/* ************************************************************************

   qooxdoo - the new era of web development

   http://qooxdoo.org

   Copyright:
     2008 1&1 Internet AG, Germany, http://www.1und1.de

   License:
     LGPL: http://www.gnu.org/licenses/lgpl.html
     EPL: http://www.eclipse.org/org/documents/epl-v10.php
     See the LICENSE file in the project's top-level directory for details.

   Authors:
     * Christian Hagendorn (chris_schmidt)

************************************************************************ */

/**
 * Responsible for the single selection management.
 *
 * The class manage a list of {@link qx.ui.core.Widget} which are returned from
 * {@link qx.ui.core.ISingleSelectionProvider#getItems}.
 *
 * @internal
 */
qx.Class.define("qx.ui.core.SingleSelectionManager",
{
  extend : qx.core.Object,


  /*
  *****************************************************************************
     CONSTRUCTOR
  *****************************************************************************
  */


  /**
   * Construct the single selection manager.
   *
   * @param selectionProvider {qx.ui.core.ISingleSelectionProvider} The provider
   * for selection.
   */
  construct : function(selectionProvider) {
    this.base(arguments);

    if (qx.core.Environment.get("qx.debug")) {
      qx.core.Assert.assertInterface(selectionProvider,
        qx.ui.core.ISingleSelectionProvider,
        "Invalid selectionProvider!");
    }

    this.__selectionProvider = selectionProvider;
  },


  /*
  *****************************************************************************
     EVENTS
  *****************************************************************************
  */


  events :
  {
    /** Fires after the selection was modified */
    "changeSelected" : "qx.event.type.Data"
  },


  /*
  *****************************************************************************
     PROPERTIES
  *****************************************************************************
  */


  properties :
  {
    /**
     * If the value is <code>true</code> the manager allows an empty selection,
     * otherwise the first selectable element returned from the
     * <code>qx.ui.core.ISingleSelectionProvider</code> will be selected.
     */
    allowEmptySelection :
    {
      check : "Boolean",
      init : true,
      apply : "__applyAllowEmptySelection"
    }
  },


  /*
  *****************************************************************************
     MEMBERS
  *****************************************************************************
  */


  members :
  {
    /** {qx.ui.core.Widget} The selected widget. */
    __selected : null,

    /** {qx.ui.core.ISingleSelectionProvider} The provider for selection management */
    __selectionProvider : null,


    /*
    ---------------------------------------------------------------------------
       PUBLIC API
    ---------------------------------------------------------------------------
    */


    /**
     * Returns the current selected element.
     *
     * @return {qx.ui.core.Widget | null} The current selected widget or
     *    <code>null</code> if the selection is empty.
     */
    getSelected : function() {
      return this.__selected;
    },

    /**
     * Selects the passed element.
     *
     * @param item {qx.ui.core.Widget} Element to select.
     * @throws {Error} if the element is not a child element.
     */
    setSelected : function(item) {
      if (!this.__isChildElement(item)) {
        throw new Error("Could not select " + item +
          ", because it is not a child element!");
      }

      this.__setSelected(item);
    },

    /**
     * Reset the current selection. If {@link #allowEmptySelection} is set to
     * <code>true</code> the first element will be selected.
     */
    resetSelected : function(){
      this.__setSelected(null);
    },

    /**
     * Return <code>true</code> if the passed element is selected.
     *
     * @param item {qx.ui.core.Widget} Element to check if selected.
     * @return {Boolean} <code>true</code> if passed element is selected,
     *    <code>false</code> otherwise.
     * @throws {Error} if the element is not a child element.
     */
    isSelected : function(item) {
      if (!this.__isChildElement(item)) {
        throw new Error("Could not check if " + item + " is selected," +
          " because it is not a child element!");
      }
      return this.__selected === item;
    },

    /**
     * Returns <code>true</code> if selection is empty.
     *
     * @return {Boolean} <code>true</code> if selection is empty,
     *    <code>false</code> otherwise.
     */
    isSelectionEmpty : function() {
      return this.__selected == null;
    },

    /**
     * Returns all elements which are selectable.
     *
     * @param all {Boolean} true for all selectables, false for the
     *   selectables the user can interactively select
     * @return {qx.ui.core.Widget[]} The contained items.
     */
    getSelectables : function(all)
    {
      var items = this.__selectionProvider.getItems();
      var result = [];

      for (var i = 0; i < items.length; i++)
      {
        if (this.__selectionProvider.isItemSelectable(items[i])) {
          result.push(items[i]);
        }
      }

      // in case of an user selecable list, remove the enabled items
      if (!all) {
        for (var i = result.length -1; i >= 0; i--) {
          if (!result[i].getEnabled()) {
            result.splice(i, 1);
          }
        };
      }

      return result;
    },


    /*
    ---------------------------------------------------------------------------
       APPLY METHODS
    ---------------------------------------------------------------------------
    */


    // apply method
    __applyAllowEmptySelection : function(value, old)
    {
      if (!value) {
        this.__setSelected(this.__selected);
      }
    },


    /*
    ---------------------------------------------------------------------------
       HELPERS
    ---------------------------------------------------------------------------
    */

    /**
     * Set selected element.
     *
     * If passes value is <code>null</code>, the selection will be reseted.
     *
     * @param item {qx.ui.core.Widget | null} element to select, or
     *    <code>null</code> to reset selection.
     */
    __setSelected : function(item) {
      var oldSelected = this.__selected;
      var newSelected = item;

      if (newSelected != null && oldSelected === newSelected) {
        return;
      }

      if (!this.isAllowEmptySelection() && newSelected == null) {
        var firstElement = this.getSelectables(true)[0];

        if (firstElement) {
          newSelected = firstElement;
        }
      }

      this.__selected = newSelected;
      this.fireDataEvent("changeSelected", newSelected, oldSelected);
    },

    /**
     * Checks if passed element is a child element.
     *
     * @param item {qx.ui.core.Widget} Element to check if child element.
     * @return {Boolean} <code>true</code> if element is child element,
     *    <code>false</code> otherwise.
     */
    __isChildElement : function(item)
    {
      var items = this.__selectionProvider.getItems();

      for (var i = 0; i < items.length; i++)
      {
        if (items[i] === item)
        {
          return true;
        }
      }
      return false;
    }
  },



  /*
   *****************************************************************************
      DESTRUCTOR
   *****************************************************************************
   */
  destruct : function() {
    if (this.__selectionProvider.toHashCode) {
      this._disposeObjects("__selectionProvider");
    } else {
      this.__selectionProvider = null;
    }

    this._disposeObjects("__selected");
  }
});
