/**
 * @class Images
 * This class loads images and keeps them stored.
 */
function Images() {
  this.images = {};
  this.callback = undefined;
}

Images.prototype._resolveRelativeUrl = function(url){
  var img = document.createElement('img');
  img.src = url; // set string url
  url = img.src; // get qualified url
  img.src = null; // no server request
  return url;
}

/**
 * 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
 * @param {string} url          Url of an image to use if the url image is not found
 * @return {Image} img          The image object
 */
Images.prototype.load = function(url, brokenUrl) {
  var img = this.images[url];
  if (img === undefined) {
    // create the image
    var me = this;
    img = new Image();
    img.onload = function () {

      // IE11 fix -- thanks dponch!
      if (this.width == 0) {
        document.body.appendChild(this);
        this.width = this.offsetWidth;
        this.height = this.offsetHeight;
        document.body.removeChild(this);
      }

      if (me.callback) {
        me.images[url] = img;
        me.callback(this);
      }
    };

    img.onerror = function () {
      if (brokenUrl === undefined) {
        console.error("Could not load image:", url);
        delete this.src;
        if (me.callback) {
          me.callback(this);
        }
      }
      else if (this.src === me._resolveRelativeUrl(brokenUrl)){
        console.error("Could not load brokenImage:", brokenUrl);
        delete this.src;
        if (me.callback) {
          me.callback(this);
        }          
      }
      else {
        this.src = brokenUrl;
      }
    };

    img.src = url;
  }

  return img;
};

module.exports = Images;