<!--
@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">
<link rel="import" href="../iron-a11y-keys-behavior/iron-a11y-keys-behavior.html">
<link rel="import" href="../iron-selector/iron-selectable.html">
<link rel="import" href="../paper-radio-button/paper-radio-button.html">

<!--
Material design: [Radio button](https://www.google.com/design/spec/components/selection-controls.html#selection-controls-radio-button)

`paper-radio-group` allows user to select at most one radio button from a set.
Checking one radio button that belongs to a radio group unchecks any
previously checked radio button within the same group. Use
`selected` to get or set the selected radio button.

The <paper-radio-buttons> inside the group must have the `name` attribute
set.

Example:

    <paper-radio-group selected="small">
      <paper-radio-button name="small">Small</paper-radio-button>
      <paper-radio-button name="medium">Medium</paper-radio-button>
      <paper-radio-button name="large">Large</paper-radio-button>
    </paper-radio-group>

Radio-button-groups can be made optional, and allow zero buttons to be selected:

    <paper-radio-group selected="small" allow-empty-selection>
      <paper-radio-button name="small">Small</paper-radio-button>
      <paper-radio-button name="medium">Medium</paper-radio-button>
      <paper-radio-button name="large">Large</paper-radio-button>
    </paper-radio-group>

See <a href="paper-radio-button">paper-radio-button</a> for more
information about `paper-radio-button`.

@group Paper Elements
@element paper-radio-group
@hero hero.svg
@demo demo/index.html
-->

<dom-module id="paper-radio-group">
  <style>
    :host {
      display: inline-block;
    }

    :host ::content > * {
      padding: 12px;
    }
  </style>

  <template>
      <content id="items" select="*"></content>
  </template>

</dom-module>

<script>
  Polymer({
    is: 'paper-radio-group',

    behaviors: [
      Polymer.IronA11yKeysBehavior,
      Polymer.IronSelectableBehavior
    ],

    hostAttributes: {
      role: 'radiogroup',
      tabindex: 0
    },

    properties: {
      /**
       * Fired when the radio group selection changes.
       *
       * @event paper-radio-group-changed
       */

      /**
       * Overriden from Polymer.IronSelectableBehavior
       */
      attrForSelected: {
        type: String,
        value: 'name'
      },

      /**
       * Overriden from Polymer.IronSelectableBehavior
       */
      selectedAttribute: {
        type: String,
        value: 'checked'
      },

      /**
       * Overriden from Polymer.IronSelectableBehavior
       */
      selectable: {
        type: String,
        value: 'paper-radio-button'
      },

      /**
       * If true, radio-buttons can be deselected
       */
      allowEmptySelection: {
        type: Boolean,
        value: false
      }
    },

    keyBindings: {
      'left up': 'selectPrevious',
      'right down': 'selectNext',
    },

    /**
     * Selects the given value.
     */
     select: function(value) {
      if (this.selected) {
        var oldItem = this._valueToItem(this.selected);

        if (this.selected == value) {
          // If deselecting is allowed we'll have to apply an empty selection.
          // Otherwise, we should force the selection to stay and make this
          // action a no-op.
          if (this.allowEmptySelection) {
            value = '';
          } else {
            oldItem.checked = true;
            return;
          }
        }

        if (oldItem)
          oldItem.checked = false;
      }

      Polymer.IronSelectableBehavior.select.apply(this, [value]);
      this.fire('paper-radio-group-changed');
    },

    /**
     * Selects the previous item. If the previous item is disabled, then it is
     * skipped, and its previous item is selected
     */
    selectPrevious: function() {
      var length = this.items.length;
      var newIndex = Number(this._valueToIndex(this.selected));

      do {
        newIndex = (newIndex - 1 + length) % length;
      } while (this.items[newIndex].disabled)

      this.select(this._indexToValue(newIndex));
    },

    /**
     * Selects the next item. If the next item is disabled, then it is
     * skipped, and the next item after it is selected.
     */
    selectNext: function() {
      var length = this.items.length;
      var newIndex = Number(this._valueToIndex(this.selected));

      do {
        newIndex = (newIndex + 1 + length) % length;
      } while (this.items[newIndex].disabled)

      this.select(this._indexToValue(newIndex));
    },
  });
</script>