SGH / COMPONENTS

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

<!--
The `iron-iconset` element allows users to define their own icon sets.
The `src` property specifies the url of the icon image. Multiple icons may
be included in this image and they may be organized into rows.
The `icons` property is a space separated list of names corresponding to the
icons. The names must be ordered as the icons are ordered in the icon image.
Icons are expected to be square and are the size specified by the `size`
property. The `width` property corresponds to the width of the icon image
and must be specified if icons are arranged into multiple rows in the image.

All `iron-iconset` elements are available for use by other `iron-iconset`
elements via a database keyed by id. Typically, an element author that wants
to support a set of custom icons uses a `iron-iconset` to retrieve
and use another, user-defined iconset.

Example:

    <iron-iconset id="my-icons" src="my-icons.png" width="96" size="24"
        icons="location place starta stopb bus car train walk">
    </iron-iconset>

This will automatically register the icon set "my-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 to an element, use the
`applyIcon` method. For example:

    iconset.applyIcon(iconNode, 'car');

Themed icon sets are also supported. The `iron-iconset` can contain child
`property` elements that specify a theme with an offsetX and offsetY of the
theme within the icon resource. For example.

    <iron-iconset id="my-icons" src="my-icons.png" width="96" size="24"
        icons="location place starta stopb bus car train walk">
      <property theme="special" offsetX="256" offsetY="24"></property>
    </iron-iconset>

Then a themed icon can be applied like this:

    iconset.applyIcon(iconNode, 'car', 'special');

@element iron-iconset
@demo demo/index.html
-->

<script>

  /**
   * @implements {Polymer.Iconset}
   */
  Polymer({

    is: 'iron-iconset',

    properties: {

      /**
       * The URL of the iconset image.
       */
      src: {
        type: String,
        observer: '_srcChanged'
      },

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

      /**
       * The width of the iconset image. This must only be specified if the
       * icons are arranged into separate rows inside the image.
       *
       * @attribute width
       * @type number
       * @default 0
       */
      width: {
        type: Number,
        value: 0
      },

      /**
       * A space separated list of names corresponding to icons in the iconset
       * image file. This list must be ordered the same as the icon images
       * in the image file.
       */
      icons: {
        type: String
      },

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

      /**
       * The horizontal offset of the icon images in the inconset src image.
       * This is typically used if the image resource contains additional images
       * beside those intended for the iconset.
       */
      _offsetX: {
        type: Number,
        value: 0
      },

      /**
       * The vertical offset of the icon images in the inconset src image.
       * This is typically used if the image resource contains additional images
       * beside those intended for the iconset.
       */
      _offsetY: {
        type: Number,
        value: 0
      },

      /**
       * Array of fully-qualified names of icons in this set.
       */
      iconNames: {
        type: Array,
        notify: true
      }

    },

    hostAttributes: {
      // non-visual
      style: 'display: none;'
    },

    ready: function() {
      // theme data must exist at ready-time
      this._themes = this._mapThemes();
    },

    /**
     * Applies an icon to the given element as a css background image. This
     * method does not size the element, and it's usually necessary to set
     * the element's height and width so that the background image is visible.
     *
     * @param {Element} element The element to which the icon is applied.
     * @param {string|number} icon The name or index of the icon to apply.
     * @param {string=} theme (optional) The name or index of the icon to apply.
     * @param {number=} scale (optional, defaults to 1) Icon scaling factor.
     */
    applyIcon: function(element, icon, theme, scale) {
      this._validateIconMap();
      var offset = this._getThemedOffset(icon, theme);
      if (element && offset) {
        this._addIconStyles(element, this._srcUrl, offset, scale || 1,
          this.size, this.width);
      }
    },

    /**
     * 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) {
      this._removeIconStyles(element.style);
    },

    _mapThemes: function() {
      var themes = Object.create(null);
      Polymer.dom(this).querySelectorAll('property[theme]')
        .forEach(function(property) {
          var offsetX = window.parseInt(
            property.getAttribute('offset-x'), 10
          ) || 0;
          var offsetY = window.parseInt(
            property.getAttribute('offset-y'), 10
          ) || 0;
          themes[property.getAttribute('theme')] = {
            offsetX: offsetX,
            offsetY: offsetY
          };
        });
      return themes;
    },

    _srcChanged: function(src) {
      // ensure `srcUrl` is always relative to the main document
      this._srcUrl = this.ownerDocument !== document
        ? this.resolveUrl(src) : src;
      this._prepareIconset();
    },

    _nameChanged: function(name) {
      this._prepareIconset();
    },

    _prepareIconset: function() {
      new Polymer.IronMeta({type: 'iconset', key: this.name, value: this});
      this.async(function() {
        this.fire('iron-iconset-added', this, {node: window});
      });
    },

    _invalidateIconMap: function() {
      this._iconMapValid = false;
    },

    _validateIconMap: function() {
      if (!this._iconMapValid) {
        this._recomputeIconMap();
        this._iconMapValid = true;
      }
    },

    _recomputeIconMap: function() {
      this.iconNames = this._computeIconNames(this.icons);
      this.iconMap = this._computeIconMap(this._offsetX, this._offsetY,
        this.size, this.width, this.iconNames);
    },

    _computeIconNames: function(icons) {
      return icons.split(/\s+/g);
    },

    _computeIconMap: function(offsetX, offsetY, size, width, iconNames) {
      var iconMap = {};
      if (offsetX !== undefined && offsetY !== undefined) {
        var x0 = offsetX;
        iconNames.forEach(function(iconName) {
          iconMap[iconName] = {
            offsetX: offsetX,
            offsetY: offsetY
          };
          if ((offsetX + size) < width) {
            offsetX += size;
          } else {
            offsetX = x0;
            offsetY += size;
          }
        }, this);
      }
      return iconMap;
    },

    /**
     * Returns an object containing `offsetX` and `offsetY` properties which
     * specify the pixel location in the iconset's src file for the given
     * `icon` and `theme`. It's uncommon to call this method. It is useful,
     * for example, to manually position a css backgroundImage to the proper
     * offset. It's more common to use the `applyIcon` method.
     *
     * @param {string|number} identifier The name of the icon or the index of
     * the icon within in the icon image.
     * @param {string=} theme The name of the theme.
     * @returns {?{offsetX: number, offsetY: number}} An object specifying the
     *     offset of the given icon within the icon resource file; `offsetX` is
     *     the horizontal offset and `offsetY` is the vertical offset. Both
     *     values are in pixel units.
     */
    _getThemedOffset: function(identifier, theme) {
      var iconOffset = this._getIconOffset(identifier);
      var themeOffset = this._themes[theme];
      if (iconOffset && themeOffset) {
        return {
          offsetX: iconOffset.offsetX + themeOffset.offsetX,
          offsetY: iconOffset.offsetY + themeOffset.offsetY
        };
      }
      return iconOffset;
    },

    _getIconOffset: function(identifier) {
      // TODO(sjmiles): consider creating offsetArray (indexed by Number)
      // and having iconMap map names to indices, then and index is just
      // iconMap[identifier] || identifier (be careful of zero, store indices
      // as 1-based)
      return this.iconMap[identifier] ||
             this.iconMap[this.iconNames[Number(identifier)]];
    },

    _addIconStyles: function(element, url, offset, scale, size, width) {
      var style = element.style;
      style.backgroundImage = 'url(' + url + ')';
      style.backgroundPosition =
        (-offset.offsetX * scale + 'px') + ' ' +
        (-offset.offsetY * scale + 'px');
      style.backgroundSize = (scale === 1) ? 'auto' : width * scale + 'px';
      style.width = size + 'px';
      style.height = size + 'px';
      element.setAttribute('role', 'img');
    },

    _removeIconStyles: function(style) {
      style.background = '';
    }

  });

</script>