var obj = {a: 2};
   *     setValue(obj, 'b.c', 3);     // obj = {a: 2, b: {c: 3}}
   *
   * @param {Object} obj
   * @param {String} path  A parameter name or dot-separated parameter path,
   *                      like "color.highlight.border".
   * @param {*} value
   */
  function setValue(obj, path, value) {
    var keys = path.split('.');
    var o = obj;
    while (keys.length) {
      var key = keys.shift();
      if (keys.length) {
        // this isn't the end point
        if (!o[key]) {
          o[key] = {};
        }
        o = o[key];
      }
      else {
        // this is the end point
        o[key] = value;
      }
    }
  }

  /**
   * Add a node to a graph object. If there is already a node with
   * the same id, their attributes will be merged.
   * @param {Object} graph
   * @param {Object} node
   */
  function addNode(graph, node) {
    var i, len;
    var current = null;

    // find root graph (in case of subgraph)
    var graphs = [graph]; // list with all graphs from current graph to root graph
    var root = graph;
    while (root.parent) {
      graphs.push(root.parent);
      root = root.parent;
    }

    // find existing node (at root level) by its id
    if (root.nodes) {
      for (i = 0, len = root.nodes.length; i < len; i++) {
        if (node.id === root.nodes[i].id) {
          current = root.nodes[i];
          break;
        }
      }
    }

    if (!current) {
      // this is a new node
      current = {
        id: node.id
      };
      if (graph.node) {
        // clone default attributes
        current.attr = merge(current.attr, graph.node);
      }
    }

    // add node to this (sub)graph and all its parent graphs
    for (i = graphs.length - 1; i >= 0; i--) {
      var g = graphs[i];

      if (!g.nodes) {
        g.nodes = [];
      }
      if (g.nodes.indexOf(current) == -1) {
        g.nodes.push(current);
      }
    }

    // merge attributes
    if (node.attr) {
      current.attr = merge(current.attr, node.attr);
    }
  }

  /**
   * Add an edge to a graph object
   * @param {Object} graph
   * @param {Object} edge
   */
  function addEdge(graph, edge) {
    if (!graph.edges) {
      graph.edges = [];
    }
    graph.edges.push(edge);
    if (graph.edge) {
      var attr = merge({}, graph.edge);     // clone default attributes
      edge.attr = merge(attr, edge.attr); // merge attributes
    }
  }

  /**
   * Create an edge to a graph object
   * @param {Object} graph
   * @param {String | Number | Object} from
   * @param {String | Number | Object} to
   * @param {String} type
   * @param {Object | null} attr
   * @return {Object} edge
   */
  function createEdge(graph, from, to, type, attr) {
    var edge = {
      from: from,
      to: to,
      type: type
    };

    if (graph.edge) {
      edge.attr = merge({}, graph.edge);  // clone default attributes
    }
    edge.attr = merge(edge.attr || {}, attr); // merge attributes

    return edge;
  }

  /**
   * Get next token in the current dot file.
   * The token and token type are available as token and tokenType
   */
  function getToken() {
    tokenType = TOKENTYPE.NULL;
    token = '';

    // skip over whitespaces
    while (c == ' ' || c == '\t' || c == '\n' || c == '\r') {  // space, tab, enter
      next();
    }

    do {
      var isComment = false;

      // skip comment
      if (c == '#') {
        // find the previous non-space character
        var i = index - 1;
        while (dot.charAt(i) == ' ' || dot.charAt(i) == '\t') {
          i--;
        }
        if (dot.charAt(i) == '\n' || dot.charAt(i) == '') {
          // the # is at the start of a line, this is indeed a line comment
          while (c != '' && c != '\n') {
            next();
          }
          isComment = true;
        }
      }
      if (c == '/' && nextPreview() == '/') {
        // skip line comment
        while (c != '' && c != '\n') {
          next();
        }
        isComment = true;
      }
      if (c == '/' && nextPreview() == '*') {
        // skip block comment
        while (c != '') {
          if (c == '*' && nextPreview() == '/') {
            // end of block comment found. skip these last two characters
            next();
            next();
            break;
          }
          else {
            next();
          }
        }
        isComment = true;
      }

      // skip over whitespaces
      while (c == ' ' || c == '\t' || c == '\n' || c == '\r') {  // space, tab, enter
        next();
      }
    }
    while (isComment);

    // check for end of dot file
    if (c == '') {
      // token is still empty
      tokenType = TOKENTYPE.DELIMITER;
      return;
    }

    // check for delimiters consisting of 2 characters
    var c2 = c + nextPreview();
    if (DELIMITERS[c2]) {
      tokenType = TOKENTYPE.DELIMITER;
      token = c2;
      next();
      next();
      return;
    }

    // check for delimiters consisting of 1 character
    if (DELIMITERS[c]) {
      tokenType = TOKENTYPE.DELIMITER;
      token = c;
      next();
      return;
    }

    // check for an identifier (number or string)
    // TODO: more precise parsing of numbers/strings (and the port separator ':')
    if (isAlphaNumeric(c) || c == '-') {
      token += c;
      next();

      while (isAlphaNumeric(c)) {
        token += c;
        next();
      }
      if (token == 'false') {
        token = false;   // convert to boolean
      }
      else if (token == 'true') {
        token = true;   // convert to boolean
      }
      else if (!isNaN(Number(token))) {
        token = Number(token); // convert to number
      }
      tokenType = TOKENTYPE.IDENTIFIER;
      return;
    }

    // check for a string enclosed by double quotes
    if (c == '"') {
      next();
      while (c != '' && (c != '"' || (c == '"' && nextPreview() == '"'))) {
        token += c;
        if (c == '"') { // skip the escape character
          next();
        }
        next();
      }
      if (c != '"') {
        throw newSyntaxError('End of string " expected');
      }
      next();
      tokenType = TOKENTYPE.IDENTIFIER;
      return;
    }

    // something unknown is found, wrong characters, a syntax error
    tokenType = TOKENTYPE.UNKNOWN;
    while (c != '') {
      token += c;
      next();
    }
    throw new SyntaxError('Syntax error in part "' + chop(token, 30) + '"');
  }

  /**
   * Parse a graph.
   * @returns {Object} graph
   */
  function parseGraph() {
    var graph = {};

    first();
    getToken();

    // optional strict keyword
    if (token == 'strict') {
      graph.strict = true;
      getToken();
    }

    // graph or digraph keyword
    if (token == 'graph' || token == 'digraph') {
      graph.type = token;
      getToken();
    }

    // optional graph id
    if (tokenType == TOKENTYPE.IDENTIFIER) {
      graph.id = token;
      getToken();
    }

    // open angle bracket
    if (token != '{') {
      throw newSyntaxError('Angle bracket { expected');
    }
    getToken();

    // statements
    parseStatements(graph);

    // close angle bracket
    if (token != '}') {
      throw newSyntaxError('Angle bracket } expected');
    }
    getToken();

    // end of file
    if (token !== '') {
      throw newSyntaxError('End of file expected');
    }
    getToken();

    // remove temporary default properties
    delete graph.node;
    delete graph.edge;
    delete graph.graph;

    return graph;
  }

  /**
   * Parse a list with statements.
   * @param {Object} graph
   */
  function parseStatements (graph) {
    while (token !== '' && token != '}') {
      parseStatement(graph);
      if (token == ';') {
        getToken();
      }
    }
  }

  /**
   * Parse a single statement. Can be a an attribute statement, node
   * statement, a series of node statements and edge statements, or a
   * parameter.
   * @param {Object} graph
   */
  function parseStatement(graph) {
    // parse subgraph
    var subgraph = parseSubgraph(graph);
    if (subgraph) {
      // edge statements
      parseEdge(graph, subgraph);

      return;
    }

    // parse an attribute statement
    var attr = parseAttributeStatement(graph);
    if (attr) {
      return;
    }

    // parse node
    if (tokenType != TOKENTYPE.IDENTIFIER) {
      throw newSyntaxError('Identifier expected');
    }
    var id = token; // id can be a string or a number
    getToken();

    if (token == '=') {
      // id statement
      getToken();
      if (tokenType != TOKENTYPE.IDENTIFIER) {
        throw newSyntaxError('Identifier expected');
      }
      graph[id] = token;
      getToken();
      // TODO: implement comma separated list with "a_list: ID=ID [','] [a_list] "
    }
    else {
      parseNodeStatement(graph, id);
    }
  }

  /**
   * Parse a subgraph
   * @param {Object} graph    parent graph object
   * @return {Object | null} subgraph
   */
  function parseSubgraph (graph) {
    var subgraph = null;

    // optional subgraph keyword
    if (token == 'subgraph') {
      subgraph = {};
      subgraph.type = 'subgraph';
      getToken();

      // optional graph id
      if (tokenType == TOKENTYPE.IDENTIFIER) {
        subgraph.id = token;
        getToken();
      }
    }

    // open angle bracket
    if (token == '{') {
      getToken();

      if (!subgraph) {
        subgraph = {};
      }
      subgraph.parent = graph;
      subgraph.node = graph.node;
      subgraph.edge = graph.edge;
      subgraph.graph = graph.graph;

      // statements
      parseStatements(subgraph);

      // close angle bracket
      if (token != '}') {
        throw newSyntaxError('Angle bracket } expected');
      }
      getToken();

      // remove temporary default properties
      delete subgraph.node;
      delete subgraph.edge;
      delete subgraph.graph;
      delete subgraph.parent;

      // register at the parent graph
      if (!graph.subgraphs) {
        graph.subgraphs = [];
      }
      graph.subgraphs.push(subgraph);
    }

    return subgraph;
  }

  /**
   * parse an attribute statement like "node [shape=circle fontSize=16]".
   * Available keywords are 'node', 'edge', 'graph'.
   * The previous list with default attributes will be replaced
   * @param {Object} graph
   * @returns {String | null} keyword Returns the name of the parsed attribute
   *                                  (node, edge, graph), or null if nothing
   *                                  is parsed.
   */
  function parseAttributeStatement (graph) {
    // attribute statements
    if (token == 'node') {
      getToken();

      // node attributes
      graph.node = parseAttributeList();
      return 'node';
    }
    else if (token == 'edge') {
      getToken();

      // edge attributes
      graph.edge = parseAttributeList();
      return 'edge';
    }
    else if (token == 'graph') {
      getToken();

      // graph attributes
      graph.graph = parseAttributeList();
      return 'graph';
    }

    return null;
  }

  /**
   * parse a node statement
   * @param {Object} graph
   * @param {String | Number} id
   */
  function parseNodeStatement(graph, id) {
    // node statement
    var node = {
      id: id
    };
    var attr = parseAttributeList();
    if (attr) {
      node.attr = attr;
    }
    addNode(graph, node);

    // edge statements
    parseEdge(graph, id);
  }

  /**
   * Parse an edge or a series of edges
   * @param {Object} graph
   * @param {String | Number} from        Id of the from node
   */
  function parseEdge(graph, from) {
    while (token == '->' || token == '--') {
      var to;
      var type = token;
      getToken();

      var subgraph = parseSubgraph(graph);
      if (subgraph) {
        to = subgraph;
      }
      else {
        if (tokenType != TOKENTYPE.IDENTIFIER) {
          throw newSyntaxError('Identifier or subgraph expected');
        }
        to = token;
        addNode(graph, {
          id: to
        });
        getToken();
      }

      // parse edge attributes
      var attr = parseAttributeList();

      // create edge
      var edge = createEdge(graph, from, to, type, attr);
      addEdge(graph, edge);

      from = to;
    }
  }

  /**
   * Parse a set with attributes,
   * for example [label="1.000", shape=solid]
   * @return {Object | null} attr
   */
  function parseAttributeList() {
    var attr = null;

    while (token == '[') {
      getToken();
      attr = {};
      while (token !== '' && token != ']') {
        if (tokenType != TOKENTYPE.IDENTIFIER) {
          throw newSyntaxError('Attribute name expected');
        }
        var name = token;

        getToken();
        if (token != '=') {
          throw newSyntaxError('Equal sign = expected');
        }
        getToken();

        if (tokenType != TOKENTYPE.IDENTIFIER) {
          throw newSyntaxError('Attribute value expected');
        }
        var value = token;
        setValue(attr, name, value); // name can be a path

        getToken();
        if (token ==',') {
          getToken();
        }
      }

      if (token != ']') {
        throw newSyntaxError('Bracket ] expected');
      }
      getToken();
    }

    return attr;
  }

  /**
   * Create a syntax error with extra information on current token and index.
   * @param {String} message
   * @returns {SyntaxError} err
   */
  function newSyntaxError(message) {
    return new SyntaxError(message + ', got "' + chop(token, 30) + '" (char ' + index + ')');
  }

  /**
   * Chop off text after a maximum length
   * @param {String} text
   * @param {Number} maxLength
   * @returns {String}
   */
  function chop (text, maxLength) {
    return (text.length <= maxLength) ? text : (text.substr(0, 27) + '...');
  }

  /**
   * Execute a function fn for each pair of elements in two arrays
   * @param {Array | *} array1
   * @param {Array | *} array2
   * @param {function} fn
   */
  function forEach2(array1, array2, fn) {
    if (array1 instanceof Array) {
      array1.forEach(function (elem1) {
        if (array2 instanceof Array) {
          array2.forEach(function (elem2)  {
            fn(elem1, elem2);
          });
        }
        else {
          fn(elem1, array2);
        }
      });
    }
    else {
      if (array2 instanceof Array) {
        array2.forEach(function (elem2)  {
          fn(array1, elem2);
        });
      }
      else {
        fn(array1, array2);
      }
    }
  }

  /**
   * Convert a string containing a graph in DOT language into a map containing
   * with nodes and edges in the format of graph.
   * @param {String} data         Text containing a graph in DOT-notation
   * @return {Object} graphData
   */
  function DOTToGraph (data) {
    // parse the DOT file
    var dotData = parseDOT(data);
    var graphData = {
      nodes: [],
      edges: [],
      options: {}
    };

    // copy the nodes
    if (dotData.nodes) {
      dotData.nodes.forEach(function (dotNode) {
        var graphNode = {
          id: dotNode.id,
          label: String(dotNode.label || dotNode.id)
        };
        merge(graphNode, dotNode.attr);
        if (graphNode.image) {
          graphNode.shape = 'image';
        }
        graphData.nodes.push(graphNode);
      });
    }

    // copy the edges
    if (dotData.edges) {
      /**
       * Convert an edge in DOT format to an edge with VisGraph format
       * @param {Object} dotEdge
       * @returns {Object} graphEdge
       */
      function convertEdge(dotEdge) {
        var graphEdge = {
          from: dotEdge.from,
          to: dotEdge.to
        };
        merge(graphEdge, dotEdge.attr);
        graphEdge.style = (dotEdge.type == '->') ? 'arrow' : 'line';
        return graphEdge;
      }

      dotData.edges.forEach(function (dotEdge) {
        var from, to;
        if (dotEdge.from instanceof Object) {
          from = dotEdge.from.nodes;
        }
        else {
          from = {
            id: dotEdge.from
          }
        }

        if (dotEdge.to instanceof Object) {
          to = dotEdge.to.nodes;
        }
        else {
          to = {
            id: dotEdge.to
          }
        }

        if (dotEdge.from instanceof Object && dotEdge.from.edges) {
          dotEdge.from.edges.forEach(function (subEdge) {
            var graphEdge = convertEdge(subEdge);
            graphData.edges.push(graphEdge);
          });
        }

        forEach2(from, to, function (from, to) {
          var subEdge = createEdge(graphData, from.id, to.id, dotEdge.type, dotEdge.attr);
          var graphEdge = convertEdge(subEdge);
          graphData.edges.push(graphEdge);
        });

        if (dotEdge.to instanceof Object && dotEdge.to.edges) {
          dotEdge.to.edges.forEach(function (subEdge) {
            var graphEdge = convertEdge(subEdge);
            graphData.edges.push(graphEdge);
          });
        }
      });
    }

    // copy the options
    if (dotData.attr) {
      graphData.options = dotData.attr;
    }

    return graphData;
  }

  // exports
  exports.parseDOT = parseDOT;
  exports.DOTToGraph = DOTToGraph;

})(typeof util !== 'undefined' ? util : exports);

/**
 * Canvas shapes used by the Graph
 */
if (typeof CanvasRenderingContext2D !== 'undefined') {

  /**
   * Draw a circle shape
   */
  CanvasRenderingContext2D.prototype.circle = function(x, y, r) {
    this.beginPath();
    this.arc(x, y, r, 0, 2*Math.PI, false);
  };

  /**
   * Draw a square shape
   * @param {Number} x horizontal center
   * @param {Number} y vertical center
   * @param {Number} r   size, width and height of the square
   */
  CanvasRenderingContext2D.prototype.square = function(x, y, r) {
    this.beginPath();
    this.rect(x - r, y - r, r * 2, r * 2);
  };

  /**
   * Draw a triangle shape
   * @param {Number} x horizontal center
   * @param {Number} y vertical center
   * @param {Number} r   radius, half the length of the sides of the triangle
   */
  CanvasRenderingContext2D.prototype.triangle = function(x, y, r) {
    // http://en.wikipedia.org/wiki/Equilateral_triangle
    this.beginPath();

    var s = r * 2;
    var s2 = s / 2;
    var ir = Math.sqrt(3) / 6 * s;      // radius of inner circle
    var h = Math.sqrt(s * s - s2 * s2); // height

    this.moveTo(x, y - (h - ir));
    this.lineTo(x + s2, y + ir);
    this.lineTo(x - s2, y + ir);
    this.lineTo(x, y - (h - ir));
    this.closePath();
  };

  /**
   * Draw a triangle shape in downward orientation
   * @param {Number} x horizontal center
   * @param {Number} y vertical center
   * @param {Number} r radius
   */
  CanvasRenderingContext2D.prototype.triangleDown = function(x, y, r) {
    // http://en.wikipedia.org/wiki/Equilateral_triangle
    this.beginPath();

    var s = r * 2;
    var s2 = s / 2;
    var ir = Math.sqrt(3) / 6 * s;      // radius of inner circle
    var h = Math.sqrt(s * s - s2 * s2); // height

    this.moveTo(x, y + (h - ir));
    this.lineTo(x + s2, y - ir);
    this.lineTo(x - s2, y - ir);
    this.lineTo(x, y + (h - ir));
    this.closePath();
  };

  /**
   * Draw a star shape, a star with 5 points
   * @param {Number} x horizontal center
   * @param {Number} y vertical center
   * @param {Number} r   radius, half the length of the sides of the triangle
   */
  CanvasRenderingContext2D.prototype.star = function(x, y, r) {
    // http://www.html5canvastutorials.com/labs/html5-canvas-star-spinner/
    this.beginPath();

    for (var n = 0; n < 10; n++) {
      var radius = (n % 2 === 0) ? r * 1.3 : r * 0.5;
      this.lineTo(
          x + radius * Math.sin(n * 2 * Math.PI / 10),
          y - radius * Math.cos(n * 2 * Math.PI / 10)
      );
    }

    this.closePath();
  };

  /**
   * http://stackoverflow.com/questions/1255512/how-to-draw-a-rounded-rectangle-on-html-canvas
   */
  CanvasRenderingContext2D.prototype.roundRect = function(x, y, w, h, r) {
    var r2d = Math.PI/180;
    if( w - ( 2 * r ) < 0 ) { r = ( w / 2 ); } //ensure that the radius isn't too large for x
    if( h - ( 2 * r ) < 0 ) { r = ( h / 2 ); } //ensure that the radius isn't too large for y
    this.beginPath();
    this.moveTo(x+r,y);
    this.lineTo(x+w-r,y);
    this.arc(x+w-r,y+r,r,r2d*270,r2d*360,false);
    this.lineTo(x+w,y+h-r);
    this.arc(x+w-r,y+h-r,r,0,r2d*90,false);
    this.lineTo(x+r,y+h);
    this.arc(x+r,y+h-r,r,r2d*90,r2d*180,false);
    this.lineTo(x,y+r);
    this.arc(x+r,y+r,r,r2d*180,r2d*270,false);
  };

  /**
   * http://stackoverflow.com/questions/2172798/how-to-draw-an-oval-in-html5-canvas
   */
  CanvasRenderingContext2D.prototype.ellipse = function(x, y, w, h) {
    var kappa = .5522848,
        ox = (w / 2) * kappa, // control point offset horizontal
        oy = (h / 2) * kappa, // control point offset vertical
        xe = x + w,           // x-end
        ye = y + h,           // y-end
        xm = x + w / 2,       // x-middle
        ym = y + h / 2;       // y-middle

    this.beginPath();
    this.moveTo(x, ym);
    this.bezierCurveTo(x, ym - oy, xm - ox, y, xm, y);
    this.bezierCurveTo(xm + ox, y, xe, ym - oy, xe, ym);
    this.bezierCurveTo(xe, ym + oy, xm + ox, ye, xm, ye);
    this.bezierCurveTo(xm - ox, ye, x, ym + oy, x, ym);
  };



  /**
   * http://stackoverflow.com/questions/2172798/how-to-draw-an-oval-in-html5-canvas
   */
  CanvasRenderingContext2D.prototype.database = function(x, y, w, h) {
    var f = 1/3;
    var wEllipse = w;
    var hEllipse = h * f;

    var kappa = .5522848,
        ox = (wEllipse / 2) * kappa, // control point offset horizontal
        oy = (hEllipse / 2) * kappa, // control point offset vertical
        xe = x + wEllipse,           // x-end
        ye = y + hEllipse,           // y-end
        xm = x + wEllipse / 2,       // x-middle
        ym = y + hEllipse / 2,       // y-middle
        ymb = y + (h - hEllipse/2),  // y-midlle, bottom ellipse
        yeb = y + h;                 // y-end, bottom ellipse

    this.beginPath();
    this.moveTo(xe, ym);

    this.bezierCurveTo(xe, ym + oy, xm + ox, ye, xm, ye);
    this.bezierCurveTo(xm - ox, ye, x, ym + oy, x, ym);

    this.bezierCurveTo(x, ym - oy, xm - ox, y, xm, y);
    this.bezierCurveTo(xm + ox, y, xe, ym - oy, xe, ym);

    this.lineTo(xe, ymb);

    this.bezierCurveTo(xe, ymb + oy, xm + ox, yeb, xm, yeb);
    this.bezierCurveTo(xm - ox, yeb, x, ymb + oy, x, ymb);

    this.lineTo(x, ym);
  };


  /**
   * Draw an arrow point (no line)
   */
  CanvasRenderingContext2D.prototype.arrow = function(x, y, angle, length) {
    // tail
    var xt = x - length * Math.cos(angle);
    var yt = y - length * Math.sin(angle);

    // inner tail
    // TODO: allow to customize different shapes
    var xi = x - length * 0.9 * Math.cos(angle);
    var yi = y - length * 0.9 * Math.sin(angle);

    // left
    var xl = xt + length / 3 * Math.cos(angle + 0.5 * Math.PI);
    var yl = yt + length / 3 * Math.sin(angle + 0.5 * Math.PI);

    // right
    var xr = xt + length / 3 * Math.cos(angle - 0.5 * Math.PI);
    var yr = yt + length / 3 * Math.sin(angle - 0.5 * Math.PI);

    this.beginPath();
    this.moveTo(x, y);
    this.lineTo(xl, yl);
    this.lineTo(xi, yi);
    this.lineTo(xr, yr);
    this.closePath();
  };

  /**
   * Sets up the dashedLine functionality for drawing
   * Original code came from http://stackoverflow.com/questions/4576724/dotted-stroke-in-canvas
   * @author David Jordan
   * @date 2012-08-08
   */
  CanvasRenderingContext2D.prototype.dashedLine = function(x,y,x2,y2,dashArray){
    if (!dashArray) dashArray=[10,5];
    if (dashLength==0) dashLength = 0.001; // Hack for Safari
    var dashCount = dashArray.length;
    this.moveTo(x, y);
    var dx = (x2-x), dy = (y2-y);
    var slope = dy/dx;
    var distRemaining = Math.sqrt( dx*dx + dy*dy );
    var dashIndex=0, draw=true;
    while (distRemaining>=0.1){
      var dashLength = dashArray[dashIndex++%dashCount];
      if (dashLength > distRemaining) dashLength = distRemaining;
      var xStep = Math.sqrt( dashLength*dashLength / (1 + slope*slope) );
      if (dx<0) xStep = -xStep;
      x += xStep;
      y += slope*xStep;
      this[draw ? 'lineTo' : 'moveTo'](x,y);
      distRemaining -= dashLength;
      draw = !draw;
    }
  };

  // TODO: add diamond shape
}

/**
 * @class Node
 * A node. A node can be connected to other nodes via one or multiple edges.
 * @param {object} properties An object containing properties for the node. All
 *                            properties are optional, except for the id.
 *                              {number} id     Id of the node. Required
 *                              {string} label  Text label for the node
 *                              {number} x      Horizontal position of the node
 *                              {number} y      Vertical position of the node
 *                              {string} shape  Node shape, available:
 *                                              "database", "circle", "ellipse",
 *                                              "box", "image", "text", "dot",
 *                                              "star", "triangle", "triangleDown",
 *                                              "square"
 *                              {string} image  An image url
 *                              {string} title  An title text, can be HTML
 *                              {anytype} group A group name or number
 * @param {Graph.Images} imagelist    A list with images. Only needed
 *                                            when the node has an image
 * @param {Graph.Groups} grouplist    A list with groups. Needed for
 *                                            retrieving group properties
 * @param {Object}               constants    An object with default values for
 *                                            example for the color
 */
function Node(properties, imagelist, grouplist, constants) {
  this.selected = false;

  this.edges = []; // all edges connected to this node
  this.dynamicEdges = [];
  this.reroutedEdges = {};
  this.group = constants.nodes.group;

  this.fontSize = constants.nodes.fontSize;
  this.fontFace = constants.nodes.fontFace;
  this.fontColor = constants.nodes.fontColor;

  this.color = constants.nodes.color;

  // set defaults for the properties
  this.id = undefined;
  this.shape = constants.nodes.shape;
  this.image = constants.nodes.image;
  this.x = 0;
  this.y = 0;
  this.xFixed = false;
  this.yFixed = false;
  this.horizontalAlignLeft = true; // these are for the navigationUI
  this.verticalAlignTop    = true; // these are for the navigationUI
  this.radius = constants.nodes.radius;
  this.baseRadiusValue = constants.nodes.radius;
  this.radiusFixed = false;
  this.radiusMin = constants.nodes.radiusMin;
  this.radiusMax = constants.nodes.radiusMax;

  this.imagelist = imagelist;

  this.grouplist = grouplist;

  this.setProperties(properties, constants);

  // creating the variables for clustering
  this.resetCluster();
  this.dynamicEdgesLength = 0;
  this.clusterSession = 0;

  this.clusterSizeWidthFactor  = constants.clustering.clusterSizeWidthFactor;
  this.clusterSizeHeightFactor = constants.clustering.clusterSizeHeightFactor;
  this.clusterSizeRadiusFactor = constants.clustering.clusterSizeRadiusFactor;

  // mass, force, velocity
  this.mass = 1;  // kg (mass is adjusted for the number of connected edges)
  this.fx = 0.0;  // external force x
  this.fy = 0.0;  // external force y
  this.vx = 0.0;  // velocity x
  this.vy = 0.0;  // velocity y
  this.minForce = constants.minForce;
  this.damping = 0.9;
  this.dampingFactor = 75;

  this.graphScaleInv = 1;
  this.canvasTopLeft = {"x": -300, "y": -300};
  this.canvasBottomRight = {"x":  300, "y":  300};
}

/**
 * (re)setting the clustering variables and objects
 */
Node.prototype.resetCluster = function() {
  // clustering variables
  this.formationScale = undefined; // this is used to determine when to open the cluster
  this.clusterSize = 1;            // this signifies the total amount of nodes in this cluster
  this.containedNodes = {};
  this.containedEdges = {};
  this.clusterSessions = [];
};

/**
 * Attach a edge to the node
 * @param {Edge} edge
 */
Node.prototype.attachEdge = function(edge) {
  if (this.edges.indexOf(edge) == -1) {
    this.edges.push(edge);
  }
  if (this.dynamicEdges.indexOf(edge) == -1) {
    this.dynamicEdges.push(edge);
  }
  this.dynamicEdgesLength = this.dynamicEdges.length;
  this._updateMass();
};

/**
 * Detach a edge from the node
 * @param {Edge} edge
 */
Node.prototype.detachEdge = function(edge) {
  var index = this.edges.indexOf(edge);
  if (index != -1) {
    this.edges.splice(index, 1);
    this.dynamicEdges.splice(index, 1);
  }
  this.dynamicEdgesLength = this.dynamicEdges.length;
  this._updateMass();
};

/**
 * Update the nodes mass, which is determined by the number of edges connecting
 * to it (more edges -> heavier node).
 * @private
 */
Node.prototype._updateMass = function() {
  this.mass = 1 + 0.6 * this.edges.length; // kg
};

/**
 * Set or overwrite properties for the node
 * @param {Object} properties an object with properties
 * @param {Object} constants  and object with default, global properties
 */
Node.prototype.setProperties = function(properties, constants) {
  if (!properties) {
    return;
  }
  this.originalLabel = undefined;
  // basic properties
  if (properties.id !== undefined)        {this.id = properties.id;}
  if (properties.label !== undefined)     {this.label = properties.label; this.originalLabel = properties.label;}
  if (properties.title !== undefined)     {this.title = properties.title;}
  if (properties.group !== undefined)     {this.group = properties.group;}
  if (properties.x !== undefined)         {this.x = properties.x;}
  if (properties.y !== undefined)         {this.y = properties.y;}
  if (properties.value !== undefined)     {this.value = properties.value;}

  // navigationUI properties
  if (properties.horizontalAlignLeft !== undefined) {this.horizontalAlignLeft = properties.horizontalAlignLeft;}
  if (properties.verticalAlignTop    !== undefined) {this.verticalAlignTop    = properties.verticalAlignTop;}
  if (properties.triggerFunction     !== undefined) {this.triggerFunction     = properties.triggerFunction;}

  if (this.id === undefined) {
    throw "Node must have an id";
  }

  // copy group properties
  if (this.group) {
    var groupObj = this.grouplist.get(this.group);
    for (var prop in groupObj) {
      if (groupObj.hasOwnProperty(prop)) {
        this[prop] = groupObj[prop];
      }
    }
  }

  // individual shape properties
  if (properties.shape !== undefined)          {this.shape = properties.shape;}
  if (properties.image !== undefined)          {this.image = properties.image;}
  if (properties.radius !== undefined)         {this.radius = properties.radius;}
  if (properties.color !== undefined)          {this.color = Node.parseColor(properties.color);}

  if (properties.fontColor !== undefined)      {this.fontColor = properties.fontColor;}
  if (properties.fontSize !== undefined)       {this.fontSize = properties.fontSize;}
  if (properties.fontFace !== undefined)       {this.fontFace = properties.fontFace;}

  if (this.image !== undefined) {
    if (this.imagelist) {
      this.imageObj = this.imagelist.load(this.image);
    }
    else {
      throw "No imagelist provided";
    }
  }

  this.xFixed = this.xFixed || (properties.x !== undefined);
  this.yFixed = this.yFixed || (properties.y !== undefined);
  this.radiusFixed = this.radiusFixed || (properties.radius !== undefined);

  if (this.shape == 'image') {
    this.radiusMin = constants.nodes.widthMin;
    this.radiusMax = constants.nodes.widthMax;
  }

  // choose draw method depending on the shape
  switch (this.shape) {
    case 'database':      this.draw = this._drawDatabase; this.resize = this._resizeDatabase; break;
    case 'box':           this.draw = this._drawBox; this.resize = this._resizeBox; break;
    case 'circle':        this.draw = this._drawCircle; this.resize = this._resizeCircle; break;
    case 'ellipse':       this.draw = this._drawEllipse; this.resize = this._resizeEllipse; break;
    // TODO: add diamond shape
    case 'image':         this.draw = this._drawImage; this.resize = this._resizeImage; break;
    case 'text':          this.draw = this._drawText; this.resize = this._resizeText; break;
    case 'dot':           this.draw = this._drawDot; this.resize = this._resizeShape; break;
    case 'square':        this.draw = this._drawSquare; this.resize = this._resizeShape; break;
    case 'triangle':      this.draw = this._drawTriangle; this.resize = this._resizeShape; break;
    case 'triangleDown':  this.draw = this._drawTriangleDown; this.resize = this._resizeShape; break;
    case 'star':          this.draw = this._drawStar; this.resize = this._resizeShape; break;
    default:              this.draw = this._drawEllipse; this.resize = this._resizeEllipse; break;
  }
  // reset the size of the node, this can be changed
  this._reset();
};

/**
 * Parse a color property into an object with border, background, and
 * hightlight colors
 * @param {Object | String} color
 * @return {Object} colorObject
 */
Node.parseColor = function(color) {
  var c;
  if (util.isString(color)) {
    c = {
      border: color,
      background: color,
      highlight: {
        border: color,
        background: color
      }
    };
    // TODO: automatically generate a nice highlight color
  }
  else {
    c = {};
    c.background = color.background || 'white';
    c.border = color.border || c.background;

    if (util.isString(color.highlight)) {
      c.highlight = {
        border: color.highlight,
        background: color.highlight
      }
    }
    else {
      c.highlight = {};
      c.highlight.background = color.highlight && color.highlight.background || c.background;
      c.highlight.border = color.highlight && color.highlight.border || c.border;
    }
  }

  return c;
};

/**
 * select this node
 */
Node.prototype.select = function() {
  this.selected = true;
  this._reset();
};

/**
 * unselect this node
 */
Node.prototype.unselect = function() {
  this.selected = false;
  this._reset();
};


/**
 * Reset the calculated size of the node, forces it to recalculate its size
 */
Node.prototype.clearSizeCache = function() {
  this._reset();
};

/**
 * Reset the calculated size of the node, forces it to recalculate its size
 * @private
 */
Node.prototype._reset = function() {
  this.width = undefined;
  this.height = undefined;
};

/**
 * get the title of this node.
 * @return {string} title    The title of the node, or undefined when no title
 *                           has been set.
 */
Node.prototype.getTitle = function() {
  return this.title;
};

/**
 * Calculate the distance to the border of the Node
 * @param {CanvasRenderingContext2D}   ctx
 * @param {Number} angle        Angle in radians
 * @returns {number} distance   Distance to the border in pixels
 */
Node.prototype.distanceToBorder = function (ctx, angle) {
  var borderWidth = 1;

  if (!this.width) {
    this.resize(ctx);
  }

  //noinspection FallthroughInSwitchStatementJS
  switch (this.shape) {
    case 'circle':
    case 'dot':
      return this.radius + borderWidth;

    case 'ellipse':
      var a = this.width / 2;
      var b = this.height / 2;
      var w = (Math.sin(angle) * a);
      var h = (Math.cos(angle) * b);
      return a * b / Math.sqrt(w * w + h * h);

    // TODO: implement distanceToBorder for database
    // TODO: implement distanceToBorder for triangle
    // TODO: implement distanceToBorder for triangleDown

    case 'box':
    case 'image':
    case 'text':
    default:
      if (this.width) {
        return Math.min(
            Math.abs(this.width / 2 / Math.cos(angle)),
            Math.abs(this.height / 2 / Math.sin(angle))) + borderWidth;
        // TODO: reckon with border radius too in case of box
      }
      else {
        return 0;
      }

  }

  // TODO: implement calculation of distance to border for all shapes
};

/**
 * Set forces acting on the node
 * @param {number} fx   Force in horizontal direction
 * @param {number} fy   Force in vertical direction
 */
Node.prototype._setForce = function(fx, fy) {
  this.fx = fx;
  this.fy = fy;
};

/**
 * Add forces acting on the node
 * @param {number} fx   Force in horizontal direction
 * @param {number} fy   Force in vertical direction
 * @private
 */
Node.prototype._addForce = function(fx, fy) {
  this.fx += fx;
  this.fy += fy;
};

/**
 * Perform one discrete step for the node
 * @param {number} interval    Time interval in seconds
 */
Node.prototype.discreteStep = function(interval) {
  if (!this.xFixed) {
    var dx   = -this.damping * this.vx;     // damping force
    var ax   = (this.fx + dx) / this.mass;  // acceleration
    this.vx += ax * interval;               // velocity
    this.x  += this.vx * interval;          // position
  }

  if (!this.yFixed) {
    var dy   = -this.damping * this.vy;     // damping force
    var ay   = (this.fy + dy) / this.mass;  // acceleration
    this.vy += ay * interval;               // velocity
    this.y  += this.vy * interval;          // position
  }
};


/**
 * Check if this node has a fixed x and y position
 * @return {boolean}      true if fixed, false if not
 */
Node.prototype.isFixed = function() {
  return (this.xFixed && this.yFixed);
};

/**
 * Check if this node is moving
 * @param {number} vmin   the minimum velocity considered as "moving"
 * @return {boolean}      true if moving, false if it has no velocity
 */
// TODO: replace this method with calculating the kinetic energy
Node.prototype.isMoving = function(vmin) {
  if (Math.abs(this.vx) > vmin || Math.abs(this.vy) > vmin) {
    return true;
  }
  else {
    this.vx = 0; this.vy = 0;
    return false;
  }
  //return (Math.abs(this.vx) > vmin || Math.abs(this.vy) > vmin);
};

/**
 * check if this node is selecte
 * @return {boolean} selected   True if node is selected, else false
 */
Node.prototype.isSelected = function() {
  return this.selected;
};

/**
 * Retrieve the value of the node. Can be undefined
 * @return {Number} value
 */
Node.prototype.getValue = function() {
  return this.value;
};

/**
 * Calculate the distance from the nodes location to the given location (x,y)
 * @param {Number} x
 * @param {Number} y
 * @return {Number} value
 */
Node.prototype.getDistance = function(x, y) {
  var dx = this.x - x,
      dy = this.y - y;
  return Math.sqrt(dx * dx + dy * dy);
};


/**
 * Adjust the value range of the node. The node will adjust it's radius
 * based on its value.
 * @param {Number} min
 * @param {Number} max
 */
Node.prototype.setValueRange = function(min, max) {
  if (!this.radiusFixed && this.value !== undefined) {
    if (max == min) {
      this.radius = (this.radiusMin + this.radiusMax) / 2;
    }
    else {
      var scale = (this.radiusMax - this.radiusMin) / (max - min);
      this.radius = (this.value - min) * scale + this.radiusMin;
    }
  }
  this.baseRadiusValue = this.radius;
};

/**
 * Draw this node in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 */
Node.prototype.draw = function(ctx) {
  throw "Draw method not initialized for node";
};

/**
 * Recalculate the size of this node in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 */
Node.prototype.resize = function(ctx) {
  throw "Resize method not initialized for node";
};

/**
 * Check if this object is overlapping with the provided object
 * @param {Object} obj   an object with parameters left, top, right, bottom
 * @return {boolean}     True if location is located on node
 */
Node.prototype.isOverlappingWith = function(obj) {
  return (this.left              < obj.right  &&
          this.left + this.width > obj.left   &&
          this.top               < obj.bottom &&
          this.top + this.height > obj.top);
};

Node.prototype._resizeImage = function (ctx) {
  // TODO: pre calculate the image size

  if (!this.width || !this.height) {  // undefined or 0
    var width, height;
    if (this.value) {
      this.radius = this.baseRadiusValue;
      var scale = this.imageObj.height / this.imageObj.width;
      if (scale !== undefined) {
        width = this.radius || this.imageObj.width;
        height = this.radius * scale || this.imageObj.height;
      }
      else {
        width = 0;
        height = 0;
      }
    }
    else {
      width = this.imageObj.width;
      height = this.imageObj.height;
    }
    this.width  = width;
    this.height = height;

    if (this.width > 0 && this.height > 0) {
      this.width  += (this.clusterSize - 1) * this.clusterSizeWidthFactor;
      this.height += (this.clusterSize - 1) * this.clusterSizeHeightFactor;
      this.radius += (this.clusterSize - 1) * this.clusterSizeRadiusFactor;
    }
  }

};

Node.prototype._drawImage = function (ctx) {
  this._resizeImage(ctx);

  this.left   = this.x - this.width / 2;
  this.top    = this.y - this.height / 2;

  var yLabel;
  if (this.imageObj.width != 0 ) {
    // draw the shade
    if (this.clusterSize > 1) {
      var lineWidth = ((this.clusterSize > 1) ? 10 : 0.0);
      lineWidth *= this.graphScaleInv;
      lineWidth = Math.min(0.2 * this.width,lineWidth);

      ctx.globalAlpha = 0.5;
      ctx.drawImage(this.imageObj, this.left - lineWidth, this.top - lineWidth, this.width + 2*lineWidth, this.height + 2*lineWidth);
    }

    // draw the image
    ctx.globalAlpha = 1.0;
    ctx.drawImage(this.imageObj, this.left, this.top, this.width, this.height);
    yLabel = this.y + this.height / 2;
  }
  else {
    // image still loading... just draw the label for now
    yLabel = this.y;
  }

  this._label(ctx, this.label, this.x, yLabel, undefined, "top");
};


Node.prototype._resizeBox = function (ctx) {
  if (!this.width) {
    var margin = 5;
    var textSize = this.getTextSize(ctx);
    this.width = textSize.width + 2 * margin;
    this.height = textSize.height + 2 * margin;

    this.width  += (this.clusterSize - 1) * 0.5 * this.clusterSizeWidthFactor;
    this.height += (this.clusterSize - 1) * 0.5 * this.clusterSizeHeightFactor;
//    this.radius += (this.clusterSize - 1) * 0.5 * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawBox = function (ctx) {
  this._resizeBox(ctx);

  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  var clusterLineWidth = 2.5;
  var selectionLineWidth = 2;

  ctx.strokeStyle = this.selected ? this.color.highlight.border : this.color.border;

  // draw the outer border
  if (this.clusterSize > 1) {
    ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
    ctx.lineWidth *= this.graphScaleInv;
    ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

    ctx.roundRect(this.left-2*ctx.lineWidth, this.top-2*ctx.lineWidth, this.width+4*ctx.lineWidth, this.height+4*ctx.lineWidth, this.radius);
    ctx.stroke();
  }
  ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
  ctx.lineWidth *= this.graphScaleInv;
  ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

  ctx.fillStyle = this.selected ? this.color.highlight.background : this.color.background;

  ctx.roundRect(this.left, this.top, this.width, this.height, this.radius);
  ctx.fill();
  ctx.stroke();

  this._label(ctx, this.label, this.x, this.y);
};


Node.prototype._resizeDatabase = function (ctx) {
  if (!this.width) {
    var margin = 5;
    var textSize = this.getTextSize(ctx);
    var size = textSize.width + 2 * margin;
    this.width = size;
    this.height = size;

    // scaling used for clustering
    this.width  += (this.clusterSize - 1) * this.clusterSizeWidthFactor;
    this.height += (this.clusterSize - 1) * this.clusterSizeHeightFactor;
    this.radius += (this.clusterSize - 1) * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawDatabase = function (ctx) {
  this._resizeDatabase(ctx);
  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  var clusterLineWidth = 2.5;
  var selectionLineWidth = 2;

  ctx.strokeStyle = this.selected ? this.color.highlight.border : this.color.border;

  // draw the outer border
  if (this.clusterSize > 1) {
    ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
    ctx.lineWidth *= this.graphScaleInv;
    ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

    ctx.database(this.x - this.width/2 - 2*ctx.lineWidth, this.y - this.height*0.5 - 2*ctx.lineWidth, this.width + 4*ctx.lineWidth, this.height + 4*ctx.lineWidth);
    ctx.stroke();
  }
  ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
  ctx.lineWidth *= this.graphScaleInv;
  ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

  ctx.fillStyle = this.selected ? this.color.highlight.background : this.color.background;
  ctx.database(this.x - this.width/2, this.y - this.height*0.5, this.width, this.height);
  ctx.fill();
  ctx.stroke();

  this._label(ctx, this.label, this.x, this.y);
};


Node.prototype._resizeCircle = function (ctx) {
  if (!this.width) {
    var margin = 5;
    var textSize = this.getTextSize(ctx);
    var diameter = Math.max(textSize.width, textSize.height) + 2 * margin;
    this.radius = diameter / 2;

    this.width = diameter;
    this.height = diameter;

    // scaling used for clustering
//    this.width  += (this.clusterSize - 1) * 0.5 * this.clusterSizeWidthFactor;
//    this.height += (this.clusterSize - 1) * 0.5 * this.clusterSizeHeightFactor;
    this.radius += (this.clusterSize - 1) * 0.5 * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawCircle = function (ctx) {
  this._resizeCircle(ctx);
  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  var clusterLineWidth = 2.5;
  var selectionLineWidth = 2;

  ctx.strokeStyle = this.selected ? this.color.highlight.border : this.color.border;

  // draw the outer border
  if (this.clusterSize > 1) {
    ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
    ctx.lineWidth *= this.graphScaleInv;
    ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

    ctx.circle(this.x, this.y, this.radius+2*ctx.lineWidth);
    ctx.stroke();
  }
  ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
  ctx.lineWidth *= this.graphScaleInv;
  ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

  ctx.fillStyle = this.selected ? this.color.highlight.background : this.color.background;
  ctx.circle(this.x, this.y, this.radius);
  ctx.fill();
  ctx.stroke();

  this._label(ctx, this.label, this.x, this.y);
};

Node.prototype._resizeEllipse = function (ctx) {
  if (!this.width) {
    var textSize = this.getTextSize(ctx);

    this.width = textSize.width * 1.5;
    this.height = textSize.height * 2;
    if (this.width < this.height) {
      this.width = this.height;
    }

    // scaling used for clustering
    this.width  += (this.clusterSize - 1) * this.clusterSizeWidthFactor;
    this.height += (this.clusterSize - 1) * this.clusterSizeHeightFactor;
    this.radius += (this.clusterSize - 1) * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawEllipse = function (ctx) {
  this._resizeEllipse(ctx);
  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  var clusterLineWidth = 2.5;
  var selectionLineWidth = 2;

  ctx.strokeStyle = this.selected ? this.color.highlight.border : this.color.border;

  // draw the outer border
  if (this.clusterSize > 1) {
    ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
    ctx.lineWidth *= this.graphScaleInv;
    ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

    ctx.ellipse(this.left-2*ctx.lineWidth, this.top-2*ctx.lineWidth, this.width+4*ctx.lineWidth, this.height+4*ctx.lineWidth);
    ctx.stroke();
  }
  ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
  ctx.lineWidth *= this.graphScaleInv;
  ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

  ctx.fillStyle = this.selected ? this.color.highlight.background : this.color.background;

  ctx.ellipse(this.left, this.top, this.width, this.height);
  ctx.fill();
  ctx.stroke();
  this._label(ctx, this.label, this.x, this.y);
};

Node.prototype._drawDot = function (ctx) {
  this._drawShape(ctx, 'circle');
};

Node.prototype._drawTriangle = function (ctx) {
  this._drawShape(ctx, 'triangle');
};

Node.prototype._drawTriangleDown = function (ctx) {
  this._drawShape(ctx, 'triangleDown');
};

Node.prototype._drawSquare = function (ctx) {
  this._drawShape(ctx, 'square');
};

Node.prototype._drawStar = function (ctx) {
  this._drawShape(ctx, 'star');
};

Node.prototype._resizeShape = function (ctx) {
  if (!this.width) {
    this.radius = this.baseRadiusValue;
    var size = 2 * this.radius;
    this.width = size;
    this.height = size;

    // scaling used for clustering
    this.width  += (this.clusterSize - 1) * this.clusterSizeWidthFactor;
    this.height += (this.clusterSize - 1) * this.clusterSizeHeightFactor;
    this.radius += (this.clusterSize - 1) * 0.5 * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawShape = function (ctx, shape) {
  this._resizeShape(ctx);

  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  var clusterLineWidth = 2.5;
  var selectionLineWidth = 2;
  var radiusMultiplier = 2;

  // choose draw method depending on the shape
  switch (shape) {
    case 'dot':           radiusMultiplier = 2; break;
    case 'square':        radiusMultiplier = 2; break;
    case 'triangle':      radiusMultiplier = 3; break;
    case 'triangleDown':  radiusMultiplier = 3; break;
    case 'star':          radiusMultiplier = 4; break;
  }

  ctx.strokeStyle = this.selected ? this.color.highlight.border : this.color.border;

  // draw the outer border
  if (this.clusterSize > 1) {
    ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
    ctx.lineWidth *= this.graphScaleInv;
    ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

    ctx[shape](this.x, this.y, this.radius + radiusMultiplier * ctx.lineWidth);
    ctx.stroke();
  }
  ctx.lineWidth = (this.selected ? selectionLineWidth : 1.0) + ((this.clusterSize > 1) ? clusterLineWidth : 0.0);
  ctx.lineWidth *= this.graphScaleInv;
  ctx.lineWidth = Math.min(0.1 * this.width,ctx.lineWidth);

  ctx.fillStyle = this.selected ? this.color.highlight.background : this.color.background;

  ctx[shape](this.x, this.y, this.radius);
  ctx.fill();
  ctx.stroke();

  if (this.label) {
    this._label(ctx, this.label, this.x, this.y + this.height / 2, undefined, 'top');
  }
};

Node.prototype._resizeText = function (ctx) {
  if (!this.width) {
    var margin = 5;
    var textSize = this.getTextSize(ctx);
    this.width = textSize.width + 2 * margin;
    this.height = textSize.height + 2 * margin;

    // scaling used for clustering
    this.width  += (this.clusterSize - 1) * this.clusterSizeWidthFactor;
    this.height += (this.clusterSize - 1) * this.clusterSizeHeightFactor;
    this.radius += (this.clusterSize - 1) * this.clusterSizeRadiusFactor;
  }
};

Node.prototype._drawText = function (ctx) {
  this._resizeText(ctx);
  this.left = this.x - this.width / 2;
  this.top = this.y - this.height / 2;

  this._label(ctx, this.label, this.x, this.y);
};


Node.prototype._label = function (ctx, text, x, y, align, baseline) {
  if (text) {
    ctx.font = (this.selected ? "bold " : "") + this.fontSize + "px " + this.fontFace;
    ctx.fillStyle = this.fontColor || "black";
    ctx.textAlign = align || "center";
    ctx.textBaseline = baseline || "middle";

    var lines = text.split('\n'),
        lineCount = lines.length,
        fontSize = (this.fontSize + 4),
        yLine = y + (1 - lineCount) / 2 * fontSize;

    for (var i = 0; i < lineCount; i++) {
      ctx.fillText(lines[i], x, yLine);
      yLine += fontSize;
    }
  }
};


Node.prototype.getTextSize = function(ctx) {
  if (this.label !== undefined) {
    ctx.font = (this.selected ? "bold " : "") + this.fontSize + "px " + this.fontFace;

    var lines = this.label.split('\n'),
        height = (this.fontSize + 4) * lines.length,
        width = 0;

    for (var i = 0, iMax = lines.length; i < iMax; i++) {
      width = Math.max(width, ctx.measureText(lines[i]).width);
    }

    return {"width": width, "height": height};
  }
  else {
    return {"width": 0, "height": 0};
  }
};

/**
 * this is used to determine if a node is visible at all. this is used to determine when it needs to be drawn.
 * there is a safety margin of 0.3 * width;
 *
 * @returns {boolean}
 */
Node.prototype.inArea = function() {
  if (this.width !== undefined) {
  return (this.x + this.width*this.graphScaleInv  >= this.canvasTopLeft.x    &&
          this.x - this.width*this.graphScaleInv  <  this.canvasBottomRight.x &&
          this.y + this.height*this.graphScaleInv >= this.canvasTopLeft.y    &&
          this.y - this.height*this.graphScaleInv <  this.canvasBottomRight.y);
  }
  else {
    return true;
  }
}

/**
 * checks if the core of the node is in the display area, this is used for opening clusters around zoom
 * @returns {boolean}
 */
Node.prototype.inView = function() {
  return (this.x >= this.canvasTopLeft.x    &&
          this.x < this.canvasBottomRight.x &&
          this.y >= this.canvasTopLeft.y    &&
          this.y < this.canvasBottomRight.y);
}

/**
 * This allows the zoom level of the graph to influence the rendering
 * We store the inverted scale and the coordinates of the top left, and bottom right points of the canvas
 *
 * @param scale
 * @param canvasTopLeft
 * @param canvasBottomRight
 */
Node.prototype.setScaleAndPos = function(scale,canvasTopLeft,canvasBottomRight) {
  this.graphScaleInv = 1.0/scale;
  this.canvasTopLeft = canvasTopLeft;
  this.canvasBottomRight = canvasBottomRight;
};


/**
 * This allows the zoom level of the graph to influence the rendering
 *
 * @param scale
 */
Node.prototype.setScale = function(scale) {
  this.graphScaleInv = 1.0/scale;
};

/**
 * This function updates the damping parameter for clusters, based ont he
 *
 * @param {Number} numberOfNodes
 */
Node.prototype.updateDamping = function(numberOfNodes) {
  this.damping = (0.8 + 0.1*this.clusterSize * (1 + Math.pow(numberOfNodes,-2)));
  this.damping *= this.dampingFactor;
};


/**
 * set the velocity at 0. Is called when this node is contained in another during clustering
 */
Node.prototype.clearVelocity = function() {
  this.vx = 0;
  this.vy = 0;
};


/**
 * Basic preservation of (kinectic) energy
 *
 * @param massBeforeClustering
 */
Node.prototype.updateVelocity = function(massBeforeClustering) {
  var energyBefore = this.vx * this.vx * massBeforeClustering;
  this.vx = Math.sqrt(energyBefore/this.mass);
  energyBefore = this.vy * this.vy * massBeforeClustering;
  this.vy = Math.sqrt(energyBefore/this.mass);
};


/**
 * @class Edge
 *
 * A edge connects two nodes
 * @param {Object} properties     Object with properties. Must contain
 *                                At least properties from and to.
 *                                Available properties: from (number),
 *                                to (number), label (string, color (string),
 *                                width (number), style (string),
 *                                length (number), title (string)
 * @param {Graph} graph A graph object, used to find and edge to
 *                                nodes.
 * @param {Object} constants      An object with default values for
 *                                example for the color
 */
function Edge (properties, graph, constants) {
  if (!graph) {
    throw "No graph provided";
  }
  this.graph = graph;

  // initialize constants
  this.widthMin = constants.edges.widthMin;
  this.widthMax = constants.edges.widthMax;

  // initialize variables
  this.id     = undefined;
  this.fromId = undefined;
  this.toId   = undefined;
  this.style  = constants.edges.style;
  this.title  = undefined;
  this.width  = constants.edges.width;
  this.value  = undefined;
  this.length = constants.edges.length;

  this.from = null;   // a node
  this.to = null;     // a node

  // we use this to be able to reconnect the edge to a cluster if its node is put into a cluster
  // by storing the original information we can revert to the original connection when the cluser is opened.
  this.originalFromId = [];
  this.originalToId = [];

  this.connected = false;

  // Added to support dashed lines
  // David Jordan
  // 2012-08-08
  this.dash = util.extend({}, constants.edges.dash); // contains properties length, gap, altLength

  this.stiffness   = undefined; // depends on the length of the edge
  this.color       = constants.edges.color;
  this.widthFixed  = false;
  this.lengthFixed = false;

  this.setProperties(properties, constants);

}

/**
 * Set or overwrite properties for the edge
 * @param {Object} properties  an object with properties
 * @param {Object} constants   and object with default, global properties
 */
Edge.prototype.setProperties = function(properties, constants) {
  if (!properties) {
    return;
  }

  if (properties.from !== undefined)           {this.fromId = properties.from;}
  if (properties.to !== undefined)             {this.toId = properties.to;}

  if (properties.id !== undefined)             {this.id = properties.id;}
  if (properties.style !== undefined)          {this.style = properties.style;}
  if (properties.label !== undefined)          {this.label = properties.label;}
  if (this.label) {
    this.fontSize = constants.edges.fontSize;
    this.fontFace = constants.edges.fontFace;
    this.fontColor = constants.edges.fontColor;
    if (properties.fontColor !== undefined)  {this.fontColor = properties.fontColor;}
    if (properties.fontSize !== undefined)   {this.fontSize = properties.fontSize;}
    if (properties.fontFace !== undefined)   {this.fontFace = properties.fontFace;}
  }
  if (properties.title !== undefined)          {this.title = properties.title;}
  if (properties.width !== undefined)          {this.width = properties.width;}
  if (properties.value !== undefined)          {this.value = properties.value;}
  if (properties.length !== undefined)         {this.length = properties.length;}

  // Added to support dashed lines
  // David Jordan
  // 2012-08-08
  if (properties.dash) {
    if (properties.dash.length !== undefined)    {this.dash.length = properties.dash.length;}
    if (properties.dash.gap !== undefined)       {this.dash.gap = properties.dash.gap;}
    if (properties.dash.altLength !== undefined) {this.dash.altLength = properties.dash.altLength;}
  }

  if (properties.color !== undefined) {this.color = properties.color;}

  // A node is connected when it has a from and to node.
  this.connect();

  this.widthFixed = this.widthFixed || (properties.width !== undefined);
  this.lengthFixed = this.lengthFixed || (properties.length !== undefined);
  this.stiffness = 1 / this.length;

  // set draw method based on style
  switch (this.style) {
    case 'line':          this.draw = this._drawLine; break;
    case 'arrow':         this.draw = this._drawArrow; break;
    case 'arrow-center':  this.draw = this._drawArrowCenter; break;
    case 'dash-line':     this.draw = this._drawDashLine; break;
    default:              this.draw = this._drawLine; break;
  }
};

/**
 * Connect an edge to its nodes
 */
Edge.prototype.connect = function () {
  this.disconnect();

  this.from = this.graph.nodes[this.fromId] || null;
  this.to = this.graph.nodes[this.toId] || null;
  this.connected = (this.from && this.to);

  if (this.connected) {
    this.from.attachEdge(this);
    this.to.attachEdge(this);
  }
  else {
    if (this.from) {
      this.from.detachEdge(this);
    }
    if (this.to) {
      this.to.detachEdge(this);
    }
  }
};

/**
 * Disconnect an edge from its nodes
 */
Edge.prototype.disconnect = function () {
  if (this.from) {
    this.from.detachEdge(this);
    this.from = null;
  }
  if (this.to) {
    this.to.detachEdge(this);
    this.to = null;
  }

  this.connected = false;
};

/**
 * get the title of this edge.
 * @return {string} title    The title of the edge, or undefined when no title
 *                           has been set.
 */
Edge.prototype.getTitle = function() {
  return this.title;
};


/**
 * Retrieve the value of the edge. Can be undefined
 * @return {Number} value
 */
Edge.prototype.getValue = function() {
  return this.value;
};

/**
 * Adjust the value range of the edge. The edge will adjust it's width
 * based on its value.
 * @param {Number} min
 * @param {Number} max
 */
Edge.prototype.setValueRange = function(min, max) {
  if (!this.widthFixed && this.value !== undefined) {
    var scale = (this.widthMax - this.widthMin) / (max - min);
    this.width = (this.value - min) * scale + this.widthMin;
  }
};

/**
 * Redraw a edge
 * Draw this edge in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 */
Edge.prototype.draw = function(ctx) {
  throw "Method draw not initialized in edge";
};

/**
 * Check if this object is overlapping with the provided object
 * @param {Object} obj   an object with parameters left, top
 * @return {boolean}     True if location is located on the edge
 */
Edge.prototype.isOverlappingWith = function(obj) {
  var distMax = 10;

  var xFrom = this.from.x;
  var yFrom = this.from.y;
  var xTo = this.to.x;
  var yTo = this.to.y;
  var xObj = obj.left;
  var yObj = obj.top;


  var dist = Edge._dist(xFrom, yFrom, xTo, yTo, xObj, yObj);

  return (dist < distMax);
};


/**
 * Redraw a edge as a line
 * Draw this edge in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 * @private
 */
Edge.prototype._drawLine = function(ctx) {
  // set style
  ctx.strokeStyle = this.color;
  ctx.lineWidth = this._getLineWidth();

  var point;
  if (this.from != this.to) {
    // draw line
    this._line(ctx);

    // draw label
    if (this.label) {
      point = this._pointOnLine(0.5);
      this._label(ctx, this.label, point.x, point.y);
    }
  }
  else {
    var x, y;
    var radius = this.length / 4;
    var node = this.from;
    if (!node.width) {
      node.resize(ctx);
    }
    if (node.width > node.height) {
      x = node.x + node.width / 2;
      y = node.y - radius;
    }
    else {
      x = node.x + radius;
      y = node.y - node.height / 2;
    }
    this._circle(ctx, x, y, radius);
    point = this._pointOnCircle(x, y, radius, 0.5);
    this._label(ctx, this.label, point.x, point.y);
  }
};

/**
 * Get the line width of the edge. Depends on width and whether one of the
 * connected nodes is selected.
 * @return {Number} width
 * @private
 */
Edge.prototype._getLineWidth = function() {
  if (this.from.selected || this.to.selected) {
    return Math.min(this.width * 2, this.widthMax)*this.graphScaleInv;
  }
  else {
    return this.width*this.graphScaleInv;
  }
};

/**
 * Draw a line between two nodes
 * @param {CanvasRenderingContext2D} ctx
 * @private
 */
Edge.prototype._line = function (ctx) {
  // draw a straight line
  ctx.beginPath();
  ctx.moveTo(this.from.x, this.from.y);
  ctx.lineTo(this.to.x, this.to.y);
  ctx.stroke();
};

/**
 * Draw a line from a node to itself, a circle
 * @param {CanvasRenderingContext2D} ctx
 * @param {Number} x
 * @param {Number} y
 * @param {Number} radius
 * @private
 */
Edge.prototype._circle = function (ctx, x, y, radius) {
  // draw a circle
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, 2 * Math.PI, false);
  ctx.stroke();
};

/**
 * Draw label with white background and with the middle at (x, y)
 * @param {CanvasRenderingContext2D} ctx
 * @param {String} text
 * @param {Number} x
 * @param {Number} y
 * @private
 */
Edge.prototype._label = function (ctx, text, x, y) {
  if (text) {
    // TODO: cache the calculated size
    ctx.font = ((this.from.selected || this.to.selected) ? "bold " : "") +
        this.fontSize + "px " + this.fontFace;
    ctx.fillStyle = 'white';
    var width = ctx.measureText(text).width;
    var height = this.fontSize;
    var left = x - width / 2;
    var top = y - height / 2;

    ctx.fillRect(left, top, width, height);

    // draw text
    ctx.fillStyle = this.fontColor || "black";
    ctx.textAlign = "left";
    ctx.textBaseline = "top";
    ctx.fillText(text, left, top);
  }
};

/**
 * Redraw a edge as a dashed line
 * Draw this edge in the given canvas
 * @author David Jordan
 * @date 2012-08-08
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 * @private
 */
Edge.prototype._drawDashLine = function(ctx) {
  // set style
  ctx.strokeStyle = this.color;
  ctx.lineWidth = this._getLineWidth();

  // draw dashed line
  ctx.beginPath();
  ctx.lineCap = 'round';
  if (this.dash.altLength !== undefined) //If an alt dash value has been set add to the array this value
  {
    ctx.dashedLine(this.from.x,this.from.y,this.to.x,this.to.y,
        [this.dash.length,this.dash.gap,this.dash.altLength,this.dash.gap]);
  }
  else if (this.dash.length !== undefined && this.dash.gap !== undefined) //If a dash and gap value has been set add to the array this value
  {
    ctx.dashedLine(this.from.x,this.from.y,this.to.x,this.to.y,
        [this.dash.length,this.dash.gap]);
  }
  else //If all else fails draw a line
  {
    ctx.moveTo(this.from.x, this.from.y);
    ctx.lineTo(this.to.x, this.to.y);
  }
  ctx.stroke();

  // draw label
  if (this.label) {
    var point = this._pointOnLine(0.5);
    this._label(ctx, this.label, point.x, point.y);
  }
};

/**
 * Get a point on a line
 * @param {Number} percentage. Value between 0 (line start) and 1 (line end)
 * @return {Object} point
 * @private
 */
Edge.prototype._pointOnLine = function (percentage) {
  return {
    x: (1 - percentage) * this.from.x + percentage * this.to.x,
    y: (1 - percentage) * this.from.y + percentage * this.to.y
  }
};

/**
 * Get a point on a circle
 * @param {Number} x
 * @param {Number} y
 * @param {Number} radius
 * @param {Number} percentage. Value between 0 (line start) and 1 (line end)
 * @return {Object} point
 * @private
 */
Edge.prototype._pointOnCircle = function (x, y, radius, percentage) {
  var angle = (percentage - 3/8) * 2 * Math.PI;
  return {
    x: x + radius * Math.cos(angle),
    y: y - radius * Math.sin(angle)
  }
};

/**
 * Redraw a edge as a line with an arrow halfway the line
 * Draw this edge in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 * @private
 */
Edge.prototype._drawArrowCenter = function(ctx) {
  var point;
  // set style
  ctx.strokeStyle = this.color;
  ctx.fillStyle = this.color;
  ctx.lineWidth = this._getLineWidth();

  if (this.from != this.to) {
    // draw line
    this._line(ctx);

    // draw an arrow halfway the line
    var angle = Math.atan2((this.to.y - this.from.y), (this.to.x - this.from.x));
    var length = 10 + 5 * this.width; // TODO: make customizable?
    point = this._pointOnLine(0.5);
    ctx.arrow(point.x, point.y, angle, length);
    ctx.fill();
    ctx.stroke();

    // draw label
    if (this.label) {
      point = this._pointOnLine(0.5);
      this._label(ctx, this.label, point.x, point.y);
    }
  }
  else {
    // draw circle
    var x, y;
    var radius = this.length / 4;
    var node = this.from;
    if (!node.width) {
      node.resize(ctx);
    }
    if (node.width > node.height) {
      x = node.x + node.width / 2;
      y = node.y - radius;
    }
    else {
      x = node.x + radius;
      y = node.y - node.height / 2;
    }
    this._circle(ctx, x, y, radius);

    // draw all arrows
    var angle = 0.2 * Math.PI;
    var length = 10 + 5 * this.width; // TODO: make customizable?
    point = this._pointOnCircle(x, y, radius, 0.5);
    ctx.arrow(point.x, point.y, angle, length);
    ctx.fill();
    ctx.stroke();

    // draw label
    if (this.label) {
      point = this._pointOnCircle(x, y, radius, 0.5);
      this._label(ctx, this.label, point.x, point.y);
    }
  }
};



/**
 * Redraw a edge as a line with an arrow
 * Draw this edge in the given canvas
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext("2d");
 * @param {CanvasRenderingContext2D}   ctx
 * @private
 */
Edge.prototype._drawArrow = function(ctx) {
  // set style
  ctx.strokeStyle = this.color;
  ctx.fillStyle = this.color;
  ctx.lineWidth = this._getLineWidth();

  // draw line
  var angle, length;
  if (this.from != this.to) {
    // calculate length and angle of the line
    angle = Math.atan2((this.to.y - this.from.y), (this.to.x - this.from.x));
    var dx = (this.to.x - this.from.x);
    var dy = (this.to.y - this.from.y);
    var lEdge = Math.sqrt(dx * dx + dy * dy);

    var lFrom = this.from.distanceToBorder(ctx, angle + Math.PI);
    var pFrom = (lEdge - lFrom) / lEdge;
    var xFrom = (pFrom) * this.from.x + (1 - pFrom) * this.to.x;
    var yFrom = (pFrom) * this.from.y + (1 - pFrom) * this.to.y;

    var lTo = this.to.distanceToBorder(ctx, angle);
    var pTo = (lEdge - lTo) / lEdge;
    var xTo = (1 - pTo) * this.from.x + pTo * this.to.x;
    var yTo = (1 - pTo) * this.from.y + pTo * this.to.y;

    ctx.beginPath();
    ctx.moveTo(xFrom, yFrom);
    ctx.lineTo(xTo, yTo);
    ctx.stroke();

    // draw arrow at the end of the line
    length = 10 + 5 * this.width; // TODO: make customizable?
    ctx.arrow(xTo, yTo, angle, length);
    ctx.fill();
    ctx.stroke();

    // draw label
    if (this.label) {
      var point = this._pointOnLine(0.5);
      this._label(ctx, this.label, point.x, point.y);
    }
  }
  else {
    // draw circle
    var node = this.from;
    var x, y, arrow;
    var radius = this.length / 4;
    if (!node.width) {
      node.resize(ctx);
    }
    if (node.width > node.height) {
      x = node.x + node.width / 2;
      y = node.y - radius;
      arrow = {
        x: x,
        y: node.y,
        angle: 0.9 * Math.PI
      };
    }
    else {
      x = node.x + radius;
      y = node.y - node.height / 2;
      arrow = {
        x: node.x,
        y: y,
        angle: 0.6 * Math.PI
      };
    }
    ctx.beginPath();
    // TODO: do not draw a circle, but an arc
    // TODO: similarly, for a line without arrows, draw to the border of the nodes instead of the center
    ctx.arc(x, y, radius, 0, 2 * Math.PI, false);
    ctx.stroke();

    // draw all arrows
    length = 10 + 5 * this.width; // TODO: make customizable?
    ctx.arrow(arrow.x, arrow.y, arrow.angle, length);
    ctx.fill();
    ctx.stroke();

    // draw label
    if (this.label) {
      point = this._pointOnCircle(x, y, radius, 0.5);
      this._label(ctx, this.label, point.x, point.y);
    }
  }
};



/**
 * Calculate the distance between a point (x3,y3) and a line segment from
 * (x1,y1) to (x2,y2).
 * http://stackoverflow.com/questions/849211/shortest-distancae-between-a-point-and-a-line-segment
 * @param {number} x1
 * @param {number} y1
 * @param {number} x2
 * @param {number} y2
 * @param {number} x3
 * @param {number} y3
 * @private
 */
Edge._dist = function (x1,y1, x2,y2, x3,y3) { // x3,y3 is the point
  var px = x2-x1,
      py = y2-y1,
      something = px*px + py*py,
      u =  ((x3 - x1) * px + (y3 - y1) * py) / something;

  if (u > 1) {
    u = 1;
  }
  else if (u < 0) {
    u = 0;
  }

  var x = x1 + u * px,
      y = y1 + u * py,
      dx = x - x3,
      dy = y - y3;

  //# Note: If the actual distance does not matter,
  //# if you only want to compare what this function
  //# returns to other results of this function, you
  //# can just return the squared distance instead
  //# (i.e. remove the sqrt) to gain a little performance

  return Math.sqrt(dx*dx + dy*dy);
};



/**
 * This allows the zoom level of the graph to influence the rendering
 *
 * @param scale
 */
Edge.prototype.setScale = function(scale) {
  this.graphScaleInv = 1.0/scale;
};
/**
 * Popup is a class to create a popup window with some text
 * @param {Element}  container     The container object.
 * @param {Number} [x]
 * @param {Number} [y]
 * @param {String} [text]
 */
function Popup(container, x, y, text) {
  if (container) {
    this.container = container;
  }
  else {
    this.container = document.body;
  }
  this.x = 0;
  this.y = 0;
  this.padding = 5;

  if (x !== undefined && y !== undefined ) {
    this.setPosition(x, y);
  }
  if (text !== undefined) {
    this.setText(text);
  }

  // create the frame
  this.frame = document.createElement("div");
  var style = this.frame.style;
  style.position = "absolute";
  style.visibility = "hidden";
  style.border = "1px solid #666";
  style.color = "black";
  style.padding = this.padding + "px";
  style.backgroundColor = "#FFFFC6";
  style.borderRadius = "3px";
  style.MozBorderRadius = "3px";
  style.WebkitBorderRadius = "3px";
  style.boxShadow = "3px 3px 10px rgba(128, 128, 128, 0.5)";
  style.whiteSpace = "nowrap";
  this.container.appendChild(this.frame);
}

/**
 * @param {number} x   Horizontal position of the popup window
 * @param {number} y   Vertical position of the popup window
 */
Popup.prototype.setPosition = function(x, y) {
  this.x = parseInt(x);
  this.y = parseInt(y);
};

/**
 * Set the text for the popup window. This can be HTML code
 * @param {string} text
 */
Popup.prototype.setText = function(text) {
  this.frame.innerHTML = text;
};

/**
 * Show the popup window
 * @param {boolean} show    Optional. Show or hide the window
 */
Popup.prototype.show = function (show) {
  if (show === undefined) {
    show = true;
  }

  if (show) {
    var height = this.frame.clientHeight;
    var width =  this.frame.clientWidth;
    var maxHeight = this.frame.parentNode.clientHeight;
    var maxWidth = this.frame.parentNode.clientWidth;

    var top = (this.y - height);
    if (top + height + this.padding > maxHeight) {
      top = maxHeight - height - this.padding;
    }
    if (top < this.padding) {
      top = this.padding;
    }

    var left = this.x;
    if (left + width + this.padding > maxWidth) {
      left = maxWidth - width - this.padding;
    }
    if (left < this.padding) {
      left = this.padding;
    }

    this.frame.style.left = left + "px";
    this.frame.style.top = top + "px";
    this.frame.style.visibility = "visible";
  }
  else {
    this.hide();
  }
};

/**
 * Hide the popup window
 */
Popup.prototype.hide = function () {
  this.frame.style.visibility = "hidden";
};

/**
 * @class Groups
 * This class can store groups and properties specific for groups.
 */
Groups = function () {
  this.clear();
  this.defaultIndex = 0;
};


/**
 * default constants for group colors
 */
Groups.DEFAULT = [
  {border: "#2B7CE9", background: "#97C2FC", highlight: {border: "#2B7CE9", background: "#D2E5FF"}}, // blue
  {border: "#FFA500", background: "#FFFF00", highlight: {border: "#FFA500", background: "#FFFFA3"}}, // yellow
  {border: "#FA0A10", background: "#FB7E81", highlight: {border: "#FA0A10", background: "#FFAFB1"}}, // red
  {border: "#41A906", background: "#7BE141", highlight: {border: "#41A906", background: "#A1EC76"}}, // green
  {border: "#E129F0", background: "#EB7DF4", highlight: {border: "#E129F0", background: "#F0B3F5"}}, // magenta
  {border: "#7C29F0", background: "#AD85E4", highlight: {border: "#7C29F0", background: "#D3BDF0"}}, // purple
  {border: "#C37F00", background: "#FFA807", highlight: {border: "#C37F00", background: "#FFCA66"}}, // orange
  {border: "#4220FB", background: "#6E6EFD", highlight: {border: "#4220FB", background: "#9B9BFD"}}, // darkblue
  {border: "#FD5A77", background: "#FFC0CB", highlight: {border: "#FD5A77", background: "#FFD1D9"}}, // pink
  {border: "#4AD63A", background: "#C2FABC", highlight: {border: "#4AD63A", background: "#E6FFE3"}}  // mint
];


/**
 * Clear all groups
 */
Groups.prototype.clear = function () {
  this.groups = {};
  this.groups.length = function()
  {
    var i = 0;
    for ( var p in this ) {
      if (this.hasOwnProperty(p)) {
        i++;
      }
    }
    return i;
  }
};


/**
 * get group properties of a groupname. If groupname is not found, a new group
 * is added.
 * @param {*} groupname        Can be a number, string, Date, etc.
 * @return {Object} group      The created group, containing all group properties
 */
Groups.prototype.get = function (groupname) {
  var group = this.groups[groupname];

  if (group == undefined) {
    // create new group
    var index = this.defaultIndex % Groups.DEFAULT.length;
    this.defaultIndex++;
    group = {};
    group.color = Groups.DEFAULT[index];
    this.groups[groupname] = group;
  }

  return group;
};

/**
 * Add a custom group style
 * @param {String} groupname
 * @param {Object} style       An object containing borderColor,
 *                             backgroundColor, etc.
 * @return {Object} group      The created group object
 */
Groups.prototype.add = function (groupname, style) {
  this.groups[groupname] = style;
  if (style.color) {
    style.color = Node.parseColor(style.color);
  }
  return style;
};

/**
 * @class Images
 * This class loads images and keeps them stored.
 */
Images = function () {
  this.images = {};

  this.callback = undefined;
};

/**
 * Set an onload callback function. This will be called each time an image
 * is loaded
 * @param {function} callback
 */
Images.prototype.setOnloadCallback = function(callback) {
  this.callback = callback;
};

/**
 *
 * @param {string} url          Url of the image
 * @return {Image} img          The image object
 */
Images.prototype.load = function(url) {
  var img = this.images[url];
  if (img == undefined) {
    // create the image
    var images = this;
    img = new Image();
    this.images[url] = img;
    img.onload = function() {
      if (images.callback) {
        images.callback(this);
      }
    };
    img.src = url;
  }

  return img;
};

/**
 * Creation of the SectorMixin var.
 *
 * This contains all the functions the Graph object can use to employ the sector system.
 * The sector system is always used by Graph, though the benefits only apply to the use of clustering.
 * If clustering is not used, there is no overhead except for a duplicate object with references to nodes and edges.
 *
 * Alex de Mulder
 * 21-01-2013
 */
var SectorMixin = {

  /**
   * This function is only called by the setData function of the Graph object.
   * This loads the global references into the active sector. This initializes the sector.
   *
   * @private
   */
  _putDataInSector : function() {
    this.sectors["active"][this._sector()].nodes = this.nodes;
    this.sectors["active"][this._sector()].edges = this.edges;
    this.sectors["active"][this._sector()].nodeIndices = this.nodeIndices;
  },


  /**
   *  /**
   * This function sets the global references to nodes, edges and nodeIndices back to
   * those of the supplied (active) sector. If a type is defined, do the specific type
   *
   * @param {String} sectorId
   * @param {String} [sectorType] | "active" or "frozen"
   * @private
   */
  _switchToSector : function(sectorId, sectorType) {
    if (sectorType === undefined || sectorType == "active") {
      this._switchToActiveSector(sectorId);
    }
    else {
      this._switchToFrozenSector(sectorId);
    }
  },


  /**
   * This function sets the global references to nodes, edges and nodeIndices back to
   * those of the supplied active sector.
   *
   * @param sectorId
   * @private
   */
  _switchToActiveSector : function(sectorId) {
    this.nodeIndices = this.sectors["active"][sectorId]["nodeIndices"];
    this.nodes       = this.sectors["active"][sectorId]["nodes"];
    this.edges       = this.sectors["active"][sectorId]["edges"];
  },


  /**
   * This function sets the global references to nodes, edges and nodeIndices back to
   * those of the supplied frozen sector.
   *
   * @param sectorId
   * @private
   */
  _switchToFrozenSector : function(sectorId) {
    this.nodeIndices = this.sectors["frozen"][sectorId]["nodeIndices"];
    this.nodes       = this.sectors["frozen"][sectorId]["nodes"];
    this.edges       = this.sectors["frozen"][sectorId]["edges"];
  },


  /**
   * This function sets the global references to nodes, edges and nodeIndices to
   * those of the navigationUI sector.
   *
   * @private
   */
  _switchToUISector : function() {
    this.nodeIndices = this.sectors["navigationUI"]["nodeIndices"];
    this.nodes       = this.sectors["navigationUI"]["nodes"];
    this.edges       = this.sectors["navigationUI"]["edges"];
  },


  /**
   * This function sets the global references to nodes, edges and nodeIndices back to
   * those of the currently active sector.
   *
   * @private
   */
  _loadLatestSector : function() {
    this._switchToSector(this._sector());
  },


  /**
   * This function returns the currently active sector Id
   *
   * @returns {String}
   * @private
   */
  _sector : function() {
    return this.activeSector[this.activeSector.length-1];
  },


  /**
   * This function returns the previously active sector Id
   *
   * @returns {String}
   * @private
   */
  _previousSector : function() {
    if (this.activeSector.length > 1) {
      return this.activeSector[this.activeSector.length-2];
    }
    else {
      throw new TypeError('there are not enough sectors in the this.activeSector array.');
    }
  },


  /**
   * We add the active sector at the end of the this.activeSector array
   * This ensures it is the currently active sector returned by _sector() and it reaches the top
   * of the activeSector stack. When we reverse our steps we move from the end to the beginning of this stack.
   *
   * @param newId
   * @private
   */
  _setActiveSector : function(newId) {
    this.activeSector.push(newId);
  },


  /**
   * We remove the currently active sector id from the active sector stack. This happens when
   * we reactivate the previously active sector
   *
   * @private
   */
  _forgetLastSector : function() {
    this.activeSector.pop();
  },


  /**
   * This function creates a new active sector with the supplied newId. This newId
   * is the expanding node id.
   *
   * @param {String} newId   | Id of the new active sector
   * @private
   */
  _createNewSector : function(newId) {
    // create the new sector
    this.sectors["active"][newId] = {"nodes":{},
                                     "edges":{},
                                     "nodeIndices":[],
                                     "formationScale": this.scale,
                                     "drawingNode": undefined};

    // create the new sector render node. This gives visual feedback that you are in a new sector.
    this.sectors["active"][newId]['drawingNode'] = new Node(
        {id:newId,
          color: {
            background: "#eaefef",
            border: "495c5e"
          }
        },{},{},this.constants);
    this.sectors["active"][newId]['drawingNode'].clusterSize = 2;
  },


  /**
   * This function removes the currently active sector. This is called when we create a new
   * active sector.
   *
   * @param {String} sectorId   | Id of the active sector that will be removed
   * @private
   */
  _deleteActiveSector : function(sectorId) {
    delete this.sectors["active"][sectorId];
  },


  /**
   * This function removes the currently active sector. This is called when we reactivate
   * the previously active sector.
   *
   * @param {String} sectorId   | Id of the active sector that will be removed
   * @private
   */
  _deleteFrozenSector : function(sectorId) {
    delete this.sectors["frozen"][sectorId];
  },


  /**
   * Freezing an active sector means moving it from the "active" object to the "frozen" object.
   * We copy the references, then delete the active entree.
   *
   * @param sectorId
   * @private
   */
  _freezeSector : function(sectorId) {
    // we move the set references from the active to the frozen stack.
    this.sectors["frozen"][sectorId] = this.sectors["active"][sectorId];

    // we have moved the sector data into the frozen set, we now remove it from the active set
    this._deleteActiveSector(sectorId);
  },


  /**
   * This is the reverse operation of _freezeSector. Activating means moving the sector from the "frozen"
   * object to the "active" object.
   *
   * @param sectorId
   * @private
   */
  _activateSector : function(sectorId) {
    // we move the set references from the frozen to the active stack.
    this.sectors["active"][sectorId] = this.sectors["frozen"][sectorId];

    // we have moved the sector data into the active set, we now remove it from the frozen stack
    this._deleteFrozenSector(sectorId);
  },


  /**
   * This function merges the data from the currently active sector with a frozen sector. This is used
   * in the process of reverting back to the previously active sector.
   * The data that is placed in the frozen (the previously active) sector is the node that has been removed from it
   * upon the creation of a new active sector.
   *
   * @param sectorId
   * @private
   */
  _mergeThisWithFrozen : function(sectorId) {
    // copy all nodes
    for (var nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        this.sectors["frozen"][sectorId]["nodes"][nodeId] = this.nodes[nodeId];
      }
    }

    // copy all edges (if not fully clustered, else there are no edges)
    for (var edgeId in this.edges) {
      if (this.edges.hasOwnProperty(edgeId)) {
        this.sectors["frozen"][sectorId]["edges"][edgeId] = this.edges[edgeId];
      }
    }

    // merge the nodeIndices
    for (var i = 0; i < this.nodeIndices.length; i++) {
      this.sectors["frozen"][sectorId]["nodeIndices"].push(this.nodeIndices[i]);
    }
  },


  /**
   * This clusters the sector to one cluster. It was a single cluster before this process started so
   * we revert to that state. The clusterToFit function with a maximum size of 1 node does this.
   *
   * @private
   */
  _collapseThisToSingleCluster : function() {
    this.clusterToFit(1,false);
  },


  /**
   * We create a new active sector from the node that we want to open.
   *
   * @param node
   * @private
   */
  _addSector : function(node) {
    // this is the currently active sector
    var sector = this._sector();

//    // this should allow me to select nodes from a frozen set.
//    if (this.sectors['active'][sector]["nodes"].hasOwnProperty(node.id)) {
//      console.log("the node is part of the active sector");
//    }
//    else {
//      console.log("I dont know what the fuck happened!!");
//    }

    // when we switch to a new sector, we remove the node that will be expanded from the current nodes list.
    delete this.nodes[node.id];

    var unqiueIdentifier = util.randomUUID();

    // we fully freeze the currently active sector
    this._freezeSector(sector);

    // we create a new active sector. This sector has the Id of the node to ensure uniqueness
    this._createNewSector(unqiueIdentifier);

    // we add the active sector to the sectors array to be able to revert these steps later on
    this._setActiveSector(unqiueIdentifier);

    // we redirect the global references to the new sector's references. this._sector() now returns unqiueIdentifier
    this._switchToSector(this._sector());

    // finally we add the node we removed from our previous active sector to the new active sector
    this.nodes[node.id] = node;
  },


  /**
   * We close the sector that is currently open and revert back to the one before.
   * If the active sector is the "default" sector, nothing happens.
   *
   * @private
   */
  _collapseSector : function() {
    // the currently active sector
    var sector = this._sector();

    // we cannot collapse the default sector
    if (sector != "default") {
      if ((this.nodeIndices.length == 1) ||
       (this.sectors["active"][sector]["drawingNode"].width*this.scale < this.constants.clustering.screenSizeThreshold * this.frame.canvas.clientWidth) ||
       (this.sectors["active"][sector]["drawingNode"].height*this.scale < this.constants.clustering.screenSizeThreshold * this.frame.canvas.clientHeight)) {
        var previousSector = this._previousSector();

        // we collapse the sector back to a single cluster
        this._collapseThisToSingleCluster();

        // we move the remaining nodes, edges and nodeIndices to the previous sector.
        // This previous sector is the one we will reactivate
        this._mergeThisWithFrozen(previousSector);

        // the previously active (frozen) sector now has all the data from the currently active sector.
        // we can now delete the active sector.
        this._deleteActiveSector(sector);

        // we activate the previously active (and currently frozen) sector.
        this._activateSector(previousSector);

        // we load the references from the newly active sector into the global references
        this._switchToSector(previousSector);

        // we forget the previously active sector because we reverted to the one before
        this._forgetLastSector();

        // finally, we update the node index list.
        this._updateNodeIndexList();
      }
    }
  },


  /**
   * This runs a function in all active sectors. This is used in _redraw() and the _initializeForceCalculation().
   *
   * @param {String} runFunction  |   This is the NAME of a function we want to call in all active sectors
   *                              |   we dont pass the function itself because then the "this" is the window object
   *                              |   instead of the Graph object
   * @param {*} [argument]            |   Optional: arguments to pass to the runFunction
   * @private
   */
  _doInAllActiveSectors : function(runFunction,argument) {
    if (argument === undefined) {
      for (var sector in this.sectors["active"]) {
        if (this.sectors["active"].hasOwnProperty(sector)) {
          // switch the global references to those of this sector
          this._switchToActiveSector(sector);
          this[runFunction]();
        }
      }
    }
    else {
      for (var sector in this.sectors["active"]) {
        if (this.sectors["active"].hasOwnProperty(sector)) {
          // switch the global references to those of this sector
          this._switchToActiveSector(sector);
          var args = Array.prototype.splice.call(arguments, 1);
          if (args.length > 1) {
            this[runFunction](args[0],args[1]);
          }
          else {
            this[runFunction](argument);
          }
        }
      }
    }
    // we revert the global references back to our active sector
    this._loadLatestSector();
  },


  /**
   * This runs a function in all frozen sectors. This is used in the _redraw().
   *
   * @param {String} runFunction  |   This is the NAME of a function we want to call in all active sectors
   *                              |   we don't pass the function itself because then the "this" is the window object
   *                              |   instead of the Graph object
   * @param {*} [argument]            |   Optional: arguments to pass to the runFunction
   * @private
   */
  _doInAllFrozenSectors : function(runFunction,argument) {
    if (argument === undefined) {
      for (var sector in this.sectors["frozen"]) {
        if (this.sectors["frozen"].hasOwnProperty(sector)) {
          // switch the global references to those of this sector
          this._switchToFrozenSector(sector);
          this[runFunction]();
        }
      }
    }
    else {
      for (var sector in this.sectors["frozen"]) {
        if (this.sectors["frozen"].hasOwnProperty(sector)) {
          // switch the global references to those of this sector
          this._switchToFrozenSector(sector);
          var args = Array.prototype.splice.call(arguments, 1);
          if (args.length > 1) {
            this[runFunction](args[0],args[1]);
          }
          else {
            this[runFunction](argument);
          }
        }
      }
    }
    this._loadLatestSector();
  },


  /**
   * This runs a function in the navigationUI sector.
   *
   * @param {String} runFunction  |   This is the NAME of a function we want to call in all active sectors
   *                              |   we don't pass the function itself because then the "this" is the window object
   *                              |   instead of the Graph object
   * @param {*} [argument]            |   Optional: arguments to pass to the runFunction
   * @private
   */
  _doInUISector : function(runFunction,argument) {
    this._switchToUISector();
    if (argument === undefined) {
      this[runFunction]();
    }
    else {
      var args = Array.prototype.splice.call(arguments, 1);
      if (args.length > 1) {
        this[runFunction](args[0],args[1]);
      }
      else {
        this[runFunction](argument);
      }
    }
    this._loadLatestSector();
  },


  /**
   * This runs a function in all sectors. This is used in the _redraw().
   *
   * @param {String} runFunction  |   This is the NAME of a function we want to call in all active sectors
   *                              |   we don't pass the function itself because then the "this" is the window object
   *                              |   instead of the Graph object
   * @param {*} [argument]        |   Optional: arguments to pass to the runFunction
   * @private
   */
  _doInAllSectors : function(runFunction,argument) {
    var args = Array.prototype.splice.call(arguments, 1);
    if (argument === undefined) {
      this._doInAllActiveSectors(runFunction);
      this._doInAllFrozenSectors(runFunction);
    }
    else {
      if (args.length > 1) {
        this._doInAllActiveSectors(runFunction,args[0],args[1]);
        this._doInAllFrozenSectors(runFunction,args[0],args[1]);
      }
      else {
        this._doInAllActiveSectors(runFunction,argument);
        this._doInAllFrozenSectors(runFunction,argument);
      }
    }

  },


  /**
   * This clears the nodeIndices list. We cannot use this.nodeIndices = [] because we would break the link with the
   * active sector. Thus we clear the nodeIndices in the active sector, then reconnect the this.nodeIndices to it.
   *
   * @private
   */
  _clearNodeIndexList : function() {
    var sector = this._sector();
    this.sectors["active"][sector]["nodeIndices"] = [];
    this.nodeIndices = this.sectors["active"][sector]["nodeIndices"];
  },


  /**
   * Draw the encompassing sector node
   *
   * @param ctx
   * @param sectorType
   * @private
   */
  _drawSectorNodes : function(ctx,sectorType) {
    var minY = 1e9, maxY = -1e9, minX = 1e9, maxX = -1e9, node;
    for (var sector in this.sectors[sectorType]) {
      if (this.sectors[sectorType].hasOwnProperty(sector)) {
        if (this.sectors[sectorType][sector]["drawingNode"] !== undefined) {

          this._switchToSector(sector,sectorType);

          minY = 1e9; maxY = -1e9; minX = 1e9; maxX = -1e9;
          for (var nodeId in this.nodes) {
            if (this.nodes.hasOwnProperty(nodeId)) {
              node = this.nodes[nodeId];
              node.resize(ctx);
              if (minX > node.x - 0.5 * node.width) {minX = node.x - 0.5 * node.width;}
              if (maxX < node.x + 0.5 * node.width) {maxX = node.x + 0.5 * node.width;}
              if (minY > node.y - 0.5 * node.height) {minY = node.y - 0.5 * node.height;}
              if (maxY < node.y + 0.5 * node.height) {maxY = node.y + 0.5 * node.height;}
            }
          }
          node = this.sectors[sectorType][sector]["drawingNode"];
          node.x = 0.5 * (maxX + minX);
          node.y = 0.5 * (maxY + minY);
          node.width = 2 * (node.x - minX);
          node.height = 2 * (node.y - minY);
          node.radius = Math.sqrt(Math.pow(0.5*node.width,2) + Math.pow(0.5*node.height,2));
          node.setScale(this.scale);
          node._drawCircle(ctx);
        }
      }
    }
  },

  _drawAllSectorNodes : function(ctx) {
    this._drawSectorNodes(ctx,"frozen");
    this._drawSectorNodes(ctx,"active");
    this._loadLatestSector();
  }
};
/**
 * Creation of the ClusterMixin var.
 *
 * This contains all the functions the Graph object can use to employ clustering
 *
 * Alex de Mulder
 * 21-01-2013
 */
var ClusterMixin = {

/**
 * This is only called in the constructor of the graph object
 * */
 startWithClustering : function() {
    // cluster if the data set is big
    this.clusterToFit(this.constants.clustering.initialMaxNumberOfNodes, true);

    // updates the lables after clustering
    this.updateLabels();

    // this is called here because if clusterin is disabled, the start and stabilize are called in
    // the setData function.
    if (this.stabilize) {
      this._doStabilize();
    }
    this.start();
  },

  /**
   * This function clusters until the initialMaxNumberOfNodes has been reached
   *
   * @param {Number}  maxNumberOfNodes
   * @param {Boolean} reposition
   */
  clusterToFit : function(maxNumberOfNodes, reposition) {
    var numberOfNodes = this.nodeIndices.length;

    var maxLevels = 50;
    var level = 0;

    // we first cluster the hubs, then we pull in the outliers, repeat
    while (numberOfNodes > maxNumberOfNodes && level < maxLevels) {
      if (level % 3 == 0) {
        this.forceAggregateHubs();
      }
      else {
        this.increaseClusterLevel();
      }
      numberOfNodes = this.nodeIndices.length;
      level += 1;
    }

    // after the clustering we reposition the nodes to reduce the initial chaos
    if (level > 1 && reposition == true) {
      this.repositionNodes();
    }
   },

  /**
   * This function can be called to open up a specific cluster. It is only called by
   * It will unpack the cluster back one level.
   *
   * @param node    | Node object: cluster to open.
   */
  openCluster : function(node) {
    var isMovingBeforeClustering = this.moving;
    if (node.clusterSize > this.constants.clustering.sectorThreshold && this._nodeInActiveArea(node) &&
      !(this._sector() == "default" && this.nodeIndices.length == 1)) {
      this._addSector(node);
      var level = 0;
      while ((this.nodeIndices.length < this.constants.clustering.initialMaxNumberOfNodes) && (level < 10)) {
        this.decreaseClusterLevel();
        level += 1;
      }
    }
    else {
      this._expandClusterNode(node,false,true);

      // update the index list, dynamic edges and labels
      this._updateNodeIndexList();
      this._updateDynamicEdges();
      this.updateLabels();
    }

    // if the simulation was settled, we restart the simulation if a cluster has been formed or expanded
    if (this.moving != isMovingBeforeClustering) {
      this.start();
    }
   },

  /**
   * This calls the updateClustes with default arguments
   */
  updateClustersDefault : function() {
    if (this.constants.clustering.enabled == true) {
      this.updateClusters(0,false,false);
    }
  },

  /**
   * This function can be called to increase the cluster level. This means that the nodes with only one edge connection will
   * be clustered with their connected node. This can be repeated as many times as needed.
   * This can be called externally (by a keybind for instance) to reduce the complexity of big datasets.
   */
  increaseClusterLevel : function() {
    this.updateClusters(-1,false,true);
   },



  /**
   * This function can be called to decrease the cluster level. This means that the nodes with only one edge connection will
   * be unpacked if they are a cluster. This can be repeated as many times as needed.
   * This can be called externally (by a key-bind for instance) to look into clusters without zooming.
   */
  decreaseClusterLevel : function() {
    this.updateClusters(1,false,true);
   },


  /**
   * This is the main clustering function. It clusters and declusters on zoom or forced
   * This function clusters on zoom, it can be called with a predefined zoom direction
   * If out, check if we can form clusters, if in, check if we can open clusters.
   * This function is only called from _zoom()
   *
   * @param {Number} zoomDirection  | -1 / 0 / +1   for  zoomOut / determineByZoom / zoomIn
   * @param {Boolean} recursive     | enabled or disable recursive calling of the opening of clusters
   * @param {Boolean} force         | enabled or disable forcing
   *
   */
  updateClusters : function(zoomDirection,recursive,force) {
    var isMovingBeforeClustering = this.moving;
    var amountOfNodes = this.nodeIndices.length;

    // on zoom out collapse the sector if the scale is at the level the sector was made
    if (this.previousScale > this.scale && zoomDirection == 0) {
      this._collapseSector();
    }

    // check if we zoom in or out
    if (this.previousScale > this.scale || zoomDirection == -1) { // zoom out
      // forming clusters when forced pulls outliers in. When not forced, the edge length of the
      // outer nodes determines if it is being clustered
      this._formClusters(force);
    }
    else if (this.previousScale < this.scale || zoomDirection == 1) { // zoom in
      if (force == true) {
        // _openClusters checks for each node if the formationScale of the cluster is smaller than
        // the current scale and if so, declusters. When forced, all clusters are reduced by one step
        this._openClusters(recursive,force);
      }
      else {
        // if a cluster takes up a set percentage of the active window
        this._openClustersBySize();
      }
    }
    this._updateNodeIndexList();

    // if a cluster was NOT formed and the user zoomed out, we try clustering by hubs
    if (this.nodeIndices.length == amountOfNodes && (this.previousScale > this.scale || zoomDirection == -1))  {
      this._aggregateHubs(force);
      this._updateNodeIndexList();
    }

    // we now reduce chains.
    if (this.previousScale > this.scale || zoomDirection == -1) { // zoom out
      this.handleChains();
      this._updateNodeIndexList();
    }

    this.previousScale = this.scale;

    // rest of the update the index list, dynamic edges and labels
    this._updateDynamicEdges();
    this.updateLabels();

    // if a cluster was formed, we increase the clusterSession
    if (this.nodeIndices.length < amountOfNodes) { // this means a clustering operation has taken place
      this.clusterSession += 1;
    }

    // if the simulation was settled, we restart the simulation if a cluster has been formed or expanded
    if (this.moving != isMovingBeforeClustering) {
      this.start();
    }
   },

  /**
   * This function handles the chains. It is called on every updateClusters().
   */
  handleChains : function() {
    // after clustering we check how many chains there are
    var chainPercentage = this._getChainFraction();
    if (chainPercentage > this.constants.clustering.chainThreshold) {
      this._reduceAmountOfChains(1 - this.constants.clustering.chainThreshold / chainPercentage)

    }
   },

  /**
   * this functions starts clustering by hubs
   * The minimum hub threshold is set globally
   *
   * @private
   */
  _aggregateHubs : function(force) {
    this._getHubSize();
    this._formClustersByHub(force,false);
   },


  /**
   * This function is fired by keypress. It forces hubs to form.
   *
   */
  forceAggregateHubs : function() {
    var isMovingBeforeClustering = this.moving;
    var amountOfNodes = this.nodeIndices.length;

    this._aggregateHubs(true);

    // update the index list, dynamic edges and labels
    this._updateNodeIndexList();
    this._updateDynamicEdges();
    this.updateLabels();

    // if a cluster was formed, we increase the clusterSession
    if (this.nodeIndices.length != amountOfNodes) {
      this.clusterSession += 1;
    }

    // if the simulation was settled, we restart the simulation if a cluster has been formed or expanded
    if (this.moving != isMovingBeforeClustering) {
      this.start();
    }
   },

  /**
   * If a cluster takes up more than a set percentage of the screen, open the cluster
   *
   * @private
   */
  _openClustersBySize : function() {
    for (var nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        var node = this.nodes[nodeId];
        if (node.inView() == true) {
          if ((node.width*this.scale > this.constants.clustering.screenSizeThreshold * this.frame.canvas.clientWidth) ||
              (node.height*this.scale > this.constants.clustering.screenSizeThreshold * this.frame.canvas.clientHeight)) {
            this.openCluster(node);
          }
        }
      }
    }
   },


  /**
   * This function loops over all nodes in the nodeIndices list. For each node it checks if it is a cluster and if it
   * has to be opened based on the current zoom level.
   *
   * @private
   */
  _openClusters : function(recursive,force) {
    for (var i = 0; i < this.nodeIndices.length; i++) {
      var node = this.nodes[this.nodeIndices[i]];
      this._expandClusterNode(node,recursive,force);
    }
   },

  /**
   * This function checks if a node has to be opened. This is done by checking the zoom level.
   * If the node contains child nodes, this function is recursively called on the child nodes as well.
   * This recursive behaviour is optional and can be set by the recursive argument.
   *
   * @param {Node}    parentNode    | to check for cluster and expand
   * @param {Boolean} recursive     | enabled or disable recursive calling
   * @param {Boolean} force         | enabled or disable forcing
   * @param {Boolean} [openAll]     | This will recursively force all nodes in the parent to be released
   * @private
   */
  _expandClusterNode : function(parentNode, recursive, force, openAll) {
    // first check if node is a cluster
    if (parentNode.clusterSize > 1) {
      // this means that on a double tap event or a zoom event, the cluster fully unpacks if it is smaller than 20
      if (parentNode.clusterSize < this.constants.clustering.sectorThreshold) {
        openAll = true;
      }
      recursive = openAll ? true : recursive;

      // if the last child has been added on a smaller scale than current scale decluster
      if (parentNode.formationScale < this.scale || force == true) {
        // we will check if any of the contained child nodes should be removed from the cluster
        for (var containedNodeId in parentNode.containedNodes) {
          if (parentNode.containedNodes.hasOwnProperty(containedNodeId)) {
            var childNode = parentNode.containedNodes[containedNodeId];

            // force expand will expand the largest cluster size clusters. Since we cluster from outside in, we assume that
            // the largest cluster is the one that comes from outside
            if (force == true) {
              if (childNode.clusterSession == parentNode.clusterSessions[parentNode.clusterSessions.length-1]
                  || openAll) {
                this._expelChildFromParent(parentNode,containedNodeId,recursive,force,openAll);
              }
            }
            else {
              if (this._nodeInActiveArea(parentNode)) {
                this._expelChildFromParent(parentNode,containedNodeId,recursive,force,openAll);
              }
            }
          }
        }
      }
    }
   },

  /**
   * ONLY CALLED FROM _expandClusterNode
   *
   * This function will expel a child_node from a parent_node. This is to de-cluster the node. This function will remove
   * the child node from the parent contained_node object and put it back into the global nodes object.
   * The same holds for the edge that was connected to the child node. It is moved back into the global edges object.
   *
   * @param {Node}    parentNode        | the parent node
   * @param {String}  containedNodeId   | child_node id as it is contained in the containedNodes object of the parent node
   * @param {Boolean} recursive         | This will also check if the child needs to be expanded.
   *                                      With force and recursive both true, the entire cluster is unpacked
   * @param {Boolean} force             | This will disregard the zoom level and will expel this child from the parent
   * @param {Boolean} openAll           | This will recursively force all nodes in the parent to be released
   * @private
   */
  _expelChildFromParent : function(parentNode, containedNodeId, recursive, force, openAll) {
    var childNode = parentNode.containedNodes[containedNodeId];

    // if child node has been added on smaller scale than current, kick out
    if (childNode.formationScale < this.scale || force == true) {
      // put the child node back in the global nodes object
      this.nodes[containedNodeId] = childNode;

      // release the contained edges from this childNode back into the global edges
      this._releaseContainedEdges(parentNode,childNode);

      // reconnect rerouted edges to the childNode
      this._connectEdgeBackToChild(parentNode,childNode);

      // validate all edges in dynamicEdges
      this._validateEdges(parentNode);

      // undo the changes from the clustering operation on the parent node
      parentNode.mass -= this.constants.clustering.massTransferCoefficient * childNode.mass;
      parentNode.fontSize -= this.constants.clustering.fontSizeMultiplier * childNode.clusterSize;
      parentNode.clusterSize -= childNode.clusterSize;
      parentNode.dynamicEdgesLength = parentNode.dynamicEdges.length;

      // place the child node near the parent, not at the exact same location to avoid chaos in the system
      childNode.x = parentNode.x + this.constants.edges.length * 0.3 * (0.5 - Math.random()) * parentNode.clusterSize;
      childNode.y = parentNode.y + this.constants.edges.length * 0.3 * (0.5 - Math.random()) * parentNode.clusterSize;

      // remove node from the list
      delete parentNode.containedNodes[containedNodeId];

      // check if there are other childs with this clusterSession in the parent.
      var othersPresent = false;
      for (var childNodeId in parentNode.containedNodes) {
        if (parentNode.containedNodes.hasOwnProperty(childNodeId)) {
          if (parentNode.containedNodes[childNodeId].clusterSession == childNode.clusterSession) {
            othersPresent = true;
            break;
          }
        }
      }
      // if there are no others, remove the cluster session from the list
      if (othersPresent == false) {
        parentNode.clusterSessions.pop();
      }

      // remove the clusterSession from the child node
      childNode.clusterSession = 0;

      // restart the simulation to reorganise all nodes
      this.moving = true;

      // recalculate the size of the node on the next time the node is rendered
      parentNode.clearSizeCache();
    }

    // check if a further expansion step is possible if recursivity is enabled
    if (recursive == true) {
      this._expandClusterNode(childNode,recursive,force,openAll);
    }
   },


  /**
   * This function checks if any nodes at the end of their trees have edges below a threshold length
   * This function is called only from updateClusters()
   * forceLevelCollapse ignores the length of the edge and collapses one level
   * This means that a node with only one edge will be clustered with its connected node
   *
   * @private
   * @param {Boolean} force
   */
  _formClusters : function(force) {
    if (force == false) {
      this._formClustersByZoom();
    }
    else {
      this._forceClustersByZoom();
    }
   },

  /**
   * This function handles the clustering by zooming out, this is based on a minimum edge distance
   *
   * @private
   */
  _formClustersByZoom : function() {
    var dx,dy,length,
        minLength = this.constants.clustering.clusterEdgeThreshold/this.scale;

    // check if any edges are shorter than minLength and start the clustering
    // the clustering favours the node with the larger mass
    for (var edgeId in this.edges) {
      if (this.edges.hasOwnProperty(edgeId)) {
        var edge = this.edges[edgeId];
        if (edge.connected) {
          if (edge.toId != edge.fromId) {
            dx = (edge.to.x - edge.from.x);
            dy = (edge.to.y - edge.from.y);
            length = Math.sqrt(dx * dx + dy * dy);


            if (length < minLength) {
              // first check which node is larger
              var parentNode = edge.from;
              var childNode = edge.to;
              if (edge.to.mass > edge.from.mass) {
                parentNode = edge.to;
                childNode = edge.from;
              }

              if (childNode.dynamicEdgesLength == 1) {
                this._addToCluster(parentNode,childNode,false);
              }
              else if (parentNode.dynamicEdgesLength == 1) {
                this._addToCluster(childNode,parentNode,false);
              }
            }
          }
        }
      }
    }
   },

  /**
   * This function forces the graph to cluster all nodes with only one connecting edge to their
   * connected node.
   *
   * @private
   */
  _forceClustersByZoom : function() {
    for (var nodeId in this.nodes) {
      // another node could have absorbed this child.
      if (this.nodes.hasOwnProperty(nodeId)) {
        var childNode = this.nodes[nodeId];

        // the edges can be swallowed by another decrease
        if (childNode.dynamicEdgesLength == 1 && childNode.dynamicEdges.length != 0) {
          var edge = childNode.dynamicEdges[0];
          var parentNode = (edge.toId == childNode.id) ? this.nodes[edge.fromId] : this.nodes[edge.toId];

          // group to the largest node
          if (childNode.id != parentNode.id) {
            if (parentNode.mass > childNode.mass) {
              this._addToCluster(parentNode,childNode,true);
            }
            else {
              this._addToCluster(childNode,parentNode,true);
            }
          }
        }
      }
    }
   },



  /**
   * This function forms clusters from hubs, it loops over all nodes
   *
   * @param {Boolean} force         |   Disregard zoom level
   * @param {Boolean} onlyEqual     |   This only clusters a hub with a specific number of edges
   * @private
   */
  _formClustersByHub : function(force, onlyEqual) {
    // we loop over all nodes in the list
    for (var nodeId in this.nodes) {
      // we check if it is still available since it can be used by the clustering in this loop
      if (this.nodes.hasOwnProperty(nodeId)) {
        this._formClusterFromHub(this.nodes[nodeId],force,onlyEqual);
      }
    }
   },

  /**
   * This function forms a cluster from a specific preselected hub node
   *
   * @param {Node}    hubNode       |   the node we will cluster as a hub
   * @param {Boolean} force         |   Disregard zoom level
   * @param {Boolean} onlyEqual     |   This only clusters a hub with a specific number of edges
   * @param {Number} [absorptionSizeOffset] |
   * @private
   */
  _formClusterFromHub : function(hubNode, force, onlyEqual, absorptionSizeOffset) {
    if (absorptionSizeOffset === undefined) {
      absorptionSizeOffset = 0;
    }
    // we decide if the node is a hub
    if ((hubNode.dynamicEdgesLength >= this.hubThreshold && onlyEqual == false) ||
      (hubNode.dynamicEdgesLength == this.hubThreshold && onlyEqual == true)) {
      // initialize variables
      var dx,dy,length;
      var minLength = this.constants.clustering.clusterEdgeThreshold/this.scale;
      var allowCluster = false;

      // we create a list of edges because the dynamicEdges change over the course of this loop
      var edgesIdarray = [];
      var amountOfInitialEdges = hubNode.dynamicEdges.length;
      for (var j = 0; j < amountOfInitialEdges; j++) {
        edgesIdarray.push(hubNode.dynamicEdges[j].id);
      }

      // if the hub clustering is not forces, we check if one of the edges connected
      // to a cluster is small enough based on the constants.clustering.clusterEdgeThreshold
      if (force == false) {
        allowCluster = false;
        for (j = 0; j < amountOfInitialEdges; j++) {
          var edge = this.edges[edgesIdarray[j]];
          if (edge !== undefined) {
            if (edge.connected) {
              if (edge.toId != edge.fromId) {
                dx = (edge.to.x - edge.from.x);
                dy = (edge.to.y - edge.from.y);
                length = Math.sqrt(dx * dx + dy * dy);

                if (length < minLength) {
                  allowCluster = true;
                  break;
                }
              }
            }
          }
        }
      }

      // start the clustering if allowed
      if ((!force && allowCluster) || force) {
        // we loop over all edges INITIALLY connected to this hub
        for (j = 0; j < amountOfInitialEdges; j++) {
          edge = this.edges[edgesIdarray[j]];
          // the edge can be clustered by this function in a previous loop
          if (edge !== undefined) {
            var childNode = this.nodes[(edge.fromId == hubNode.id) ? edge.toId : edge.fromId];
            // we do not want hubs to merge with other hubs nor do we want to cluster itself.
            if ((childNode.dynamicEdges.length <= (this.hubThreshold + absorptionSizeOffset)) &&
                (childNode.id != hubNode.id)) {
              this._addToCluster(hubNode,childNode,force);
            }
          }
        }
      }
    }
   },



  /**
   * This function adds the child node to the parent node, creating a cluster if it is not already.
   *
   * @param {Node} parentNode           | this is the node that will house the child node
   * @param {Node} childNode            | this node will be deleted from the global this.nodes and stored in the parent node
   * @param {Boolean} force             | true will only update the remainingEdges at the very end of the clustering, ensuring single level collapse
   * @private
   */
  _addToCluster : function(parentNode, childNode, force) {
    // join child node in the parent node
    parentNode.containedNodes[childNode.id] = childNode;

    // manage all the edges connected to the child and parent nodes
    for (var i = 0; i < childNode.dynamicEdges.length; i++) {
      var edge = childNode.dynamicEdges[i];
      if (edge.toId == parentNode.id || edge.fromId == parentNode.id) { // edge connected to parentNode
        this._addToContainedEdges(parentNode,childNode,edge);
      }
      else {
        this._connectEdgeToCluster(parentNode,childNode,edge);
      }
    }
    // a contained node has no dynamic edges.
    childNode.dynamicEdges = [];

    // remove circular edges from clusters
    this._containCircularEdgesFromNode(parentNode,childNode);


    // remove the childNode from the global nodes object
    delete this.nodes[childNode.id];

    // update the properties of the child and parent
    var massBefore = parentNode.mass;
    childNode.clusterSession = this.clusterSession;
    parentNode.mass += this.constants.clustering.massTransferCoefficient * childNode.mass;
    parentNode.clusterSize += childNode.clusterSize;
    parentNode.fontSize += this.constants.clustering.fontSizeMultiplier * childNode.clusterSize;

    // keep track of the clustersessions so we can open the cluster up as it has been formed.
    if (parentNode.clusterSessions[parentNode.clusterSessions.length - 1] != this.clusterSession) {
      parentNode.clusterSessions.push(this.clusterSession);
    }

    // forced clusters only open from screen size and double tap
    if (force == true) {
      // parentNode.formationScale = Math.pow(1 - (1.0/11.0),this.clusterSession+3);
      parentNode.formationScale = 0;
    }
    else {
      parentNode.formationScale = this.scale; // The latest child has been added on this scale
    }

    // recalculate the size of the node on the next time the node is rendered
    parentNode.clearSizeCache();

    // set the pop-out scale for the childnode
    parentNode.containedNodes[childNode.id].formationScale = parentNode.formationScale;

    // nullify the movement velocity of the child, this is to avoid hectic behaviour
    childNode.clearVelocity();

    // the mass has altered, preservation of energy dictates the velocity to be updated
    parentNode.updateVelocity(massBefore);

    // restart the simulation to reorganise all nodes
    this.moving = true;
   },


  /**
   * This function will apply the changes made to the remainingEdges during the formation of the clusters.
   * This is a seperate function to allow for level-wise collapsing of the node tree.
   * It has to be called if a level is collapsed. It is called by _formClusters().
   * @private
   */
  _updateDynamicEdges : function() {
    for (var i = 0; i < this.nodeIndices.length; i++) {
      var node = this.nodes[this.nodeIndices[i]];
      node.dynamicEdgesLength = node.dynamicEdges.length;

      // this corrects for multiple edges pointing at the same other node
      var correction = 0;
      if (node.dynamicEdgesLength > 1) {
        for (var j = 0; j < node.dynamicEdgesLength - 1; j++) {
          var edgeToId = node.dynamicEdges[j].toId;
          var edgeFromId = node.dynamicEdges[j].fromId;
          for (var k = j+1; k < node.dynamicEdgesLength; k++) {
            if ((node.dynamicEdges[k].toId == edgeToId && node.dynamicEdges[k].fromId == edgeFromId) ||
                (node.dynamicEdges[k].fromId == edgeToId && node.dynamicEdges[k].toId == edgeFromId)) {
              correction += 1;
            }
          }
        }
      }
      node.dynamicEdgesLength -= correction;
    }
   },


  /**
   * This adds an edge from the childNode to the contained edges of the parent node
   *
   * @param parentNode    | Node object
   * @param childNode     | Node object
   * @param edge          | Edge object
   * @private
   */
  _addToContainedEdges : function(parentNode, childNode, edge) {
    // create an array object if it does not yet exist for this childNode
    if (!(parentNode.containedEdges.hasOwnProperty(childNode.id))) {
      parentNode.containedEdges[childNode.id] = []
    }
    // add this edge to the list
    parentNode.containedEdges[childNode.id].push(edge);

    // remove the edge from the global edges object
    delete this.edges[edge.id];

    // remove the edge from the parent object
    for (var i = 0; i < parentNode.dynamicEdges.length; i++) {
      if (parentNode.dynamicEdges[i].id == edge.id) {
        parentNode.dynamicEdges.splice(i,1);
        break;
      }
    }
   },

  /**
   * This function connects an edge that was connected to a child node to the parent node.
   * It keeps track of which nodes it has been connected to with the originalId array.
   *
   * @param {Node} parentNode    | Node object
   * @param {Node} childNode     | Node object
   * @param {Edge} edge          | Edge object
   * @private
   */
  _connectEdgeToCluster : function(parentNode, childNode, edge) {
    // handle circular edges
    if (edge.toId == edge.fromId) {
      this._addToContainedEdges(parentNode, childNode, edge);
    }
    else {
      if (edge.toId == childNode.id) {    // edge connected to other node on the "to" side
        edge.originalToId.push(childNode.id);
        edge.to = parentNode;
        edge.toId = parentNode.id;
      }
      else {          // edge connected to other node with the "from" side

        edge.originalFromId.push(childNode.id);
        edge.from = parentNode;
        edge.fromId = parentNode.id;
      }

      this._addToReroutedEdges(parentNode,childNode,edge);
    }
   },


  _containCircularEdgesFromNode : function(parentNode, childNode) {
    // manage all the edges connected to the child and parent nodes
    for (var i = 0; i < parentNode.dynamicEdges.length; i++) {
      var edge = parentNode.dynamicEdges[i];
      // handle circular edges
      if (edge.toId == edge.fromId) {
        this._addToContainedEdges(parentNode, childNode, edge);
      }
    }
  },


  /**
   * This adds an edge from the childNode to the rerouted edges of the parent node
   *
   * @param parentNode    | Node object
   * @param childNode     | Node object
   * @param edge          | Edge object
   * @private
   */
  _addToReroutedEdges : function(parentNode, childNode, edge) {
    // create an array object if it does not yet exist for this childNode
    // we store the edge in the rerouted edges so we can restore it when the cluster pops open
    if (!(parentNode.reroutedEdges.hasOwnProperty(childNode.id))) {
      parentNode.reroutedEdges[childNode.id] = [];
    }
    parentNode.reroutedEdges[childNode.id].push(edge);

    // this edge becomes part of the dynamicEdges of the cluster node
    parentNode.dynamicEdges.push(edge);
   },



  /**
   * This function connects an edge that was connected to a cluster node back to the child node.
   *
   * @param parentNode    | Node object
   * @param childNode     | Node object
   * @private
   */
  _connectEdgeBackToChild : function(parentNode, childNode) {
    if (parentNode.reroutedEdges.hasOwnProperty(childNode.id)) {
      for (var i = 0; i < parentNode.reroutedEdges[childNode.id].length; i++) {
        var edge = parentNode.reroutedEdges[childNode.id][i];
        if (edge.originalFromId[edge.originalFromId.length-1] == childNode.id) {
          edge.originalFromId.pop();
          edge.fromId = childNode.id;
          edge.from = childNode;
        }
        else {
          edge.originalToId.pop();
          edge.toId = childNode.id;
          edge.to = childNode;
        }

        // append this edge to the list of edges connecting to the childnode
        childNode.dynamicEdges.push(edge);

        // remove the edge from the parent object
        for (var j = 0; j < parentNode.dynamicEdges.length; j++) {
          if (parentNode.dynamicEdges[j].id == edge.id) {
            parentNode.dynamicEdges.splice(j,1);
            break;
          }
        }
      }
      // remove the entry from the rerouted edges
      delete parentNode.reroutedEdges[childNode.id];
    }
   },


  /**
   * When loops are clustered, an edge can be both in the rerouted array and the contained array.
   * This function is called last to verify that all edges in dynamicEdges are in fact connected to the
   * parentNode
   *
   * @param parentNode    | Node object
   * @private
   */
  _validateEdges : function(parentNode) {
    for (var i = 0; i < parentNode.dynamicEdges.length; i++) {
      var edge = parentNode.dynamicEdges[i];
      if (parentNode.id != edge.toId && parentNode.id != edge.fromId) {
        parentNode.dynamicEdges.splice(i,1);
      }
    }
   },


  /**
   * This function released the contained edges back into the global domain and puts them back into the
   * dynamic edges of both parent and child.
   *
   * @param {Node} parentNode    |
   * @param {Node} childNode     |
   * @private
   */
  _releaseContainedEdges : function(parentNode, childNode) {
    for (var i = 0; i < parentNode.containedEdges[childNode.id].length; i++) {
      var edge = parentNode.containedEdges[childNode.id][i];

      // put the edge back in the global edges object
      this.edges[edge.id] = edge;

      // put the edge back in the dynamic edges of the child and parent
      childNode.dynamicEdges.push(edge);
      parentNode.dynamicEdges.push(edge);
    }
    // remove the entry from the contained edges
    delete parentNode.containedEdges[childNode.id];

   },




  // ------------------- UTILITY FUNCTIONS ---------------------------- //


  /**
   * This updates the node labels for all nodes (for debugging purposes)
   */
  updateLabels : function() {
    var nodeId;
    // update node labels
    for (nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        var node = this.nodes[nodeId];
        if (node.clusterSize > 1) {
          node.label = "[".concat(String(node.clusterSize),"]");
        }
      }
    }

    // update node labels
    for (nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        node = this.nodes[nodeId];
        if (node.clusterSize == 1) {
          if (node.originalLabel !== undefined) {
            node.label = node.originalLabel;
          }
          else {
            node.label = String(node.id);
          }
        }
      }
    }

    /* Debug Override */
  //  for (nodeId in this.nodes) {
  //    if (this.nodes.hasOwnProperty(nodeId)) {
  //      node = this.nodes[nodeId];
  //      node.label = String(Math.round(node.width)).concat(":",Math.round(node.width*this.scale));
  //    }
  //  }

   },


  /**
   * This function determines if the cluster we want to decluster is in the active area
   * this means around the zoom center
   *
   * @param {Node} node
   * @returns {boolean}
   * @private
   */
  _nodeInActiveArea : function(node) {
    return (
      Math.abs(node.x - this.areaCenter.x) <= this.constants.clustering.activeAreaBoxSize/this.scale
        &&
      Math.abs(node.y - this.areaCenter.y) <= this.constants.clustering.activeAreaBoxSize/this.scale
      )
   },


  /**
   * This is an adaptation of the original repositioning function. This is called if the system is clustered initially
   * It puts large clusters away from the center and randomizes the order.
   *
   */
  repositionNodes : function() {
    for (var i = 0; i < this.nodeIndices.length; i++) {
      var node = this.nodes[this.nodeIndices[i]];
      if (!node.isFixed()) {
        var radius = this.constants.edges.length * (1 + 0.6*node.clusterSize);
        var angle = 2 * Math.PI * Math.random();
        node.x = radius * Math.cos(angle);
        node.y = radius * Math.sin(angle);
      }
    }
   },





  /**
   * We determine how many connections denote an important hub.
   * We take the mean + 2*std as the important hub size. (Assuming a normal distribution of data, ~2.2%)
   *
   * @private
   */
  _getHubSize : function() {
    var average = 0;
    var averageSquared = 0;
    var hubCounter = 0;
    var largestHub = 0;

    for (var i = 0; i < this.nodeIndices.length; i++) {
      var node = this.nodes[this.nodeIndices[i]];
      if (node.dynamicEdgesLength > largestHub) {
        largestHub = node.dynamicEdgesLength;
      }
      average += node.dynamicEdgesLength;
      averageSquared += Math.pow(node.dynamicEdgesLength,2);
      hubCounter += 1;
    }
    average = average / hubCounter;
    averageSquared = averageSquared / hubCounter;

    var variance = averageSquared - Math.pow(average,2);

    var standardDeviation = Math.sqrt(variance);

    this.hubThreshold = Math.floor(average + 2*standardDeviation);

    // always have at least one to cluster
    if (this.hubThreshold > largestHub) {
      this.hubThreshold = largestHub;
    }

  //  console.log("average",average,"averageSQ",averageSquared,"var",variance,"std",standardDeviation);
  //  console.log("hubThreshold:",this.hubThreshold);
   },


  /**
   * We reduce the amount of "extension nodes" or chains. These are not quickly clustered with the outliers and hubs methods
   * with this amount we can cluster specifically on these chains.
   *
   * @param   {Number} fraction     | between 0 and 1, the percentage of chains to reduce
   * @private
   */
  _reduceAmountOfChains : function(fraction) {
    this.hubThreshold = 2;
    var reduceAmount = Math.floor(this.nodeIndices.length * fraction);
    for (var nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        if (this.nodes[nodeId].dynamicEdgesLength == 2 && this.nodes[nodeId].dynamicEdges.length >= 2) {
          if (reduceAmount > 0) {
            this._formClusterFromHub(this.nodes[nodeId],true,true,1);
            reduceAmount -= 1;
          }
        }
      }
    }
   },

  /**
   * We get the amount of "extension nodes" or chains. These are not quickly clustered with the outliers and hubs methods
   * with this amount we can cluster specifically on these chains.
   *
   * @private
   */
  _getChainFraction : function() {
    var chains = 0;
    var total = 0;
    for (var nodeId in this.nodes) {
      if (this.nodes.hasOwnProperty(nodeId)) {
        if (this.nodes[nodeId].dynamicEdgesLength == 2 && this.nodes[nodeId].dynamicEdges.length >= 2) {
          chains += 1;
        }
        total += 1;
      }
    }
    return chains/total;
   }
};


var SelectionMixin = {

  /**
   * This function can be called from the _doInAllSectors function
   *
   * @param object
   * @param overlappingNodes
   * @private
   */
  _getNodesOverlappingWith : function(object, overlappingNodes) {
    var nodes = this.nodes;
    for (var nodeId in nodes) {
      if (nodes.hasOwnProperty(nodeId)) {
        if (nodes[nodeId].isOverlappingWith(object)) {
          overlappingNodes.push(nodeId);
        }
      }
    }
  },

  /**
   * retrieve all nodes overlapping with given object
   * @param {Object} object  An object with parameters left, top, right, bottom
   * @return {Number[]}   An array with id's of the overlapping nodes
   * @private
   */
  _getAllNodesOverlappingWith : function (object) {
    var overlappingNodes = [];
    this._doInAllActiveSectors("_getNodesOverlappingWith",object,overlappingNodes);
    return overlappingNodes;
  },


  /**
   * retrieve all nodes in the navigationUI overlapping with given object
   * @param {Object} object  An object with parameters left, top, right, bottom
   * @return {Number[]}   An array with id's of the overlapping nodes
   * @private
   */
  _getAllUINodesOverlappingWith : function (object) {
    var overlappingNodes = [];
    this._doInUISector("_getNodesOverlappingWith",object,overlappingNodes);
    return overlappingNodes;
  },

  /**
   * Return a position object in canvasspace from a single point in screenspace
   *
   * @param pointer
   * @returns {{left: number, top: number, right: number, bottom: number}}
   * @private
   */
  _pointerToPositionObject : function(pointer) {
    var x = this._canvasToX(pointer.x);
    var y = this._canvasToY(pointer.y);

    return {left:   x,
            top:    y,
            right:  x,
            bottom: y};
  },

  /**
   * Return a position object in canvasspace from a single point in screenspace
   *
   * @param pointer
   * @returns {{left: number, top: number, right: number, bottom: number}}
   * @private
   */
  _pointerToScreenPositionObject : function(pointer) {
    var x = pointer.x;
    var y = pointer.y;

    return {left:   x,
      top:    y,
      right:  x,
      bottom: y};
  },


  /**
   * Get the top navigationUI node at the a specific point (like a click)
   *
   * @param {{x: Number, y: Number}} pointer
   * @return {Node | null} node
   * @private
   */
  _getUINodeAt : function (pointer) {
    var screenPositionObject = this._pointerToScreenPositionObject(pointer);
    var overlappingNodes = this._getAllUINodesOverlappingWith(screenPositionObject);
    if (this.UIvisible && overlappingNodes.length > 0) {
      return this.sectors["navigationUI"]["nodes"][overlappingNodes[overlappingNodes.length - 1]];
    }
    else {
      return null;
    }
  },


  /**
   * Get the top node at the a specific point (like a click)
   *
   * @param {{x: Number, y: Number}} pointer
   * @return {Node | null} node
   * @private
   */
  _getNodeAt : function (pointer) {
    // we first check if this is an navigationUI element
    var positionObject = this._pointerToPositionObject(pointer);
    overlappingNodes = this._getAllNodesOverlappingWith(positionObject);

    // if there are overlapping nodes, select the last one, this is the
    // one which is drawn on top of the others
    if (overlappingNodes.length > 0) {
       return this.nodes[overlappingNodes[overlappingNodes.length - 1]];
    }
    else {
      return null;
    }
  },


  /**
   * Place holder. To implement change the _getNodeAt to a _getObjectAt. Have the _getObjectAt call
   * _getNodeAt and _getEdgesAt, then priortize the selection to user preferences.
   *
   * @param pointer
   * @returns {null}
   * @private
   */
  _getEdgeAt : function(pointer) {
    return null;
  },


  /**
   * Add object to the selection array. The this.selection id array may not be needed.
   *
   * @param obj
   * @private
   */
  _addToSelection : function(obj) {
    this.selection.push(obj.id);
    this.selectionObj[obj.id] = obj;
  },


  /**
   * Remove a single option from selection.
   *
   * @param obj
   * @private
   */
  _removeFromSelection : function(obj) {
    for (var i = 0; i < this.selection.length; i++) {
      if (obj.id == this.selection[i]) {
        this.selection.splice(i,1);
        break;
      }
    }
    delete this.selectionObj[obj.id];
  },


  /**
   * Unselect all. The selectionObj is useful for this.
   *
   * @private
   */
  _unselectAll : function() {
    this.selection = [];
    for (var objId in this.selectionObj) {
      if (this.selectionObj.hasOwnProperty(objId)) {
        this.selectionObj[objId].unselect();
      }
    }
    this.selectionObj = {};

    this._trigger('select');
  },


  /**
   * Check if anything is selected
   *
   * @returns {boolean}
   * @private
   */
  _selectionIsEmpty : function() {
    if (this.selection.length == 0) {
      return true;
    }
    else {
      return false;
    }
  },


  /**
   * This is called when someone clicks on a node. either select or deselect it.
   * If there is an existing selection and we don't want to append to it, clear the existing selection
   *
   * @param {Node} node
   * @param {Boolean} append
   * @private
   */
  _selectNode : function(node, append) {
    if (this._selectionIsEmpty() == false && append == false) {
      this._unselectAll();
    }

    if (node.selected == false) {
      node.select();
      this._addToSelection(node);
    }
    else {
      node.unselect();
      this._removeFromSelection(node);
    }
    this._trigger('select');
  },


  /**
   * handles the selection part of the touch, only for navigationUI elements;
   * Touch is triggered before tap, also before hold. Hold triggers after a while.
   * This is the most responsive solution
   *
   * @param {Object} pointer
   * @private
   */
  _handleTouch : function(pointer) {
    var node = this._getUINodeAt(pointer);
    if (node != null) {
      if (this[node.triggerFunction] !== undefined) {
        this[node.triggerFunction]();
      }
    }
  },


  /**
   * handles the selection part of the tap;
   *
   * @param {Object} pointer
   * @private
   */
  _handleTap : function(pointer) {
    var node = this._getNodeAt(pointer);
    if (node != null) {
      this._selectNode(node,false);
    }
    else {
      this._unselectAll();
    }
    this._redraw();
  },


  /**
   * handles the selection part of the double tap and opens a cluster if needed
   *
   * @param {Object} pointer
   * @private
   */
  _handleDoubleTap : function(pointer) {
    var node = this._getNodeAt(pointer);
    if (node != null && node !== undefined) {
      // we reset the areaCenter here so the opening of the node will occur
      this.areaCenter =  {"x" : this._canvasToX(pointer.x),
                          "y" : this._canvasToY(pointer.y)};
      this.openCluster(node);
    }
  },


  /**
   * Handle the onHold selection part
   *
   * @param pointer
   * @private
   */
  _handleOnHold : function(pointer) {
    var node = this._getNodeAt(pointer);
    if (node != null) {
      this._selectNode(node,true);
    }
    this._redraw();
  },


  /**
   * handle the onRelease event. These functions are here for the navigationUI module.
   *
    * @private
   */
  _handleOnRelease : function() {
    this.xIncrement = 0;
    this.yIncrement = 0;
    this.zoomIncrement = 0;
    this._unHighlightAll();
  },



  /**
   * * // TODO: rework this function, it is from the old system
   *
   * retrieve the currently selected nodes
   * @return {Number[] | String[]} selection    An array with the ids of the
   *                                            selected nodes.
   */
  getSelection : function() {
    return this.selection.concat([]);
  },

  /**
   * // TODO: rework this function, it is from the old system
   *
   * select zero or more nodes
   * @param {Number[] | String[]} selection     An array with the ids of the
   *                                            selected nodes.
   */
  setSelection : function(selection) {
    var i, iMax, id;

    if (!selection || (selection.length == undefined))
      throw 'Selection must be an array with ids';

    // first unselect any selected node
    for (i = 0, iMax = this.selection.length; i < iMax; i++) {
      id = this.selection[i];
      this.nodes[id].unselect();
    }

    this.selection = [];

    for (i = 0, iMax = selection.length; i < iMax; i++) {
      id = selection[i];

      var node = this.nodes[id];
      if (!node) {
        throw new RangeError('Node with id "' + id + '" not found');
      }
      node.select();
      this.selection.push(id);
    }

    this.redraw();
  },


  /**
   * TODO: rework this function, it is from the old system
   *
   * Validate the selection: remove ids of nodes which no longer exist
   * @private
   */
  _updateSelection : function () {
    var i = 0;
    while (i < this.selection.length) {
      var nodeId = this.selection[i];
      if (!this.nodes.hasOwnProperty(nodeId)) {
        this.selection.splice(i, 1);
        delete this.selectionObj[nodeId];
      }
      else {
        i++;
      }
    }
  }


  /**
   * Unselect selected nodes. If no selection array is provided, all nodes
   * are unselected
   * @param {Object[]} selection     Array with selection objects, each selection
   *                                 object has a parameter row. Optional
   * @param {Boolean} triggerSelect  If true (default), the select event
   *                                 is triggered when nodes are unselected
   * @return {Boolean} changed       True if the selection is changed
   * @private
   */
 /* _unselectNodes : function(selection, triggerSelect) {
    var changed = false;
    var i, iMax, id;

    if (selection) {
      // remove provided selections
      for (i = 0, iMax = selection.length; i < iMax; i++) {
        id = selection[i];
        if (this.nodes.hasOwnProperty(id)) {
          this.nodes[id].unselect();
        }
        var j = 0;
        while (j < this.selection.length) {
          if (this.selection[j] == id) {
            this.selection.splice(j, 1);
            changed = true;
          }
          else {
            j++;
          }
        }
      }
    }
    else if (this.selection && this.selection.length) {
      // remove all selections
      for (i = 0, iMax = this.selection.length; i < iMax; i++) {
        id = this.selection[i];
        if (this.nodes.hasOwnProperty(id)) {
          this.nodes[id].unselect();
        }
        changed = true;
      }
      this.selection = [];
    }

    if (changed && (triggerSelect == true || triggerSelect == undefined)) {
      // fire the select event
      this._trigger('select');
    }

    return changed;
  },
*/
/**
 * select all nodes on given location x, y
 * @param {Array} selection   an array with node ids
 * @param {boolean} append    If true, the new selection will be appended to the
 *                            current selection (except for duplicate entries)
 * @return {Boolean} changed  True if the selection is changed
 * @private
 */
/*  _selectNodes : function(selection, append) {
    var changed = false;
    var i, iMax;

    // TODO: the selectNodes method is a little messy, rework this

    // check if the current selection equals the desired selection
    var selectionAlreadyThere = true;
    if (selection.length != this.selection.length) {
      selectionAlreadyThere = false;
    }
    else {
      for (i = 0, iMax = Math.min(selection.length, this.selection.length); i < iMax; i++) {
        if (selection[i] != this.selection[i]) {
          selectionAlreadyThere = false;
          break;
        }
      }
    }
    if (selectionAlreadyThere) {
      return changed;
    }

    if (append == undefined || append == false) {
      // first deselect any selected node
      var triggerSelect = false;
      changed = this._unselectNodes(undefined, triggerSelect);
    }

    for (i = 0, iMax = selection.length; i < iMax; i++) {
      // add each of the new selections, but only when they are not duplicate
      var id = selection[i];
      var isDuplicate = (this.selection.indexOf(id) != -1);
      if (!isDuplicate) {
        this.nodes[id].select();
        this.selection.push(id);
        changed = true;
      }
    }

    if (changed) {
      // fire the select event
      this._trigger('select');
    }

    return changed;
  },
  */
};




/**
 * Created by Alex on 1/22/14.
 */

var UIMixin = {

  /**
   * This function moves the navigationUI if the canvas size has been changed. If the arugments
   * verticaAlignTop and horizontalAlignLeft are false, the correction will be made
   *
   * @private
   */
  _relocateUI : function() {
    if (this.sectors !== undefined) {
      var xOffset = this.UIclientWidth - this.frame.canvas.clientWidth;
      var yOffset = this.UIclientHeight - this.frame.canvas.clientHeight;
      this.UIclientWidth = this.frame.canvas.clientWidth;
      this.UIclientHeight = this.frame.canvas.clientHeight;
      var node = null;

      for (var nodeId in this.sectors["navigationUI"]["nodes"]) {
        if (this.sectors["navigationUI"]["nodes"].hasOwnProperty(nodeId)) {
          node = this.sectors["navigationUI"]["nodes"][nodeId];
          if (!node.horizontalAlignLeft) {
            node.x -= xOffset;
          }
          if (!node.verticalAlignTop) {
            node.y -= yOffset;
          }
        }
      }
    }
  },


  /**
   * Creation of the navigationUI nodes. They are drawn over the rest of the nodes and are not affected by scale and translation
   * they have a triggerFunction which is called on click. If the position of the navigationUI is dependent
   * on this.frame.canvas.clientWidth or this.frame.canvas.clientHeight, we flag horizontalAlignLeft and verticalAlignTop false.
   * This means that the location will be corrected by the _relocateUI function on a size change of the canvas.
   *
   * @private
   */
  _loadUIElements : function() {
    var DIR = this.constants.navigationUI.iconPath;
    this.UIclientWidth = this.frame.canvas.clientWidth;
    this.UIclientHeight = this.frame.canvas.clientHeight;
    if (this.UIclientWidth === undefined) {
      this.UIclientWidth = 0;
      this.UIclientHeight = 0;
    }
    var offset = 15;
    var intermediateOffset = 7;
    var UINodes = [
      {id: 'UI_up',    shape: 'image', image: DIR + 'uparrow.png',   triggerFunction: "_moveUp",
        verticalAlignTop: false,  x: 45 + offset + intermediateOffset,  y: this.UIclientHeight - 45 - offset - intermediateOffset},
      {id: 'UI_down',  shape: 'image', image: DIR + 'downarrow.png', triggerFunction: "_moveDown",
        verticalAlignTop: false,  x: 45 + offset + intermediateOffset,  y: this.UIclientHeight - 15 - offset},
      {id: 'UI_left',  shape: 'image', image: DIR + 'leftarrow.png', triggerFunction: "_moveLeft",
        verticalAlignTop: false,  x: 15 + offset,  y: this.UIclientHeight - 15 - offset},
      {id: 'UI_right', shape: 'image', image: DIR + 'rightarrow.png',triggerFunction: "_moveRight",
        verticalAlignTop: false,  x: 75 + offset + 2 * intermediateOffset,  y: this.UIclientHeight - 15 - offset},

      {id: 'UI_plus',  shape: 'image', image: DIR + 'plus.png',      triggerFunction: "_zoomIn",
        verticalAlignTop: false, horizontalAlignLeft: false,
        x: this.UIclientWidth - 45 - offset - intermediateOffset, y: this.UIclientHeight - 15 - offset},
      {id: 'UI_min', shape: 'image', image: DIR + 'minus.png',       triggerFunction: "_zoomOut",
        verticalAlignTop: false, horizontalAlignLeft: false,
        x: this.UIclientWidth - 15 - offset, y: this.UIclientHeight - 15 - offset},
      {id: 'UI_zoomExtends', shape: 'image', image: DIR + 'zoomExtends.png', triggerFunction: "zoomToFit",
        verticalAlignTop: false, horizontalAlignLeft: false,
        x: this.UIclientWidth - 15 - offset, y: this.UIclientHeight - 45 - offset - intermediateOffset}
    ];

    var nodeObj = null;
    for (var i = 0; i < UINodes.length; i++) {
      nodeObj = this.sectors["navigationUI"]['nodes'];
      nodeObj[UINodes[i]['id']] = new Node(UINodes[i], this.images, this.groups, this.constants);
    }
  },


  /**
   * By setting the clustersize to be larger than 1, we use the clustering drawing method
   * to illustrate the buttons are presed. We call this highlighting.
   *
   * @param {String} elementId
   * @private
   */
  _highlightUIElement : function(elementId) {
    if (this.sectors["navigationUI"]["nodes"].hasOwnProperty(elementId)) {
      this.sectors["navigationUI"]["nodes"][elementId].clusterSize = 2;
    }
  },


  /**
   * Reverting back to a normal button
   *
   * @param {String} elementId
   * @private
   */
  _unHighlightUIElement : function(elementId) {
    if (this.sectors["navigationUI"]["nodes"].hasOwnProperty(elementId)) {
      this.sectors["navigationUI"]["nodes"][elementId].clusterSize = 1;
    }
  },


  /**
   * toggle the visibility of the navigationUI
   *
   * @private
   */
  _toggleUI : function() {
    if (this.UIvisible === undefined) {
      this.UIvisible = false;
    }
    this.UIvisible = !this.UIvisible;
    this._redraw();
  },


  /**
   * un-highlight (for lack of a better term) all navigationUI elements
   * @private
   */
  _unHighlightAll : function() {
    for (var nodeId in this.sectors['navigationUI']['nodes']) {
      this._unHighlightUIElement(nodeId);
    }
  },


  _preventDefault : function(event) {
    if (event !== undefined) {
      if (event.preventDefault) {
        event.preventDefault();
      } else {
        event.returnValue = false;
      }
    }
  },


  /**
   * move the screen up
   * By using the increments, instead of adding a fixed number to the translation, we keep fluent and
   * instant movement. The onKeypress event triggers immediately, then pauses, then triggers frequently
   * To avoid this behaviour, we do the translation in the start loop.
   *
   * @private
   */
  _moveUp : function(event) {
    this._highlightUIElement("UI_up");
    this.yIncrement = this.constants.navigationUI.yMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * move the screen down
   * @private
   */
  _moveDown : function(event) {
    this._highlightUIElement("UI_down");
    this.yIncrement = -this.constants.navigationUI.yMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * move the screen left
   * @private
   */
  _moveLeft : function(event) {
    this._highlightUIElement("UI_left");
    this.xIncrement = this.constants.navigationUI.xMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * move the screen right
   * @private
   */
  _moveRight : function(event) {
    this._highlightUIElement("UI_right");
    this.xIncrement = -this.constants.navigationUI.xMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * Zoom in, using the same method as the movement.
   * @private
   */
  _zoomIn : function(event) {
    this._highlightUIElement("UI_plus");
    this.zoomIncrement = this.constants.navigationUI.zoomMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * Zoom out
   * @private
   */
  _zoomOut : function() {
    this._highlightUIElement("UI_min");
    this.zoomIncrement = -this.constants.navigationUI.zoomMovementSpeed;
    this.start(); // if there is no node movement, the calculation wont be done
    this._preventDefault(event);
  },


  /**
   * Stop zooming and unhighlight the zoom controls
   * @private
   */
  _stopZoom : function() {
    this._unHighlightUIElement("UI_plus");
    this._unHighlightUIElement("UI_min");

    this.zoomIncrement = 0;
  },


  /**
   * Stop moving in the Y direction and unHighlight the up and down
   * @private
   */
  _yStopMoving : function() {
    this._unHighlightUIElement("UI_up");
    this._unHighlightUIElement("UI_down");

    this.yIncrement = 0;
  },


  /**
   * Stop moving in the X direction and unHighlight left and right.
   * @private
   */
  _xStopMoving : function() {
    this._unHighlightUIElement("UI_left");
    this._unHighlightUIElement("UI_right");

    this.xIncrement = 0;
  }


};

/**
 * @constructor Graph
 * Create a graph visualization, displaying nodes and edges.
 *
 * @param {Element} container   The DOM element in which the Graph will
 *                                  be created. Normally a div element.
 * @param {Object} data         An object containing parameters
 *                              {Array} nodes
 *                              {Array} edges
 * @param {Object} options      Options
 */
function Graph (container, data, options) {
  // create variables and set default values
  this.containerElement = container;
  this.width = '100%';
  this.height = '100%';
  // to give everything a nice fluidity, we seperate the rendering and calculating of the forces
  this.renderRefreshRate = 60; // hz (fps)
  this.renderTimestep = 1000 / this.renderRefreshRate; // ms -- saves calculation later on
  this.stabilize = true; // stabilize before displaying the graph
  this.selectable = true;

  this.forceFactor = 50000;

  // set constant values
  this.constants = {
    nodes: {
      radiusMin: 5,
      radiusMax: 20,
      radius: 5,
      distance: 100, // px
      shape: 'ellipse',
      image: undefined,
      widthMin: 16, // px
      widthMax: 64, // px
      fontColor: 'black',
      fontSize: 14, // px
      //fontFace: verdana,
      fontFace: 'arial',
      color: {
          border: '#2B7CE9',
          background: '#97C2FC',
        highlight: {
          border: '#2B7CE9',
          background: '#D2E5FF'
        }
      },
      borderColor: '#2B7CE9',
      backgroundColor: '#97C2FC',
      highlightColor: '#D2E5FF',
      group: undefined
    },
    edges: {
      widthMin: 1,
      widthMax: 15,
      width: 1,
      style: 'line',
      color: '#343434',
      fontColor: '#343434',
      fontSize: 14, // px
      fontFace: 'arial',
      //distance: 100, //px
      length: 100,   // px
      dash: {
        length: 10,
        gap: 5,
        altLength: undefined
      }
    },
    clustering: {                   // Per Node in Cluster = PNiC
      enabled: false,               // (Boolean)             | global on/off switch for clustering.
      initialMaxNumberOfNodes: 100, // (# nodes)             | if the initial amount of nodes is larger than this, we cluster until the total number is less than this threshold.
      absoluteMaxNumberOfNodes:500, // (# nodes)             | during calculate forces, we check if the total number of nodes is larger than this. If it is, cluster until reduced to reduceToMaxNumberOfNodes
      reduceToMaxNumberOfNodes:300, // (# nodes)             | during calculate forces, we check if the total number of nodes is larger than absoluteMaxNumberOfNodes. If it is, cluster until reduced to this
      chainThreshold: 0.4,          // (% of all drawn nodes)| maximum percentage of allowed chainnodes (long strings of connected nodes) within all nodes. (lower means less chains).
      clusterEdgeThreshold: 20,     // (px)                  | edge length threshold. if smaller, this node is clustered.
      sectorThreshold: 50,          // (# nodes in cluster)  | cluster size threshold. If larger, expanding in own sector.
      screenSizeThreshold: 0.2,     // (% of canvas)         | relative size threshold. If the width or height of a clusternode takes up this much of the screen, decluster node.
      fontSizeMultiplier: 4.0,      // (px PNiC)             | how much the cluster font size grows per node in cluster (in px).
      forceAmplification: 0.6,      // (multiplier PNiC)     | factor of increase fo the repulsion force of a cluster (per node in cluster).
      distanceAmplification: 0.2,   // (multiplier PNiC)     | factor how much the repulsion distance of a cluster increases (per node in cluster).
      edgeGrowth: 11,               // (px PNiC)             | amount of clusterSize connected to the edge is multiplied with this and added to edgeLength.
      clusterSizeWidthFactor:  10,  // (px PNiC)             | growth of the width  per node in cluster.
      clusterSizeHeightFactor: 10,  // (px PNiC)             | growth of the height per node in cluster.
      clusterSizeRadiusFactor: 10,  // (px PNiC)             | growth of the radius per node in cluster.
      activeAreaBoxSize: 100,       // (px)                  | box area around the curser where clusters are popped open.
      massTransferCoefficient: 1    // (multiplier)          | parent.mass += massTransferCoefficient * child.mass
    },
    navigationUI: {
      enabled: false,
      initiallyVisible: true,
      enableToggling: true,
      xMovementSpeed: 10,
      yMovementSpeed: 10,
      zoomMovementSpeed: 0.02,
      iconPath: this._getIconURL()
    },
    keyboardNavigation: {
      enabled: false
    },
    minVelocity: 1.0,   // px/s
    maxIterations: 1000  // maximum number of iteration to stabilize
  };

  // Node variables
  this.groups = new Groups(); // object with groups
  this.images = new Images(); // object with images
  this.images.setOnloadCallback(function () {
    graph._redraw();
  });

  // navigationUI variables
  this.UIvisible = this.constants.navigationUI.initiallyVisible;
  this.xIncrement = 0;
  this.yIncrement = 0;
  this.zoomIncrement = 0;

  // create a frame and canvas
  this._create();

  // apply options
  this.setOptions(options);

  // load the cluster system.   (mandatory, even when not using the cluster system, there are function calls to it)
  this._loadClusterSystem();

  // load the sector system.    (mandatory, fully integrated with Graph)
  this._loadSectorSystem();

  // load the selection system. (mandatory, required by Graph)
  this._loadSelectionSystem();

  // load the navigationUI system.        (mandatory, few function calls even when navigationUI is disabled (in this.setSize)
  this._loadUISystem();

  // bind keys. If disabled, this will not do anything;
  this._createKeyBinds();

  // other vars
  var graph = this;
  this.freezeSimulation = false;// freeze the simulation

  this.nodeIndices = [];        // array with all the indices of the nodes. Used to speed up forces calculation
  this.nodes = {};              // object with Node objects
  this.edges = {};              // object with Edge objects

  this.canvasTopLeft     = {"x": 0,"y": 0};   // coordinates of the top left of the canvas.     they will be set during _redraw.
  this.canvasBottomRight = {"x": 0,"y": 0};   // coordinates of the bottom right of the canvas. they will be set during _redraw

  this.areaCenter = {};               // object with x and y elements used for determining the center of the zoom action
  this.scale = 1;                     // defining the global scale variable in the constructor
  this.previousScale = this.scale;    // this is used to check if the zoom operation is zooming in or out
  this.lastPointerPosition = {"x": 0,"y": 0}; // this is used for keyboard navigation
  // TODO: create a counter to keep track on the number of nodes having values
  // TODO: create a counter to keep track on the number of nodes currently moving
  // TODO: create a counter to keep track on the number of edges having values

  this.nodesData = null;      // A DataSet or DataView
  this.edgesData = null;      // A DataSet or DataView

  // create event listeners used to subscribe on the DataSets of the nodes and edges
  var me = this;
  this.nodesListeners = {
    'add': function (event, params) {
      me._addNodes(params.items);
      me.start();
    },
    'update': function (event, params) {
      me._updateNodes(params.items);
      me.start();
    },
    'remove': function (event, params) {
      me._removeNodes(params.items);
      me.start();
    }
  };
  this.edgesListeners = {
    'add': function (event, params) {
      me._addEdges(params.items);
      me.start();
    },
    'update': function (event, params) {
      me._updateEdges(params.items);
      me.start();
    },
    'remove': function (event, params) {
      me._removeEdges(params.items);
      me.start();
    }
  };

  // properties of the data
  this.moving = false;    // True if any of the nodes have an undefined position
  this.timer = undefined;

  // load data (the disable start variable will be the same as the enabled clustering)
  this.setData(data,this.constants.clustering.enabled);

  // zoom so all data will fit on the screen
  this.zoomToFit(true);

  // if clustering is disabled, the simulation will have started in the setData function
  if (this.constants.clustering.enabled) {
    this.startWithClustering();
  }
}

/**
 * get the URL where the UI icons are located
 *
 * @returns {string}
 * @private
 */
Graph.prototype._getIconURL = function() {
  var scripts = document.getElementsByTagName( 'script' );
  var scriptNamePosition, srcPosition, imagePath;
  for (var i = 0; i < scripts.length; i++) {
    srcPosition = scripts[i].outerHTML.search("src");
    if (srcPosition != -1) {
      scriptNamePosition = util._getLowestPositiveNumber(scripts[i].outerHTML.search("vis.js"),
                                                  scripts[i].outerHTML.search("vis.min.js"));
      if (scriptNamePosition != -1) {
        imagePath = scripts[i].outerHTML.substring(srcPosition+5,scriptNamePosition).concat("UI_icons/");
        return imagePath;
      }
    }
  }
};


/**
 * Find the center position of the graph
 * @private
 */
Graph.prototype._getRange = function() {
  var minY = 1e9, maxY = -1e9, minX = 1e9, maxX = -1e9, node;
  for (var i = 0; i < this.nodeIndices.length; i++) {
    node = this.nodes[this.nodeIndices[i]];
    if (minX > (node.x - node.width)) {minX = node.x - node.width;}
    if (maxX < (node.x + node.width)) {maxX = node.x + node.width;}
    if (minY > (node.y - node.height)) {minY = node.y - node.height;}
    if (maxY < (node.y + node.height)) {maxY = node.y + node.height;}
  }
  return {minX: minX, maxX: maxX, minY: minY, maxY: maxY};
};


/**
 * @param {object} range = {minX: minX, maxX: maxX, minY: minY, maxY: maxY};
 * @returns {{x: number, y: number}}
 * @private
 */
Graph.prototype._findCenter = function(range) {
  var center = {x: (0.5 * (range.maxX + range.minX)),
                y: (0.5 * (range.maxY + range.minY))};
  return center;
};


/**
 * center the graph
 *
 * @param {object} range = {minX: minX, maxX: maxX, minY: minY, maxY: maxY};
 */
Graph.prototype._centerGraph = function(range) {
  var center = this._findCenter(range);

  center.x *= this.scale;
  center.y *= this.scale;
  center.x -= 0.5 * this.frame.canvas.clientWidth;
  center.y -= 0.5 * this.frame.canvas.clientHeight;

  this._setTranslation(-center.x,-center.y); // set at 0,0
};


/**
 * This function zooms out to fit all data on screen based on amount of nodes
 *
 * @param {Boolean} [initialZoom]  | zoom based on fitted formula or range, true = fitted, default = false;
 */
Graph.prototype.zoomToFit = function(initialZoom) {
  if (initialZoom === undefined) {
    initialZoom = false;
  }

  var numberOfNodes = this.nodeIndices.length;
  var range = this._getRange();

  if (initialZoom == true) {
    if (this.constants.clustering.enabled == true &&
        numberOfNodes >= this.constants.clustering.initialMaxNumberOfNodes) {
      var zoomLevel = 38.8467 / (numberOfNodes - 14.50184) + 0.0116; // this is obtained from fitting a dataset from 5 points with scale levels that looked good.
    }
    else {
      var zoomLevel = 42.54117319 / (numberOfNodes + 39.31966387) + 0.1944405; // this is obtained from fitting a dataset from 5 points with scale levels that looked good.
    }
  }
  else {
    var xDistance = (Math.abs(range.minX) + Math.abs(range.maxX)) * 1.1;
    var yDistance = (Math.abs(range.minY) + Math.abs(range.maxY)) * 1.1;

    var xZoomLevel = this.frame.canvas.clientWidth / xDistance;
    var yZoomLevel = this.frame.canvas.clientHeight / yDistance;

    zoomLevel = (xZoomLevel <= yZoomLevel) ? xZoomLevel : yZoomLevel;
  }

  if (zoomLevel > 1.0) {
    zoomLevel = 1.0;
  }

  this.pinch.mousewheelScale = zoomLevel;
  this._setScale(zoomLevel);
  this._centerGraph(range);
};


/**
 * Update the this.nodeIndices with the most recent node index list
 * @private
 */
Graph.prototype._updateNodeIndexList = function() {
  this._clearNodeIndexList();
  for (var idx in this.nodes) {
    if (this.nodes.hasOwnProperty(idx)) {
      this.nodeIndices.push(idx);
    }
  }
};


/**
 * Set nodes and edges, and optionally options as well.
 *
 * @param {Object} data              Object containing parameters:
 *                                   {Array | DataSet | DataView} [nodes] Array with nodes
 *                                   {Array | DataSet | DataView} [edges] Array with edges
 *                                   {String} [dot] String containing data in DOT format
 *                                   {Options} [options] Object with options
 * @param {Boolean} [disableStart]   | optional: disable the calling of the start function.
 */
Graph.prototype.setData = function(data, disableStart) {
  if (disableStart === undefined) {
    disableStart = false;
  }

  if (data && data.dot && (data.nodes || data.edges)) {
    throw new SyntaxError('Data must contain either parameter "dot" or ' +
        ' parameter pair "nodes" and "edges", but not both.');
  }

  // set options
  this.setOptions(data && data.options);

  // set all data
  if (data && data.dot) {
    // parse DOT file
    if(data && data.dot) {
      var dotData = vis.util.DOTToGraph(data.dot);
      this.setData(dotData);
      return;
    }
  }
  else {
    this._setNodes(data && data.nodes);
    this._setEdges(data && data.edges);
  }

  this._putDataInSector();

  if (!disableStart) {
    // find a stable position or start animating to a stable position
    if (this.stabilize) {
      this._doStabilize();
    }
    this.start();
  }
};

/**
 * Set options
 * @param {Object} options
 */
Graph.prototype.setOptions = function (options) {
  if (options) {
    // retrieve parameter values
    if (options.width !== undefined)           {this.width = options.width;}
    if (options.height !== undefined)          {this.height = options.height;}
    if (options.stabilize !== undefined)       {this.stabilize = options.stabilize;}
    if (options.selectable !== undefined)      {this.selectable = options.selectable;}

    if (options.clustering) {
      for (var prop in options.clustering) {
        if (options.clustering.hasOwnProperty(prop)) {
          this.constants.clustering[prop] = options.clustering[prop];
        }
      }
    }

    if (options.navigationUI) {
      for (var prop in options.navigationUI) {
        if (options.navigationUI.hasOwnProperty(prop)) {
          this.constants.navigationUI[prop] = options.navigationUI[prop];
        }
      }
    }

    // TODO: work out these options and document them
    if (options.edges) {
      for (prop in options.edges) {
        if (options.edges.hasOwnProperty(prop)) {
          this.constants.edges[prop] = options.edges[prop];
        }
      }

      if (options.edges.length !== undefined &&
          options.nodes && options.nodes.distance === undefined) {
        this.constants.edges.length   = options.edges.length;
        this.constants.nodes.distance = options.edges.length * 1.25;
      }

      if (!options.edges.fontColor) {
        this.constants.edges.fontColor = options.edges.color;
      }

      // Added to support dashed lines
      // David Jordan
      // 2012-08-08
      if (options.edges.dash) {
        if (options.edges.dash.length !== undefined) {
          this.constants.edges.dash.length = options.edges.dash.length;
        }
        if (options.edges.dash.gap !== undefined) {
          this.constants.edges.dash.gap = options.edges.dash.gap;
        }
        if (options.edges.dash.altLength !== undefined) {
          this.constants.edges.dash.altLength = options.edges.dash.altLength;
        }
      }
    }

    if (options.nodes) {
      for (prop in options.nodes) {
        if (options.nodes.hasOwnProperty(prop)) {
          this.constants.nodes[prop] = options.nodes[prop];
        }
      }

      if (options.nodes.color) {
        this.constants.nodes.color = Node.parseColor(options.nodes.color);
      }

      /*
       if (options.nodes.widthMin) this.constants.nodes.radiusMin = options.nodes.widthMin;
       if (options.nodes.widthMax) this.constants.nodes.radiusMax = options.nodes.widthMax;
       */
    }
    if (options.groups) {
      for (var groupname in options.groups) {
        if (options.groups.hasOwnProperty(groupname)) {
          var group = options.groups[groupname];
          this.groups.add(groupname, group);
        }
      }
    }
  }

  this.setSize(this.width, this.height);
  this._setTranslation(this.frame.clientWidth / 2, this.frame.clientHeight / 2);
  this._setScale(1);
};

/**
 * fire an event
 * @param {String} event   The name of an event, for example 'select'
 * @param {Object} params  Optional object with event parameters
 * @private
 */
Graph.prototype._trigger = function (event, params) {
  events.trigger(this, event, params);
};


/**
 * Create the main frame for the Graph.
 * This function is executed once when a Graph object is created. The frame
 * contains a canvas, and this canvas contains all objects like the axis and
 * nodes.
 * @private
 */
Graph.prototype._create = function () {
  // remove all elements from the container element.
  while (this.containerElement.hasChildNodes()) {
    this.containerElement.removeChild(this.containerElement.firstChild);
  }

  this.frame = document.createElement('div');
  this.frame.className = 'graph-frame';
  this.frame.style.position = 'relative';
  this.frame.style.overflow = 'hidden';

  // create the graph canvas (HTML canvas element)
  this.frame.canvas = document.createElement( 'canvas' );
  this.frame.canvas.style.position = 'relative';
  this.frame.appendChild(this.frame.canvas);
  if (!this.frame.canvas.getContext) {
    var noCanvas = document.createElement( 'DIV' );
    noCanvas.style.color = 'red';
    noCanvas.style.fontWeight =  'bold' ;
    noCanvas.style.padding =  '10px';
    noCanvas.innerHTML =  'Error: your browser does not support HTML canvas';
    this.frame.canvas.appendChild(noCanvas);
  }

  var me = this;
  this.drag = {};
  this.pinch = {};
  this.hammer = Hammer(this.frame.canvas, {
    prevent_default: true
  });
  this.hammer.on('tap',       me._onTap.bind(me) );
  this.hammer.on('doubletap', me._onDoubleTap.bind(me) );
  this.hammer.on('hold',      me._onHold.bind(me) );
  this.hammer.on('pinch',     me._onPinch.bind(me) );
  this.hammer.on('touch',     me._onTouch.bind(me) );
  this.hammer.on('dragstart', me._onDragStart.bind(me) );
  this.hammer.on('drag',      me._onDrag.bind(me) );
  this.hammer.on('dragend',   me._onDragEnd.bind(me) );
  this.hammer.on('release',   me._onRelease.bind(me) );
  this.hammer.on('mousewheel',me._onMouseWheel.bind(me) );
  this.hammer.on('DOMMouseScroll',me._onMouseWheel.bind(me) ); // for FF
  this.hammer.on('mousemove', me._onMouseMoveTitle.bind(me) );

  // add the frame to the container element
  this.containerElement.appendChild(this.frame);
};


/**
 * Binding the keys for keyboard navigation. These functions are defined in the UIMixin
 * @private
 */
Graph.prototype._createKeyBinds = function() {
  var me = this;
  this.mousetrap = mousetrap;

  if (this.constants.navigationUI.enabled == true &&
      this.constants.navigationUI.enableToggling == true) {
    this.mousetrap.bind("u",this._toggleUI.bind(me)     , "keydown");
  }

  if (this.constants.keyboardNavigation.enabled == true) {
    this.mousetrap.bind("up",   this._moveUp.bind(me)   , "keydown");
    this.mousetrap.bind("up",   this._yStopMoving.bind(me), "keyup");
    this.mousetrap.bind("down", this._moveDown.bind(me) , "keydown");
    this.mousetrap.bind("down", this._yStopMoving.bind(me), "keyup");
    this.mousetrap.bind("left", this._moveLeft.bind(me) , "keydown");
    this.mousetrap.bind("left", this._xStopMoving.bind(me), "keyup");
    this.mousetrap.bind("right",this._moveRight.bind(me), "keydown");
    this.mousetrap.bind("right",this._xStopMoving.bind(me), "keyup");
    this.mousetrap.bind("=",    this._zoomIn.bind(me),    "keydown");
    this.mousetrap.bind("=",    this._stopZoom.bind(me),    "keyup");
    this.mousetrap.bind("-",    this._zoomOut.bind(me),   "keydown");
    this.mousetrap.bind("-",    this._stopZoom.bind(me),    "keyup");
    this.mousetrap.bind("[",    this._zoomIn.bind(me),    "keydown");
    this.mousetrap.bind("[",    this._stopZoom.bind(me),    "keyup");
    this.mousetrap.bind("]",    this._zoomOut.bind(me),   "keydown");
    this.mousetrap.bind("]",    this._stopZoom.bind(me),    "keyup");
    this.mousetrap.bind("pageup",this._zoomIn.bind(me),   "keydown");
    this.mousetrap.bind("pageup",this._stopZoom.bind(me),   "keyup");
    this.mousetrap.bind("pagedown",this._zoomOut.bind(me),"keydown");
    this.mousetrap.bind("pagedown",this._stopZoom.bind(me), "keyup");
  }
  /*
   this.mousetrap.bind("=",this.decreaseClusterLevel.bind(me));
   this.mousetrap.bind("-",this.increaseClusterLevel.bind(me));
   this.mousetrap.bind("s",this.singleStep.bind(me));
   this.mousetrap.bind("h",this.updateClustersDefault.bind(me));
   this.mousetrap.bind("c",this._collapseSector.bind(me));
   this.mousetrap.bind("f",this.toggleFreeze.bind(me));
   */
}

/**
 * Get the pointer location from a touch location
 * @param {{pageX: Number, pageY: Number}} touch
 * @return {{x: Number, y: Number}} pointer
 * @private
 */
Graph.prototype._getPointer = function (touch) {
  return {
    x: touch.pageX - vis.util.getAbsoluteLeft(this.frame.canvas),
    y: touch.pageY - vis.util.getAbsoluteTop(this.frame.canvas)
  };
};

/**
 * On start of a touch gesture, store the pointer
 * @param event
 * @private
 */
Graph.prototype._onTouch = function (event) {
  this.drag.pointer = this._getPointer(event.gesture.touches[0]);
  this.drag.pinched = false;
  this.pinch.scale = this._getScale();

  this._handleTouch(this.drag.pointer);
};

/**
 * handle drag start event
 * @private
 */
Graph.prototype._onDragStart = function () {
  var drag = this.drag;
  var node = this._getNodeAt(drag.pointer);
  // note: drag.pointer is set in _onTouch to get the initial touch location

  drag.selection = [];
  drag.translation = this._getTranslation();
  drag.nodeId = null;

  if (node != null) {
    drag.nodeId = node.id;
    // select the clicked node if not yet selected
    if (!node.isSelected()) {
      this._selectNode(node,false);
    }

    // create an array with the selected nodes and their original location and status
    var me = this;
    this.selection.forEach(function (id) {
      var node = me.nodes[id];
      if (node) {
        var s = {
          id: id,
          node: node,

          // store original x, y, xFixed and yFixed, make the node temporarily Fixed
          x: node.x,
          y: node.y,
          xFixed: node.xFixed,
          yFixed: node.yFixed
        };

        node.xFixed = true;
        node.yFixed = true;

        drag.selection.push(s);
      }
    });
  }
};

/**
 * handle drag event
 * @private
 */
Graph.prototype._onDrag = function (event) {
  if (this.drag.pinched) {
    return;
  }

  var pointer = this._getPointer(event.gesture.touches[0]);

  var me = this,
      drag = this.drag,
      selection = drag.selection;
  if (selection && selection.length) {
    // calculate delta's and new location
    var deltaX = pointer.x - drag.pointer.x,
        deltaY = pointer.y - drag.pointer.y;

    // update position of all selected nodes
    selection.forEach(function (s) {
      var node = s.node;

      if (!s.xFixed) {
        node.x = me._canvasToX(me._xToCanvas(s.x) + deltaX);
      }

      if (!s.yFixed) {
        node.y = me._canvasToY(me._yToCanvas(s.y) + deltaY);
      }
    });

    // start animation if not yet running
    if (!this.moving) {
      this.moving = true;
      this.start();
    }
  }
  else {
    // move the graph
    var diffX = pointer.x - this.drag.pointer.x;
    var diffY = pointer.y - this.drag.pointer.y;

    this._setTranslation(
        this.drag.translation.x + diffX,
        this.drag.translation.y + diffY);
    this._redraw();
    this.moved = true;
  }
};

/**
 * handle drag start event
 * @private
 */
Graph.prototype._onDragEnd = function () {
  var selection = this.drag.selection;
  if (selection) {
    selection.forEach(function (s) {
      // restore original xFixed and yFixed
      s.node.xFixed = s.xFixed;
      s.node.yFixed = s.yFixed;
    });
  }
};

/**
 * handle tap/click event: select/unselect a node
 * @private
 */
Graph.prototype._onTap = function (event) {
  var pointer = this._getPointer(event.gesture.touches[0]);
  this._handleTap(pointer);
};


/**
 * handle doubletap event
 * @private
 */
Graph.prototype._onDoubleTap = function (event) {
  var pointer = this._getPointer(event.gesture.touches[0]);
  this._handleDoubleTap(pointer);

};


/**
 * handle long tap event: multi select nodes
 * @private
 */
Graph.prototype._onHold = function (event) {
  var pointer = this._getPointer(event.gesture.touches[0]);
  this._handleOnHold(pointer);
};

/**
 * handle the release of the screen
 *
 * @param event
 * @private
 */
Graph.prototype._onRelease = function (event) {
  this._handleOnRelease();
};

/**
 * Handle pinch event
 * @param event
 * @private
 */
Graph.prototype._onPinch = function (event) {
  var pointer = this._getPointer(event.gesture.center);

  this.drag.pinched = true;
  if (!('scale' in this.pinch)) {
    this.pinch.scale = 1;
  }

  // TODO: enabled moving while pinching?
  var scale = this.pinch.scale * event.gesture.scale;
  this._zoom(scale, pointer)
};

/**
 * Zoom the graph in or out
 * @param {Number} scale a number around 1, and between 0.01 and 10
 * @param {{x: Number, y: Number}} pointer
 * @return {Number} appliedScale    scale is limited within the boundaries
 * @private
 */
Graph.prototype._zoom = function(scale, pointer) {
  var scaleOld = this._getScale();
  if (scale < 0.00001) {
    scale = 0.00001;
  }
  if (scale > 10) {
    scale = 10;
  }
// + this.frame.canvas.clientHeight / 2
  var translation = this._getTranslation();

  var scaleFrac = scale / scaleOld;
  var tx = (1 - scaleFrac) * pointer.x + translation.x * scaleFrac;
  var ty = (1 - scaleFrac) * pointer.y + translation.y * scaleFrac;

  this.areaCenter = {"x" : this._canvasToX(pointer.x),
                     "y" : this._canvasToY(pointer.y)};

 // this.areaCenter = {"x" : pointer.x,"y" : pointer.y };
//  console.log(translation.x,translation.y,pointer.x,pointer.y,scale);
  this.pinch.mousewheelScale = scale;
  this._setScale(scale);
  this._setTranslation(tx, ty);
  this.updateClustersDefault();
  this._redraw();

  return scale;
};

/**
 * Event handler for mouse wheel event, used to zoom the timeline
 * See http://adomas.org/javascript-mouse-wheel/
 *     https://github.com/EightMedia/hammer.js/issues/256
 * @param {MouseEvent}  event
 * @private
 */
Graph.prototype._onMouseWheel = function(event) {
  // retrieve delta
  var delta = 0;
  if (event.wheelDelta) { /* IE/Opera. */
    delta = event.wheelDelta/120;
  } else if (event.detail) { /* Mozilla case. */
    // In Mozilla, sign of delta is different than in IE.
    // Also, delta is multiple of 3.
    delta = -event.detail/3;
  }

  // If delta is nonzero, handle it.
  // Basically, delta is now positive if wheel was scrolled up,
  // and negative, if wheel was scrolled down.
  if (delta) {
    if (!('mousewheelScale' in this.pinch)) {
      this.pinch.mousewheelScale = 1;
    }

    // calculate the new scale
    var scale = this.pinch.mousewheelScale;
    var zoom = delta / 10;
    if (delta < 0) {
      zoom = zoom / (1 - zoom);
    }
    scale *= (1 + zoom);

    // calculate the pointer location
    var gesture = util.fakeGesture(this, event);
    var pointer = this._getPointer(gesture.center);

    // apply the new scale
    scale = this._zoom(scale, pointer);

    // store the new, applied scale -- this is now done in _zoom
//    this.pinch.mousewheelScale = scale;
  }

  // Prevent default actions caused by mouse wheel.
  event.preventDefault();
};


/**
 * Mouse move handler for checking whether the title moves over a node with a title.
 * @param  {Event} event
 * @private
 */
Graph.prototype._onMouseMoveTitle = function (event) {
  var gesture = util.fakeGesture(this, event);
  var pointer = this._getPointer(gesture.center);

  this.lastPointerPosition = pointer;

  // check if the previously selected node is still selected
  if (this.popupNode) {
    this._checkHidePopup(pointer);
  }

  // start a timeout that will check if the mouse is positioned above
  // an element
  var me = this;
  var checkShow = function() {
    me._checkShowPopup(pointer);
  };
  if (this.popupTimer) {
    clearInterval(this.popupTimer); // stop any running calculationTimer
  }
  if (!this.leftButtonDown) {
    this.popupTimer = setTimeout(checkShow, 300);
  }
};

/**
 * Check if there is an element on the given position in the graph
 * (a node or edge). If so, and if this element has a title,
 * show a popup window with its title.
 *
 * @param {{x:Number, y:Number}} pointer
 * @private
 */
Graph.prototype._checkShowPopup = function (pointer) {
  var obj = {
    left:   this._canvasToX(pointer.x),
    top:    this._canvasToY(pointer.y),
    right:  this._canvasToX(pointer.x),
    bottom: this._canvasToY(pointer.y)
  };

  var id;
  var lastPopupNode = this.popupNode;

  if (this.popupNode == undefined) {
    // search the nodes for overlap, select the top one in case of multiple nodes
    var nodes = this.nodes;
    for (id in nodes) {
      if (nodes.hasOwnProperty(id)) {
        var node = nodes[id];
        if (node.getTitle() !== undefined && node.isOverlappingWith(obj)) {
          this.popupNode = node;
          break;
        }
      }
    }
  }

  if (this.popupNode === undefined) {
    // search the edges for overlap
    var edges = this.edges;
    for (id in edges) {
      if (edges.hasOwnProperty(id)) {
        var edge = edges[id];
        if (edge.connected && (edge.getTitle() !== undefined) &&
            edge.isOverlappingWith(obj)) {
          this.popupNode = edge;
          break;
        }
      }
    }
  }

  if (this.popupNode) {
    // show popup message window
    if (this.popupNode != lastPopupNode) {
      var me = this;
      if (!me.popup) {
        me.popup = new Popup(me.frame);
      }

      // adjust a small offset such that the mouse cursor is located in the
      // bottom left location of the popup, and you can easily move over the
      // popup area
      me.popup.setPosition(pointer.x - 3, pointer.y - 3);
      me.popup.setText(me.popupNode.getTitle());
      me.popup.show();
    }
  }
  else {
    if (this.popup) {
      this.popup.hide();
    }
  }
};

/**
 * Check if the popup must be hided, which is the case when the mouse is no
 * longer hovering on the object
 * @param {{x:Number, y:Number}} pointer
 * @private
 */
Graph.prototype._checkHidePopup = function (pointer) {
  if (!this.popupNode || !this._getNodeAt(pointer) ) {
    this.popupNode = undefined;
    if (this.popup) {
      this.popup.hide();
    }
  }
};


/**
 * Temporary method to test calculating a hub value for the nodes
 * @param {number} level        Maximum number edges between two nodes in order
 *                              to call them connected. Optional, 1 by default
 * @return {Number[]} connectioncount array with the connection count
 *                                    for each node
 * @private
 */
Graph.prototype._getConnectionCount = function(level) {
  if (level == undefined) {
    level = 1;
  }

  // get the nodes connected to given nodes
  function getConnectedNodes(nodes) {
    var connectedNodes = [];

    for (var j = 0, jMax = nodes.length; j < jMax; j++) {
      var node = nodes[j];

      // find all nodes connected to this node
      var edges = node.edges;
      for (var i = 0, iMax = edges.length; i < iMax; i++) {
        var edge = edges[i];
        var other = null;

        // check if connected
        if (edge.from == node)
          other = edge.to;
        else if (edge.to == node)
          other = edge.from;

        // check if the other node is not already in the list with nodes
        var k, kMax;
        if (other) {
          for (k = 0, kMax = nodes.length; k < kMax; k++) {
            if (nodes[k] == other) {
              other = null;
              break;
            }
          }
        }
        if (other) {
          for (k = 0, kMax = connectedNodes.length; k < kMax; k++) {
            if (connectedNodes[k] == other) {
              other = null;
              break;
            }
          }
        }

        if (other)
          connectedNodes.push(other);
      }
    }

    return connectedNodes;
  }

  var connections = [];
  var nodes = this.nodes;
  for (var id in nodes) {
    if (nodes.hasOwnProperty(id)) {
      var c = [nodes[id]];
      for (var l = 0; l < level; l++) {
        c = c.concat(getConnectedNodes(c));
      }
      connections.push(c);
    }
  }

  var hubs = [];
  for (var i = 0, len = connections.length; i < len; i++) {
    hubs.push(connections[i].length);
  }

  return hubs;
};

/**
 * Set a new size for the graph
 * @param {string} width   Width in pixels or percentage (for example '800px'
 *                         or '50%')
 * @param {string} height  Height in pixels or percentage  (for example '400px'
 *                         or '30%')
 */
Graph.prototype.setSize = function(width, height) {
  this.frame.style.width = width;
  this.frame.style.height = height;

  this.frame.canvas.style.width = '100%';
  this.frame.canvas.style.height = '100%';

  this.frame.canvas.width = this.frame.canvas.clientWidth;
  this.frame.canvas.height = this.frame.canvas.clientHeight;

  if (this.constants.navigationUI.enabled == true) {
    this._relocateUI();
  }
};

/**
 * Set a data set with nodes for the graph
 * @param {Array | DataSet | DataView} nodes         The data containing the nodes.
 * @private
 */
Graph.prototype._setNodes = function(nodes) {
  var oldNodesData = this.nodesData;

  if (nodes instanceof DataSet || nodes instanceof DataView) {
    this.nodesData = nodes;
  }
  else if (nodes instanceof Array) {
    this.nodesData = new DataSet();
    this.nodesData.add(nodes);
  }
  else if (!nodes) {
    this.nodesData = new DataSet();
  }
  else {
    throw new TypeError('Array or DataSet expected');
  }

  if (oldNodesData) {
    // unsubscribe from old dataset
    util.forEach(this.nodesListeners, function (callback, event) {
      oldNodesData.unsubscribe(event, callback);
    });
  }

  // remove drawn nodes
  this.nodes = {};

  if (this.nodesData) {
    // subscribe to new dataset
    var me = this;
    util.forEach(this.nodesListeners, function (callback, event) {
      me.nodesData.subscribe(event, callback);
    });

    // draw all new nodes
    var ids = this.nodesData.getIds();
    this._addNodes(ids);
  }
  this._updateSelection();
};

/**
 * Add nodes
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._addNodes = function(ids) {
  var id;
  for (var i = 0, len = ids.length; i < len; i++) {
    id = ids[i];
    var data = this.nodesData.get(id);
    var node = new Node(data, this.images, this.groups, this.constants);
    this.nodes[id] = node; // note: this may replace an existing node

    if (!node.isFixed()) {
      // TODO: position new nodes in a smarter way!
      var radius = this.constants.edges.length * 2;
      var count = ids.length;
      var angle = 2 * Math.PI * (i / count);
      node.x = radius * Math.cos(angle);
      node.y = radius * Math.sin(angle);

      // note: no not use node.isMoving() here, as that gives the current
      // velocity of the node, which is zero after creation of the node.
      this.moving = true;
    }
  }
  this._updateNodeIndexList();
  this._reconnectEdges();
  this._updateValueRange(this.nodes);
};

/**
 * Update existing nodes, or create them when not yet existing
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._updateNodes = function(ids) {
  var nodes = this.nodes,
      nodesData = this.nodesData;
  for (var i = 0, len = ids.length; i < len; i++) {
    var id = ids[i];
    var node = nodes[id];
    var data = nodesData.get(id);
    if (node) {
      // update node
      node.setProperties(data, this.constants);
    }
    else {
      // create node
      node = new Node(properties, this.images, this.groups, this.constants);
      nodes[id] = node;

      if (!node.isFixed()) {
        this.moving = true;
      }
    }
  }
  this._updateNodeIndexList();
  this._reconnectEdges();
  this._updateValueRange(nodes);
};

/**
 * Remove existing nodes. If nodes do not exist, the method will just ignore it.
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._removeNodes = function(ids) {
  var nodes = this.nodes;
  for (var i = 0, len = ids.length; i < len; i++) {
    var id = ids[i];
    delete nodes[id];
  }
  this._updateNodeIndexList();
  this._reconnectEdges();
  this._updateSelection();
  this._updateValueRange(nodes);
};

/**
 * Load edges by reading the data table
 * @param {Array | DataSet | DataView} edges    The data containing the edges.
 * @private
 * @private
 */
Graph.prototype._setEdges = function(edges) {
  var oldEdgesData = this.edgesData;

  if (edges instanceof DataSet || edges instanceof DataView) {
    this.edgesData = edges;
  }
  else if (edges instanceof Array) {
    this.edgesData = new DataSet();
    this.edgesData.add(edges);
  }
  else if (!edges) {
    this.edgesData = new DataSet();
  }
  else {
    throw new TypeError('Array or DataSet expected');
  }

  if (oldEdgesData) {
    // unsubscribe from old dataset
    util.forEach(this.edgesListeners, function (callback, event) {
      oldEdgesData.unsubscribe(event, callback);
    });
  }

  // remove drawn edges
  this.edges = {};

  if (this.edgesData) {
    // subscribe to new dataset
    var me = this;
    util.forEach(this.edgesListeners, function (callback, event) {
      me.edgesData.subscribe(event, callback);
    });

    // draw all new nodes
    var ids = this.edgesData.getIds();
    this._addEdges(ids);
  }

  this._reconnectEdges();
};

/**
 * Add edges
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._addEdges = function (ids) {
  var edges = this.edges,
      edgesData = this.edgesData;

  for (var i = 0, len = ids.length; i < len; i++) {
    var id = ids[i];

    var oldEdge = edges[id];
    if (oldEdge) {
      oldEdge.disconnect();
    }

    var data = edgesData.get(id, {"showInternalIds" : true});
    edges[id] = new Edge(data, this, this.constants);
  }

  this.moving = true;
  this._updateValueRange(edges);
};

/**
 * Update existing edges, or create them when not yet existing
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._updateEdges = function (ids) {
  var edges = this.edges,
      edgesData = this.edgesData;
  for (var i = 0, len = ids.length; i < len; i++) {
    var id = ids[i];

    var data = edgesData.get(id);
    var edge = edges[id];
    if (edge) {
      // update edge
      edge.disconnect();
      edge.setProperties(data, this.constants);
      edge.connect();
    }
    else {
      // create edge
      edge = new Edge(data, this, this.constants);
      this.edges[id] = edge;
    }
  }

  this.moving = true;
  this._updateValueRange(edges);
};

/**
 * Remove existing edges. Non existing ids will be ignored
 * @param {Number[] | String[]} ids
 * @private
 */
Graph.prototype._removeEdges = function (ids) {
  var edges = this.edges;
  for (var i = 0, len = ids.length; i < len; i++) {
    var id = ids[i];
    var edge = edges[id];
    if (edge) {
      edge.disconnect();
      delete edges[id];
    }
  }

  this.moving = true;
  this._updateValueRange(edges);
};

/**
 * Reconnect all edges
 * @private
 */
Graph.prototype._reconnectEdges = function() {
  var id,
      nodes = this.nodes,
      edges = this.edges;
  for (id in nodes) {
    if (nodes.hasOwnProperty(id)) {
      nodes[id].edges = [];
    }
  }

  for (id in edges) {
    if (edges.hasOwnProperty(id)) {
      var edge = edges[id];
      edge.from = null;
      edge.to = null;
      edge.connect();
    }
  }
};

/**
 * Update the values of all object in the given array according to the current
 * value range of the objects in the array.
 * @param {Object} obj    An object containing a set of Edges or Nodes
 *                        The objects must have a method getValue() and
 *                        setValueRange(min, max).
 * @private
 */
Graph.prototype._updateValueRange = function(obj) {
  var id;

  // determine the range of the objects
  var valueMin = undefined;
  var valueMax = undefined;
  for (id in obj) {
    if (obj.hasOwnProperty(id)) {
      var value = obj[id].getValue();
      if (value !== undefined) {
        valueMin = (valueMin === undefined) ? value : Math.min(value, valueMin);
        valueMax = (valueMax === undefined) ? value : Math.max(value, valueMax);
      }
    }
  }

  // adjust the range of all objects
  if (valueMin !== undefined && valueMax !== undefined) {
    for (id in obj) {
      if (obj.hasOwnProperty(id)) {
        obj[id].setValueRange(valueMin, valueMax);
      }
    }
  }
};

/**
 * Redraw the graph with the current data
 * chart will be resized too.
 */
Graph.prototype.redraw = function() {
  this.setSize(this.width, this.height);

  this._redraw();
};

/**
 * Redraw the graph with the current data
 * @private
 */
Graph.prototype._redraw = function() {
  var ctx = this.frame.canvas.getContext('2d');

  // clear the canvas
  var w = this.frame.canvas.width;
  var h = this.frame.canvas.height;
  ctx.clearRect(0, 0, w, h);

  // set scaling and translation
  ctx.save();
  ctx.translate(this.translation.x, this.translation.y);
  ctx.scale(this.scale, this.scale);

  this.canvasTopLeft = {"x": this._canvasToX(0),
                        "y": this._canvasToY(0)};
  this.canvasBottomRight = {"x": this._canvasToX(this.frame.canvas.clientWidth),
                            "y": this._canvasToY(this.frame.canvas.clientHeight)};

  this._doInAllSectors("_drawAllSectorNodes",ctx);
  this._doInAllSectors("_drawEdges",ctx);
  this._doInAllSectors("_drawNodes",ctx);

  // restore original scaling and translation
  ctx.restore();

  if (this.UIvisible == true) {
    this._doInUISector("_drawNodes",ctx,true);
  }
};

/**
 * Set the translation of the graph
 * @param {Number} offsetX    Horizontal offset
 * @param {Number} offsetY    Vertical offset
 * @private
 */
Graph.prototype._setTranslation = function(offsetX, offsetY) {
  if (this.translation === undefined) {
    this.translation = {
      x: 0,
      y: 0
    };
  }

  if (offsetX !== undefined) {
    this.translation.x = offsetX;
  }
  if (offsetY !== undefined) {
    this.translation.y = offsetY;
  }
};

/**
 * Get the translation of the graph
 * @return {Object} translation    An object with parameters x and y, both a number
 * @private
 */
Graph.prototype._getTranslation = function() {
  return {
    x: this.translation.x,
    y: this.translation.y
  };
};

/**
 * Scale the graph
 * @param {Number} scale   Scaling factor 1.0 is unscaled
 * @private
 */
Graph.prototype._setScale = function(scale) {
  this.scale = scale;
};

/**
 * Get the current scale of  the graph
 * @return {Number} scale   Scaling factor 1.0 is unscaled
 * @private
 */
Graph.prototype._getScale = function() {
  return this.scale;
};

/**
 * Convert a horizontal point on the HTML canvas to the x-value of the model
 * @param {number} x
 * @returns {number}
 * @private
 */
Graph.prototype._canvasToX = function(x) {
  return (x - this.translation.x) / this.scale;
};

/**
 * Convert an x-value in the model to a horizontal point on the HTML canvas
 * @param {number} x
 * @returns {number}
 * @private
 */
Graph.prototype._xToCanvas = function(x) {
  return x * this.scale + this.translation.x;
};

/**
 * Convert a vertical point on the HTML canvas to the y-value of the model
 * @param {number} y
 * @returns {number}
 * @private
 */
Graph.prototype._canvasToY = function(y) {
  return (y - this.translation.y) / this.scale;
};

/**
 * Convert an y-value in the model to a vertical point on the HTML canvas
 * @param {number} y
 * @returns {number}
 * @private
 */
Graph.prototype._yToCanvas = function(y) {
  return y * this.scale + this.translation.y ;
};

/**
 * Redraw all nodes
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext('2d');
 * @param {CanvasRenderingContext2D}   ctx
 * @param {Boolean} [alwaysShow]
 * @private
 */
Graph.prototype._drawNodes = function(ctx,alwaysShow) {
  if (alwaysShow === undefined) {
    alwaysShow = false;
  }

  // first draw the unselected nodes
  var nodes = this.nodes;
  var selected = [];

  for (var id in nodes) {
    if (nodes.hasOwnProperty(id)) {
      nodes[id].setScaleAndPos(this.scale,this.canvasTopLeft,this.canvasBottomRight);
      if (nodes[id].isSelected()) {
        selected.push(id);
      }
      else {
        if (nodes[id].inArea() || alwaysShow) {
          nodes[id].draw(ctx);
        }
      }
    }
  }

  // draw the selected nodes on top
  for (var s = 0, sMax = selected.length; s < sMax; s++) {
    if (nodes[selected[s]].inArea() || alwaysShow) {
      nodes[selected[s]].draw(ctx);
    }
  }
};

/**
 * Redraw all edges
 * The 2d context of a HTML canvas can be retrieved by canvas.getContext('2d');
 * @param {CanvasRenderingContext2D}   ctx
 * @private
 */
Graph.prototype._drawEdges = function(ctx) {
  var edges = this.edges;
  for (var id in edges) {
    if (edges.hasOwnProperty(id)) {
      var edge = edges[id];
      edge.setScale(this.scale);
      if (edge.connected) {
        edges[id].draw(ctx);
      }
    }
  }
};

/**
 * Find a stable position for all nodes
 * @private
 */
Graph.prototype._doStabilize = function() {
  //var start = new Date();

  // find stable position
  var count = 0;
  var vmin = this.constants.minVelocity;
  var stable = false;
  while (!stable && count < this.constants.maxIterations) {
    this._initializeForceCalculation();
    this._discreteStepNodes();
    stable = !this._isMoving(vmin);
    count++;
  }
  this.zoomToFit();

 // var end = new Date();

  // console.log('Stabilized in ' + (end-start) + ' ms, ' + count + ' iterations' ); // TODO: cleanup
};


/**
 * Before calculating the forces, we check if we need to cluster to keep up performance and we check
 * if there is more than one node. If it is just one node, we dont calculate anything.
 *
 * @private
 */
Graph.prototype._initializeForceCalculation = function() {
  // stop calculation if there is only one node
  if (this.nodeIndices.length == 1) {
    this.nodes[this.nodeIndices[0]]._setForce(0,0);
  }
  else {
    // if there are too many nodes on screen, we cluster without repositioning
    if (this.nodeIndices.length > this.constants.clustering.absoluteMaxNumberOfNodes && this.constants.clustering.enabled == true) {
      this.clusterToFit(this.constants.clustering.reduceToMaxNumberOfNodes, false);
    }

    // we now start the force calculation
    this._calculateForces();
  }
};


/**
 * Calculate the external forces acting on the nodes
 * Forces are caused by: edges, repulsing forces between nodes, gravity
 * @private
 */
Graph.prototype._calculateForces = function() {
  var screenCenterPos = {"x":(0.5*(this.canvasTopLeft.x + this.canvasBottomRight.x)),
                         "y":(0.5*(this.canvasTopLeft.y + this.canvasBottomRight.y))}
  // create a local edge to the nodes and edges, that is faster
  var dx, dy, angle, distance, fx, fy,
    repulsingForce, springForce, length, edgeLength,
    node, node1, node2, edge, edgeId, i, j, nodeId, xCenter, yCenter;
  var clusterSize;
  var nodes = this.nodes;
  var edges = this.edges;

  // Gravity is required to keep separated groups from floating off
  // the forces are reset to zero in this loop by using _setForce instead
  // of _addForce
  var gravity = 0.10 * this.forceFactor;
  for (i = 0; i < this.nodeIndices.length; i++) {
      node = nodes[this.nodeIndices[i]];
      // gravity does not apply when we are in a pocket sector
      if (this._sector() == "default") {
        dx = -node.x + screenCenterPos.x;
        dy = -node.y + screenCenterPos.y;

        angle = Math.atan2(dy, dx);
        fx = Math.cos(angle) * gravity;
        fy = Math.sin(angle) * gravity;
      }
      else {
        fx = 0;
        fy = 0;
      }
      node._setForce(fx, fy);

      node.updateDamping(this.nodeIndices.length);
  }

  // repulsing forces between nodes
  var minimumDistance = this.constants.nodes.distance,
      steepness = 10; // higher value gives steeper slope of the force around the given minimumDistance


  // we loop from i over all but the last entree in the array
  // j loops from i+1 to the last. This way we do not double count any of the indices, nor i == j
  for (i = 0; i < this.nodeIndices.length-1; i++) {
    node1 = nodes[this.nodeIndices[i]];
    for (j = i+1; j < this.nodeIndices.length; j++) {
      node2 = nodes[this.nodeIndices[j]];
      clusterSize = (node1.clusterSize + node2.clusterSize - 2);
      dx = node2.x - node1.x;
      dy = node2.y - node1.y;
      distance = Math.sqrt(dx * dx + dy * dy);


      // clusters have a larger region of influence
      minimumDistance = (clusterSize == 0) ? this.constants.nodes.distance : (this.constants.nodes.distance * (1 + clusterSize * this.constants.clustering.distanceAmplification));
      if (distance < 2*minimumDistance) { // at 2.0 * the minimum distance, the force is 0.000045
        angle = Math.atan2(dy, dx);

        if (distance < 0.5*minimumDistance) { // at 0.5 * the minimum distance, the force is 0.993307
          repulsingForce = 1.0;
        }
        else {
          // TODO: correct factor for repulsing force
          //repulsingForce = 2 * Math.exp(-5 * (distance * distance) / (dmin * dmin) ); // TODO: customize the repulsing force
          //repulsingForce = Math.exp(-1 * (distance * distance) / (dmin * dmin) ); // TODO: customize the repulsing force
          repulsingForce = 1 / (1 + Math.exp((distance / minimumDistance - 1) * steepness)); // TODO: customize the repulsing force
        }
        // amplify the repulsion for clusters.
        repulsingForce *= (clusterSize == 0) ? 1 : 1 + clusterSize * this.constants.clustering.forceAmplification;
        repulsingForce *= this.forceFactor;


        fx = Math.cos(angle) * repulsingForce;
        fy = Math.sin(angle) * repulsingForce ;

        node1._addForce(-fx, -fy);
        node2._addForce(fx, fy);
      }
    }
  }

/*
  // repulsion of the edges on the nodes and
  for (var nodeId in nodes) {
    if (nodes.hasOwnProperty(nodeId)) {
      node = nodes[nodeId];
      for(var edgeId in edges) {
        if (edges.hasOwnProperty(edgeId)) {
          edge = edges[edgeId];

          // get the center of the edge
          xCenter = edge.from.x+(edge.to.x - edge.from.x)/2;
          yCenter = edge.from.y+(edge.to.y - edge.from.y)/2;

          // calculate normally distributed force
          dx = node.x - xCenter;
          dy = node.y - yCenter;
          distance = Math.sqrt(dx * dx + dy * dy);
          if (distance < 2*minimumDistance) { // at 2.0 * the minimum distance, the force is 0.000045
            angle = Math.atan2(dy, dx);

            if (distance < 0.5*minimumDistance) { // at 0.5 * the minimum distance, the force is 0.993307
              repulsingForce = 1.0;
            }
            else {
              // TODO: correct factor for repulsing force
              //var repulsingforce = 2 * Math.exp(-5 * (distance * distance) / (dmin * dmin) ); // TODO: customize the repulsing force
              //repulsingforce = Math.exp(-1 * (distance * distance) / (dmin * dmin) ), // TODO: customize the repulsing force
              repulsingForce = 1 / (1 + Math.exp((distance / (minimumDistance / 2) - 1) * steepness)); // TODO: customize the repulsing force
            }
            fx = Math.cos(angle) * repulsingForce;
            fy = Math.sin(angle) * repulsingForce;
            node._addForce(fx, fy);
            edge.from._addForce(-fx/2,-fy/2);
            edge.to._addForce(-fx/2,-fy/2);
          }
        }
      }
    }
  }
*/

  // forces caused by the edges, modelled as springs
  for (edgeId in edges) {
    if (edges.hasOwnProperty(edgeId)) {
      edge = edges[edgeId];
      if (edge.connected) {
        // only calculate forces if nodes are in the same sector
        if (this.nodes.hasOwnProperty(edge.toId) && this.nodes.hasOwnProperty(edge.fromId)) {
          clusterSize = (edge.to.clusterSize + edge.from.clusterSize - 2);
          dx = (edge.to.x - edge.from.x);
          dy = (edge.to.y - edge.from.y);
          //edgeLength = (edge.from.width + edge.from.height + edge.to.width + edge.to.height)/2 || edge.length; // TODO: dmin
          //edgeLength = (edge.from.width + edge.to.width)/2 || edge.length; // TODO: dmin
          //edgeLength = 20 + ((edge.from.width + edge.to.width) || 0) / 2;
          edgeLength = edge.length;
          // this implies that the edges between big clusters are longer
          edgeLength += clusterSize * this.constants.clustering.edgeGrowth;
          length =  Math.sqrt(dx * dx + dy * dy);
          angle = Math.atan2(dy, dx);

          springForce = edge.stiffness * (edgeLength - length) * this.forceFactor;

          fx = Math.cos(angle) * springForce;
          fy = Math.sin(angle) * springForce;

          edge.from._addForce(-fx, -fy);
          edge.to._addForce(fx, fy);
        }
      }
    }
  }
/*
  // TODO: re-implement repulsion of edges

   // repulsing forces between edges
   var minimumDistance = this.constants.edges.distance,
   steepness = 10; // higher value gives steeper slope of the force around the given minimumDistance
   for (var l = 0; l < edges.length; l++) {
   //Keep distance from other edge centers
   for (var l2 = l + 1; l2 < this.edges.length; l2++) {
   //var dmin = (nodes[n].width + nodes[n].height + nodes[n2].width + nodes[n2].height) / 1 || minimumDistance, // TODO: dmin
   //var dmin = (nodes[n].width + nodes[n2].width)/2  || minimumDistance, // TODO: dmin
   //dmin = 40 + ((nodes[n].width/2 + nodes[n2].width/2) || 0),
   var lx = edges[l].from.x+(edges[l].to.x - edges[l].from.x)/2,
   ly = edges[l].from.y+(edges[l].to.y - edges[l].from.y)/2,
   l2x = edges[l2].from.x+(edges[l2].to.x - edges[l2].from.x)/2,
   l2y = edges[l2].from.y+(edges[l2].to.y - edges[l2].from.y)/2,

   // calculate normally distributed force
   dx = l2x - lx,
   dy = l2y - ly,
   distance = Math.sqrt(dx * dx + dy * dy),
   angle = Math.atan2(dy, dx),


   // TODO: correct factor for repulsing force
   //var repulsingforce = 2 * Math.exp(-5 * (distance * distance) / (dmin * dmin) ); // TODO: customize the repulsing force
   //repulsingforce = Math.exp(-1 * (distance * distance) / (dmin * dmin) ), // TODO: customize the repulsing force
   repulsingforce = 1 / (1 + Math.exp((distance / minimumDistance - 1) * steepness)), // TODO: customize the repulsing force
   fx = Math.cos(angle) * repulsingforce,
   fy = Math.sin(angle) * repulsingforce;

   edges[l].from._addForce(-fx, -fy);
   edges[l].to._addForce(-fx, -fy);
   edges[l2].from._addForce(fx, fy);
   edges[l2].to._addForce(fx, fy);
   }
   }
*/
};


/**
 * Check if any of the nodes is still moving
 * @param {number} vmin   the minimum velocity considered as 'moving'
 * @return {boolean}      true if moving, false if non of the nodes is moving
 * @private
 */
Graph.prototype._isMoving = function(vmin) {
  var vminCorrected = vmin / this.scale;
  var nodes = this.nodes;
  for (var id in nodes) {
    if (nodes.hasOwnProperty(id) && nodes[id].isMoving(vminCorrected)) {
      return true;
    }
  }
  return false;
};


/**
 * /**
 * Perform one discrete step for all nodes
 *
 * @param interval
 * @private
 */
Graph.prototype._discreteStepNodes = function() {
  var interval = 0.010;
  var nodes = this.nodes;
  for (var id in nodes) {
    if (nodes.hasOwnProperty(id)) {
      nodes[id].discreteStep(interval);
    }
  }

  var vmin = this.constants.minVelocity;
  this.moving = this._isMoving(vmin);
};



/**
 * Start animating nodes and edges
 *
 * @poram {Boolean} runCalculationStep
 */
Graph.prototype.start = function() {
  if (!this.freezeSimulation) {

    if (this.moving) {
      this._doInAllActiveSectors("_initializeForceCalculation");
      this._doInAllActiveSectors("_discreteStepNodes");

      this._findCenter(this._getRange())
    }

    if (this.moving || this.xIncrement != 0 || this.yIncrement != 0 || this.zoomIncrement != 0) {
      // start animation. only start calculationTimer if it is not already running
      if (!this.timer) {
        var graph = this;
        this.timer = window.setTimeout(function () {
          graph.timer = undefined;

          // keyboad movement
          if (graph.xIncrement != 0 || graph.yIncrement != 0) {
            var translation = graph._getTranslation();
            graph._setTranslation(translation.x+graph.xIncrement,translation.y+graph.yIncrement);
          }
          if (graph.zoomIncrement != 0) {
            graph._zoom(graph.scale*(1 + graph.zoomIncrement),graph.lastPointerPosition);
          }

          graph.start();
          graph._redraw();


          //this.end = window.performance.now();
          //this.time = this.end - this.startTime;
          //console.log('refresh time: ' + this.time);
          //this.startTime = window.performance.now();

        }, this.renderTimestep);
      }
    }
    else {
      this._redraw();
    }
  }
};




Graph.prototype.singleStep = function() {
  if (this.moving) {
    this._initializeForceCalculation();
    this._discreteStepNodes();

    var vmin = this.constants.minVelocity;
    this.moving = this._isMoving(vmin);
    this._redraw();
  }
};



/**
 *  Freeze the animation
 */
Graph.prototype.toggleFreeze = function() {
  if (this.freezeSimulation == false) {
    this.freezeSimulation = true;
  }
  else {
    this.freezeSimulation = false;
    this.start();
  }
};

/**
 * Mixin the cluster system and initialize the parameters required.
 *
 * @private
 */
Graph.prototype._loadClusterSystem = function() {
  this.clusterSession = 0;
  this.hubThreshold = 5;

  for (var mixinFunction in ClusterMixin) {
    if (ClusterMixin.hasOwnProperty(mixinFunction)) {
      Graph.prototype[mixinFunction] = ClusterMixin[mixinFunction];
    }
  }
}

/**
 * Mixin the sector system and initialize the parameters required
 *
 * @private
 */
Graph.prototype._loadSectorSystem = function() {
  this.sectors = {};
  this.activeSector = ["default"];
  this.sectors["active"] = {};
  this.sectors["active"]["default"] = {"nodes":{},
                                       "edges":{},
                                       "nodeIndices":[],
                                       "formationScale": 1.0,
                                       "drawingNode": undefined};
  this.sectors["frozen"] = {};
  this.sectors["navigationUI"] = {"nodes":{},
                        "edges":{},
                        "nodeIndices":[],
                        "formationScale": 1.0,
                        "drawingNode": undefined};

  this.nodeIndices = this.sectors["active"]["default"]["nodeIndices"];  // the node indices list is used to speed up the computation of the repulsion fields
  for (var mixinFunction in SectorMixin) {
    if (SectorMixin.hasOwnProperty(mixinFunction)) {
      Graph.prototype[mixinFunction] = SectorMixin[mixinFunction];
    }
  }
};


/**
 * Mixin the selection system and initialize the parameters required
 *
 * @private
 */
Graph.prototype._loadSelectionSystem = function() {
  this.selection = [];
  this.selectionObj = {};

  for (var mixinFunction in SelectionMixin) {
    if (SelectionMixin.hasOwnProperty(mixinFunction)) {
      Graph.prototype[mixinFunction] = SelectionMixin[mixinFunction];
    }
  }
}


/**
 * Mixin the navigationUI (User Interface) system and initialize the parameters required
 *
 * @private
 */
Graph.prototype._loadUISystem = function() {
  for (var mixinFunction in UIMixin) {
    if (UIMixin.hasOwnProperty(mixinFunction)) {
      Graph.prototype[mixinFunction] = UIMixin[mixinFunction];
    }
  }

  if (this.constants.navigationUI.enabled == true) {
    this._loadUIElements();
  }
}

/**
 * this function exists to avoid errors when not loading the navigationUI system
 */
Graph.prototype._relocateUI = function() {
  // empty, is overloaded by navigationUI system
}

/**
 * * this function exists to avoid errors when not loading the navigationUI system
 */
Graph.prototype._unHighlightAll = function() {
  // empty, is overloaded by the navigationUI system
}

























/**
 * vis.js module exports
 */
var vis = {
  util: util,
  events: events,

  Controller: Controller,
  DataSet: DataSet,
  DataView: DataView,
  Range: Range,
  Stack: Stack,
  TimeStep: TimeStep,
  EventBus: EventBus,

  components: {
    items: {
      Item: Item,
      ItemBox: ItemBox,
      ItemPoint: ItemPoint,
      ItemRange: ItemRange
    },

    Component: Component,
    Panel: Panel,
    RootPanel: RootPanel,
    ItemSet: ItemSet,
    TimeAxis: TimeAxis
  },

  graph: {
    Node: Node,
    Edge: Edge,
    Popup: Popup,
    Groups: Groups,
    Images: Images
  },

  Timeline: Timeline,
  Graph: Graph
};

/**
 * CommonJS module exports
 */
if (typeof exports !== 'undefined') {
  exports = vis;
}
if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
  module.exports = vis;
}

/**
 * AMD module exports
 */
if (typeof(define) === 'function') {
  define(function () {
    return vis;
  });
}

/**
 * Window exports
 */
if (typeof window !== 'undefined') {
  // attach the module to the window, load as a regular javascript file
  window['vis'] = vis;
}


},{"hammerjs":2,"moment":3,"mousetrap":4}],2:[function(require,module,exports){
/*! Hammer.JS - v1.0.5 - 2013-04-07
 * http://eightmedia.github.com/hammer.js
 *
 * Copyright (c) 2013 Jorik Tangelder <j.tangelder@gmail.com>;
 * Licensed under the MIT license */

(function(window, undefined) {
    'use strict';

/**
 * Hammer
 * use this to create instances
 * @param   {HTMLElement}   element
 * @param   {Object}        options
 * @returns {Hammer.Instance}
 * @constructor
 */
var Hammer = function(element, options) {
    return new Hammer.Instance(element, options || {});
};

// default settings
Hammer.defaults = {
    // add styles and attributes to the element to prevent the browser from doing
    // its native behavior. this doesnt prevent the scrolling, but cancels
    // the contextmenu, tap highlighting etc
    // set to false to disable this
    stop_browser_behavior: {
		// this also triggers onselectstart=false for IE
        userSelect: 'none',
		// this makes the element blocking in IE10 >, you could experiment with the value
		// see for more options this issue; https://github.com/EightMedia/hammer.js/issues/241
        touchAction: 'none',
		touchCallout: 'none',
        contentZooming: 'none',
        userDrag: 'none',
        tapHighlightColor: 'rgba(0,0,0,0)'
    }

    // more settings are defined per gesture at gestures.js
};

// detect touchevents
Hammer.HAS_POINTEREVENTS = navigator.pointerEnabled || navigator.msPointerEnabled;
Hammer.HAS_TOUCHEVENTS = ('ontouchstart' in window);

// dont use mouseevents on mobile devices
Hammer.MOBILE_REGEX = /mobile|tablet|ip(ad|hone|od)|android/i;
Hammer.NO_MOUSEEVENTS = Hammer.HAS_TOUCHEVENTS && navigator.userAgent.match(Hammer.MOBILE_REGEX);

// eventtypes per touchevent (start, move, end)
// are filled by Hammer.event.determineEventTypes on setup
Hammer.EVENT_TYPES = {};

// direction defines
Hammer.DIRECTION_DOWN = 'down';
Hammer.DIRECTION_LEFT = 'left';
Hammer.DIRECTION_UP = 'up';
Hammer.DIRECTION_RIGHT = 'right';

// pointer type
Hammer.POINTER_MOUSE = 'mouse';
Hammer.POINTER_TOUCH = 'touch';
Hammer.POINTER_PEN = 'pen';

// touch event defines
Hammer.EVENT_START = 'start';
Hammer.EVENT_MOVE = 'move';
Hammer.EVENT_END = 'end';

// hammer document where the base events are added at
Hammer.DOCUMENT = document;

// plugins namespace
Hammer.plugins = {};

// if the window events are set...
Hammer.READY = false;

/**
 * setup events to detect gestures on the document
 */
function setup() {
    if(Hammer.READY) {
        return;
    }

    // find what eventtypes we add listeners to
    Hammer.event.determineEventTypes();

    // Register all gestures inside Hammer.gestures
    for(var name in Hammer.gestures) {
        if(Hammer.gestures.hasOwnProperty(name)) {
            Hammer.detection.register(Hammer.gestures[name]);
        }
    }

    // Add touch events on the document
    Hammer.event.onTouch(Hammer.DOCUMENT, Hammer.EVENT_MOVE, Hammer.detection.detect);
    Hammer.event.onTouch(Hammer.DOCUMENT, Hammer.EVENT_END, Hammer.detection.detect);

    // Hammer is ready...!
    Hammer.READY = true;
}

/**
 * create new hammer instance
 * all methods should return the instance itself, so it is chainable.
 * @param   {HTMLElement}       element
 * @param   {Object}            [options={}]
 * @returns {Hammer.Instance}
 * @constructor
 */
Hammer.Instance = function(element, options) {
    var self = this;

    // setup HammerJS window events and register all gestures
    // this also sets up the default options
    setup();

    this.element = element;

    // start/stop detection option
    this.enabled = true;

    // merge options
    this.options = Hammer.utils.extend(
        Hammer.utils.extend({}, Hammer.defaults),
        options || {});

    // add some css to the element to prevent the browser from doing its native behavoir
    if(this.options.stop_browser_behavior) {
        Hammer.utils.stopDefaultBrowserBehavior(this.element, this.options.stop_browser_behavior);
    }

    // start detection on touchstart
    Hammer.event.onTouch(element, Hammer.EVENT_START, function(ev) {
        if(self.enabled) {
            Hammer.detection.startDetect(self, ev);
        }
    });

    // return instance
    return this;
};


Hammer.Instance.prototype = {
    /**
     * bind events to the instance
     * @param   {String}      gesture
     * @param   {Function}    handler
     * @returns {Hammer.Instance}
     */
    on: function onEvent(gesture, handler){
        var gestures = gesture.split(' ');
        for(var t=0; t<gestures.length; t++) {
            this.element.addEventListener(gestures[t], handler, false);
        }
        return this;
    },


    /**
     * unbind events to the instance
     * @param   {String}      gesture
     * @param   {Function}    handler
     * @returns {Hammer.Instance}
     */
    off: function offEvent(gesture, handler){
        var gestures = gesture.split(' ');
        for(var t=0; t<gestures.length; t++) {
            this.element.removeEventListener(gestures[t], handler, false);
        }
        return this;
    },


    /**
     * trigger gesture event
     * @param   {String}      gesture
     * @param   {Object}      eventData
     * @returns {Hammer.Instance}
     */
    trigger: function triggerEvent(gesture, eventData){
        // create DOM event
        var event = Hammer.DOCUMENT.createEvent('Event');
		event.initEvent(gesture, true, true);
		event.gesture = eventData;

        // trigger on the target if it is in the instance element,
        // this is for event delegation tricks
        var element = this.element;
        if(Hammer.utils.hasParent(eventData.target, element)) {
            element = eventData.target;
        }

        element.dispatchEvent(event);
        return this;
    },


    /**
     * enable of disable hammer.js detection
     * @param   {Boolean}   state
     * @returns {Hammer.Instance}
     */
    enable: function enable(state) {
        this.enabled = state;
        return this;
    }
};

/**
 * this holds the last move event,
 * used to fix empty touchend issue
 * see the onTouch event for an explanation
 * @type {Object}
 */
var last_move_event = null;


/**
 * when the mouse is hold down, this is true
 * @type {Boolean}
 */
var enable_detect = false;


/**
 * when touch events have been fired, this is true
 * @type {Boolean}
 */
var touch_triggered = false;


Hammer.event = {
    /**
     * simple addEventListener
     * @param   {HTMLElement}   element
     * @param   {String}        type
     * @param   {Function}      handler
     */
    bindDom: function(element, type, handler) {
        var types = type.split(' ');
        for(var t=0; t<types.length; t++) {
            element.addEventListener(types[t], handler, false);
        }
    },


    /**
     * touch events with mouse fallback
     * @param   {HTMLElement}   element
     * @param   {String}        eventType        like Hammer.EVENT_MOVE
     * @param   {Function}      handler
     */
    onTouch: function onTouch(element, eventType, handler) {
		var self = this;

        this.bindDom(element, Hammer.EVENT_TYPES[eventType], function bindDomOnTouch(ev) {
            var sourceEventType = ev.type.toLowerCase();

            // onmouseup, but when touchend has been fired we do nothing.
            // this is for touchdevices which also fire a mouseup on touchend
            if(sourceEventType.match(/mouse/) && touch_triggered) {
                return;
            }

            // mousebutton must be down or a touch event
            else if( sourceEventType.match(/touch/) ||   // touch events are always on screen
                sourceEventType.match(/pointerdown/) || // pointerevents touch
                (sourceEventType.match(/mouse/) && ev.which === 1)   // mouse is pressed
            ){
                enable_detect = true;
            }

            // we are in a touch event, set the touch triggered bool to true,
            // this for the conflicts that may occur on ios and android
            if(sourceEventType.match(/touch|pointer/)) {
                touch_triggered = true;
            }

            // count the total touches on the screen
            var count_touches = 0;

            // when touch has been triggered in this detection session
            // and we are now handling a mouse event, we stop that to prevent conflicts
            if(enable_detect) {
                // update pointerevent
                if(Hammer.HAS_POINTEREVENTS && eventType != Hammer.EVENT_END) {
                    count_touches = Hammer.PointerEvent.updatePointer(eventType, ev);
                }
                // touch
                else if(sourceEventType.match(/touch/)) {
                    count_touches = ev.touches.length;
                }
                // mouse
                else if(!touch_triggered) {
                    count_touches = sourceEventType.match(/up/) ? 0 : 1;
                }

                // if we are in a end event, but when we remove one touch and
                // we still have enough, set eventType to move
                if(count_touches > 0 && eventType == Hammer.EVENT_END) {
                    eventType = Hammer.EVENT_MOVE;
                }
                // no touches, force the end event
                else if(!count_touches) {
                    eventType = Hammer.EVENT_END;
                }

                // because touchend has no touches, and we often want to use these in our gestures,
                // we send the last move event as our eventData in touchend
                if(!count_touches && last_move_event !== null) {
                    ev = last_move_event;
                }
                // store the last move event
                else {
                    last_move_event = ev;
                }

                // trigger the handler
                handler.call(Hammer.detection, self.collectEventData(element, eventType, ev));

                // remove pointerevent from list
                if(Hammer.HAS_POINTEREVENTS && eventType == Hammer.EVENT_END) {
                    count_touches = Hammer.PointerEvent.updatePointer(eventType, ev);
                }
            }

            //debug(sourceEventType +" "+ eventType);

            // on the end we reset everything
            if(!count_touches) {
                last_move_event = null;
                enable_detect = false;
                touch_triggered = false;
                Hammer.PointerEvent.reset();
            }
        });
    },


    /**
     * we have different events for each device/browser
     * determine what we need and set them in the Hammer.EVENT_TYPES constant
     */
    determineEventTypes: function determineEventTypes() {
        // determine the eventtype we want to set
        var types;

        // pointerEvents magic
        if(Hammer.HAS_POINTEREVENTS) {
            types = Hammer.PointerEvent.getEvents();
        }
        // on Android, iOS, blackberry, windows mobile we dont want any mouseevents
        else if(Hammer.NO_MOUSEEVENTS) {
            types = [
                'touchstart',
                'touchmove',
                'touchend touchcancel'];
        }
        // for non pointer events browsers and mixed browsers,
        // like chrome on windows8 touch laptop
        else {
            types = [
                'touchstart mousedown',
                'touchmove mousemove',
                'touchend touchcancel mouseup'];
        }

        Hammer.EVENT_TYPES[Hammer.EVENT_START]  = types[0];
        Hammer.EVENT_TYPES[Hammer.EVENT_MOVE]   = types[1];
        Hammer.EVENT_TYPES[Hammer.EVENT_END]    = types[2];
    },


    /**
     * create touchlist depending on the event
     * @param   {Object}    ev
     * @param   {String}    eventType   used by the fakemultitouch plugin
     */
    getTouchList: function getTouchList(ev/*, eventType*/) {
        // get the fake pointerEvent touchlist
        if(Hammer.HAS_POINTEREVENTS) {
            return Hammer.PointerEvent.getTouchList();
        }
        // get the touchlist
        else if(ev.touches) {
            return ev.touches;
        }
        // make fake touchlist from mouse position
        else {
            return [{
                identifier: 1,
                pageX: ev.pageX,
                pageY: ev.pageY,
                target: ev.target
            }];
        }
    },


    /**
     * collect event data for Hammer js
     * @param   {HTMLElement}   element
     * @param   {String}        eventType        like Hammer.EVENT_MOVE
     * @param   {Object}        eventData
     */
    collectEventData: function collectEventData(element, eventType, ev) {
        var touches = this.getTouchList(ev, eventType);

        // find out pointerType
        var pointerType = Hammer.POINTER_TOUCH;
        if(ev.type.match(/mouse/) || Hammer.PointerEvent.matchType(Hammer.POINTER_MOUSE, ev)) {
            pointerType = Hammer.POINTER_MOUSE;
        }

        return {
            center      : Hammer.utils.getCenter(touches),
            timeStamp   : new Date().getTime(),
            target      : ev.target,
            touches     : touches,
            eventType   : eventType,
            pointerType : pointerType,
            srcEvent    : ev,

            /**
             * prevent the browser default actions
             * mostly used to disable scrolling of the browser
             */
            preventDefault: function() {
                if(this.srcEvent.preventManipulation) {
                    this.srcEvent.preventManipulation();
                }

                if(this.srcEvent.preventDefault) {
                    this.srcEvent.preventDefault();
                }
            },

            /**
             * stop bubbling the event up to its parents
             */
            stopPropagation: function() {
                this.srcEvent.stopPropagation();
            },

            /**
             * immediately stop gesture detection
             * might be useful after a swipe was detected
             * @return {*}
             */
            stopDetect: function() {
                return Hammer.detection.stopDetect();
            }
        };
    }
};

Hammer.PointerEvent = {
    /**
     * holds all pointers
     * @type {Object}
     */
    pointers: {},

    /**
     * get a list of pointers
     * @returns {Array}     touchlist
     */
    getTouchList: function() {
        var self = this;
        var touchlist = [];

        // we can use forEach since pointerEvents only is in IE10
        Object.keys(self.pointers).sort().forEach(function(id) {
            touchlist.push(self.pointers[id]);
        });
        return touchlist;
    },

    /**
     * update the position of a pointer
     * @param   {String}   type             Hammer.EVENT_END
     * @param   {Object}   pointerEvent
     */
    updatePointer: function(type, pointerEvent) {
        if(type == Hammer.EVENT_END) {
            this.pointers = {};
        }
        else {
            pointerEvent.identifier = pointerEvent.pointerId;
            this.pointers[pointerEvent.pointerId] = pointerEvent;
        }

        return Object.keys(this.pointers).length;
    },

    /**
     * check if ev matches pointertype
     * @param   {String}        pointerType     Hammer.POINTER_MOUSE
     * @param   {PointerEvent}  ev
     */
    matchType: function(pointerType, ev) {
        if(!ev.pointerType) {
            return false;
        }

        var types = {};
        types[Hammer.POINTER_MOUSE] = (ev.pointerType == ev.MSPOINTER_TYPE_MOUSE || ev.pointerType == Hammer.POINTER_MOUSE);
        types[Hammer.POINTER_TOUCH] = (ev.pointerType == ev.MSPOINTER_TYPE_TOUCH || ev.pointerType == Hammer.POINTER_TOUCH);
        types[Hammer.POINTER_PEN] = (ev.pointerType == ev.MSPOINTER_TYPE_PEN || ev.pointerType == Hammer.POINTER_PEN);
        return types[pointerType];
    },


    /**
     * get events
     */
    getEvents: function() {
        return [
            'pointerdown MSPointerDown',
            'pointermove MSPointerMove',
            'pointerup pointercancel MSPointerUp MSPointerCancel'
        ];
    },

    /**
     * reset the list
     */
    reset: function() {
        this.pointers = {};
    }
};


Hammer.utils = {
    /**
     * extend method,
     * also used for cloning when dest is an empty object
     * @param   {Object}    dest
     * @param   {Object}    src
	 * @parm	{Boolean}	merge		do a merge
     * @returns {Object}    dest
     */
    extend: function extend(dest, src, merge) {
        for (var key in src) {
			if(dest[key] !== undefined && merge) {
				continue;
			}
            dest[key] = src[key];
        }
        return dest;
    },


    /**
     * find if a node is in the given parent
     * used for event delegation tricks
     * @param   {HTMLElement}   node
     * @param   {HTMLElement}   parent
     * @returns {boolean}       has_parent
     */
    hasParent: function(node, parent) {
        while(node){
            if(node == parent) {
                return true;
            }
            node = node.parentNode;
        }
        return false;
    },


    /**
     * get the center of all the touches
     * @param   {Array}     touches
     * @returns {Object}    center
     */
    getCenter: function getCenter(touches) {
        var valuesX = [], valuesY = [];

        for(var t= 0,len=touches.length; t<len; t++) {
            valuesX.push(touches[t].pageX);
            valuesY.push(touches[t].pageY);
        }

        return {
            pageX: ((Math.min.apply(Math, valuesX) + Math.max.apply(Math, valuesX)) / 2),
            pageY: ((Math.min.apply(Math, valuesY) + Math.max.apply(Math, valuesY)) / 2)
        };
    },


    /**
     * calculate the velocity between two points
     * @param   {Number}    delta_time
     * @param   {Number}    delta_x
     * @param   {Number}    delta_y
     * @returns {Object}    velocity
     */
    getVelocity: function getVelocity(delta_time, delta_x, delta_y) {
        return {
            x: Math.abs(delta_x / delta_time) || 0,
            y: Math.abs(delta_y / delta_time) || 0
        };
    },


    /**
     * calculate the angle between two coordinates
     * @param   {Touch}     touch1
     * @param   {Touch}     touch2
     * @returns {Number}    angle
     */
    getAngle: function getAngle(touch1, touch2) {
        var y = touch2.pageY - touch1.pageY,
            x = touch2.pageX - touch1.pageX;
        return Math.atan2(y, x) * 180 / Math.PI;
    },


    /**
     * angle to direction define
     * @param   {Touch}     touch1
     * @param   {Touch}     touch2
     * @returns {String}    direction constant, like Hammer.DIRECTION_LEFT
     */
    getDirection: function getDirection(touch1, touch2) {
        var x = Math.abs(touch1.pageX - touch2.pageX),
            y = Math.abs(touch1.pageY - touch2.pageY);

        if(x >= y) {
            return touch1.pageX - touch2.pageX > 0 ? Hammer.DIRECTION_LEFT : Hammer.DIRECTION_RIGHT;
        }
        else {
            return touch1.pageY - touch2.pageY > 0 ? Hammer.DIRECTION_UP : Hammer.DIRECTION_DOWN;
        }
    },


    /**
     * calculate the distance between two touches
     * @param   {Touch}     touch1
     * @param   {Touch}     touch2
     * @returns {Number}    distance
     */
    getDistance: function getDistance(touch1, touch2) {
        var x = touch2.pageX - touch1.pageX,
            y = touch2.pageY - touch1.pageY;
        return Math.sqrt((x*x) + (y*y));
    },


    /**
     * calculate the scale factor between two touchLists (fingers)
     * no scale is 1, and goes down to 0 when pinched together, and bigger when pinched out
     * @param   {Array}     start
     * @param   {Array}     end
     * @returns {Number}    scale
     */
    getScale: function getScale(start, end) {
        // need two fingers...
        if(start.length >= 2 && end.length >= 2) {
            return this.getDistance(end[0], end[1]) /
                this.getDistance(start[0], start[1]);
        }
        return 1;
    },


    /**
     * calculate the rotation degrees between two touchLists (fingers)
     * @param   {Array}     start
     * @param   {Array}     end
     * @returns {Number}    rotation
     */
    getRotation: function getRotation(start, end) {
        // need two fingers
        if(start.length >= 2 && end.length >= 2) {
            return this.getAngle(end[1], end[0]) -
                this.getAngle(start[1], start[0]);
        }
        return 0;
    },


    /**
     * boolean if the direction is vertical
     * @param    {String}    direction
     * @returns  {Boolean}   is_vertical
     */
    isVertical: function isVertical(direction) {
        return (direction == Hammer.DIRECTION_UP || direction == Hammer.DIRECTION_DOWN);
    },


    /**
     * stop browser default behavior with css props
     * @param   {HtmlElement}   element
     * @param   {Object}        css_props
     */
    stopDefaultBrowserBehavior: function stopDefaultBrowserBehavior(element, css_props) {
        var prop,
            vendors = ['webkit','khtml','moz','ms','o',''];

        if(!css_props || !element.style) {
            return;
        }

        // with css properties for modern browsers
        for(var i = 0; i < vendors.length; i++) {
            for(var p in css_props) {
                if(css_props.hasOwnProperty(p)) {
                    prop = p;

                    // vender prefix at the property
                    if(vendors[i]) {
                        prop = vendors[i] + prop.substring(0, 1).toUpperCase() + prop.substring(1);
                    }

                    // set the style
                    element.style[prop] = css_props[p];
                }
            }
        }

        // also the disable onselectstart
        if(css_props.userSelect == 'none') {
            element.onselectstart = function() {
                return false;
            };
        }
    }
};

Hammer.detection = {
    // contains all registred Hammer.gestures in the correct order
    gestures: [],

    // data of the current Hammer.gesture detection session
    current: null,

    // the previous Hammer.gesture session data
    // is a full clone of the previous gesture.current object
    previous: null,

    // when this becomes true, no gestures are fired
    stopped: false,


    /**
     * start Hammer.gesture detection
     * @param   {Hammer.Instance}   inst
     * @param   {Object}            eventData
     */
    startDetect: function startDetect(inst, eventData) {
        // already busy with a Hammer.gesture detection on an element
        if(this.current) {
            return;
        }

        this.stopped = false;

        this.current = {
            inst        : inst, // reference to HammerInstance we're working for
            startEvent  : Hammer.utils.extend({}, eventData), // start eventData for distances, timing etc
            lastEvent   : false, // last eventData
            name        : '' // current gesture we're in/detected, can be 'tap', 'hold' etc
        };

        this.detect(eventData);
    },


    /**
     * Hammer.gesture detection
     * @param   {Object}    eventData
     * @param   {Object}    eventData
     */
    detect: function detect(eventData) {
        if(!this.current || this.stopped) {
            return;
        }

        // extend event data with calculations about scale, distance etc
        eventData = this.extendEventData(eventData);

        // instance options
        var inst_options = this.current.inst.options;

        // call Hammer.gesture handlers
        for(var g=0,len=this.gestures.length; g<len; g++) {
            var gesture = this.gestures[g];

            // only when the instance options have enabled this gesture
            if(!this.stopped && inst_options[gesture.name] !== false) {
                // if a handler returns false, we stop with the detection
                if(gesture.handler.call(gesture, eventData, this.current.inst) === false) {
                    this.stopDetect();
                    break;
                }
            }
        }

        // store as previous event event
        if(this.current) {
            this.current.lastEvent = eventData;
        }

        // endevent, but not the last touch, so dont stop
        if(eventData.eventType == Hammer.EVENT_END && !eventData.touches.length-1) {
            this.stopDetect();
        }

        return eventData;
    },


    /**
     * clear the Hammer.gesture vars
     * this is called on endDetect, but can also be used when a final Hammer.gesture has been detected
     * to stop other Hammer.gestures from being fired
     */
    stopDetect: function stopDetect() {
        // clone current data to the store as the previous gesture
        // used for the double tap gesture, since this is an other gesture detect session
        this.previous = Hammer.utils.extend({}, this.current);

        // reset the current
        this.current = null;

        // stopped!
        this.stopped = true;
    },


    /**
     * extend eventData for Hammer.gestures
     * @param   {Object}   ev
     * @returns {Object}   ev
     */
    extendEventData: function extendEventData(ev) {
        var startEv = this.current.startEvent;

        // if the touches change, set the new touches over the startEvent touches
        // this because touchevents don't have all the touches on touchstart, or the
        // user must place his fingers at the EXACT same time on the screen, which is not realistic
        // but, sometimes it happens that both fingers are touching at the EXACT same time
        if(startEv && (ev.touches.length != startEv.touches.length || ev.touches === startEv.touches)) {
            // extend 1 level deep to get the touchlist with the touch objects
            startEv.touches = [];
            for(var i=0,len=ev.touches.length; i<len; i++) {
                startEv.touches.push(Hammer.utils.extend({}, ev.touches[i]));
            }
        }

        var delta_time = ev.timeStamp - startEv.timeStamp,
            delta_x = ev.center.pageX - startEv.center.pageX,
            delta_y = ev.center.pageY - startEv.center.pageY,
            velocity = Hammer.utils.getVelocity(delta_time, delta_x, delta_y);

        Hammer.utils.extend(ev, {
            deltaTime   : delta_time,

            deltaX      : delta_x,
            deltaY      : delta_y,

            velocityX   : velocity.x,
            velocityY   : velocity.y,

            distance    : Hammer.utils.getDistance(startEv.center, ev.center),
            angle       : Hammer.utils.getAngle(startEv.center, ev.center),
            direction   : Hammer.utils.getDirection(startEv.center, ev.center),

            scale       : Hammer.utils.getScale(startEv.touches, ev.touches),
            rotation    : Hammer.utils.getRotation(startEv.touches, ev.touches),

            startEvent  : startEv
        });

        return ev;
    },


    /**
     * register new gesture
     * @param   {Object}    gesture object, see gestures.js for documentation
     * @returns {Array}     gestures
     */
    register: function register(gesture) {
        // add an enable gesture options if there is no given
        var options = gesture.defaults || {};
        if(options[gesture.name] === undefined) {
            options[gesture.name] = true;
        }

        // extend Hammer default options with the Hammer.gesture options
        Hammer.utils.extend(Hammer.defaults, options, true);

        // set its index
        gesture.index = gesture.index || 1000;

        // add Hammer.gesture to the list
        this.gestures.push(gesture);

        // sort the list by index
        this.gestures.sort(function(a, b) {
            if (a.index < b.index) {
                return -1;
            }
            if (a.index > b.index) {
                return 1;
            }
            return 0;
        });

        return this.gestures;
    }
};


Hammer.gestures = Hammer.gestures || {};

/**
 * Custom gestures
 * ==============================
 *
 * Gesture object
 * --------------------
 * The object structure of a gesture:
 *
 * { name: 'mygesture',
 *   index: 1337,
 *   defaults: {
 *     mygesture_option: true
 *   }
 *   handler: function(type, ev, inst) {
 *     // trigger gesture event
 *     inst.trigger(this.name, ev);
 *   }
 * }

 * @param   {String}    name
 * this should be the name of the gesture, lowercase
 * it is also being used to disable/enable the gesture per instance config.
 *
 * @param   {Number}    [index=1000]
 * the index of the gesture, where it is going to be in the stack of gestures detection
 * like when you build an gesture that depends on the drag gesture, it is a good
 * idea to place it after the index of the drag gesture.
 *
 * @param   {Object}    [defaults={}]
 * the default settings of the gesture. these are added to the instance settings,
 * and can be overruled per instance. you can also add the name of the gesture,
 * but this is also added by default (and set to true).
 *
 * @param   {Function}  handler
 * this handles the gesture detection of your custom gesture and receives the
 * following arguments:
 *
 *      @param  {Object}    eventData
 *      event data containing the following properties:
 *          timeStamp   {Number}        time the event occurred
 *          target      {HTMLElement}   target element
 *          touches     {Array}         touches (fingers, pointers, mouse) on the screen
 *          pointerType {String}        kind of pointer that was used. matches Hammer.POINTER_MOUSE|TOUCH
 *          center      {Object}        center position of the touches. contains pageX and pageY
 *          deltaTime   {Number}        the total time of the touches in the screen
 *          deltaX      {Number}        the delta on x axis we haved moved
 *          deltaY      {Number}        the delta on y axis we haved moved
 *          velocityX   {Number}        the velocity on the x
 *          velocityY   {Number}        the velocity on y
 *          angle       {Number}        the angle we are moving
 *          direction   {String}        the direction we are moving. matches Hammer.DIRECTION_UP|DOWN|LEFT|RIGHT
 *          distance    {Number}        the distance we haved moved
 *          scale       {Number}        scaling of the touches, needs 2 touches
 *          rotation    {Number}        rotation of the touches, needs 2 touches *
 *          eventType   {String}        matches Hammer.EVENT_START|MOVE|END
 *          srcEvent    {Object}        the source event, like TouchStart or MouseDown *
 *          startEvent  {Object}        contains the same properties as above,
 *                                      but from the first touch. this is used to calculate
 *                                      distances, deltaTime, scaling etc
 *
 *      @param  {Hammer.Instance}    inst
 *      the instance we are doing the detection for. you can get the options from
 *      the inst.options object and trigger the gesture event by calling inst.trigger
 *
 *
 * Handle gestures
 * --------------------
 * inside the handler you can get/set Hammer.detection.current. This is the current
 * detection session. It has the following properties
 *      @param  {String}    name
 *      contains the name of the gesture we have detected. it has not a real function,
 *      only to check in other gestures if something is detected.
 *      like in the drag gesture we set it to 'drag' and in the swipe gesture we can
 *      check if the current gesture is 'drag' by accessing Hammer.detection.current.name
 *
 *      @readonly
 *      @param  {Hammer.Instance}    inst
 *      the instance we do the detection for
 *
 *      @readonly
 *      @param  {Object}    startEvent
 *      contains the properties of the first gesture detection in this session.
 *      Used for calculations about timing, distance, etc.
 *
 *      @readonly
 *      @param  {Object}    lastEvent
 *      contains all the properties of the last gesture detect in this session.
 *
 * after the gesture detection session has been completed (user has released the screen)
 * the Hammer.detection.current object is copied into Hammer.detection.previous,
 * this is usefull for gestures like doubletap, where you need to know if the
 * previous gesture was a tap
 *
 * options that have been set by the instance can be received by calling inst.options
 *
 * You can trigger a gesture event by calling inst.trigger("mygesture", event).
 * The first param is the name of your gesture, the second the event argument
 *
 *
 * Register gestures
 * --------------------
 * When an gesture is added to the Hammer.gestures object, it is auto registered
 * at the setup of the first Hammer instance. You can also call Hammer.detection.register
 * manually and pass your gesture object as a param
 *
 */

/**
 * Hold
 * Touch stays at the same place for x time
 * @events  hold
 */
Hammer.gestures.Hold = {
    name: 'hold',
    index: 10,
    defaults: {
        hold_timeout	: 500,
        hold_threshold	: 1
    },
    timer: null,
    handler: function holdGesture(ev, inst) {
        switch(ev.eventType) {
            case Hammer.EVENT_START:
                // clear any running timers
                clearTimeout(this.timer);

                // set the gesture so we can check in the timeout if it still is
                Hammer.detection.current.name = this.name;

                // set timer and if after the timeout it still is hold,
                // we trigger the hold event
                this.timer = setTimeout(function() {
                    if(Hammer.detection.current.name == 'hold') {
                        inst.trigger('hold', ev);
                    }
                }, inst.options.hold_timeout);
                break;

            // when you move or end we clear the timer
            case Hammer.EVENT_MOVE:
                if(ev.distance > inst.options.hold_threshold) {
                    clearTimeout(this.timer);
                }
                break;

            case Hammer.EVENT_END:
                clearTimeout(this.timer);
                break;
        }
    }
};


/**
 * Tap/DoubleTap
 * Quick touch at a place or double at the same place
 * @events  tap, doubletap
 */
Hammer.gestures.Tap = {
    name: 'tap',
    index: 100,
    defaults: {
        tap_max_touchtime	: 250,
        tap_max_distance	: 10,
		tap_always			: true,
        doubletap_distance	: 20,
        doubletap_interval	: 300
    },
    handler: function tapGesture(ev, inst) {
        if(ev.eventType == Hammer.EVENT_END) {
            // previous gesture, for the double tap since these are two different gesture detections
            var prev = Hammer.detection.previous,
				did_doubletap = false;

            // when the touchtime is higher then the max touch time
            // or when the moving distance is too much
            if(ev.deltaTime > inst.options.tap_max_touchtime ||
                ev.distance > inst.options.tap_max_distance) {
                return;
            }

            // check if double tap
            if(prev && prev.name == 'tap' &&
                (ev.timeStamp - prev.lastEvent.timeStamp) < inst.options.doubletap_interval &&
                ev.distance < inst.options.doubletap_distance) {
				inst.trigger('doubletap', ev);
				did_doubletap = true;
            }

			// do a single tap
			if(!did_doubletap || inst.options.tap_always) {
				Hammer.detection.current.name = 'tap';
				inst.trigger(Hammer.detection.current.name, ev);
			}
        }
    }
};


/**
 * Swipe
 * triggers swipe events when the end velocity is above the threshold
 * @events  swipe, swipeleft, swiperight, swipeup, swipedown
 */
Hammer.gestures.Swipe = {
    name: 'swipe',
    index: 40,
    defaults: {
        // set 0 for unlimited, but this can conflict with transform
        swipe_max_touches  : 1,
        swipe_velocity     : 0.7
    },
    handler: function swipeGesture(ev, inst) {
        if(ev.eventType == Hammer.EVENT_END) {
            // max touches
            if(inst.options.swipe_max_touches > 0 &&
                ev.touches.length > inst.options.swipe_max_touches) {
                return;
            }

            // when the distance we moved is too small we skip this gesture
            // or we can be already in dragging
            if(ev.velocityX > inst.options.swipe_velocity ||
                ev.velocityY > inst.options.swipe_velocity) {
                // trigger swipe events
                inst.trigger(this.name, ev);
                inst.trigger(this.name + ev.direction, ev);
            }
        }
    }
};


/**
 * Drag
 * Move with x fingers (default 1) around on the page. Blocking the scrolling when
 * moving left and right is a good practice. When all the drag events are blocking
 * you disable scrolling on that area.
 * @events  drag, drapleft, dragright, dragup, dragdown
 */
Hammer.gestures.Drag = {
    name: 'drag',
    index: 50,
    defaults: {
        drag_min_distance : 10,
        // set 0 for unlimited, but this can conflict with transform
        drag_max_touches  : 1,
        // prevent default browser behavior when dragging occurs
        // be careful with it, it makes the element a blocking element
        // when you are using the drag gesture, it is a good practice to set this true
        drag_block_horizontal   : false,
        drag_block_vertical     : false,
        // drag_lock_to_axis keeps the drag gesture on the axis that it started on,
        // It disallows vertical directions if the initial direction was horizontal, and vice versa.
        drag_lock_to_axis       : false,
        // drag lock only kicks in when distance > drag_lock_min_distance
        // This way, locking occurs only when the distance has become large enough to reliably determine the direction
        drag_lock_min_distance : 25
    },
    triggered: false,
    handler: function dragGesture(ev, inst) {
        // current gesture isnt drag, but dragged is true
        // this means an other gesture is busy. now call dragend
        if(Hammer.detection.current.name != this.name && this.triggered) {
            inst.trigger(this.name +'end', ev);
            this.triggered = false;
            return;
        }

        // max touches
        if(inst.options.drag_max_touches > 0 &&
            ev.touches.length > inst.options.drag_max_touches) {
            return;
        }

        switch(ev.eventType) {
            case Hammer.EVENT_START:
                this.triggered = false;
                break;

            case Hammer.EVENT_MOVE:
                // when the distance we moved is too small we skip this gesture
                // or we can be already in dragging
                if(ev.distance < inst.options.drag_min_distance &&
                    Hammer.detection.current.name != this.name) {
                    return;
                }

                // we are dragging!
                Hammer.detection.current.name = this.name;

                // lock drag to axis?
                if(Hammer.detection.current.lastEvent.drag_locked_to_axis || (inst.options.drag_lock_to_axis && inst.options.drag_lock_min_distance<=ev.distance)) {
                    ev.drag_locked_to_axis = true;
                }
                var last_direction = Hammer.detection.current.lastEvent.direction;
                if(ev.drag_locked_to_axis && last_direction !== ev.direction) {
                    // keep direction on the axis that the drag gesture started on
                    if(Hammer.utils.isVertical(last_direction)) {
                        ev.direction = (ev.deltaY < 0) ? Hammer.DIRECTION_UP : Hammer.DIRECTION_DOWN;
                    }
                    else {
                        ev.direction = (ev.deltaX < 0) ? Hammer.DIRECTION_LEFT : Hammer.DIRECTION_RIGHT;
                    }
                }

                // first time, trigger dragstart event
                if(!this.triggered) {
                    inst.trigger(this.name +'start', ev);
                    this.triggered = true;
                }

                // trigger normal event
                inst.trigger(this.name, ev);

                // direction event, like dragdown
                inst.trigger(this.name + ev.direction, ev);

                // block the browser events
                if( (inst.options.drag_block_vertical && Hammer.utils.isVertical(ev.direction)) ||
                    (inst.options.drag_block_horizontal && !Hammer.utils.isVertical(ev.direction))) {
                    ev.preventDefault();
                }
                break;

            case Hammer.EVENT_END:
                // trigger dragend
                if(this.triggered) {
                    inst.trigger(this.name +'end', ev);
                }

                this.triggered = false;
                break;
        }
    }
};


/**
 * Transform
 * User want to scale or rotate with 2 fingers
 * @events  transform, pinch, pinchin, pinchout, rotate
 */
Hammer.gestures.Transform = {
    name: 'transform',
    index: 45,
    defaults: {
        // factor, no scale is 1, zoomin is to 0 and zoomout until higher then 1
        transform_min_scale     : 0.01,
        // rotation in degrees
        transform_min_rotation  : 1,
        // prevent default browser behavior when two touches are on the screen
        // but it makes the element a blocking element
        // when you are using the transform gesture, it is a good practice to set this true
        transform_always_block  : false
    },
    triggered: false,
    handler: function transformGesture(ev, inst) {
        // current gesture isnt drag, but dragged is true
        // this means an other gesture is busy. now call dragend
        if(Hammer.detection.current.name != this.name && this.triggered) {
            inst.trigger(this.name +'end', ev);
            this.triggered = false;
            return;
        }

        // atleast multitouch
        if(ev.touches.length < 2) {
            return;
        }

        // prevent default when two fingers are on the screen
        if(inst.options.transform_always_block) {
            ev.preventDefault();
        }

        switch(ev.eventType) {
            case Hammer.EVENT_START:
                this.triggered = false;
                break;

            case Hammer.EVENT_MOVE:
                var scale_threshold = Math.abs(1-ev.scale);
                var rotation_threshold = Math.abs(ev.rotation);

                // when the distance we moved is too small we skip this gesture
                // or we can be already in dragging
                if(scale_threshold < inst.options.transform_min_scale &&
                    rotation_threshold < inst.options.transform_min_rotation) {
                    return;
                }

                // we are transforming!
                Hammer.detection.current.name = this.name;

                // first time, trigger dragstart event
                if(!this.triggered) {
                    inst.trigger(this.name +'start', ev);
                    this.triggered = true;
                }

                inst.trigger(this.name, ev); // basic transform event

                // trigger rotate event
                if(rotation_threshold > inst.options.transform_min_rotation) {
                    inst.trigger('rotate', ev);
                }

                // trigger pinch event
                if(scale_threshold > inst.options.transform_min_scale) {
                    inst.trigger('pinch', ev);
                    inst.trigger('pinch'+ ((ev.scale < 1) ? 'in' : 'out'), ev);
                }
                break;

            case Hammer.EVENT_END:
                // trigger dragend
                if(this.triggered) {
                    inst.trigger(this.name +'end', ev);
                }

                this.triggered = false;
                break;
        }
    }
};


/**
 * Touch
 * Called as first, tells the user has touched the screen
 * @events  touch
 */
Hammer.gestures.Touch = {
    name: 'touch',
    index: -Infinity,
    defaults: {
        // call preventDefault at touchstart, and makes the element blocking by
        // disabling the scrolling of the page, but it improves gestures like
        // transforming and dragging.
        // be careful with using this, it can be very annoying for users to be stuck
        // on the page
        prevent_default: false,

        // disable mouse events, so only touch (or pen!) input triggers events
        prevent_mouseevents: false
    },
    handler: function touchGesture(ev, inst) {
        if(inst.options.prevent_mouseevents && ev.pointerType == Hammer.POINTER_MOUSE) {
            ev.stopDetect();
            return;
        }

        if(inst.options.prevent_default) {
            ev.preventDefault();
        }

        if(ev.eventType ==  Hammer.EVENT_START) {
            inst.trigger(this.name, ev);
        }
    }
};


/**
 * Release
 * Called as last, tells the user has released the screen
 * @events  release
 */
Hammer.gestures.Release = {
    name: 'release',
    index: Infinity,
    handler: function releaseGesture(ev, inst) {
        if(ev.eventType ==  Hammer.EVENT_END) {
            inst.trigger(this.name, ev);
        }
    }
};

// node export
if(typeof module === 'object' && typeof module.exports === 'object'){
    module.exports = Hammer;
}
// just window export
else {
    window.Hammer = Hammer;

    // requireJS module definition
    if(typeof window.define === 'function' && window.define.amd) {
        window.define('hammer', [], function() {
            return Hammer;
        });
    }
}
})(this);
},{}],3:[function(require,module,exports){
//! moment.js
//! version : 2.5.1
//! authors : Tim Wood, Iskren Chernev, Moment.js contributors
//! license : MIT
//! momentjs.com

(function (undefined) {

    /************************************
        Constants
    ************************************/

    var moment,
        VERSION = "2.5.1",
        global = this,
        round = Math.round,
        i,

        YEAR = 0,
        MONTH = 1,
        DATE = 2,
        HOUR = 3,
        MINUTE = 4,
        SECOND = 5,
        MILLISECOND = 6,

        // internal storage for language config files
        languages = {},

        // moment internal properties
        momentProperties = {
            _isAMomentObject: null,
            _i : null,
            _f : null,
            _l : null,
            _strict : null,
            _isUTC : null,
            _offset : null,  // optional. Combine with _isUTC
            _pf : null,
            _lang : null  // optional
        },

        // check for nodeJS
        hasModule = (typeof module !== 'undefined' && module.exports && typeof require !== 'undefined'),

        // ASP.NET json date format regex
        aspNetJsonRegex = /^\/?Date\((\-?\d+)/i,
        aspNetTimeSpanJsonRegex = /(\-)?(?:(\d*)\.)?(\d+)\:(\d+)(?:\:(\d+)\.?(\d{3})?)?/,

        // from http://docs.closure-library.googlecode.com/git/closure_goog_date_date.js.source.html
        // somewhat more in line with 4.4.3.2 2004 spec, but allows decimal anywhere
        isoDurationRegex = /^(-)?P(?:(?:([0-9,.]*)Y)?(?:([0-9,.]*)M)?(?:([0-9,.]*)D)?(?:T(?:([0-9,.]*)H)?(?:([0-9,.]*)M)?(?:([0-9,.]*)S)?)?|([0-9,.]*)W)$/,

        // format tokens
        formattingTokens = /(\[[^\[]*\])|(\\)?(Mo|MM?M?M?|Do|DDDo|DD?D?D?|ddd?d?|do?|w[o|w]?|W[o|W]?|YYYYYY|YYYYY|YYYY|YY|gg(ggg?)?|GG(GGG?)?|e|E|a|A|hh?|HH?|mm?|ss?|S{1,4}|X|zz?|ZZ?|.)/g,
        localFormattingTokens = /(\[[^\[]*\])|(\\)?(LT|LL?L?L?|l{1,4})/g,

        // parsing token regexes
        parseTokenOneOrTwoDigits = /\d\d?/, // 0 - 99
        parseTokenOneToThreeDigits = /\d{1,3}/, // 0 - 999
        parseTokenOneToFourDigits = /\d{1,4}/, // 0 - 9999
        parseTokenOneToSixDigits = /[+\-]?\d{1,6}/, // -999,999 - 999,999
        parseTokenDigits = /\d+/, // nonzero number of digits
        parseTokenWord = /[0-9]*['a-z\u00A0-\u05FF\u0700-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]+|[\u0600-\u06FF\/]+(\s*?[\u0600-\u06FF]+){1,2}/i, // any word (or two) characters or numbers including two/three word month in arabic.
        parseTokenTimezone = /Z|[\+\-]\d\d:?\d\d/gi, // +00:00 -00:00 +0000 -0000 or Z
        parseTokenT = /T/i, // T (ISO separator)
        parseTokenTimestampMs = /[\+\-]?\d+(\.\d{1,3})?/, // 123456789 123456789.123

        //strict parsing regexes
        parseTokenOneDigit = /\d/, // 0 - 9
        parseTokenTwoDigits = /\d\d/, // 00 - 99
        parseTokenThreeDigits = /\d{3}/, // 000 - 999
        parseTokenFourDigits = /\d{4}/, // 0000 - 9999
        parseTokenSixDigits = /[+-]?\d{6}/, // -999,999 - 999,999
        parseTokenSignedNumber = /[+-]?\d+/, // -inf - inf

        // iso 8601 regex
        // 0000-00-00 0000-W00 or 0000-W00-0 + T + 00 or 00:00 or 00:00:00 or 00:00:00.000 + +00:00 or +0000 or +00)
        isoRegex = /^\s*(?:[+-]\d{6}|\d{4})-(?:(\d\d-\d\d)|(W\d\d$)|(W\d\d-\d)|(\d\d\d))((T| )(\d\d(:\d\d(:\d\d(\.\d+)?)?)?)?([\+\-]\d\d(?::?\d\d)?|\s*Z)?)?$/,

        isoFormat = 'YYYY-MM-DDTHH:mm:ssZ',

        isoDates = [
            ['YYYYYY-MM-DD', /[+-]\d{6}-\d{2}-\d{2}/],
            ['YYYY-MM-DD', /\d{4}-\d{2}-\d{2}/],
            ['GGGG-[W]WW-E', /\d{4}-W\d{2}-\d/],
            ['GGGG-[W]WW', /\d{4}-W\d{2}/],
            ['YYYY-DDD', /\d{4}-\d{3}/]
        ],

        // iso time formats and regexes
        isoTimes = [
            ['HH:mm:ss.SSSS', /(T| )\d\d:\d\d:\d\d\.\d{1,3}/],
            ['HH:mm:ss', /(T| )\d\d:\d\d:\d\d/],
            ['HH:mm', /(T| )\d\d:\d\d/],
            ['HH', /(T| )\d\d/]
        ],

        // timezone chunker "+10:00" > ["10", "00"] or "-1530" > ["-15", "30"]
        parseTimezoneChunker = /([\+\-]|\d\d)/gi,

        // getter and setter names
        proxyGettersAndSetters = 'Date|Hours|Minutes|Seconds|Milliseconds'.split('|'),
        unitMillisecondFactors = {
            'Milliseconds' : 1,
            'Seconds' : 1e3,
            'Minutes' : 6e4,
            'Hours' : 36e5,
            'Days' : 864e5,
            'Months' : 2592e6,
            'Years' : 31536e6
        },

        unitAliases = {
            ms : 'millisecond',
            s : 'second',
            m : 'minute',
            h : 'hour',
            d : 'day',
            D : 'date',
            w : 'week',
            W : 'isoWeek',
            M : 'month',
            y : 'year',
            DDD : 'dayOfYear',
            e : 'weekday',
            E : 'isoWeekday',
            gg: 'weekYear',
            GG: 'isoWeekYear'
        },

        camelFunctions = {
            dayofyear : 'dayOfYear',
            isoweekday : 'isoWeekday',
            isoweek : 'isoWeek',
            weekyear : 'weekYear',
            isoweekyear : 'isoWeekYear'
        },

        // format function strings
        formatFunctions = {},

        // tokens to ordinalize and pad
        ordinalizeTokens = 'DDD w W M D d'.split(' '),
        paddedTokens = 'M D H h m s w W'.split(' '),

        formatTokenFunctions = {
            M    : function () {
                return this.month() + 1;
            },
            MMM  : function (format) {
                return this.lang().monthsShort(this, format);
            },
            MMMM : function (format) {
                return this.lang().months(this, format);
            },
            D    : function () {
                return this.date();
            },
            DDD  : function () {
                return this.dayOfYear();
            },
            d    : function () {
                return this.day();
            },
            dd   : function (format) {
                return this.lang().weekdaysMin(this, format);
            },
            ddd  : function (format) {
                return this.lang().weekdaysShort(this, format);
            },
            dddd : function (format) {
                return this.lang().weekdays(this, format);
            },
            w    : function () {
                return this.week();
            },
            W    : function () {
                return this.isoWeek();
            },
            YY   : function () {
                return leftZeroFill(this.year() % 100, 2);
            },
            YYYY : function () {
                return leftZeroFill(this.year(), 4);
            },
            YYYYY : function () {
                return leftZeroFill(this.year(), 5);
            },
            YYYYYY : function () {
                var y = this.year(), sign = y >= 0 ? '+' : '-';
                return sign + leftZeroFill(Math.abs(y), 6);
            },
            gg   : function () {
                return leftZeroFill(this.weekYear() % 100, 2);
            },
            gggg : function () {
                return leftZeroFill(this.weekYear(), 4);
            },
            ggggg : function () {
                return leftZeroFill(this.weekYear(), 5);
            },
            GG   : function () {
                return leftZeroFill(this.isoWeekYear() % 100, 2);
            },
            GGGG : function () {
                return leftZeroFill(this.isoWeekYear(), 4);
            },
            GGGGG : function () {
                return leftZeroFill(this.isoWeekYear(), 5);
            },
            e : function () {
                return this.weekday();
            },
            E : function () {
                return this.isoWeekday();
            },
            a    : function () {
                return this.lang().meridiem(this.hours(), this.minutes(), true);
            },
            A    : function () {
                return this.lang().meridiem(this.hours(), this.minutes(), false);
            },
            H    : function () {
                return this.hours();
            },
            h    : function () {
                return this.hours() % 12 || 12;
            },
            m    : function () {
                return this.minutes();
            },
            s    : function () {
                return this.seconds();
            },
            S    : function () {
                return toInt(this.milliseconds() / 100);
            },
            SS   : function () {
                return leftZeroFill(toInt(this.milliseconds() / 10), 2);
            },
            SSS  : function () {
                return leftZeroFill(this.milliseconds(), 3);
            },
            SSSS : function () {
                return leftZeroFill(this.milliseconds(), 3);
            },
            Z    : function () {
                var a = -this.zone(),
                    b = "+";
                if (a < 0) {
                    a = -a;
                    b = "-";
                }
                return b + leftZeroFill(toInt(a / 60), 2) + ":" + leftZeroFill(toInt(a) % 60, 2);
            },
            ZZ   : function () {
                var a = -this.zone(),
                    b = "+";
                if (a < 0) {
                    a = -a;
                    b = "-";
                }
                return b + leftZeroFill(toInt(a / 60), 2) + leftZeroFill(toInt(a) % 60, 2);
            },
            z : function () {
                return this.zoneAbbr();
            },
            zz : function () {
                return this.zoneName();
            },
            X    : function () {
                return this.unix();
            },
            Q : function () {
                return this.quarter();
            }
        },

        lists = ['months', 'monthsShort', 'weekdays', 'weekdaysShort', 'weekdaysMin'];

    function defaultParsingFlags() {
        // We need to deep clone this object, and es5 standard is not very
        // helpful.
        return {
            empty : false,
            unusedTokens : [],
            unusedInput : [],
            overflow : -2,
            charsLeftOver : 0,
            nullInput : false,
            invalidMonth : null,
            invalidFormat : false,
            userInvalidated : false,
            iso: false
        };
    }

    function padToken(func, count) {
        return function (a) {
            return leftZeroFill(func.call(this, a), count);
        };
    }
    function ordinalizeToken(func, period) {
        return function (a) {
            return this.lang().ordinal(func.call(this, a), period);
        };
    }

    while (ordinalizeTokens.length) {
        i = ordinalizeTokens.pop();
        formatTokenFunctions[i + 'o'] = ordinalizeToken(formatTokenFunctions[i], i);
    }
    while (paddedTokens.length) {
        i = paddedTokens.pop();
        formatTokenFunctions[i + i] = padToken(formatTokenFunctions[i], 2);
    }
    formatTokenFunctions.DDDD = padToken(formatTokenFunctions.DDD, 3);


    /************************************
        Constructors
    ************************************/

    function Language() {

    }

    // Moment prototype object
    function Moment(config) {
        checkOverflow(config);
        extend(this, config);
    }

    // Duration Constructor
    function Duration(duration) {
        var normalizedInput = normalizeObjectUnits(duration),
            years = normalizedInput.year || 0,
            months = normalizedInput.month || 0,
            weeks = normalizedInput.week || 0,
            days = normalizedInput.day || 0,
            hours = normalizedInput.hour || 0,
            minutes = normalizedInput.minute || 0,
            seconds = normalizedInput.second || 0,
            milliseconds = normalizedInput.millisecond || 0;

        // representation for dateAddRemove
        this._milliseconds = +milliseconds +
            seconds * 1e3 + // 1000
            minutes * 6e4 + // 1000 * 60
            hours * 36e5; // 1000 * 60 * 60
        // Because of dateAddRemove treats 24 hours as different from a
        // day when working around DST, we need to store them separately
        this._days = +days +
            weeks * 7;
        // It is impossible translate months into days without knowing
        // which months you are are talking about, so we have to store
        // it separately.
        this._months = +months +
            years * 12;

        this._data = {};

        this._bubble();
    }

    /************************************
        Helpers
    ************************************/


    function extend(a, b) {
        for (var i in b) {
            if (b.hasOwnProperty(i)) {
                a[i] = b[i];
            }
        }

        if (b.hasOwnProperty("toString")) {
            a.toString = b.toString;
        }

        if (b.hasOwnProperty("valueOf")) {
            a.valueOf = b.valueOf;
        }

        return a;
    }

    function cloneMoment(m) {
        var result = {}, i;
        for (i in m) {
            if (m.hasOwnProperty(i) && momentProperties.hasOwnProperty(i)) {
                result[i] = m[i];
            }
        }

        return result;
    }

    function absRound(number) {
        if (number < 0) {
            return Math.ceil(number);
        } else {
            return Math.floor(number);
        }
    }

    // left zero fill a number
    // see http://jsperf.com/left-zero-filling for performance comparison
    function leftZeroFill(number, targetLength, forceSign) {
        var output = '' + Math.abs(number),
            sign = number >= 0;

        while (output.length < targetLength) {
            output = '0' + output;
        }
        return (sign ? (forceSign ? '+' : '') : '-') + output;
    }

    // helper function for _.addTime and _.subtractTime
    function addOrSubtractDurationFromMoment(mom, duration, isAdding, ignoreUpdateOffset) {
        var milliseconds = duration._milliseconds,
            days = duration._days,
            months = duration._months,
            minutes,
            hours;

        if (milliseconds) {
            mom._d.setTime(+mom._d + milliseconds * isAdding);
        }
        // store the minutes and hours so we can restore them
        if (days || months) {
            minutes = mom.minute();
            hours = mom.hour();
        }
        if (days) {
            mom.date(mom.date() + days * isAdding);
        }
        if (months) {
            mom.month(mom.month() + months * isAdding);
        }
        if (milliseconds && !ignoreUpdateOffset) {
            moment.updateOffset(mom);
        }
        // restore the minutes and hours after possibly changing dst
        if (days || months) {
            mom.minute(minutes);
            mom.hour(hours);
        }
    }

    // check if is an array
    function isArray(input) {
        return Object.prototype.toString.call(input) === '[object Array]';
    }

    function isDate(input) {
        return  Object.prototype.toString.call(input) === '[object Date]' ||
                input instanceof Date;
    }

    // compare two arrays, return the number of differences
    function compareArrays(array1, array2, dontConvert) {
        var len = Math.min(array1.length, array2.length),
            lengthDiff = Math.abs(array1.length - array2.length),
            diffs = 0,
            i;
        for (i = 0; i < len; i++) {
            if ((dontConvert && array1[i] !== array2[i]) ||
                (!dontConvert && toInt(array1[i]) !== toInt(array2[i]))) {
                diffs++;
            }
        }
        return diffs + lengthDiff;
    }

    function normalizeUnits(units) {
        if (units) {
            var lowered = units.toLowerCase().replace(/(.)s$/, '$1');
            units = unitAliases[units] || camelFunctions[lowered] || lowered;
        }
        return units;
    }

    function normalizeObjectUnits(inputObject) {
        var normalizedInput = {},
            normalizedProp,
            prop;

        for (prop in inputObject) {
            if (inputObject.hasOwnProperty(prop)) {
                normalizedProp = normalizeUnits(prop);
                if (normalizedProp) {
                    normalizedInput[normalizedProp] = inputObject[prop];
                }
            }
        }

        return normalizedInput;
    }

    function makeList(field) {
        var count, setter;

        if (field.indexOf('week') === 0) {
            count = 7;
            setter = 'day';
        }
        else if (field.indexOf('month') === 0) {
            count = 12;
            setter = 'month';
        }
        else {
            return;
        }

        moment[field] = function (format, index) {
            var i, getter,
                method = moment.fn._lang[field],
                results = [];

            if (typeof format === 'number') {
                index = format;
                format = undefined;
            }

            getter = function (i) {
                var m = moment().utc().set(setter, i);
                return method.call(moment.fn._lang, m, format || '');
            };

            if (index != null) {
                return getter(index);
            }
            else {
                for (i = 0; i < count; i++) {
                    results.push(getter(i));
                }
                return results;
            }
        };
    }

    function toInt(argumentForCoercion) {
        var coercedNumber = +argumentForCoercion,
            value = 0;

        if (coercedNumber !== 0 && isFinite(coercedNumber)) {
            if (coercedNumber >= 0) {
                value = Math.floor(coercedNumber);
            } else {
                value = Math.ceil(coercedNumber);
            }
        }

        return value;
    }

    function daysInMonth(year, month) {
        return new Date(Date.UTC(year, month + 1, 0)).getUTCDate();
    }

    function daysInYear(year) {
        return isLeapYear(year) ? 366 : 365;
    }

    function isLeapYear(year) {
        return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
    }

    function checkOverflow(m) {
        var overflow;
        if (m._a && m._pf.overflow === -2) {
            overflow =
                m._a[MONTH] < 0 || m._a[MONTH] > 11 ? MONTH :
                m._a[DATE] < 1 || m._a[DATE] > daysInMonth(m._a[YEAR], m._a[MONTH]) ? DATE :
                m._a[HOUR] < 0 || m._a[HOUR] > 23 ? HOUR :
                m._a[MINUTE] < 0 || m._a[MINUTE] > 59 ? MINUTE :
                m._a[SECOND] < 0 || m._a[SECOND] > 59 ? SECOND :
                m._a[MILLISECOND] < 0 || m._a[MILLISECOND] > 999 ? MILLISECOND :
                -1;

            if (m._pf._overflowDayOfYear && (overflow < YEAR || overflow > DATE)) {
                overflow = DATE;
            }

            m._pf.overflow = overflow;
        }
    }

    function isValid(m) {
        if (m._isValid == null) {
            m._isValid = !isNaN(m._d.getTime()) &&
                m._pf.overflow < 0 &&
                !m._pf.empty &&
                !m._pf.invalidMonth &&
                !m._pf.nullInput &&
                !m._pf.invalidFormat &&
                !m._pf.userInvalidated;

            if (m._strict) {
                m._isValid = m._isValid &&
                    m._pf.charsLeftOver === 0 &&
                    m._pf.unusedTokens.length === 0;
            }
        }
        return m._isValid;
    }

    function normalizeLanguage(key) {
        return key ? key.toLowerCase().replace('_', '-') : key;
    }

    // Return a moment from input, that is local/utc/zone equivalent to model.
    function makeAs(input, model) {
        return model._isUTC ? moment(input).zone(model._offset || 0) :
            moment(input).local();
    }

    /************************************
        Languages
    ************************************/


    extend(Language.prototype, {

        set : function (config) {
            var prop, i;
            for (i in config) {
                prop = config[i];
                if (typeof prop === 'function') {
                    this[i] = prop;
                } else {
                    this['_' + i] = prop;
                }
            }
        },

        _months : "January_February_March_April_May_June_July_August_September_October_November_December".split("_"),
        months : function (m) {
            return this._months[m.month()];
        },

        _monthsShort : "Jan_Feb_Mar_Apr_May_Jun_Jul_Aug_Sep_Oct_Nov_Dec".split("_"),
        monthsShort : function (m) {
            return this._monthsShort[m.month()];
        },

        monthsParse : function (monthName) {
            var i, mom, regex;

            if (!this._monthsParse) {
                this._monthsParse = [];
            }

            for (i = 0; i < 12; i++) {
                // make the regex if we don't have it already
                if (!this._monthsParse[i]) {
                    mom = moment.utc([2000, i]);
                    regex = '^' + this.months(mom, '') + '|^' + this.monthsShort(mom, '');
                    this._monthsParse[i] = new RegExp(regex.replace('.', ''), 'i');
                }
                // test the regex
                if (this._monthsParse[i].test(monthName)) {
                    return i;
                }
            }
        },

        _weekdays : "Sunday_Monday_Tuesday_Wednesday_Thursday_Friday_Saturday".split("_"),
        weekdays : function (m) {
            return this._weekdays[m.day()];
        },

        _weekdaysShort : "Sun_Mon_Tue_Wed_Thu_Fri_Sat".split("_"),
        weekdaysShort : function (m) {
            return this._weekdaysShort[m.day()];
        },

        _weekdaysMin : "Su_Mo_Tu_We_Th_Fr_Sa".split("_"),
        weekdaysMin : function (m) {
            return this._weekdaysMin[m.day()];
        },

        weekdaysParse : function (weekdayName) {
            var i, mom, regex;

            if (!this._weekdaysParse) {
                this._weekdaysParse = [];
            }

            for (i = 0; i < 7; i++) {
                // make the regex if we don't have it already
                if (!this._weekdaysParse[i]) {
                    mom = moment([2000, 1]).day(i);
                    regex = '^' + this.weekdays(mom, '') + '|^' + this.weekdaysShort(mom, '') + '|^' + this.weekdaysMin(mom, '');
                    this._weekdaysParse[i] = new RegExp(regex.replace('.', ''), 'i');
                }
                // test the regex
                if (this._weekdaysParse[i].test(weekdayName)) {
                    return i;
                }
            }
        },

        _longDateFormat : {
            LT : "h:mm A",
            L : "MM/DD/YYYY",
            LL : "MMMM D YYYY",
            LLL : "MMMM D YYYY LT",
            LLLL : "dddd, MMMM D YYYY LT"
        },
        longDateFormat : function (key) {
            var output = this._longDateFormat[key];
            if (!output && this._longDateFormat[key.toUpperCase()]) {
                output = this._longDateFormat[key.toUpperCase()].replace(/MMMM|MM|DD|dddd/g, function (val) {
                    return val.slice(1);
                });
                this._longDateFormat[key] = output;
            }
            return output;
        },

        isPM : function (input) {
            // IE8 Quirks Mode & IE7 Standards Mode do not allow accessing strings like arrays
            // Using charAt should be more compatible.
            return ((input + '').toLowerCase().charAt(0) === 'p');
        },

        _meridiemParse : /[ap]\.?m?\.?/i,
        meridiem : function (hours, minutes, isLower) {
            if (hours > 11) {
                return isLower ? 'pm' : 'PM';
            } else {
                return isLower ? 'am' : 'AM';
            }
        },

        _calendar : {
            sameDay : '[Today at] LT',
            nextDay : '[Tomorrow at] LT',
            nextWeek : 'dddd [at] LT',
            lastDay : '[Yesterday at] LT',
            lastWeek : '[Last] dddd [at] LT',
            sameElse : 'L'
        },
        calendar : function (key, mom) {
            var output = this._calendar[key];
            return typeof output === 'function' ? output.apply(mom) : output;
        },

        _relativeTime : {
            future : "in %s",
            past : "%s ago",
            s : "a few seconds",
            m : "a minute",
            mm : "%d minutes",
            h : "an hour",
            hh : "%d hours",
            d : "a day",
            dd : "%d days",
            M : "a month",
            MM : "%d months",
            y : "a year",
            yy : "%d years"
        },
        relativeTime : function (number, withoutSuffix, string, isFuture) {
            var output = this._relativeTime[string];
            return (typeof output === 'function') ?
                output(number, withoutSuffix, string, isFuture) :
                output.replace(/%d/i, number);
        },
        pastFuture : function (diff, output) {
            var format = this._relativeTime[diff > 0 ? 'future' : 'past'];
            return typeof format === 'function' ? format(output) : format.replace(/%s/i, output);
        },

        ordinal : function (number) {
            return this._ordinal.replace("%d", number);
        },
        _ordinal : "%d",

        preparse : function (string) {
            return string;
        },

        postformat : function (string) {
            return string;
        },

        week : function (mom) {
            return weekOfYear(mom, this._week.dow, this._week.doy).week;
        },

        _week : {
            dow : 0, // Sunday is the first day of the week.
            doy : 6  // The week that contains Jan 1st is the first week of the year.
        },

        _invalidDate: 'Invalid date',
        invalidDate: function () {
            return this._invalidDate;
        }
    });

    // Loads a language definition into the `languages` cache.  The function
    // takes a key and optionally values.  If not in the browser and no values
    // are provided, it will load the language file module.  As a convenience,
    // this function also returns the language values.
    function loadLang(key, values) {
        values.abbr = key;
        if (!languages[key]) {
            languages[key] = new Language();
        }
        languages[key].set(values);
        return languages[key];
    }

    // Remove a language from the `languages` cache. Mostly useful in tests.
    function unloadLang(key) {
        delete languages[key];
    }

    // Determines which language definition to use and returns it.
    //
    // With no parameters, it will return the global language.  If you
    // pass in a language key, such as 'en', it will return the
    // definition for 'en', so long as 'en' has already been loaded using
    // moment.lang.
    function getLangDefinition(key) {
        var i = 0, j, lang, next, split,
            get = function (k) {
                if (!languages[k] && hasModule) {
                    try {
                        require('./lang/' + k);
                    } catch (e) { }
                }
                return languages[k];
            };

        if (!key) {
            return moment.fn._lang;
        }

        if (!isArray(key)) {
            //short-circuit everything else
            lang = get(key);
            if (lang) {
                return lang;
            }
            key = [key];
        }

        //pick the language from the array
        //try ['en-au', 'en-gb'] as 'en-au', 'en-gb', 'en', as in move through the list trying each
        //substring from most specific to least, but move to the next array item if it's a more specific variant than the current root
        while (i < key.length) {
            split = normalizeLanguage(key[i]).split('-');
            j = split.length;
            next = normalizeLanguage(key[i + 1]);
            next = next ? next.split('-') : null;
            while (j > 0) {
                lang = get(split.slice(0, j).join('-'));
                if (lang) {
                    return lang;
                }
                if (next && next.length >= j && compareArrays(split, next, true) >= j - 1) {
                    //the next array item is better than a shallower substring of this one
                    break;
                }
                j--;
            }
            i++;
        }
        return moment.fn._lang;
    }

    /************************************
        Formatting
    ************************************/


    function removeFormattingTokens(input) {
        if (input.match(/\[[\s\S]/)) {
            return input.replace(/^\[|\]$/g, "");
        }
        return input.replace(/\\/g, "");
    }

    function makeFormatFunction(format) {
        var array = format.match(formattingTokens), i, length;

        for (i = 0, length = array.length; i < length; i++) {
            if (formatTokenFunctions[array[i]]) {
                array[i] = formatTokenFunctions[array[i]];
            } else {
                array[i] = removeFormattingTokens(array[i]);
            }
        }

        return function (mom) {
            var output = "";
            for (i = 0; i < length; i++) {
                output += array[i] instanceof Function ? array[i].call(mom, format) : array[i];
            }
            return output;
        };
    }

    // format date using native date object
    function formatMoment(m, format) {

        if (!m.isValid()) {
            return m.lang().invalidDate();
        }

        format = expandFormat(format, m.lang());

        if (!formatFunctions[format]) {
            formatFunctions[format] = makeFormatFunction(format);
        }

        return formatFunctions[format](m);
    }

    function expandFormat(format, lang) {
        var i = 5;

        function replaceLongDateFormatTokens(input) {
            return lang.longDateFormat(input) || input;
        }

        localFormattingTokens.lastIndex = 0;
        while (i >= 0 && localFormattingTokens.test(format)) {
            format = format.replace(localFormattingTokens, replaceLongDateFormatTokens);
            localFormattingTokens.lastIndex = 0;
            i -= 1;
        }

        return format;
    }


    /************************************
        Parsing
    ************************************/


    // get the regex to find the next token
    function getParseRegexForToken(token, config) {
        var a, strict = config._strict;
        switch (token) {
        case 'DDDD':
            return parseTokenThreeDigits;
        case 'YYYY':
        case 'GGGG':
        case 'gggg':
            return strict ? parseTokenFourDigits : parseTokenOneToFourDigits;
        case 'Y':
        case 'G':
        case 'g':
            return parseTokenSignedNumber;
        case 'YYYYYY':
        case 'YYYYY':
        case 'GGGGG':
        case 'ggggg':
            return strict ? parseTokenSixDigits : parseTokenOneToSixDigits;
        case 'S':
            if (strict) { return parseTokenOneDigit; }
            /* falls through */
        case 'SS':
            if (strict) { return parseTokenTwoDigits; }
            /* falls through */
        case 'SSS':
            if (strict) { return parseTokenThreeDigits; }
            /* falls through */
        case 'DDD':
            return parseTokenOneToThreeDigits;
        case 'MMM':
        case 'MMMM':
        case 'dd':
        case 'ddd':
        case 'dddd':
            return parseTokenWord;
        case 'a':
        case 'A':
            return getLangDefinition(config._l)._meridiemParse;
        case 'X':
            return parseTokenTimestampMs;
        case 'Z':
        case 'ZZ':
            return parseTokenTimezone;
        case 'T':
            return parseTokenT;
        case 'SSSS':
            return parseTokenDigits;
        case 'MM':
        case 'DD':
        case 'YY':
        case 'GG':
        case 'gg':
        case 'HH':
        case 'hh':
        case 'mm':
        case 'ss':
        case 'ww':
        case 'WW':
            return strict ? parseTokenTwoDigits : parseTokenOneOrTwoDigits;
        case 'M':
        case 'D':
        case 'd':
        case 'H':
        case 'h':
        case 'm':
        case 's':
        case 'w':
        case 'W':
        case 'e':
        case 'E':
            return parseTokenOneOrTwoDigits;
        default :
            a = new RegExp(regexpEscape(unescapeFormat(token.replace('\\', '')), "i"));
            return a;
        }
    }

    function timezoneMinutesFromString(string) {
        string = string || "";
        var possibleTzMatches = (string.match(parseTokenTimezone) || []),
            tzChunk = possibleTzMatches[possibleTzMatches.length - 1] || [],
            parts = (tzChunk + '').match(parseTimezoneChunker) || ['-', 0, 0],
            minutes = +(parts[1] * 60) + toInt(parts[2]);

        return parts[0] === '+' ? -minutes : minutes;
    }

    // function to convert string input to date
    function addTimeToArrayFromToken(token, input, config) {
        var a, datePartArray = config._a;

        switch (token) {
        // MONTH
        case 'M' : // fall through to MM
        case 'MM' :
            if (input != null) {
                datePartArray[MONTH] = toInt(input) - 1;
            }
            break;
        case 'MMM' : // fall through to MMMM
        case 'MMMM' :
            a = getLangDefinition(config._l).monthsParse(input);
            // if we didn't find a month name, mark the date as invalid.
            if (a != null) {
                datePartArray[MONTH] = a;
            } else {
                config._pf.invalidMonth = input;
            }
            break;
        // DAY OF MONTH
        case 'D' : // fall through to DD
        case 'DD' :
            if (input != null) {
                datePartArray[DATE] = toInt(input);
            }
            break;
        // DAY OF YEAR
        case 'DDD' : // fall through to DDDD
        case 'DDDD' :
            if (input != null) {
                config._dayOfYear = toInt(input);
            }

            break;
        // YEAR
        case 'YY' :
            datePartArray[YEAR] = toInt(input) + (toInt(input) > 68 ? 1900 : 2000);
            break;
        case 'YYYY' :
        case 'YYYYY' :
        case 'YYYYYY' :
            datePartArray[YEAR] = toInt(input);
            break;
        // AM / PM
        case 'a' : // fall through to A
        case 'A' :
            config._isPm = getLangDefinition(config._l).isPM(input);
            break;
        // 24 HOUR
        case 'H' : // fall through to hh
        case 'HH' : // fall through to hh
        case 'h' : // fall through to hh
        case 'hh' :
            datePartArray[HOUR] = toInt(input);
            break;
        // MINUTE
        case 'm' : // fall through to mm
        case 'mm' :
            datePartArray[MINUTE] = toInt(input);
            break;
        // SECOND
        case 's' : // fall through to ss
        case 'ss' :
            datePartArray[SECOND] = toInt(input);
            break;
        // MILLISECOND
        case 'S' :
        case 'SS' :
        case 'SSS' :
        case 'SSSS' :
            datePartArray[MILLISECOND] = toInt(('0.' + input) * 1000);
            break;
        // UNIX TIMESTAMP WITH MS
        case 'X':
            config._d = new Date(parseFloat(input) * 1000);
            break;
        // TIMEZONE
        case 'Z' : // fall through to ZZ
        case 'ZZ' :
            config._useUTC = true;
            config._tzm = timezoneMinutesFromString(input);
            break;
        case 'w':
        case 'ww':
        case 'W':
        case 'WW':
        case 'd':
        case 'dd':
        case 'ddd':
        case 'dddd':
        case 'e':
        case 'E':
            token = token.substr(0, 1);
            /* falls through */
        case 'gg':
        case 'gggg':
        case 'GG':
        case 'GGGG':
        case 'GGGGG':
            token = token.substr(0, 2);
            if (input) {
                config._w = config._w || {};
                config._w[token] = input;
            }
            break;
        }
    }

    // convert an array to a date.
    // the array should mirror the parameters below
    // note: all values past the year are optional and will default to the lowest possible value.
    // [year, month, day , hour, minute, second, millisecond]
    function dateFromConfig(config) {
        var i, date, input = [], currentDate,
            yearToUse, fixYear, w, temp, lang, weekday, week;

        if (config._d) {
            return;
        }

        currentDate = currentDateArray(config);

        //compute day of the year from weeks and weekdays
        if (config._w && config._a[DATE] == null && config._a[MONTH] == null) {
            fixYear = function (val) {
                var int_val = parseInt(val, 10);
                return val ?
                  (val.length < 3 ? (int_val > 68 ? 1900 + int_val : 2000 + int_val) : int_val) :
                  (config._a[YEAR] == null ? moment().weekYear() : config._a[YEAR]);
            };

            w = config._w;
            if (w.GG != null || w.W != null || w.E != null) {
                temp = dayOfYearFromWeeks(fixYear(w.GG), w.W || 1, w.E, 4, 1);
            }
            else {
                lang = getLangDefinition(config._l);
                weekday = w.d != null ?  parseWeekday(w.d, lang) :
                  (w.e != null ?  parseInt(w.e, 10) + lang._week.dow : 0);

                week = parseInt(w.w, 10) || 1;

                //if we're parsing 'd', then the low day numbers may be next week
                if (w.d != null && weekday < lang._week.dow) {
                    week++;
                }

                temp = dayOfYearFromWeeks(fixYear(w.gg), week, weekday, lang._week.doy, lang._week.dow);
            }

            config._a[YEAR] = temp.year;
            config._dayOfYear = temp.dayOfYear;
        }

        //if the day of the year is set, figure out what it is
        if (config._dayOfYear) {
            yearToUse = config._a[YEAR] == null ? currentDate[YEAR] : config._a[YEAR];

            if (config._dayOfYear > daysInYear(yearToUse)) {
                config._pf._overflowDayOfYear = true;
            }

            date = makeUTCDate(yearToUse, 0, config._dayOfYear);
            config._a[MONTH] = date.getUTCMonth();
            config._a[DATE] = date.getUTCDate();
        }

        // Default to current date.
        // * if no year, month, day of month are given, default to today
        // * if day of month is given, default month and year
        // * if month is given, default only year
        // * if year is given, don't default anything
        for (i = 0; i < 3 && config._a[i] == null; ++i) {
            config._a[i] = input[i] = currentDate[i];
        }

        // Zero out whatever was not defaulted, including time
        for (; i < 7; i++) {
            config._a[i] = input[i] = (config._a[i] == null) ? (i === 2 ? 1 : 0) : config._a[i];
        }

        // add the offsets to the time to be parsed so that we can have a clean array for checking isValid
        input[HOUR] += toInt((config._tzm || 0) / 60);
        input[MINUTE] += toInt((config._tzm || 0) % 60);

        config._d = (config._useUTC ? makeUTCDate : makeDate).apply(null, input);
    }

    function dateFromObject(config) {
        var normalizedInput;

        if (config._d) {
            return;
        }

        normalizedInput = normalizeObjectUnits(config._i);
        config._a = [
            normalizedInput.year,
            normalizedInput.month,
            normalizedInput.day,
            normalizedInput.hour,
            normalizedInput.minute,
            normalizedInput.second,
            normalizedInput.millisecond
        ];

        dateFromConfig(config);
    }

    function currentDateArray(config) {
        var now = new Date();
        if (config._useUTC) {
            return [
                now.getUTCFullYear(),
                now.getUTCMonth(),
                now.getUTCDate()
            ];
        } else {
            return [now.getFullYear(), now.getMonth(), now.getDate()];
        }
    }

    // date from string and format string
    function makeDateFromStringAndFormat(config) {

        config._a = [];
        config._pf.empty = true;

        // This array is used to make a Date, either with `new Date` or `Date.UTC`
        var lang = getLangDefinition(config._l),
            string = '' + config._i,
            i, parsedInput, tokens, token, skipped,
            stringLength = string.length,
            totalParsedInputLength = 0;

        tokens = expandFormat(config._f, lang).match(formattingTokens) || [];

        for (i = 0; i < tokens.length; i++) {
            token = tokens[i];
            parsedInput = (string.match(getParseRegexForToken(token, config)) || [])[0];
            if (parsedInput) {
                skipped = string.substr(0, string.indexOf(parsedInput));
                if (skipped.length > 0) {
                    config._pf.unusedInput.push(skipped);
                }
                string = string.slice(string.indexOf(parsedInput) + parsedInput.length);
                totalParsedInputLength += parsedInput.length;
            }
            // don't parse if it's not a known token
            if (formatTokenFunctions[token]) {
                if (parsedInput) {
                    config._pf.empty = false;
                }
                else {
                    config._pf.unusedTokens.push(token);
                }
                addTimeToArrayFromToken(token, parsedInput, config);
            }
            else if (config._strict && !parsedInput) {
                config._pf.unusedTokens.push(token);
            }
        }

        // add remaining unparsed input length to the string
        config._pf.charsLeftOver = stringLength - totalParsedInputLength;
        if (string.length > 0) {
            config._pf.unusedInput.push(string);
        }

        // handle am pm
        if (config._isPm && config._a[HOUR] < 12) {
            config._a[HOUR] += 12;
        }
        // if is 12 am, change hours to 0
        if (config._isPm === false && config._a[HOUR] === 12) {
            config._a[HOUR] = 0;
        }

        dateFromConfig(config);
        checkOverflow(config);
    }

    function unescapeFormat(s) {
        return s.replace(/\\(\[)|\\(\])|\[([^\]\[]*)\]|\\(.)/g, function (matched, p1, p2, p3, p4) {
            return p1 || p2 || p3 || p4;
        });
    }

    // Code from http://stackoverflow.com/questions/3561493/is-there-a-regexp-escape-function-in-javascript
    function regexpEscape(s) {
        return s.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
    }

    // date from string and array of format strings
    function makeDateFromStringAndArray(config) {
        var tempConfig,
            bestMoment,

            scoreToBeat,
            i,
            currentScore;

        if (config._f.length === 0) {
            config._pf.invalidFormat = true;
            config._d = new Date(NaN);
            return;
        }

        for (i = 0; i < config._f.length; i++) {
            currentScore = 0;
            tempConfig = extend({}, config);
            tempConfig._pf = defaultParsingFlags();
            tempConfig._f = config._f[i];
            makeDateFromStringAndFormat(tempConfig);

            if (!isValid(tempConfig)) {
                continue;
            }

            // if there is any input that was not parsed add a penalty for that format
            currentScore += tempConfig._pf.charsLeftOver;

            //or tokens
            currentScore += tempConfig._pf.unusedTokens.length * 10;

            tempConfig._pf.score = currentScore;

            if (scoreToBeat == null || currentScore < scoreToBeat) {
                scoreToBeat = currentScore;
                bestMoment = tempConfig;
            }
        }

        extend(config, bestMoment || tempConfig);
    }

    // date from iso format
    function makeDateFromString(config) {
        var i, l,
            string = config._i,
            match = isoRegex.exec(string);

        if (match) {
            config._pf.iso = true;
            for (i = 0, l = isoDates.length; i < l; i++) {
                if (isoDates[i][1].exec(string)) {
                    // match[5] should be "T" or undefined
                    config._f = isoDates[i][0] + (match[6] || " ");
                    break;
                }
            }
            for (i = 0, l = isoTimes.length; i < l; i++) {
                if (isoTimes[i][1].exec(string)) {
                    config._f += isoTimes[i][0];
                    break;
                }
            }
            if (string.match(parseTokenTimezone)) {
                config._f += "Z";
            }
            makeDateFromStringAndFormat(config);
        }
        else {
            config._d = new Date(string);
        }
    }

    function makeDateFromInput(config) {
        var input = config._i,
            matched = aspNetJsonRegex.exec(input);

        if (input === undefined) {
            config._d = new Date();
        } else if (matched) {
            config._d = new Date(+matched[1]);
        } else if (typeof input === 'string') {
            makeDateFromString(config);
        } else if (isArray(input)) {
            config._a = input.slice(0);
            dateFromConfig(config);
        } else if (isDate(input)) {
            config._d = new Date(+input);
        } else if (typeof(input) === 'object') {
            dateFromObject(config);
        } else {
            config._d = new Date(input);
        }
    }

    function makeDate(y, m, d, h, M, s, ms) {
        //can't just apply() to create a date:
        //http://stackoverflow.com/questions/181348/instantiating-a-javascript-object-by-calling-prototype-constructor-apply
        var date = new Date(y, m, d, h, M, s, ms);

        //the date constructor doesn't accept years < 1970
        if (y < 1970) {
            date.setFullYear(y);
        }
        return date;
    }

    function makeUTCDate(y) {
        var date = new Date(Date.UTC.apply(null, arguments));
        if (y < 1970) {
            date.setUTCFullYear(y);
        }
        return date;
    }

    function parseWeekday(input, language) {
        if (typeof input === 'string') {
            if (!isNaN(input)) {
                input = parseInt(input, 10);
            }
            else {
                input = language.weekdaysParse(input);
                if (typeof input !== 'number') {
                    return null;
                }
            }
        }
        return input;
    }

    /************************************
        Relative Time
    ************************************/


    // helper function for moment.fn.from, moment.fn.fromNow, and moment.duration.fn.humanize
    function substituteTimeAgo(string, number, withoutSuffix, isFuture, lang) {
        return lang.relativeTime(number || 1, !!withoutSuffix, string, isFuture);
    }

    function relativeTime(milliseconds, withoutSuffix, lang) {
        var seconds = round(Math.abs(milliseconds) / 1000),
            minutes = round(seconds / 60),
            hours = round(minutes / 60),
            days = round(hours / 24),
            years = round(days / 365),
            args = seconds < 45 && ['s', seconds] ||
                minutes === 1 && ['m'] ||
                minutes < 45 && ['mm', minutes] ||
                hours === 1 && ['h'] ||
                hours < 22 && ['hh', hours] ||
                days === 1 && ['d'] ||
                days <= 25 && ['dd', days] ||
                days <= 45 && ['M'] ||
                days < 345 && ['MM', round(days / 30)] ||
                years === 1 && ['y'] || ['yy', years];
        args[2] = withoutSuffix;
        args[3] = milliseconds > 0;
        args[4] = lang;
        return substituteTimeAgo.apply({}, args);
    }


    /************************************
        Week of Year
    ************************************/


    // firstDayOfWeek       0 = sun, 6 = sat
    //                      the day of the week that starts the week
    //                      (usually sunday or monday)
    // firstDayOfWeekOfYear 0 = sun, 6 = sat
    //                      the first week is the week that contains the first
    //                      of this day of the week
    //                      (eg. ISO weeks use thursday (4))
    function weekOfYear(mom, firstDayOfWeek, firstDayOfWeekOfYear) {
        var end = firstDayOfWeekOfYear - firstDayOfWeek,
            daysToDayOfWeek = firstDayOfWeekOfYear - mom.day(),
            adjustedMoment;


        if (daysToDayOfWeek > end) {
            daysToDayOfWeek -= 7;
        }

        if (daysToDayOfWeek < end - 7) {
            daysToDayOfWeek += 7;
        }

        adjustedMoment = moment(mom).add('d', daysToDayOfWeek);
        return {
            week: Math.ceil(adjustedMoment.dayOfYear() / 7),
            year: adjustedMoment.year()
        };
    }

    //http://en.wikipedia.org/wiki/ISO_week_date#Calculating_a_date_given_the_year.2C_week_number_and_weekday
    function dayOfYearFromWeeks(year, week, weekday, firstDayOfWeekOfYear, firstDayOfWeek) {
        var d = makeUTCDate(year, 0, 1).getUTCDay(), daysToAdd, dayOfYear;

        weekday = weekday != null ? weekday : firstDayOfWeek;
        daysToAdd = firstDayOfWeek - d + (d > firstDayOfWeekOfYear ? 7 : 0) - (d < firstDayOfWeek ? 7 : 0);
        dayOfYear = 7 * (week - 1) + (weekday - firstDayOfWeek) + daysToAdd + 1;

        return {
            year: dayOfYear > 0 ? year : year - 1,
            dayOfYear: dayOfYear > 0 ?  dayOfYear : daysInYear(year - 1) + dayOfYear
        };
    }

    /************************************
        Top Level Functions
    ************************************/

    function makeMoment(config) {
        var input = config._i,
            format = config._f;

        if (input === null) {
            return moment.invalid({nullInput: true});
        }

        if (typeof input === 'string') {
            config._i = input = getLangDefinition().preparse(input);
        }

        if (moment.isMoment(input)) {
            config = cloneMoment(input);

            config._d = new Date(+input._d);
        } else if (format) {
            if (isArray(format)) {
                makeDateFromStringAndArray(config);
            } else {
                makeDateFromStringAndFormat(config);
            }
        } else {
            makeDateFromInput(config);
        }

        return new Moment(config);
    }

    moment = function (input, format, lang, strict) {
        var c;

        if (typeof(lang) === "boolean") {
            strict = lang;
            lang = undefined;
        }
        // object construction must be done this way.
        // https://github.com/moment/moment/issues/1423
        c = {};
        c._isAMomentObject = true;
        c._i = input;
        c._f = format;
        c._l = lang;
        c._strict = strict;
        c._isUTC = false;
        c._pf = defaultParsingFlags();

        return makeMoment(c);
    };

    // creating with utc
    moment.utc = function (input, format, lang, strict) {
        var c;

        if (typeof(lang) === "boolean") {
            strict = lang;
            lang = undefined;
        }
        // object construction must be done this way.
        // https://github.com/moment/moment/issues/1423
        c = {};
        c._isAMomentObject = true;
        c._useUTC = true;
        c._isUTC = true;
        c._l = lang;
        c._i = input;
        c._f = format;
        c._strict = strict;
        c._pf = defaultParsingFlags();

        return makeMoment(c).utc();
    };

    // creating with unix timestamp (in seconds)
    moment.unix = function (input) {
        return moment(input * 1000);
    };

    // duration
    moment.duration = function (input, key) {
        var duration = input,
            // matching against regexp is expensive, do it on demand
            match = null,
            sign,
            ret,
            parseIso;

        if (moment.isDuration(input)) {
            duration = {
                ms: input._milliseconds,
                d: input._days,
                M: input._months
            };
        } else if (typeof input === 'number') {
            duration = {};
            if (key) {
                duration[key] = input;
            } else {
                duration.milliseconds = input;
            }
        } else if (!!(match = aspNetTimeSpanJsonRegex.exec(input))) {
            sign = (match[1] === "-") ? -1 : 1;
            duration = {
                y: 0,
                d: toInt(match[DATE]) * sign,
                h: toInt(match[HOUR]) * sign,
                m: toInt(match[MINUTE]) * sign,
                s: toInt(match[SECOND]) * sign,
                ms: toInt(match[MILLISECOND]) * sign
            };
        } else if (!!(match = isoDurationRegex.exec(input))) {
            sign = (match[1] === "-") ? -1 : 1;
            parseIso = function (inp) {
                // We'd normally use ~~inp for this, but unfortunately it also
                // converts floats to ints.
                // inp may be undefined, so careful calling replace on it.
                var res = inp && parseFloat(inp.replace(',', '.'));
                // apply sign while we're at it
                return (isNaN(res) ? 0 : res) * sign;
            };
            duration = {
                y: parseIso(match[2]),
                M: parseIso(match[3]),
                d: parseIso(match[4]),
                h: parseIso(match[5]),
                m: parseIso(match[6]),
                s: parseIso(match[7]),
                w: parseIso(match[8])
            };
        }

        ret = new Duration(duration);

        if (moment.isDuration(input) && input.hasOwnProperty('_lang')) {
            ret._lang = input._lang;
        }

        return ret;
    };

    // version number
    moment.version = VERSION;

    // default format
    moment.defaultFormat = isoFormat;

    // This function will be called whenever a moment is mutated.
    // It is intended to keep the offset in sync with the timezone.
    moment.updateOffset = function () {};

    // This function will load languages and then set the global language.  If
    // no arguments are passed in, it will simply return the current global
    // language key.
    moment.lang = function (key, values) {
        var r;
        if (!key) {
            return moment.fn._lang._abbr;
        }
        if (values) {
            loadLang(normalizeLanguage(key), values);
        } else if (values === null) {
            unloadLang(key);
            key = 'en';
        } else if (!languages[key]) {
            getLangDefinition(key);
        }
        r = moment.duration.fn._lang = moment.fn._lang = getLangDefinition(key);
        return r._abbr;
    };

    // returns language data
    moment.langData = function (key) {
        if (key && key._lang && key._lang._abbr) {
            key = key._lang._abbr;
        }
        return getLangDefinition(key);
    };

    // compare moment object
    moment.isMoment = function (obj) {
        return obj instanceof Moment ||
            (obj != null &&  obj.hasOwnProperty('_isAMomentObject'));
    };

    // for typechecking Duration objects
    moment.isDuration = function (obj) {
        return obj instanceof Duration;
    };

    for (i = lists.length - 1; i >= 0; --i) {
        makeList(lists[i]);
    }

    moment.normalizeUnits = function (units) {
        return normalizeUnits(units);
    };

    moment.invalid = function (flags) {
        var m = moment.utc(NaN);
        if (flags != null) {
            extend(m._pf, flags);
        }
        else {
            m._pf.userInvalidated = true;
        }

        return m;
    };

    moment.parseZone = function (input) {
        return moment(input).parseZone();
    };

    /************************************
        Moment Prototype
    ************************************/


    extend(moment.fn = Moment.prototype, {

        clone : function () {
            return moment(this);
        },

        valueOf : function () {
            return +this._d + ((this._offset || 0) * 60000);
        },

        unix : function () {
            return Math.floor(+this / 1000);
        },

        toString : function () {
            return this.clone().lang('en').format("ddd MMM DD YYYY HH:mm:ss [GMT]ZZ");
        },

        toDate : function () {
            return this._offset ? new Date(+this) : this._d;
        },

        toISOString : function () {
            var m = moment(this).utc();
            if (0 < m.year() && m.year() <= 9999) {
                return formatMoment(m, 'YYYY-MM-DD[T]HH:mm:ss.SSS[Z]');
            } else {
                return formatMoment(m, 'YYYYYY-MM-DD[T]HH:mm:ss.SSS[Z]');
            }
        },

        toArray : function () {
            var m = this;
            return [
                m.year(),
                m.month(),
                m.date(),
                m.hours(),
                m.minutes(),
                m.seconds(),
                m.milliseconds()
            ];
        },

        isValid : function () {
            return isValid(this);
        },

        isDSTShifted : function () {

            if (this._a) {
                return this.isValid() && compareArrays(this._a, (this._isUTC ? moment.utc(this._a) : moment(this._a)).toArray()) > 0;
            }

            return false;
        },

        parsingFlags : function () {
            return extend({}, this._pf);
        },

        invalidAt: function () {
            return this._pf.overflow;
        },

        utc : function () {
            return this.zone(0);
        },

        local : function () {
            this.zone(0);
            this._isUTC = false;
            return this;
        },

        format : function (inputString) {
            var output = formatMoment(this, inputString || moment.defaultFormat);
            return this.lang().postformat(output);
        },

        add : function (input, val) {
            var dur;
            // switch args to support add('s', 1) and add(1, 's')
            if (typeof input === 'string') {
                dur = moment.duration(+val, input);
            } else {
                dur = moment.duration(input, val);
            }
            addOrSubtractDurationFromMoment(this, dur, 1);
            return this;
        },

        subtract : function (input, val) {
            var dur;
            // switch args to support subtract('s', 1) and subtract(1, 's')
            if (typeof input === 'string') {
                dur = moment.duration(+val, input);
            } else {
                dur = moment.duration(input, val);
            }
            addOrSubtractDurationFromMoment(this, dur, -1);
            return this;
        },

        diff : function (input, units, asFloat) {
            var that = makeAs(input, this),
                zoneDiff = (this.zone() - that.zone()) * 6e4,
                diff, output;

            units = normalizeUnits(units);

            if (units === 'year' || units === 'month') {
                // average number of days in the months in the given dates
                diff = (this.daysInMonth() + that.daysInMonth()) * 432e5; // 24 * 60 * 60 * 1000 / 2
                // difference in months
                output = ((this.year() - that.year()) * 12) + (this.month() - that.month());
                // adjust by taking difference in days, average number of days
                // and dst in the given months.
                output += ((this - moment(this).startOf('month')) -
                        (that - moment(that).startOf('month'))) / diff;
                // same as above but with zones, to negate all dst
                output -= ((this.zone() - moment(this).startOf('month').zone()) -
                        (that.zone() - moment(that).startOf('month').zone())) * 6e4 / diff;
                if (units === 'year') {
                    output = output / 12;
                }
            } else {
                diff = (this - that);
                output = units === 'second' ? diff / 1e3 : // 1000
                    units === 'minute' ? diff / 6e4 : // 1000 * 60
                    units === 'hour' ? diff / 36e5 : // 1000 * 60 * 60
                    units === 'day' ? (diff - zoneDiff) / 864e5 : // 1000 * 60 * 60 * 24, negate dst
                    units === 'week' ? (diff - zoneDiff) / 6048e5 : // 1000 * 60 * 60 * 24 * 7, negate dst
                    diff;
            }
            return asFloat ? output : absRound(output);
        },

        from : function (time, withoutSuffix) {
            return moment.duration(this.diff(time)).lang(this.lang()._abbr).humanize(!withoutSuffix);
        },

        fromNow : function (withoutSuffix) {
            return this.from(moment(), withoutSuffix);
        },

        calendar : function () {
            // We want to compare the start of today, vs this.
            // Getting start-of-today depends on whether we're zone'd or not.
            var sod = makeAs(moment(), this).startOf('day'),
                diff = this.diff(sod, 'days', true),
                format = diff < -6 ? 'sameElse' :
                    diff < -1 ? 'lastWeek' :
                    diff < 0 ? 'lastDay' :
                    diff < 1 ? 'sameDay' :
                    diff < 2 ? 'nextDay' :
                    diff < 7 ? 'nextWeek' : 'sameElse';
            return this.format(this.lang().calendar(format, this));
        },

        isLeapYear : function () {
            return isLeapYear(this.year());
        },

        isDST : function () {
            return (this.zone() < this.clone().month(0).zone() ||
                this.zone() < this.clone().month(5).zone());
        },

        day : function (input) {
            var day = this._isUTC ? this._d.getUTCDay() : this._d.getDay();
            if (input != null) {
                input = parseWeekday(input, this.lang());
                return this.add({ d : input - day });
            } else {
                return day;
            }
        },

        month : function (input) {
            var utc = this._isUTC ? 'UTC' : '',
                dayOfMonth;

            if (input != null) {
                if (typeof input === 'string') {
                    input = this.lang().monthsParse(input);
                    if (typeof input !== 'number') {
                        return this;
                    }
                }

                dayOfMonth = this.date();
                this.date(1);
                this._d['set' + utc + 'Month'](input);
                this.date(Math.min(dayOfMonth, this.daysInMonth()));

                moment.updateOffset(this);
                return this;
            } else {
                return this._d['get' + utc + 'Month']();
            }
        },

        startOf: function (units) {
            units = normalizeUnits(units);
            // the following switch intentionally omits break keywords
            // to utilize falling through the cases.
            switch (units) {
            case 'year':
                this.month(0);
                /* falls through */
            case 'month':
                this.date(1);
                /* falls through */
            case 'week':
            case 'isoWeek':
            case 'day':
                this.hours(0);
                /* falls through */
            case 'hour':
                this.minutes(0);
                /* falls through */
            case 'minute':
                this.seconds(0);
                /* falls through */
            case 'second':
                this.milliseconds(0);
                /* falls through */
            }

            // weeks are a special case
            if (units === 'week') {
                this.weekday(0);
            } else if (units === 'isoWeek') {
                this.isoWeekday(1);
            }

            return this;
        },

        endOf: function (units) {
            units = normalizeUnits(units);
            return this.startOf(units).add((units === 'isoWeek' ? 'week' : units), 1).subtract('ms', 1);
        },

        isAfter: function (input, units) {
            units = typeof units !== 'undefined' ? units : 'millisecond';
            return +this.clone().startOf(units) > +moment(input).startOf(units);
        },

        isBefore: function (input, units) {
            units = typeof units !== 'undefined' ? units : 'millisecond';
            return +this.clone().startOf(units) < +moment(input).startOf(units);
        },

        isSame: function (input, units) {
            units = units || 'ms';
            return +this.clone().startOf(units) === +makeAs(input, this).startOf(units);
        },

        min: function (other) {
            other = moment.apply(null, arguments);
            return other < this ? this : other;
        },

        max: function (other) {
            other = moment.apply(null, arguments);
            return other > this ? this : other;
        },

        zone : function (input) {
            var offset = this._offset || 0;
            if (input != null) {
                if (typeof input === "string") {
                    input = timezoneMinutesFromString(input);
                }
                if (Math.abs(input) < 16) {
                    input = input * 60;
                }
                this._offset = input;
                this._isUTC = true;
                if (offset !== input) {
                    addOrSubtractDurationFromMoment(this, moment.duration(offset - input, 'm'), 1, true);
                }
            } else {
                return this._isUTC ? offset : this._d.getTimezoneOffset();
            }
            return this;
        },

        zoneAbbr : function () {
            return this._isUTC ? "UTC" : "";
        },

        zoneName : function () {
            return this._isUTC ? "Coordinated Universal Time" : "";
        },

        parseZone : function () {
            if (this._tzm) {
                this.zone(this._tzm);
            } else if (typeof this._i === 'string') {
                this.zone(this._i);
            }
            return this;
        },

        hasAlignedHourOffset : function (input) {
            if (!input) {
                input = 0;
            }
            else {
                input = moment(input).zone();
            }

            return (this.zone() - input) % 60 === 0;
        },

        daysInMonth : function () {
            return daysInMonth(this.year(), this.month());
        },

        dayOfYear : function (input) {
            var dayOfYear = round((moment(this).startOf('day') - moment(this).startOf('year')) / 864e5) + 1;
            return input == null ? dayOfYear : this.add("d", (input - dayOfYear));
        },

        quarter : function () {
            return Math.ceil((this.month() + 1.0) / 3.0);
        },

        weekYear : function (input) {
            var year = weekOfYear(this, this.lang()._week.dow, this.lang()._week.doy).year;
            return input == null ? year : this.add("y", (input - year));
        },

        isoWeekYear : function (input) {
            var year = weekOfYear(this, 1, 4).year;
            return input == null ? year : this.add("y", (input - year));
        },

        week : function (input) {
            var week = this.lang().week(this);
            return input == null ? week : this.add("d", (input - week) * 7);
        },

        isoWeek : function (input) {
            var week = weekOfYear(this, 1, 4).week;
            return input == null ? week : this.add("d", (input - week) * 7);
        },

        weekday : function (input) {
            var weekday = (this.day() + 7 - this.lang()._week.dow) % 7;
            return input == null ? weekday : this.add("d", input - weekday);
        },

        isoWeekday : function (input) {
            // behaves the same as moment#day except
            // as a getter, returns 7 instead of 0 (1-7 range instead of 0-6)
            // as a setter, sunday should belong to the previous week.
            return input == null ? this.day() || 7 : this.day(this.day() % 7 ? input : input - 7);
        },

        get : function (units) {
            units = normalizeUnits(units);
            return this[units]();
        },

        set : function (units, value) {
            units = normalizeUnits(units);
            if (typeof this[units] === 'function') {
                this[units](value);
            }
            return this;
        },

        // If passed a language key, it will set the language for this
        // instance.  Otherwise, it will return the language configuration
        // variables for this instance.
        lang : function (key) {
            if (key === undefined) {
                return this._lang;
            } else {
                this._lang = getLangDefinition(key);
                return this;
            }
        }
    });

    // helper for adding shortcuts
    function makeGetterAndSetter(name, key) {
        moment.fn[name] = moment.fn[name + 's'] = function (input) {
            var utc = this._isUTC ? 'UTC' : '';
            if (input != null) {
                this._d['set' + utc + key](input);
                moment.updateOffset(this);
                return this;
            } else {
                return this._d['get' + utc + key]();
            }
        };
    }

    // loop through and add shortcuts (Month, Date, Hours, Minutes, Seconds, Milliseconds)
    for (i = 0; i < proxyGettersAndSetters.length; i ++) {
        makeGetterAndSetter(proxyGettersAndSetters[i].toLowerCase().replace(/s$/, ''), proxyGettersAndSetters[i]);
    }

    // add shortcut for year (uses different syntax than the getter/setter 'year' == 'FullYear')
    makeGetterAndSetter('year', 'FullYear');

    // add plural methods
    moment.fn.days = moment.fn.day;
    moment.fn.months = moment.fn.month;
    moment.fn.weeks = moment.fn.week;
    moment.fn.isoWeeks = moment.fn.isoWeek;

    // add aliased format methods
    moment.fn.toJSON = moment.fn.toISOString;

    /************************************
        Duration Prototype
    ************************************/


    extend(moment.duration.fn = Duration.prototype, {

        _bubble : function () {
            var milliseconds = this._milliseconds,
                days = this._days,
                months = this._months,
                data = this._data,
                seconds, minutes, hours, years;

            // The following code bubbles up values, see the tests for
            // examples of what that means.
            data.milliseconds = milliseconds % 1000;

            seconds = absRound(milliseconds / 1000);
            data.seconds = seconds % 60;

            minutes = absRound(seconds / 60);
            data.minutes = minutes % 60;

            hours = absRound(minutes / 60);
            data.hours = hours % 24;

            days += absRound(hours / 24);
            data.days = days % 30;

            months += absRound(days / 30);
            data.months = months % 12;

            years = absRound(months / 12);
            data.years = years;
        },

        weeks : function () {
            return absRound(this.days() / 7);
        },

        valueOf : function () {
            return this._milliseconds +
              this._days * 864e5 +
              (this._months % 12) * 2592e6 +
              toInt(this._months / 12) * 31536e6;
        },

        humanize : function (withSuffix) {
            var difference = +this,
                output = relativeTime(difference, !withSuffix, this.lang());

            if (withSuffix) {
                output = this.lang().pastFuture(difference, output);
            }

            return this.lang().postformat(output);
        },

        add : function (input, val) {
            // supports only 2.0-style add(1, 's') or add(moment)
            var dur = moment.duration(input, val);

            this._milliseconds += dur._milliseconds;
            this._days += dur._days;
            this._months += dur._months;

            this._bubble();

            return this;
        },

        subtract : function (input, val) {
            var dur = moment.duration(input, val);

            this._milliseconds -= dur._milliseconds;
            this._days -= dur._days;
            this._months -= dur._months;

            this._bubble();

            return this;
        },

        get : function (units) {
            units = normalizeUnits(units);
            return this[units.toLowerCase() + 's']();
        },

        as : function (units) {
            units = normalizeUnits(units);
            return this['as' + units.charAt(0).toUpperCase() + units.slice(1) + 's']();
        },

        lang : moment.fn.lang,

        toIsoString : function () {
            // inspired by https://github.com/dordille/moment-isoduration/blob/master/moment.isoduration.js
            var years = Math.abs(this.years()),
                months = Math.abs(this.months()),
                days = Math.abs(this.days()),
                hours = Math.abs(this.hours()),
                minutes = Math.abs(this.minutes()),
                seconds = Math.abs(this.seconds() + this.milliseconds() / 1000);

            if (!this.asSeconds()) {
                // this is the same as C#'s (Noda) and python (isodate)...
                // but not other JS (goog.date)
                return 'P0D';
            }

            return (this.asSeconds() < 0 ? '-' : '') +
                'P' +
                (years ? years + 'Y' : '') +
                (months ? months + 'M' : '') +
                (days ? days + 'D' : '') +
                ((hours || minutes || seconds) ? 'T' : '') +
                (hours ? hours + 'H' : '') +
                (minutes ? minutes + 'M' : '') +
                (seconds ? seconds + 'S' : '');
        }
    });

    function makeDurationGetter(name) {
        moment.duration.fn[name] = function () {
            return this._data[name];
        };
    }

    function makeDurationAsGetter(name, factor) {
        moment.duration.fn['as' + name] = function () {
            return +this / factor;
        };
    }

    for (i in unitMillisecondFactors) {
        if (unitMillisecondFactors.hasOwnProperty(i)) {
            makeDurationAsGetter(i, unitMillisecondFactors[i]);
            makeDurationGetter(i.toLowerCase());
        }
    }

    makeDurationAsGetter('Weeks', 6048e5);
    moment.duration.fn.asMonths = function () {
        return (+this - this.years() * 31536e6) / 2592e6 + this.years() * 12;
    };


    /************************************
        Default Lang
    ************************************/


    // Set default language, other languages will inherit from English.
    moment.lang('en', {
        ordinal : function (number) {
            var b = number % 10,
                output = (toInt(number % 100 / 10) === 1) ? 'th' :
                (b === 1) ? 'st' :
                (b === 2) ? 'nd' :
                (b === 3) ? 'rd' : 'th';
            return number + output;
        }
    });

    /* EMBED_LANGUAGES */

    /************************************
        Exposing Moment
    ************************************/

    function makeGlobal(deprecate) {
        var warned = false, local_moment = moment;
        /*global ender:false */
        if (typeof ender !== 'undefined') {
            return;
        }
        // here, `this` means `window` in the browser, or `global` on the server
        // add `moment` as a global object via a string identifier,
        // for Closure Compiler "advanced" mode
        if (deprecate) {
            global.moment = function () {
                if (!warned && console && console.warn) {
                    warned = true;
                    console.warn(
                            "Accessing Moment through the global scope is " +
                            "deprecated, and will be removed in an upcoming " +
                            "release.");
                }
                return local_moment.apply(null, arguments);
            };
            extend(global.moment, local_moment);
        } else {
            global['moment'] = moment;
        }
    }

    // CommonJS module is defined
    if (hasModule) {
        module.exports = moment;
        makeGlobal(true);
    } else if (typeof define === "function" && define.amd) {
        define("moment", function (require, exports, module) {
            if (module.config && module.config() && module.config().noGlobal !== true) {
                // If user provided noGlobal, he is aware of global
                makeGlobal(module.config().noGlobal === undefined);
            }

            return moment;
        });
    } else {
        makeGlobal();
    }
}).call(this);

},{}],4:[function(require,module,exports){
/**
 * Copyright 2012 Craig Campbell
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Mousetrap is a simple keyboard shortcut library for Javascript with
 * no external dependencies
 *
 * @version 1.1.2
 * @url craig.is/killing/mice
 */

  /**
   * mapping of special keycodes to their corresponding keys
   *
   * everything in this dictionary cannot use keypress events
   * so it has to be here to map to the correct keycodes for
   * keyup/keydown events
   *
   * @type {Object}
   */
  var _MAP = {
          8: 'backspace',
          9: 'tab',
          13: 'enter',
          16: 'shift',
          17: 'ctrl',
          18: 'alt',
          20: 'capslock',
          27: 'esc',
          32: 'space',
          33: 'pageup',
          34: 'pagedown',
          35: 'end',
          36: 'home',
          37: 'left',
          38: 'up',
          39: 'right',
          40: 'down',
          45: 'ins',
          46: 'del',
          91: 'meta',
          93: 'meta',
          224: 'meta'
      },

      /**
       * mapping for special characters so they can support
       *
       * this dictionary is only used incase you want to bind a
       * keyup or keydown event to one of these keys
       *
       * @type {Object}
       */
      _KEYCODE_MAP = {
          106: '*',
          107: '+',
          109: '-',
          110: '.',
          111 : '/',
          186: ';',
          187: '=',
          188: ',',
          189: '-',
          190: '.',
          191: '/',
          192: '`',
          219: '[',
          220: '\\',
          221: ']',
          222: '\''
      },

      /**
       * this is a mapping of keys that require shift on a US keypad
       * back to the non shift equivelents
       *
       * this is so you can use keyup events with these keys
       *
       * note that this will only work reliably on US keyboards
       *
       * @type {Object}
       */
      _SHIFT_MAP = {
          '~': '`',
          '!': '1',
          '@': '2',
          '#': '3',
          '$': '4',
          '%': '5',
          '^': '6',
          '&': '7',
          '*': '8',
          '(': '9',
          ')': '0',
          '_': '-',
          '+': '=',
          ':': ';',
          '\"': '\'',
          '<': ',',
          '>': '.',
          '?': '/',
          '|': '\\'
      },

      /**
       * this is a list of special strings you can use to map
       * to modifier keys when you specify your keyboard shortcuts
       *
       * @type {Object}
       */
      _SPECIAL_ALIASES = {
          'option': 'alt',
          'command': 'meta',
          'return': 'enter',
          'escape': 'esc'
      },

      /**
       * variable to store the flipped version of _MAP from above
       * needed to check if we should use keypress or not when no action
       * is specified
       *
       * @type {Object|undefined}
       */
      _REVERSE_MAP,

      /**
       * a list of all the callbacks setup via Mousetrap.bind()
       *
       * @type {Object}
       */
      _callbacks = {},

      /**
       * direct map of string combinations to callbacks used for trigger()
       *
       * @type {Object}
       */
      _direct_map = {},

      /**
       * keeps track of what level each sequence is at since multiple
       * sequences can start out with the same sequence
       *
       * @type {Object}
       */
      _sequence_levels = {},

      /**
       * variable to store the setTimeout call
       *
       * @type {null|number}
       */
      _reset_timer,

      /**
       * temporary state where we will ignore the next keyup
       *
       * @type {boolean|string}
       */
      _ignore_next_keyup = false,

      /**
       * are we currently inside of a sequence?
       * type of action ("keyup" or "keydown" or "keypress") or false
       *
       * @type {boolean|string}
       */
      _inside_sequence = false;

  /**
   * loop through the f keys, f1 to f19 and add them to the map
   * programatically
   */
  for (var i = 1; i < 20; ++i) {
      _MAP[111 + i] = 'f' + i;
  }

  /**
   * loop through to map numbers on the numeric keypad
   */
  for (i = 0; i <= 9; ++i) {
      _MAP[i + 96] = i;
  }

  /**
   * cross browser add event method
   *
   * @param {Element|HTMLDocument} object
   * @param {string} type
   * @param {Function} callback
   * @returns void
   */
  function _addEvent(object, type, callback) {
      if (object.addEventListener) {
          return object.addEventListener(type, callback, false);
      }

      object.attachEvent('on' + type, callback);
  }

  /**
   * takes the event and returns the key character
   *
   * @param {Event} e
   * @return {string}
   */
  function _characterFromEvent(e) {

      // for keypress events we should return the character as is
      if (e.type == 'keypress') {
          return String.fromCharCode(e.which);
      }

      // for non keypress events the special maps are needed
      if (_MAP[e.which]) {
          return _MAP[e.which];
      }

      if (_KEYCODE_MAP[e.which]) {
          return _KEYCODE_MAP[e.which];
      }

      // if it is not in the special map
      return String.fromCharCode(e.which).toLowerCase();
  }

  /**
   * should we stop this event before firing off callbacks
   *
   * @param {Event} e
   * @return {boolean}
   */
  function _stop(e) {
      var element = e.target || e.srcElement,
          tag_name = element.tagName;

      // if the element has the class "mousetrap" then no need to stop
      if ((' ' + element.className + ' ').indexOf(' mousetrap ') > -1) {
          return false;
      }

      // stop for input, select, and textarea
      return tag_name == 'INPUT' || tag_name == 'SELECT' || tag_name == 'TEXTAREA' || (element.contentEditable && element.contentEditable == 'true');
  }

  /**
   * checks if two arrays are equal
   *
   * @param {Array} modifiers1
   * @param {Array} modifiers2
   * @returns {boolean}
   */
  function _modifiersMatch(modifiers1, modifiers2) {
      return modifiers1.sort().join(',') === modifiers2.sort().join(',');
  }

  /**
   * resets all sequence counters except for the ones passed in
   *
   * @param {Object} do_not_reset
   * @returns void
   */
  function _resetSequences(do_not_reset) {
      do_not_reset = do_not_reset || {};

      var active_sequences = false,
          key;

      for (key in _sequence_levels) {
          if (do_not_reset[key]) {
              active_sequences = true;
              continue;
          }
          _sequence_levels[key] = 0;
      }

      if (!active_sequences) {
          _inside_sequence = false;
      }
  }

  /**
   * finds all callbacks that match based on the keycode, modifiers,
   * and action
   *
   * @param {string} character
   * @param {Array} modifiers
   * @param {string} action
   * @param {boolean=} remove - should we remove any matches
   * @param {string=} combination
   * @returns {Array}
   */
  function _getMatches(character, modifiers, action, remove, combination) {
      var i,
          callback,
          matches = [];

      // if there are no events related to this keycode
      if (!_callbacks[character]) {
          return [];
      }

      // if a modifier key is coming up on its own we should allow it
      if (action == 'keyup' && _isModifier(character)) {
          modifiers = [character];
      }

      // loop through all callbacks for the key that was pressed
      // and see if any of them match
      for (i = 0; i < _callbacks[character].length; ++i) {
          callback = _callbacks[character][i];

          // if this is a sequence but it is not at the right level
          // then move onto the next match
          if (callback.seq && _sequence_levels[callback.seq] != callback.level) {
              continue;
          }

          // if the action we are looking for doesn't match the action we got
          // then we should keep going
          if (action != callback.action) {
              continue;
          }

          // if this is a keypress event that means that we need to only
          // look at the character, otherwise check the modifiers as
          // well
          if (action == 'keypress' || _modifiersMatch(modifiers, callback.modifiers)) {

              // remove is used so if you change your mind and call bind a
              // second time with a new function the first one is overwritten
              if (remove && callback.combo == combination) {
                  _callbacks[character].splice(i, 1);
              }

              matches.push(callback);
          }
      }

      return matches;
  }

  /**
   * takes a key event and figures out what the modifiers are
   *
   * @param {Event} e
   * @returns {Array}
   */
  function _eventModifiers(e) {
      var modifiers = [];

      if (e.shiftKey) {
          modifiers.push('shift');
      }

      if (e.altKey) {
          modifiers.push('alt');
      }

      if (e.ctrlKey) {
          modifiers.push('ctrl');
      }

      if (e.metaKey) {
          modifiers.push('meta');
      }

      return modifiers;
  }

  /**
   * actually calls the callback function
   *
   * if your callback function returns false this will use the jquery
   * convention - prevent default and stop propogation on the event
   *
   * @param {Function} callback
   * @param {Event} e
   * @returns void
   */
  function _fireCallback(callback, e) {
      if (callback(e) === false) {
          if (e.preventDefault) {
              e.preventDefault();
          }

          if (e.stopPropagation) {
              e.stopPropagation();
          }

          e.returnValue = false;
          e.cancelBubble = true;
      }
  }

  /**
   * handles a character key event
   *
   * @param {string} character
   * @param {Event} e
   * @returns void
   */
  function _handleCharacter(character, e) {

      // if this event should not happen stop here
      if (_stop(e)) {
          return;
      }

      var callbacks = _getMatches(character, _eventModifiers(e), e.type),
          i,
          do_not_reset = {},
          processed_sequence_callback = false;

      // loop through matching callbacks for this key event
      for (i = 0; i < callbacks.length; ++i) {

          // fire for all sequence callbacks
          // this is because if for example you have multiple sequences
          // bound such as "g i" and "g t" they both need to fire the
          // callback for matching g cause otherwise you can only ever
          // match the first one
          if (callbacks[i].seq) {
              processed_sequence_callback = true;

              // keep a list of which sequences were matches for later
              do_not_reset[callbacks[i].seq] = 1;
              _fireCallback(callbacks[i].callback, e);
              continue;
          }

          // if there were no sequence matches but we are still here
          // that means this is a regular match so we should fire that
          if (!processed_sequence_callback && !_inside_sequence) {
              _fireCallback(callbacks[i].callback, e);
          }
      }

      // if you are inside of a sequence and the key you are pressing
      // is not a modifier key then we should reset all sequences
      // that were not matched by this key event
      if (e.type == _inside_sequence && !_isModifier(character)) {
          _resetSequences(do_not_reset);
      }
  }

  /**
   * handles a keydown event
   *
   * @param {Event} e
   * @returns void
   */
  function _handleKey(e) {

      // normalize e.which for key events
      // @see http://stackoverflow.com/questions/4285627/javascript-keycode-vs-charcode-utter-confusion
      e.which = typeof e.which == "number" ? e.which : e.keyCode;

      var character = _characterFromEvent(e);

      // no character found then stop
      if (!character) {
          return;
      }

      if (e.type == 'keyup' && _ignore_next_keyup == character) {
          _ignore_next_keyup = false;
          return;
      }

      _handleCharacter(character, e);
  }

  /**
   * determines if the keycode specified is a modifier key or not
   *
   * @param {string} key
   * @returns {boolean}
   */
  function _isModifier(key) {
      return key == 'shift' || key == 'ctrl' || key == 'alt' || key == 'meta';
  }

  /**
   * called to set a 1 second timeout on the specified sequence
   *
   * this is so after each key press in the sequence you have 1 second
   * to press the next key before you have to start over
   *
   * @returns void
   */
  function _resetSequenceTimer() {
      clearTimeout(_reset_timer);
      _reset_timer = setTimeout(_resetSequences, 1000);
  }

  /**
   * reverses the map lookup so that we can look for specific keys
   * to see what can and can't use keypress
   *
   * @return {Object}
   */
  function _getReverseMap() {
      if (!_REVERSE_MAP) {
          _REVERSE_MAP = {};
          for (var key in _MAP) {

              // pull out the numeric keypad from here cause keypress should
              // be able to detect the keys from the character
              if (key > 95 && key < 112) {
                  continue;
              }

              if (_MAP.hasOwnProperty(key)) {
                  _REVERSE_MAP[_MAP[key]] = key;
              }
          }
      }
      return _REVERSE_MAP;
  }

  /**
   * picks the best action based on the key combination
   *
   * @param {string} key - character for key
   * @param {Array} modifiers
   * @param {string=} action passed in
   */
  function _pickBestAction(key, modifiers, action) {

      // if no action was picked in we should try to pick the one
      // that we think would work best for this key
      if (!action) {
          action = _getReverseMap()[key] ? 'keydown' : 'keypress';
      }

      // modifier keys don't work as expected with keypress,
      // switch to keydown
      if (action == 'keypress' && modifiers.length) {
          action = 'keydown';
      }

      return action;
  }

  /**
   * binds a key sequence to an event
   *
   * @param {string} combo - combo specified in bind call
   * @param {Array} keys
   * @param {Function} callback
   * @param {string=} action
   * @returns void
   */
  function _bindSequence(combo, keys, callback, action) {

      // start off by adding a sequence level record for this combination
      // and setting the level to 0
      _sequence_levels[combo] = 0;

      // if there is no action pick the best one for the first key
      // in the sequence
      if (!action) {
          action = _pickBestAction(keys[0], []);
      }

      /**
       * callback to increase the sequence level for this sequence and reset
       * all other sequences that were active
       *
       * @param {Event} e
       * @returns void
       */
      var _increaseSequence = function(e) {
              _inside_sequence = action;
              ++_sequence_levels[combo];
              _resetSequenceTimer();
          },

          /**
           * wraps the specified callback inside of another function in order
           * to reset all sequence counters as soon as this sequence is done
           *
           * @param {Event} e
           * @returns void
           */
          _callbackAndReset = function(e) {
              _fireCallback(callback, e);

              // we should ignore the next key up if the action is key down
              // or keypress.  this is so if you finish a sequence and
              // release the key the final key will not trigger a keyup
              if (action !== 'keyup') {
                  _ignore_next_keyup = _characterFromEvent(e);
              }

              // weird race condition if a sequence ends with the key
              // another sequence begins with
              setTimeout(_resetSequences, 10);
          },
          i;

      // loop through keys one at a time and bind the appropriate callback
      // function.  for any key leading up to the final one it should
      // increase the sequence. after the final, it should reset all sequences
      for (i = 0; i < keys.length; ++i) {
          _bindSingle(keys[i], i < keys.length - 1 ? _increaseSequence : _callbackAndReset, action, combo, i);
      }
  }

  /**
   * binds a single keyboard combination
   *
   * @param {string} combination
   * @param {Function} callback
   * @param {string=} action
   * @param {string=} sequence_name - name of sequence if part of sequence
   * @param {number=} level - what part of the sequence the command is
   * @returns void
   */
  function _bindSingle(combination, callback, action, sequence_name, level) {

      // make sure multiple spaces in a row become a single space
      combination = combination.replace(/\s+/g, ' ');

      var sequence = combination.split(' '),
          i,
          key,
          keys,
          modifiers = [];

      // if this pattern is a sequence of keys then run through this method
      // to reprocess each pattern one key at a time
      if (sequence.length > 1) {
          return _bindSequence(combination, sequence, callback, action);
      }

      // take the keys from this pattern and figure out what the actual
      // pattern is all about
      keys = combination === '+' ? ['+'] : combination.split('+');

      for (i = 0; i < keys.length; ++i) {
          key = keys[i];

          // normalize key names
          if (_SPECIAL_ALIASES[key]) {
              key = _SPECIAL_ALIASES[key];
          }

          // if this is not a keypress event then we should
          // be smart about using shift keys
          // this will only work for US keyboards however
          if (action && action != 'keypress' && _SHIFT_MAP[key]) {
              key = _SHIFT_MAP[key];
              modifiers.push('shift');
          }

          // if this key is a modifier then add it to the list of modifiers
          if (_isModifier(key)) {
              modifiers.push(key);
          }
      }

      // depending on what the key combination is
      // we will try to pick the best event for it
      action = _pickBestAction(key, modifiers, action);

      // make sure to initialize array if this is the first time
      // a callback is added for this key
      if (!_callbacks[key]) {
          _callbacks[key] = [];
      }

      // remove an existing match if there is one
      _getMatches(key, modifiers, action, !sequence_name, combination);

      // add this call back to the array
      // if it is a sequence put it at the beginning
      // if not put it at the end
      //
      // this is important because the way these are processed expects
      // the sequence ones to come first
      _callbacks[key][sequence_name ? 'unshift' : 'push']({
          callback: callback,
          modifiers: modifiers,
          action: action,
          seq: sequence_name,
          level: level,
          combo: combination
      });
  }

  /**
   * binds multiple combinations to the same callback
   *
   * @param {Array} combinations
   * @param {Function} callback
   * @param {string|undefined} action
   * @returns void
   */
  function _bindMultiple(combinations, callback, action) {
      for (var i = 0; i < combinations.length; ++i) {
          _bindSingle(combinations[i], callback, action);
      }
  }

  // start!
  _addEvent(document, 'keypress', _handleKey);
  _addEvent(document, 'keydown', _handleKey);
  _addEvent(document, 'keyup', _handleKey);

  var mousetrap = {

      /**
       * binds an event to mousetrap
       *
       * can be a single key, a combination of keys separated with +,
       * a comma separated list of keys, an array of keys, or
       * a sequence of keys separated by spaces
       *
       * be sure to list the modifier keys first to make sure that the
       * correct key ends up getting bound (the last key in the pattern)
       *
       * @param {string|Array} keys
       * @param {Function} callback
       * @param {string=} action - 'keypress', 'keydown', or 'keyup'
       * @returns void
       */
      bind: function(keys, callback, action) {
          _bindMultiple(keys instanceof Array ? keys : [keys], callback, action);
          _direct_map[keys + ':' + action] = callback;
          return this;
      },

      /**
       * unbinds an event to mousetrap
       *
       * the unbinding sets the callback function of the specified key combo
       * to an empty function and deletes the corresponding key in the
       * _direct_map dict.
       *
       * the keycombo+action has to be exactly the same as
       * it was defined in the bind method
       *
       * TODO: actually remove this from the _callbacks dictionary instead
       * of binding an empty function
       *
       * @param {string|Array} keys
       * @param {string} action
       * @returns void
       */
      unbind: function(keys, action) {
          if (_direct_map[keys + ':' + action]) {
              delete _direct_map[keys + ':' + action];
              this.bind(keys, function() {}, action);
          }
          return this;
      },

      /**
       * triggers an event that has already been bound
       *
       * @param {string} keys
       * @param {string=} action
       * @returns void
       */
      trigger: function(keys, action) {
          _direct_map[keys + ':' + action]();
          return this;
      },

      /**
       * resets the library back to its initial state.  this is useful
       * if you want to clear out the current keyboard shortcuts and bind
       * new ones - for example if you switch to another page
       *
       * @returns void
       */
      reset: function() {
          _callbacks = {};
          _direct_map = {};
          return this;
      }
  };

module.exports = mousetrap;


},{}]},{},[1])
(1)
});