    /**
     * @class Ext.data.Tree
     *
     * This class is used as a container for a series of nodes. The nodes themselves maintain
     * the relationship between parent/child. The tree itself acts as a manager. It gives functionality
     * to retrieve a node by its identifier: {@link #getNodeById}.
     *
     * The tree also relays events from any of it's child nodes, allowing them to be handled in a
     * centralized fashion. In general this class is not used directly, rather used internally
     * by other parts of the framework.
     *
     */
    Ext.define('Ext.data.Tree', {
        alias: 'data.tree',

        mixins: {
            observable: "Ext.util.Observable"
        },

        /**
         * The root node for this tree
         * @type Node
         */
        root: null,

        /**
         * Creates new Tree object.
         * @param {Node} root (optional) The root node
         */
        constructor: function(root) {
            var me = this;

            me.nodeHash = {};

            me.mixins.observable.constructor.call(me);

            if (root) {
                me.setRootNode(root);
            }
        },

        /**
         * Returns the root node for this tree.
         * @return {Ext.data.NodeInterface}
         */
        getRootNode : function() {
            return this.root;
        },

        /**
         * Sets the root node for this tree.
         * @param {Ext.data.NodeInterface} node
         * @return {Ext.data.NodeInterface} The root node
         */
        setRootNode : function(node) {
            var me = this;

            me.root = node;
            Ext.data.NodeInterface.decorate(node);

            if (me.fireEvent('beforeappend', null, node) !== false) {
                node.set('root', true);
                node.updateInfo();

                me.relayEvents(node, [
                    /**
                     * @event append
                     * Fires when a new child node is appended to a node in this tree.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The newly appended node
                     * @param {Number} index The index of the newly appended node
                     */
                    "append",

                    /**
                     * @event remove
                     * Fires when a child node is removed from a node in this tree.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The child node removed
                     */
                    "remove",

                    /**
                     * @event move
                     * Fires when a node is moved to a new location in the tree
                     * @param {Tree} tree The owner tree
                     * @param {Node} node The node moved
                     * @param {Node} oldParent The old parent of this node
                     * @param {Node} newParent The new parent of this node
                     * @param {Number} index The index it was moved to
                     */
                    "move",

                    /**
                     * @event insert
                     * Fires when a new child node is inserted in a node in this tree.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The child node inserted
                     * @param {Node} refNode The child node the node was inserted before
                     */
                    "insert",

                    /**
                     * @event beforeappend
                     * Fires before a new child is appended to a node in this tree, return false to cancel the append.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The child node to be appended
                     */
                    "beforeappend",

                    /**
                     * @event beforeremove
                     * Fires before a child is removed from a node in this tree, return false to cancel the remove.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The child node to be removed
                     */
                    "beforeremove",

                    /**
                     * @event beforemove
                     * Fires before a node is moved to a new location in the tree. Return false to cancel the move.
                     * @param {Tree} tree The owner tree
                     * @param {Node} node The node being moved
                     * @param {Node} oldParent The parent of the node
                     * @param {Node} newParent The new parent the node is moving to
                     * @param {Number} index The index it is being moved to
                     */
                    "beforemove",

                    /**
                     * @event beforeinsert
                     * Fires before a new child is inserted in a node in this tree, return false to cancel the insert.
                     * @param {Tree} tree The owner tree
                     * @param {Node} parent The parent node
                     * @param {Node} node The child node to be inserted
                     * @param {Node} refNode The child node the node is being inserted before
                     */
                    "beforeinsert",

                     /**
                      * @event expand
                      * Fires when this node is expanded.
                      * @param {Node} this The expanding node
                      */
                     "expand",

                     /**
                      * @event collapse
                      * Fires when this node is collapsed.
                      * @param {Node} this The collapsing node
                      */
                     "collapse",

                     /**
                      * @event beforeexpand
                      * Fires before this node is expanded.
                      * @param {Node} this The expanding node
                      */
                     "beforeexpand",

                     /**
                      * @event beforecollapse
                      * Fires before this node is collapsed.
                      * @param {Node} this The collapsing node
                      */
                     "beforecollapse" ,

                     /**
                      * @event rootchange
                      * Fires whenever the root node is changed in the tree.
                      * @param {Ext.data.Model} root The new root
                      */
                     "rootchange"
                ]);

                node.on({
                    scope: me,
                    insert: me.onNodeInsert,
                    append: me.onNodeAppend,
                    remove: me.onNodeRemove
                });

                me.registerNode(node);
                me.fireEvent('append', null, node);
                me.fireEvent('rootchange', node);
            }

            return node;
        },

        /**
         * Flattens all the nodes in the tree into an array.
         * @private
         * @return {Array} The flattened nodes.
         */
        flatten: function(){
            var nodes = [],
                hash = this.nodeHash,
                key;

            for (key in hash) {
                if (hash.hasOwnProperty(key)) {
                    nodes.push(hash[key]);
                }
            }
            return nodes;
        },

        /**
         * Fired when a node is inserted into the root or one of it's children
         * @private
         * @param {Ext.data.NodeInterface} parent The parent node
         * @param {Ext.data.NodeInterface} node The inserted node
         */
        onNodeInsert: function(parent, node) {
            this.registerNode(node);
        },

        /**
         * Fired when a node is appended into the root or one of it's children
         * @private
         * @param {Ext.data.NodeInterface} parent The parent node
         * @param {Ext.data.NodeInterface} node The appended node
         */
        onNodeAppend: function(parent, node) {
            this.registerNode(node);
        },

        /**
         * Fired when a node is removed from the root or one of it's children
         * @private
         * @param {Ext.data.NodeInterface} parent The parent node
         * @param {Ext.data.NodeInterface} node The removed node
         */
        onNodeRemove: function(parent, node) {
            this.unregisterNode(node);
        },

        /**
         * Gets a node in this tree by its id.
         * @param {String} id
         * @return {Ext.data.NodeInterface} The match node.
         */
        getNodeById : function(id) {
            return this.nodeHash[id];
        },

        /**
         * Registers a node with the tree
         * @private
         * @param {Ext.data.NodeInterface} The node to register
         */
        registerNode : function(node) {
            this.nodeHash[node.getId() || node.internalId] = node;
        },

        /**
         * Unregisters a node with the tree
         * @private
         * @param {Ext.data.NodeInterface} The node to unregister
         */
        unregisterNode : function(node) {
            delete this.nodeHash[node.getId() || node.internalId];
        },

        /**
         * Sorts this tree
         * @private
         * @param {Function} sorterFn The function to use for sorting
         * @param {Boolean} recursive True to perform recursive sorting
         */
        sort: function(sorterFn, recursive) {
            this.getRootNode().sort(sorterFn, recursive);
        },

         /**
         * Filters this tree
         * @private
         * @param {Function} sorterFn The function to use for filtering
         * @param {Boolean} recursive True to perform recursive filtering
         */
        filter: function(filters, recursive) {
            this.getRootNode().filter(filters, recursive);
        }
    });