<!--
@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-selectable.html">

<script>
  /** @polymerBehavior Polymer.IronMultiSelectableBehavior */
  Polymer.IronMultiSelectableBehaviorImpl = {
    properties: {

      /**
       * If true, multiple selections are allowed.
       */
      multi: {
        type: Boolean,
        value: false,
        observer: 'multiChanged'
      },

      /**
       * Gets or sets the selected elements. This is used instead of `selected` when `multi`
       * is true.
       */
      selectedValues: {
        type: Array,
        notify: true
      },

      /**
       * Returns an array of currently selected items.
       */
      selectedItems: {
        type: Array,
        readOnly: true,
        notify: true
      },

    },

    observers: [
      '_updateSelected(selectedValues.splices)'
    ],

    /**
     * Selects the given value. If the `multi` property is true, then the selected state of the
     * `value` will be toggled; otherwise the `value` will be selected.
     *
     * @method select
     * @param {string|number} value the value to select.
     */
    select: function(value) {
      if (this.multi) {
        if (this.selectedValues) {
          this._toggleSelected(value);
        } else {
          this.selectedValues = [value];
        }
      } else {
        this.selected = value;
      }
    },

    multiChanged: function(multi) {
      this._selection.multi = multi;
    },

    get _shouldUpdateSelection() {
      return this.selected != null ||
        (this.selectedValues != null && this.selectedValues.length);
    },

    _updateAttrForSelected: function() {
      if (!this.multi) {
        Polymer.IronSelectableBehavior._updateAttrForSelected.apply(this);
      } else if (this._shouldUpdateSelection) {
        this.selectedValues = this.selectedItems.map(function(selectedItem) {
          return this._indexToValue(this.indexOf(selectedItem));
        }, this).filter(function(unfilteredValue) {
          return unfilteredValue != null;
        }, this);
      }
    },

    _updateSelected: function() {
      if (this.multi) {
        this._selectMulti(this.selectedValues);
      } else {
        this._selectSelected(this.selected);
      }
    },

    _selectMulti: function(values) {
      if (values) {
        var selectedItems = this._valuesToItems(values);
        // clear all but the current selected items
        this._selection.clear(selectedItems);
        // select only those not selected yet
        for (var i = 0; i < selectedItems.length; i++) {
          this._selection.setItemSelected(selectedItems[i], true);
        }
        // Check for items, since this array is populated only when attached
        if (this.fallbackSelection && this.items.length && !this._selection.get().length) {
          var fallback = this._valueToItem(this.fallbackSelection);
          if (fallback) {
            this.selectedValues = [this.fallbackSelection];
          }
        }
      } else {
        this._selection.clear();
      }
    },

    _selectionChange: function() {
      var s = this._selection.get();
      if (this.multi) {
        this._setSelectedItems(s);
      } else {
        this._setSelectedItems([s]);
        this._setSelectedItem(s);
      }
    },

    _toggleSelected: function(value) {
      var i = this.selectedValues.indexOf(value);
      var unselected = i < 0;
      if (unselected) {
        this.push('selectedValues',value);
      } else {
        this.splice('selectedValues',i,1);
      }
    },

    _valuesToItems: function(values) {
      return (values == null) ? null : values.map(function(value) {
        return this._valueToItem(value);
      }, this);
    }
  };

  /** @polymerBehavior */
  Polymer.IronMultiSelectableBehavior = [
    Polymer.IronSelectableBehavior,
    Polymer.IronMultiSelectableBehaviorImpl
  ];

</script>