/**
 * Copyright (c) 2011-2013 Fabien Cazenave, Mozilla.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

/*jshint browser: true, devel: true, es5: true, globalstrict: true */
'use strict';

define(function (require) {
  var gL10nData = {};
  var gTextData = '';
  var gTextProp = 'textContent';
  var gLanguage = '';
  var gMacros = {};
  var gReadyState = 'loading';

  /**
   * Synchronously loading l10n resources significantly minimizes flickering
   * from displaying the app with non-localized strings and then updating the
   * strings. Although this will block all script execution on this page, we
   * expect that the l10n resources are available locally on flash-storage.
   *
   * As synchronous XHR is generally considered as a bad idea, we're still
   * loading l10n resources asynchronously -- but we keep this in a setting,
   * just in case... and applications using this library should hide their
   * content until the `localized' event happens.
   */

  var gAsyncResourceLoading = true; // read-only


  /**
   * Debug helpers
   *
   *   gDEBUG == 0: don't display any console message
   *   gDEBUG == 1: display only warnings, not logs
   *   gDEBUG == 2: display all console messages
   */

  var gDEBUG = 1;

  function consoleLog(message) {
    if (gDEBUG >= 2) {
      console.log('[l10n] ' + message);
    }
  };

  function consoleWarn(message) {
    if (gDEBUG) {
      console.warn('[l10n] ' + message);
    }
  };


  /**
   * DOM helpers for the so-called "HTML API".
   *
   * These functions are written for modern browsers. For old versions of IE,
   * they're overridden in the 'startup' section at the end of this file.
   */

  function getL10nResourceLinks() {
    return document.querySelectorAll('link[type="application/l10n"]');
  }

  function getL10nDictionary() {
    var script = document.querySelector('script[type="application/l10n"]');
    // TODO: support multiple and external JSON dictionaries
    return script ? JSON.parse(script.innerHTML) : null;
  }

  function getTranslatableChildren(element) {
    return element ? element.querySelectorAll('*[data-l10n-id]') : [];
  }

  function getL10nAttributes(element) {
    if (!element)
      return {};

    var l10nId = element.getAttribute('data-l10n-id');
    var l10nArgs = element.getAttribute('data-l10n-args');
    var args = {};
    if (l10nArgs) {
      try {
        args = JSON.parse(l10nArgs);
      } catch (e) {
        consoleWarn('could not parse arguments for #' + l10nId);
      }
    }
    return { id: l10nId, args: args };
  }

  function fireL10nReadyEvent(lang) {
    var evtObject = document.createEvent('Event');
    evtObject.initEvent('localized', true, false);
    evtObject.language = lang;
    document.dispatchEvent(evtObject);
  }

  function xhrLoadText(url, onSuccess, onFailure, asynchronous) {
    onSuccess = onSuccess || function _onSuccess(data) {};
    onFailure = onFailure || function _onFailure() {
      consoleWarn(url + ' not found.');
    };

    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, asynchronous);
    if (xhr.overrideMimeType) {
      xhr.overrideMimeType('text/plain; charset=utf-8');
    }
    xhr.onreadystatechange = function() {
      if (xhr.readyState == 4) {
        if (xhr.status == 200 || xhr.status === 0) {
          onSuccess(xhr.responseText);
        } else {
          onFailure();
        }
      }
    };
    xhr.onerror = onFailure;
    xhr.ontimeout = onFailure;

    // in Firefox OS with the app:// protocol, trying to XHR a non-existing
    // URL will raise an exception here -- hence this ugly try...catch.
    try {
      xhr.send(null);
    } catch (e) {
      onFailure();
    }
  }


  /**
   * l10n resource parser:
   *  - reads (async XHR) the l10n resource matching `lang';
   *  - imports linked resources (synchronously) when specified;
   *  - parses the text data (fills `gL10nData' and `gTextData');
   *  - triggers success/failure callbacks when done.
   *
   * @param {string} href
   *    URL of the l10n resource to parse.
   *
   * @param {string} lang
   *    locale (language) to parse.
   *
   * @param {Function} successCallback
   *    triggered when the l10n resource has been successully parsed.
   *
   * @param {Function} failureCallback
   *    triggered when the an error has occured.
   *
   * @return {void}
   *    uses the following global variables: gL10nData, gTextData, gTextProp.
   */

  function parseResource(href, lang, successCallback, failureCallback) {
    var baseURL = href.replace(/[^\/]*$/, '') || './';

    // handle escaped characters (backslashes) in a string
    function evalString(text) {
      if (text.lastIndexOf('\\') < 0)
        return text;
      return text.replace(/\\\\/g, '\\')
                 .replace(/\\n/g, '\n')
                 .replace(/\\r/g, '\r')
                 .replace(/\\t/g, '\t')
                 .replace(/\\b/g, '\b')
                 .replace(/\\f/g, '\f')
                 .replace(/\\{/g, '{')
                 .replace(/\\}/g, '}')
                 .replace(/\\"/g, '"')
                 .replace(/\\'/g, "'");
    }

    // parse *.properties text data into an l10n dictionary
    function parseProperties(text) {
      var dictionary = [];

      // token expressions
      var reBlank = /^\s*|\s*$/;
      var reComment = /^\s*#|^\s*$/;
      var reSection = /^\s*\[(.*)\]\s*$/;
      var reImport = /^\s*@import\s+url\((.*)\)\s*$/i;
      var reSplit = /^([^=\s]*)\s*=\s*(.+)$/; // TODO: escape EOLs with '\'

      // parse the *.properties file into an associative array
      function parseRawLines(rawText, extendedSyntax) {
        var entries = rawText.replace(reBlank, '').split(/[\r\n]+/);
        var currentLang = '*';
        var genericLang = lang.replace(/-[a-z]+$/i, '');
        var skipLang = false;
        var match = '';

        for (var i = 0; i < entries.length; i++) {
          var line = entries[i];

          // comment or blank line?
          if (reComment.test(line))
            continue;

          // the extended syntax supports [lang] sections and @import rules
          if (extendedSyntax) {
            if (reSection.test(line)) { // section start?
              match = reSection.exec(line);
              currentLang = match[1];
              skipLang = (currentLang !== '*') &&
                  (currentLang !== lang) && (currentLang !== genericLang);
              continue;
            } else if (skipLang) {
              continue;
            }
            if (reImport.test(line)) { // @import rule?
              match = reImport.exec(line);
              loadImport(baseURL + match[1]); // load the resource synchronously
            }
          }

          // key-value pair
          var tmp = line.match(reSplit);
          if (tmp && tmp.length == 3) {
            dictionary[tmp[1]] = evalString(tmp[2]);
          }
        }
      }

      // import another *.properties file
      function loadImport(url) {
        xhrLoadText(url, function(content) {
          parseRawLines(content, false); // don't allow recursive imports
        }, null, false); // load synchronously
      }

      // fill the dictionary
      parseRawLines(text, true);
      return dictionary;
    }

    // load and parse l10n data (warning: global variables are used here)
    xhrLoadText(href, function(response) {
      gTextData += response; // mostly for debug

      // parse *.properties text data into an l10n dictionary
      var data = parseProperties(response);

      // find attribute descriptions, if any
      for (var key in data) {
        var id, prop, index = key.lastIndexOf('.');
        if (index > 0) { // an attribute has been specified
          id = key.substring(0, index);
          prop = key.substr(index + 1);
        } else { // no attribute: assuming text content by default
          id = key;
          prop = gTextProp;
        }
        if (!gL10nData[id]) {
          gL10nData[id] = {};
        }
        gL10nData[id][prop] = data[key];
      }

      // trigger callback
      if (successCallback) {
        successCallback();
      }
    }, failureCallback, gAsyncResourceLoading);
  };

  // load and parse all resources for the specified locale
  function loadLocale(lang, callback) {
    callback = callback || function _callback() {};

    clear();
    gLanguage = lang;

    // check all <link type="application/l10n" href="..." /> nodes
    // and load the resource files
    var langLinks = getL10nResourceLinks();
    var langCount = langLinks.length;
    if (langCount == 0) {
      // we might have a pre-compiled dictionary instead
      var dict = getL10nDictionary();
      if (dict && dict.locales && dict.default_locale) {
        consoleLog('using the embedded JSON directory, early way out');
        gL10nData = dict.locales[lang] || dict.locales[dict.default_locale];
        callback();
      } else {
        consoleLog('no resource to load, early way out');
      }
      // early way out
      fireL10nReadyEvent(lang);
      gReadyState = 'complete';
      return;
    }

    // start the callback when all resources are loaded
    var onResourceLoaded = null;
    var gResourceCount = 0;
    onResourceLoaded = function() {
      gResourceCount++;
      if (gResourceCount >= langCount) {
        callback();
        fireL10nReadyEvent(lang);
        gReadyState = 'complete';
      }
    };

    // load all resource files
    function l10nResourceLink(link) {
      var href = link.href;
      var type = link.type;
      this.load = function(lang, callback) {
        var applied = lang;
        parseResource(href, lang, callback, function() {
          consoleWarn(href + ' not found.');
          applied = '';
        });
        return applied; // return lang if found, an empty string if not found
      };
    }

    for (var i = 0; i < langCount; i++) {
      var resource = new l10nResourceLink(langLinks[i]);
      var rv = resource.load(lang, onResourceLoaded);
      if (rv != lang) { // lang not found, used default resource instead
        consoleWarn('"' + lang + '" resource not found');
        gLanguage = '';
      }
    }
  }

  // clear all l10n data
  function clear() {
    gL10nData = {};
    gTextData = '';
    gLanguage = '';
    // TODO: clear all non predefined macros.
    // There's no such macro /yet/ but we're planning to have some...
  }


  /**
   * Get rules for plural forms (shared with JetPack), see:
   * http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html
   * https://github.com/mozilla/addon-sdk/blob/master/python-lib/plural-rules-generator.p
   *
   * @param {string} lang
   *    locale (language) used.
   *
   * @return {Function}
   *    returns a function that gives the plural form name for a given integer:
   *       var fun = getPluralRules('en');
   *       fun(1)    -> 'one'
   *       fun(0)    -> 'other'
   *       fun(1000) -> 'other'.
   */

  function getPluralRules(lang) {
    var locales2rules = {
      'af': 3,
      'ak': 4,
      'am': 4,
      'ar': 1,
      'asa': 3,
      'az': 0,
      'be': 11,
      'bem': 3,
      'bez': 3,
      'bg': 3,
      'bh': 4,
      'bm': 0,
      'bn': 3,
      'bo': 0,
      'br': 20,
      'brx': 3,
      'bs': 11,
      'ca': 3,
      'cgg': 3,
      'chr': 3,
      'cs': 12,
      'cy': 17,
      'da': 3,
      'de': 3,
      'dv': 3,
      'dz': 0,
      'ee': 3,
      'el': 3,
      'en': 3,
      'eo': 3,
      'es': 3,
      'et': 3,
      'eu': 3,
      'fa': 0,
      'ff': 5,
      'fi': 3,
      'fil': 4,
      'fo': 3,
      'fr': 5,
      'fur': 3,
      'fy': 3,
      'ga': 8,
      'gd': 24,
      'gl': 3,
      'gsw': 3,
      'gu': 3,
      'guw': 4,
      'gv': 23,
      'ha': 3,
      'haw': 3,
      'he': 2,
      'hi': 4,
      'hr': 11,
      'hu': 0,
      'id': 0,
      'ig': 0,
      'ii': 0,
      'is': 3,
      'it': 3,
      'iu': 7,
      'ja': 0,
      'jmc': 3,
      'jv': 0,
      'ka': 0,
      'kab': 5,
      'kaj': 3,
      'kcg': 3,
      'kde': 0,
      'kea': 0,
      'kk': 3,
      'kl': 3,
      'km': 0,
      'kn': 0,
      'ko': 0,
      'ksb': 3,
      'ksh': 21,
      'ku': 3,
      'kw': 7,
      'lag': 18,
      'lb': 3,
      'lg': 3,
      'ln': 4,
      'lo': 0,
      'lt': 10,
      'lv': 6,
      'mas': 3,
      'mg': 4,
      'mk': 16,
      'ml': 3,
      'mn': 3,
      'mo': 9,
      'mr': 3,
      'ms': 0,
      'mt': 15,
      'my': 0,
      'nah': 3,
      'naq': 7,
      'nb': 3,
      'nd': 3,
      'ne': 3,
      'nl': 3,
      'nn': 3,
      'no': 3,
      'nr': 3,
      'nso': 4,
      'ny': 3,
      'nyn': 3,
      'om': 3,
      'or': 3,
      'pa': 3,
      'pap': 3,
      'pl': 13,
      'ps': 3,
      'pt': 3,
      'rm': 3,
      'ro': 9,
      'rof': 3,
      'ru': 11,
      'rwk': 3,
      'sah': 0,
      'saq': 3,
      'se': 7,
      'seh': 3,
      'ses': 0,
      'sg': 0,
      'sh': 11,
      'shi': 19,
      'sk': 12,
      'sl': 14,
      'sma': 7,
      'smi': 7,
      'smj': 7,
      'smn': 7,
      'sms': 7,
      'sn': 3,
      'so': 3,
      'sq': 3,
      'sr': 11,
      'ss': 3,
      'ssy': 3,
      'st': 3,
      'sv': 3,
      'sw': 3,
      'syr': 3,
      'ta': 3,
      'te': 3,
      'teo': 3,
      'th': 0,
      'ti': 4,
      'tig': 3,
      'tk': 3,
      'tl': 4,
      'tn': 3,
      'to': 0,
      'tr': 0,
      'ts': 3,
      'tzm': 22,
      'uk': 11,
      'ur': 3,
      've': 3,
      'vi': 0,
      'vun': 3,
      'wa': 4,
      'wae': 3,
      'wo': 0,
      'xh': 3,
      'xog': 3,
      'yo': 0,
      'zh': 0,
      'zu': 3
    };

    // utility functions for plural rules methods
    function isIn(n, list) {
      return list.indexOf(n) !== -1;
    }
    function isBetween(n, start, end) {
      return start <= n && n <= end;
    }

    // list of all plural rules methods:
    // map an integer to the plural form name to use
    var pluralRules = {
      '0': function(n) {
        return 'other';
      },
      '1': function(n) {
        if ((isBetween((n % 100), 3, 10)))
          return 'few';
        if (n === 0)
          return 'zero';
        if ((isBetween((n % 100), 11, 99)))
          return 'many';
        if (n == 2)
          return 'two';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '2': function(n) {
        if (n !== 0 && (n % 10) === 0)
          return 'many';
        if (n == 2)
          return 'two';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '3': function(n) {
        if (n == 1)
          return 'one';
        return 'other';
      },
      '4': function(n) {
        if ((isBetween(n, 0, 1)))
          return 'one';
        return 'other';
      },
      '5': function(n) {
        if ((isBetween(n, 0, 2)) && n != 2)
          return 'one';
        return 'other';
      },
      '6': function(n) {
        if (n === 0)
          return 'zero';
        if ((n % 10) == 1 && (n % 100) != 11)
          return 'one';
        return 'other';
      },
      '7': function(n) {
        if (n == 2)
          return 'two';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '8': function(n) {
        if ((isBetween(n, 3, 6)))
          return 'few';
        if ((isBetween(n, 7, 10)))
          return 'many';
        if (n == 2)
          return 'two';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '9': function(n) {
        if (n === 0 || n != 1 && (isBetween((n % 100), 1, 19)))
          return 'few';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '10': function(n) {
        if ((isBetween((n % 10), 2, 9)) && !(isBetween((n % 100), 11, 19)))
          return 'few';
        if ((n % 10) == 1 && !(isBetween((n % 100), 11, 19)))
          return 'one';
        return 'other';
      },
      '11': function(n) {
        if ((isBetween((n % 10), 2, 4)) && !(isBetween((n % 100), 12, 14)))
          return 'few';
        if ((n % 10) === 0 ||
            (isBetween((n % 10), 5, 9)) ||
            (isBetween((n % 100), 11, 14)))
          return 'many';
        if ((n % 10) == 1 && (n % 100) != 11)
          return 'one';
        return 'other';
      },
      '12': function(n) {
        if ((isBetween(n, 2, 4)))
          return 'few';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '13': function(n) {
        if ((isBetween((n % 10), 2, 4)) && !(isBetween((n % 100), 12, 14)))
          return 'few';
        if (n != 1 && (isBetween((n % 10), 0, 1)) ||
            (isBetween((n % 10), 5, 9)) ||
            (isBetween((n % 100), 12, 14)))
          return 'many';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '14': function(n) {
        if ((isBetween((n % 100), 3, 4)))
          return 'few';
        if ((n % 100) == 2)
          return 'two';
        if ((n % 100) == 1)
          return 'one';
        return 'other';
      },
      '15': function(n) {
        if (n === 0 || (isBetween((n % 100), 2, 10)))
          return 'few';
        if ((isBetween((n % 100), 11, 19)))
          return 'many';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '16': function(n) {
        if ((n % 10) == 1 && n != 11)
          return 'one';
        return 'other';
      },
      '17': function(n) {
        if (n == 3)
          return 'few';
        if (n === 0)
          return 'zero';
        if (n == 6)
          return 'many';
        if (n == 2)
          return 'two';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '18': function(n) {
        if (n === 0)
          return 'zero';
        if ((isBetween(n, 0, 2)) && n !== 0 && n != 2)
          return 'one';
        return 'other';
      },
      '19': function(n) {
        if ((isBetween(n, 2, 10)))
          return 'few';
        if ((isBetween(n, 0, 1)))
          return 'one';
        return 'other';
      },
      '20': function(n) {
        if ((isBetween((n % 10), 3, 4) || ((n % 10) == 9)) && !(
            isBetween((n % 100), 10, 19) ||
            isBetween((n % 100), 70, 79) ||
            isBetween((n % 100), 90, 99)
            ))
          return 'few';
        if ((n % 1000000) === 0 && n !== 0)
          return 'many';
        if ((n % 10) == 2 && !isIn((n % 100), [12, 72, 92]))
          return 'two';
        if ((n % 10) == 1 && !isIn((n % 100), [11, 71, 91]))
          return 'one';
        return 'other';
      },
      '21': function(n) {
        if (n === 0)
          return 'zero';
        if (n == 1)
          return 'one';
        return 'other';
      },
      '22': function(n) {
        if ((isBetween(n, 0, 1)) || (isBetween(n, 11, 99)))
          return 'one';
        return 'other';
      },
      '23': function(n) {
        if ((isBetween((n % 10), 1, 2)) || (n % 20) === 0)
          return 'one';
        return 'other';
      },
      '24': function(n) {
        if ((isBetween(n, 3, 10) || isBetween(n, 13, 19)))
          return 'few';
        if (isIn(n, [2, 12]))
          return 'two';
        if (isIn(n, [1, 11]))
          return 'one';
        return 'other';
      }
    };

    // return a function that gives the plural form name for a given integer
    var index = locales2rules[lang.replace(/-.*$/, '')];
    if (!(index in pluralRules)) {
      consoleWarn('plural form unknown for [' + lang + ']');
      return function() { return 'other'; };
    }
    return pluralRules[index];
  }

  // pre-defined 'plural' macro
  gMacros.plural = function(str, param, key, prop) {
    var n = parseFloat(param);
    if (isNaN(n))
      return str;

    // TODO: support other properties (l20n still doesn't...)
    if (prop != gTextProp)
      return str;

    // initialize _pluralRules
    if (!gMacros._pluralRules) {
      gMacros._pluralRules = getPluralRules(gLanguage);
    }
    var index = '[' + gMacros._pluralRules(n) + ']';

    // try to find a [zero|one|two] key if it's defined
    if (n === 0 && (key + '[zero]') in gL10nData) {
      str = gL10nData[key + '[zero]'][prop];
    } else if (n == 1 && (key + '[one]') in gL10nData) {
      str = gL10nData[key + '[one]'][prop];
    } else if (n == 2 && (key + '[two]') in gL10nData) {
      str = gL10nData[key + '[two]'][prop];
    } else if ((key + index) in gL10nData) {
      str = gL10nData[key + index][prop];
    } else if ((key + '[other]') in gL10nData) {
      str = gL10nData[key + '[other]'][prop];
    }

    return str;
  };


  /**
   * l10n dictionary functions
   */

  // fetch an l10n object, warn if not found, apply `args' if possible
  function getL10nData(key, args) {
    var data = gL10nData[key];
    if (!data) {
      consoleWarn('#' + key + ' missing for [' + gLanguage + ']');
    }

    /** This is where l10n expressions should be processed.
      * The plan is to support C-style expressions from the l20n project;
      * until then, only two kinds of simple expressions are supported:
      *   {[ index ]} and {{ arguments }}.
      */
    var rv = {};
    for (var prop in data) {
      var str = data[prop];
      str = substIndexes(str, args, key, prop);
      str = substArguments(str, args);
      rv[prop] = str;
    }
    return rv;
  }

  // replace {[macros]} with their values
  function substIndexes(str, args, key, prop) {
    var reIndex = /\{\[\s*([a-zA-Z]+)\(([a-zA-Z]+)\)\s*\]\}/;
    var reMatch = reIndex.exec(str);
    if (!reMatch || !reMatch.length)
      return str;

    // an index/macro has been found
    // Note: at the moment, only one parameter is supported
    var macroName = reMatch[1];
    var paramName = reMatch[2];
    var param;
    if (args && paramName in args) {
      param = args[paramName];
    } else if (paramName in gL10nData) {
      param = gL10nData[paramName];
    }

    // there's no macro parser yet: it has to be defined in gMacros
    if (macroName in gMacros) {
      var macro = gMacros[macroName];
      str = macro(str, param, key, prop);
    }
    return str;
  }

  // replace {{arguments}} with their values
  function substArguments(str, args) {
    var reArgs = /\{\{\s*([a-zA-Z\.]+)\s*\}\}/;
    var match = reArgs.exec(str);
    while (match) {
      if (!match || match.length < 2)
        return str; // argument key not found

      var arg = match[1];
      var sub = '';
      if (arg in args) {
        sub = args[arg];
      } else if (arg in gL10nData) {
        sub = gL10nData[arg][gTextProp];
      } else {
        consoleWarn('could not find argument {{' + arg + '}}');
        return str;
      }

      str = str.substring(0, match.index) + sub +
            str.substr(match.index + match[0].length);
      match = reArgs.exec(str);
    }
    return str;
  }

  // translate an HTML element
  function translateElement(element) {
    var l10n = getL10nAttributes(element);
    if (!l10n.id)
      return;

    // get the related l10n object
    var data = getL10nData(l10n.id, l10n.args);
    if (!data) {
      consoleWarn('#' + l10n.id + ' missing for [' + gLanguage + ']');
      return;
    }

    // translate element (TODO: security checks?)
    // for the node content, replace the content of the first child textNode
    // and clear other child textNodes
    if (data[gTextProp]) { // XXX
      if (getChildElementCount(element) === 0) {
        element[gTextProp] = data[gTextProp];
      } else {
        var children = element.childNodes,
            found = false;
        for (var i = 0, l = children.length; i < l; i++) {
          if (children[i].nodeType === 3 &&
              /\S/.test(children[i].textContent)) { // XXX
            // using nodeValue seems cross-browser
            if (found) {
              children[i].nodeValue = '';
            } else {
              children[i].nodeValue = data[gTextProp];
              found = true;
            }
          }
        }
        if (!found) {
          consoleWarn('unexpected error, could not translate element content');
        }
      }
      delete data[gTextProp];
    }

    for (var k in data) {
      element[k] = data[k];
    }
  }

  // webkit browsers don't currently support 'children' on SVG elements...
  function getChildElementCount(element) {
    if (element.children) {
      return element.children.length;
    }
    if (typeof element.childElementCount !== 'undefined') {
      return element.childElementCount;
    }
    var count = 0;
    for (var i = 0; i < element.childNodes.length; i++) {
      count += element.nodeType === 1 ? 1 : 0;
    }
    return count;
  }

  // translate an HTML subtree
  function translateFragment(element) {
    element = element || document.documentElement;

    // check all translatable children (= w/ a `data-l10n-id' attribute)
    var children = getTranslatableChildren(element);
    var elementCount = children.length;
    for (var i = 0; i < elementCount; i++) {
      translateElement(children[i]);
    }

    // translate element itself if necessary
    translateElement(element);
  }

  // Startup & Public API

  function l10nStartup() {
    gReadyState = 'interactive';
    consoleLog('loading [' + navigator.language + '] resources, ' +
        (gAsyncResourceLoading ? 'asynchronously.' : 'synchronously.'));

    // load the default locale and translate the document if required
    if (document.documentElement.lang === navigator.language) {
      loadLocale(navigator.language);
    } else {
      loadLocale(navigator.language, translateFragment);
    }
  }

  // public API
  var l10n = {
    start: function() {
      if (document.readyState === 'complete' ||
        document.readyState === 'interactive') {
        window.setTimeout(l10nStartup);
      } else {
        document.addEventListener('DOMContentLoaded', l10nStartup);
      }
    },

    // get a localized string
    get: function l10n_get(key, args, fallback) {
      var data = getL10nData(key, args) || fallback;
      if (data) {
        return 'textContent' in data ? data.textContent : '';
      }
      return '{{' + key + '}}';
    },

    // get|set the document language and direction
    get language() {
      return {
        // get|set the document language (ISO-639-1)
        get code() { return gLanguage; },
        set code(lang) { loadLocale(lang, translateFragment); },

        // get the direction (ltr|rtl) of the current language
        get direction() {
          // http://www.w3.org/International/questions/qa-scripts
          // Arabic, Hebrew, Farsi, Pashto, Urdu
          var rtlList = ['ar', 'he', 'fa', 'ps', 'ur'];
          return (rtlList.indexOf(gLanguage) >= 0) ? 'rtl' : 'ltr';
        }
      };
    },

    // translate an element or document fragment
    translate: translateFragment,

    // get (a clone of) the dictionary for the current locale
    get dictionary() { return JSON.parse(JSON.stringify(gL10nData)); },

    // this can be used to prevent race conditions
    get readyState() { return gReadyState; },
    ready: function l10n_ready(callback) {
      if (!callback)
        return;

      if (gReadyState == 'complete') {
        window.setTimeout(callback);
      } else {
        window.addEventListener('localized', callback);
      }
    }
  };

  return l10n;
});