<!--
@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->

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

<!--
`iron-overlay-backdrop` is a backdrop used by `Polymer.IronOverlayBehavior`. It should be a
singleton.

### Styling

The following custom properties and mixins are available for styling.

Custom property | Description | Default
-------------------------------------------|------------------------|---------
`--iron-overlay-backdrop-background-color` | Backdrop background color                                     | #000
`--iron-overlay-backdrop-opacity`          | Backdrop opacity                                              | 0.6
`--iron-overlay-backdrop`                  | Mixin applied to `iron-overlay-backdrop`.                      | {}
`--iron-overlay-backdrop-opened`           | Mixin applied to `iron-overlay-backdrop` when it is displayed | {}
-->

<dom-module id="iron-overlay-backdrop">

  <template>
    <style>
      :host {
        position: fixed;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background-color: var(--iron-overlay-backdrop-background-color, #000);
        opacity: 0;
        transition: opacity 0.2s;
        pointer-events: none;
        @apply(--iron-overlay-backdrop);
      }

      :host(.opened) {
        opacity: var(--iron-overlay-backdrop-opacity, 0.6);
        pointer-events: auto;
        @apply(--iron-overlay-backdrop-opened);
      }
    </style>

    <content></content>
  </template>

</dom-module>

<script>
(function() {
'use strict';

  Polymer({

    is: 'iron-overlay-backdrop',

    properties: {

      /**
       * Returns true if the backdrop is opened.
       */
      opened: {
        reflectToAttribute: true,
        type: Boolean,
        value: false,
        observer: '_openedChanged'
      }

    },

    listeners: {
      'transitionend': '_onTransitionend'
    },

    created: function() {
      // Used to cancel previous requestAnimationFrame calls when opened changes.
      this.__openedRaf = null;
    },

    attached: function() {
      this.opened && this._openedChanged(this.opened);
    },

    /**
     * Appends the backdrop to document body if needed.
     */
    prepare: function() {
      if (this.opened && !this.parentNode) {
        Polymer.dom(document.body).appendChild(this);
      }
    },

    /**
     * Shows the backdrop.
     */
    open: function() {
      this.opened = true;
    },

    /**
     * Hides the backdrop.
     */
    close: function() {
      this.opened = false;
    },

    /**
     * Removes the backdrop from document body if needed.
     */
    complete: function() {
      if (!this.opened && this.parentNode === document.body) {
        Polymer.dom(this.parentNode).removeChild(this);
      }
    },

    _onTransitionend: function(event) {
      if (event && event.target === this) {
        this.complete();
      }
    },

    /**
     * @param {boolean} opened
     * @private
     */
    _openedChanged: function(opened) {
      if (opened) {
        // Auto-attach.
        this.prepare();
      } else {
        // Animation might be disabled via the mixin or opacity custom property.
        // If it is disabled in other ways, it's up to the user to call complete.
        var cs = window.getComputedStyle(this);
        if (cs.transitionDuration === '0s' || cs.opacity == 0) {
          this.complete();
        }
      }

      if (!this.isAttached) {
        return;
      }

      // Always cancel previous requestAnimationFrame.
      if (this.__openedRaf) {
        window.cancelAnimationFrame(this.__openedRaf);
        this.__openedRaf = null;
      }
      // Force relayout to ensure proper transitions.
      this.scrollTop = this.scrollTop;
      this.__openedRaf = window.requestAnimationFrame(function() {
        this.__openedRaf = null;
        this.toggleClass('opened', this.opened);
      }.bind(this));
    }
  });

})();

</script>