WebCompDev / COMPONENTS

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

<script>
  /**
   * `IronResizableBehavior` is a behavior that can be used in Polymer elements to
   * coordinate the flow of resize events between "resizers" (elements that control the
   * size or hidden state of their children) and "resizables" (elements that need to be
   * notified when they are resized or un-hidden by their parents in order to take
   * action on their new measurements).
   * Elements that perform measurement should add the `IronResizableBehavior` behavior to
   * their element definition and listen for the `iron-resize` event on themselves.
   * This event will be fired when they become showing after having been hidden,
   * when they are resized explicitly by another resizable, or when the window has been
   * resized.
   * Note, the `iron-resize` event is non-bubbling.
   *
   * @polymerBehavior Polymer.IronResizableBehavior
   * @demo demo/index.html
   **/
  Polymer.IronResizableBehavior = {
    properties: {
      /**
       * The closest ancestor element that implements `IronResizableBehavior`.
       */
      _parentResizable: {
        type: Object,
        observer: '_parentResizableChanged'
      },

      /**
       * True if this element is currently notifying its descedant elements of
       * resize.
       */
      _notifyingDescendant: {
        type: Boolean,
        value: false
      }
    },

    listeners: {
      'iron-request-resize-notifications': '_onIronRequestResizeNotifications'
    },

    created: function() {
      // We don't really need property effects on these, and also we want them
      // to be created before the `_parentResizable` observer fires:
      this._interestedResizables = [];
      this._boundNotifyResize = this.notifyResize.bind(this);
    },

    attached: function() {
      this.fire('iron-request-resize-notifications', null, {
        node: this,
        bubbles: true,
        cancelable: true
      });

      if (!this._parentResizable) {
        window.addEventListener('resize', this._boundNotifyResize);
        this.notifyResize();
      }
    },

    detached: function() {
      if (this._parentResizable) {
        this._parentResizable.stopResizeNotificationsFor(this);
      } else {
        window.removeEventListener('resize', this._boundNotifyResize);
      }

      this._parentResizable = null;
    },

    /**
     * Can be called to manually notify a resizable and its descendant
     * resizables of a resize change.
     */
    notifyResize: function() {
      if (!this.isAttached) {
        return;
      }

      this._interestedResizables.forEach(function(resizable) {
        if (this.resizerShouldNotify(resizable)) {
          this._notifyDescendant(resizable);
        }
      }, this);

      this._fireResize();
    },

    /**
     * Used to assign the closest resizable ancestor to this resizable
     * if the ancestor detects a request for notifications.
     */
    assignParentResizable: function(parentResizable) {
      this._parentResizable = parentResizable;
    },

    /**
     * Used to remove a resizable descendant from the list of descendants
     * that should be notified of a resize change.
     */
    stopResizeNotificationsFor: function(target) {
      var index = this._interestedResizables.indexOf(target);

      if (index > -1) {
        this._interestedResizables.splice(index, 1);
        this.unlisten(target, 'iron-resize', '_onDescendantIronResize');
      }
    },

    /**
     * This method can be overridden to filter nested elements that should or
     * should not be notified by the current element. Return true if an element
     * should be notified, or false if it should not be notified.
     *
     * @param {HTMLElement} element A candidate descendant element that
     * implements `IronResizableBehavior`.
     * @return {boolean} True if the `element` should be notified of resize.
     */
    resizerShouldNotify: function(element) { return true; },

    _onDescendantIronResize: function(event) {
      if (this._notifyingDescendant) {
        event.stopPropagation();
        return;
      }

      // NOTE(cdata): In ShadowDOM, event retargetting makes echoing of the
      // otherwise non-bubbling event "just work." We do it manually here for
      // the case where Polymer is not using shadow roots for whatever reason:
      if (!Polymer.Settings.useShadow) {
        this._fireResize();
      }
    },

    _fireResize: function() {
      this.fire('iron-resize', null, {
        node: this,
        bubbles: false
      });
    },

    _onIronRequestResizeNotifications: function(event) {
      var target = event.path ? event.path[0] : event.target;

      if (target === this) {
        return;
      }

      if (this._interestedResizables.indexOf(target) === -1) {
        this._interestedResizables.push(target);
        this.listen(target, 'iron-resize', '_onDescendantIronResize');
      }

      target.assignParentResizable(this);
      this._notifyDescendant(target);

      event.stopPropagation();
    },

    _parentResizableChanged: function(parentResizable) {
      if (parentResizable) {
        window.removeEventListener('resize', this._boundNotifyResize);
      }
    },

    _notifyDescendant: function(descendant) {
      // NOTE(cdata): In IE10, attached is fired on children first, so it's
      // important not to notify them if the parent is not attached yet (or
      // else they will get redundantly notified when the parent attaches).
      if (!this.isAttached) {
        return;
      }

      this._notifyingDescendant = true;
      descendant.notifyResize();
      this._notifyingDescendant = false;
    }
  };
</script>