SGH / COMPONENTS

<!--
@license
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This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
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Code distributed by Google as part of the polymer project is also
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<link rel="import" href="../polymer/polymer.html">

<!--
`iron-collapse` creates a collapsible block of content.  By default, the content
will be collapsed.  Use `opened` or `toggle()` to show/hide the content.

    <button on-click="toggle">toggle collapse</button>

    <iron-collapse id="collapse">
      <div>Content goes here...</div>
    </iron-collapse>

    ...

    toggle: function() {
      this.$.collapse.toggle();
    }

`iron-collapse` adjusts the height/width of the collapsible element to show/hide
the content.  So avoid putting padding/margin/border on the collapsible directly,
and instead put a div inside and style that.

    <style>
      .collapse-content {
        padding: 15px;
        border: 1px solid #dedede;
      }
    </style>

    <iron-collapse>
      <div class="collapse-content">
        <div>Content goes here...</div>
      </div>
    </iron-collapse>

@group Iron Elements
@hero hero.svg
@demo demo/index.html
@element iron-collapse
-->

<dom-module id="iron-collapse">

  <style>

    :host {
      display: block;
      transition-duration: 300ms;
      overflow: auto;
    }

    :host(.iron-collapse-closed) {
      display: none;
    }

  </style>

  <template>

    <content></content>

  </template>

</dom-module>

<script>

  Polymer({

    is: 'iron-collapse',

    properties: {

      /**
       * If true, the orientation is horizontal; otherwise is vertical.
       *
       * @attribute horizontal
       */
      horizontal: {
        type: Boolean,
        value: false,
        observer: '_horizontalChanged'
      },

      /**
       * Set opened to true to show the collapse element and to false to hide it.
       *
       * @attribute opened
       */
      opened: {
        type: Boolean,
        value: false,
        notify: true,
        observer: '_openedChanged'
      },

      /**
       * Set noAnimation to true to disable animations
       *
       * @attribute noAnimation
       */
      noAnimation: {
        type: Boolean
      },

    },

    hostAttributes: {
      role: 'group',
      'aria-hidden': 'true',
      'aria-expanded': 'false'
    },

    listeners: {
      transitionend: '_transitionEnd'
    },

    attached: function() {
      // It will take care of setting correct classes and styles.
      this._transitionEnd();
    },

    /**
     * Toggle the opened state.
     *
     * @method toggle
     */
    toggle: function() {
      this.opened = !this.opened;
    },

    show: function() {
      this.opened = true;
    },

    hide: function() {
      this.opened = false;
    },

    updateSize: function(size, animated) {
      // No change!
      if (this.style[this.dimension] === size) {
        return;
      }

      this._updateTransition(false);
      // If we can animate, must do some prep work.
      if (animated && !this.noAnimation) {
        // Animation will start at the current size.
        var startSize = this._calcSize();
        // For `auto` we must calculate what is the final size for the animation.
        // After the transition is done, _transitionEnd will set the size back to `auto`.
        if (size === 'auto') {
          this.style[this.dimension] = size;
          size = this._calcSize();
        }
        // Go to startSize without animation.
        this.style[this.dimension] = startSize;
        // Force layout to ensure transition will go. Set offsetHeight to itself
        // so that compilers won't remove it.
        this.offsetHeight = this.offsetHeight;
        // Enable animation.
        this._updateTransition(true);
      }
      // Set the final size.
      this.style[this.dimension] = size;
    },

    /**
     * enableTransition() is deprecated, but left over so it doesn't break existing code.
     * Please use `noAnimation` property instead.
     *
     * @method enableTransition
     * @deprecated since version 1.0.4
     */
    enableTransition: function(enabled) {
      console.warn('`enableTransition()` is deprecated, use `noAnimation` instead.');
      this.noAnimation = !enabled;
    },

    _updateTransition: function(enabled) {
      this.style.transitionDuration = (enabled && !this.noAnimation) ? '' : '0s';
    },

    _horizontalChanged: function() {
      this.dimension = this.horizontal ? 'width' : 'height';
      this.style.transitionProperty = this.dimension;
    },

    _openedChanged: function() {
      this.setAttribute('aria-expanded', this.opened);
      this.setAttribute('aria-hidden', !this.opened);

      this.toggleClass('iron-collapse-closed', false);
      this.toggleClass('iron-collapse-opened', false);
      this.updateSize(this.opened ? 'auto' : '0px', true);

      // Focus the current collapse.
      if (this.opened) {
        this.focus();
      }
      if (this.noAnimation) {
        this._transitionEnd();
      }
    },

    _transitionEnd: function() {
      if (this.opened) {
        this.style[this.dimension] = 'auto';
      }
      this.toggleClass('iron-collapse-closed', !this.opened);
      this.toggleClass('iron-collapse-opened', this.opened);
      this._updateTransition(false);
    },

    _calcSize: function() {
      return this.getBoundingClientRect()[this.dimension] + 'px';
    }

  });

</script>