<!--
tree-node elements are nested to create a tree menu
  <tree-node label="" icon="" iconalt="" itemtitle="" open highlight loading>

Example:
  <tree-node id="root" label="Location">
    <tree-node label="California" highlight></tree-node>
  </tree-node>
  (see demo.html for a full example)

Attributes:
  label: (string) displayed text of the tree node
  icon: (string) optional Polymer icon name; see
    https://www.polymer-project.org/components/core-icons/demo.html)
  iconalt: (string) alt text for item icon
  itemtitle: (string) title text for item
  open: (Boolean) expand to display nested children
  highlight: (Boolean) adds "highlight" CSS class to item
  loading: (Boolean) displays loading spinner
  isExpandable: (Boolean) displays the expand/collapse icon even if there are no children

Events:
  Attach one event listener to the root (or above),
  or individual listeners to each node.
  Don't forget to return false from the callback function to stop propagation.
  @event activate node item was clicked or tapped
  @event openchange node was expanded or collapsed
  The listener functions take a single parameter:
  @param {event} e the custom event object
  For both, e.detail.node is the affected tree-node.
  For the activate event, e.shiftKey, e.altKey, e.ctrlKey, and e.metaKey
  contain the state of those keyboard keys.

author: wmleler@
-->

<polymer-element name="tree-node" attributes="label icon emptytext">
  <template>
    <link rel="stylesheet" href="tree-node.css">
    <div class="indent" aria-expanded="{{open}}"
        aria-owns="{{isParent && open?'children':''}}">
      <div class="row">
        <template if="{{showEmptyIcon}}">
          <core-icon id="expander"
            icon="remove"
            alt="{{emptytext}}"
            title="{{emptytext}}">
          </core-icon>
        </template>
        <template if="{{!showEmptyIcon}}">
          <a class="expander-anchor"
             href="javascript:void(0);"
             on-click="{{openme}}"
             tabindex="{{isParent?'0':'-1'}}">
            <core-icon id="expander"
              class="{{isParent?'':'notParent'}}"
              icon="{{open?'expand-more':'chevron-right'}}"
              alt="{{open?'Collapse':'Expand'}}"
              title="{{open?'Collapse':'Expand'}}"
              >
            </core-icon>
          </a>
        </template>
        <paper-spinner active="{{loading}}" aria-label="loading">
        </paper-spinner>
        <a href="javascript:void(0);"
          on-click="{{activate}}"
          role="treeitem"
          aria-selected="{{highlight}}"
          class="item{{highlight?' highlight':''}}"
          title="{{itemtitle}}">
          <span class="itemcontent">
            <template if="{{icon}}">
              <core-icon class="itemicon" icon="{{icon}}" alt="{{iconalt}}">
              </core-icon>
            </template>
            <span class="itemtext">
              {{label}}
            </span>
          </span>
        </a>
      </div>
      <template if="{{isParent && open}}">
        <div id="children" role="group">
          <content></content>
        </div>
      </template>
    </div>
  </template>

  <script>
  Polymer('tree-node', {
    publish: {
      emptytext: 'No children',
      iconalt: 'item icon',
      itemtitle: 'item',
      open: false,
      highlight: false,
      loading: false,
      isExpandable: false
    },
    isParent: false,
    showEmptyIcon: false,
    ready: function() {
      this.isExpandableChanged();
      this.onMutation(this, this.childrenUpdated);
    },
    childrenUpdated: function(observer, mutations) {
      this.isExpandableChanged();
      this.onMutation(this, this.childrenUpdated);
      this.updateShowEmptyIcon();
    },
    isExpandableChanged: function() {
      this.isParent = !!this.firstElementChild || this.isExpandable;
    },
    openChanged: function() {
      this.updateShowEmptyIcon();
    },
    loadingChanged: function() {
      this.updateShowEmptyIcon();
    },
    updateShowEmptyIcon: function() {
      var me = this;
      setTimeout(function() {
        me.showEmptyIcon = (
          !me.firstElementChild &&
          !me.loading &&
           me.isExpandable &&
           me.open
        );
      }, 30); // delay showing the empty icon by a bit so it is less jarring
    },
    openme: function(e, d, sender) {
      this.open = !this.open;
      this.fire('openchange', { node: this });
    },
    activate: function(event, detail, sender) {
      this.fire('activate', { node: this,
          shiftKey: event.shiftKey, altKey: event.altKey,
          ctrlKey: event.ctrlKey, metaKey: event.metaKey });
    }
  });
  </script>
</polymer-element>