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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../iron-meta/iron-meta.html">

<script>
  /**
   * The `iron-iconset-svg` element allows users to define their own icon sets
   * that contain svg icons. The svg icon elements should be children of the
   * `iron-iconset-svg` element. Multiple icons should be given distinct id's.
   *
   * Using svg elements to create icons has a few advantages over traditional
   * bitmap graphics like jpg or png. Icons that use svg are vector based so
   * they are resolution independent and should look good on any device. They
   * are stylable via css. Icons can be themed, colorized, and even animated.
   *
   * Example:
   *
   *     <iron-iconset-svg name="my-svg-icons" size="24">
   *       <svg>
   *         <defs>
   *           <g id="shape">
   *             <rect x="50" y="50" width="50" height="50" />
   *             <circle cx="50" cy="50" r="50" />
   *           </g>
   *         </defs>
   *       </svg>
   *     </iron-iconset-svg>
   *
   * This will automatically register the icon set "my-svg-icons" to the iconset
   * database.  To use these icons from within another element, make a
   * `iron-iconset` element and call the `byId` method
   * to retrieve a given iconset. To apply a particular icon inside an
   * element use the `applyIcon` method. For example:
   *
   *     iconset.applyIcon(iconNode, 'car');
   *
   * @element iron-iconset-svg
   * @demo demo/index.html
   * @implements {Polymer.Iconset}
   */
  Polymer({
    is: 'iron-iconset-svg',

    properties: {

      /**
       * The name of the iconset.
       */
      name: {
        type: String,
        observer: '_nameChanged'
      },

      /**
       * The size of an individual icon. Note that icons must be square.
       */
      size: {
        type: Number,
        value: 24
      }

    },
    
    attached: function() {
      this.style.display = 'none';
    },

    /**
     * Construct an array of all icon names in this iconset.
     *
     * @return {!Array} Array of icon names.
     */
    getIconNames: function() {
      this._icons = this._createIconMap();
      return Object.keys(this._icons).map(function(n) {
        return this.name + ':' + n;
      }, this);
    },

    /**
     * Applies an icon to the given element.
     *
     * An svg icon is prepended to the element's shadowRoot if it exists,
     * otherwise to the element itself.
     *
     * @method applyIcon
     * @param {Element} element Element to which the icon is applied.
     * @param {string} iconName Name of the icon to apply.
     * @return {?Element} The svg element which renders the icon.
     */
    applyIcon: function(element, iconName) {
      // insert svg element into shadow root, if it exists
      element = element.root || element;
      // Remove old svg element
      this.removeIcon(element);
      // install new svg element
      var svg = this._cloneIcon(iconName);
      if (svg) {
        var pde = Polymer.dom(element);
        pde.insertBefore(svg, pde.childNodes[0]);
        return element._svgIcon = svg;
      }
      return null;
    },

    /**
     * Remove an icon from the given element by undoing the changes effected
     * by `applyIcon`.
     *
     * @param {Element} element The element from which the icon is removed.
     */
    removeIcon: function(element) {
      // Remove old svg element
      if (element._svgIcon) {
        Polymer.dom(element).removeChild(element._svgIcon);
        element._svgIcon = null;
      }
    },

    /**
     *
     * When name is changed, register iconset metadata
     *
     */
    _nameChanged: function() {
      new Polymer.IronMeta({type: 'iconset', key: this.name, value: this});
      this.async(function() {
        this.fire('iron-iconset-added', this, {node: window});
      });
    },

    /**
     * Create a map of child SVG elements by id.
     *
     * @return {!Object} Map of id's to SVG elements.
     */
    _createIconMap: function() {
      // Objects chained to Object.prototype (`{}`) have members. Specifically,
      // on FF there is a `watch` method that confuses the icon map, so we
      // need to use a null-based object here.
      var icons = Object.create(null);
      Polymer.dom(this).querySelectorAll('[id]')
        .forEach(function(icon) {
          icons[icon.id] = icon;
        });
      return icons;
    },

    /**
     * Produce installable clone of the SVG element matching `id` in this
     * iconset, or `undefined` if there is no matching element.
     *
     * @return {Element} Returns an installable clone of the SVG element
     * matching `id`.
     */
    _cloneIcon: function(id) {
      // create the icon map on-demand, since the iconset itself has no discrete
      // signal to know when it's children are fully parsed
      this._icons = this._icons || this._createIconMap();
      return this._prepareSvgClone(this._icons[id], this.size);
    },

    /**
     * @param {Element} sourceSvg
     * @param {number} size
     * @return {Element}
     */
    _prepareSvgClone: function(sourceSvg, size) {
      if (sourceSvg) {
        var content = sourceSvg.cloneNode(true),
            svg = document.createElementNS('http://www.w3.org/2000/svg', 'svg'),
            viewBox = content.getAttribute('viewBox') || '0 0 ' + size + ' ' + size;
        svg.setAttribute('viewBox', viewBox);
        svg.setAttribute('preserveAspectRatio', 'xMidYMid meet');
        // TODO(dfreedm): `pointer-events: none` works around https://crbug.com/370136
        // TODO(sjmiles): inline style may not be ideal, but avoids requiring a shadow-root
        svg.style.cssText = 'pointer-events: none; display: block; width: 100%; height: 100%;';
        svg.appendChild(content).removeAttribute('id');
        return svg;
      }
      return null;
    }

  });
</script>