/**
 * This class provides a container DD instance that allows dropping on multiple child target nodes.
 *
 * By default, this class requires that child nodes accepting drop are registered with {@link Ext.dd.Registry}.
 * However a simpler way to allow a DropZone to manage any number of target elements is to configure the
 * DropZone with an implementation of {@link #getTargetFromEvent} which interrogates the passed
 * mouse event to see if it has taken place within an element, or class of elements. This is easily done
 * by using the event's {@link Ext.EventObject#getTarget getTarget} method to identify a node based on a
 * {@link Ext.DomQuery} selector.
 *
 * Once the DropZone has detected through calling getTargetFromEvent, that the mouse is over
 * a drop target, that target is passed as the first parameter to {@link #onNodeEnter}, {@link #onNodeOver},
 * {@link #onNodeOut}, {@link #onNodeDrop}. You may configure the instance of DropZone with implementations
 * of these methods to provide application-specific behaviour for these events to update both
 * application state, and UI state.
 *
 * For example to make a GridPanel a cooperating target with the example illustrated in
 * {@link Ext.dd.DragZone DragZone}, the following technique might be used:
 *
 *     myGridPanel.on('render', function() {
 *         myGridPanel.dropZone = new Ext.dd.DropZone(myGridPanel.getView().scroller, {
 *
 *             // If the mouse is over a grid row, return that node. This is
 *             // provided as the "target" parameter in all "onNodeXXXX" node event handling functions
 *             getTargetFromEvent: function(e) {
 *                 return e.getTarget(myGridPanel.getView().rowSelector);
 *             },
 *
 *             // On entry into a target node, highlight that node.
 *             onNodeEnter : function(target, dd, e, data){
 *                 Ext.fly(target).addCls('my-row-highlight-class');
 *             },
 *
 *             // On exit from a target node, unhighlight that node.
 *             onNodeOut : function(target, dd, e, data){
 *                 Ext.fly(target).removeCls('my-row-highlight-class');
 *             },
 *
 *             // While over a target node, return the default drop allowed class which
 *             // places a "tick" icon into the drag proxy.
 *             onNodeOver : function(target, dd, e, data){
 *                 return Ext.dd.DropZone.prototype.dropAllowed;
 *             },
 *
 *             // On node drop we can interrogate the target to find the underlying
 *             // application object that is the real target of the dragged data.
 *             // In this case, it is a Record in the GridPanel's Store.
 *             // We can use the data set up by the DragZone's getDragData method to read
 *             // any data we decided to attach in the DragZone's getDragData method.
 *             onNodeDrop : function(target, dd, e, data){
 *                 var rowIndex = myGridPanel.getView().findRowIndex(target);
 *                 var r = myGridPanel.getStore().getAt(rowIndex);
 *                 Ext.Msg.alert('Drop gesture', 'Dropped Record id ' + data.draggedRecord.id +
 *                     ' on Record id ' + r.id);
 *                 return true;
 *             }
 *         });
 *     }
 *
 * See the {@link Ext.dd.DragZone DragZone} documentation for details about building a DragZone which
 * cooperates with this DropZone.
 */
Ext.define('Ext.dd.DropZone', {
    extend: 'Ext.dd.DropTarget',
    requires: ['Ext.dd.Registry'],

    /**
     * Returns a custom data object associated with the DOM node that is the target of the event.  By default
     * this looks up the event target in the {@link Ext.dd.Registry}, although you can override this method to
     * provide your own custom lookup.
     * @param {Event} e The event
     * @return {Object} data The custom data
     */
    getTargetFromEvent : function(e){
        return Ext.dd.Registry.getTargetFromEvent(e);
    },

    /**
     * Called when the DropZone determines that a {@link Ext.dd.DragSource} has entered a drop node
     * that has either been registered or detected by a configured implementation of {@link #getTargetFromEvent}.
     * This method has no default implementation and should be overridden to provide
     * node-specific processing if necessary.
     * @param {Object} nodeData The custom data associated with the drop node (this is the same value returned from 
     * {@link #getTargetFromEvent} for this node)
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     */
    onNodeEnter : function(n, dd, e, data){
        
    },

    /**
     * Called while the DropZone determines that a {@link Ext.dd.DragSource} is over a drop node
     * that has either been registered or detected by a configured implementation of {@link #getTargetFromEvent}.
     * The default implementation returns this.dropAllowed, so it should be
     * overridden to provide the proper feedback.
     * @param {Object} nodeData The custom data associated with the drop node (this is the same value returned from
     * {@link #getTargetFromEvent} for this node)
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {String} status The CSS class that communicates the drop status back to the source so that the
     * underlying {@link Ext.dd.StatusProxy} can be updated
     * @template
     */
    onNodeOver : function(n, dd, e, data){
        return this.dropAllowed;
    },

    /**
     * Called when the DropZone determines that a {@link Ext.dd.DragSource} has been dragged out of
     * the drop node without dropping.  This method has no default implementation and should be overridden to provide
     * node-specific processing if necessary.
     * @param {Object} nodeData The custom data associated with the drop node (this is the same value returned from
     * {@link #getTargetFromEvent} for this node)
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @template
     */
    onNodeOut : function(n, dd, e, data){
        
    },

    /**
     * Called when the DropZone determines that a {@link Ext.dd.DragSource} has been dropped onto
     * the drop node.  The default implementation returns false, so it should be overridden to provide the
     * appropriate processing of the drop event and return true so that the drag source's repair action does not run.
     * @param {Object} nodeData The custom data associated with the drop node (this is the same value returned from
     * {@link #getTargetFromEvent} for this node)
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {Boolean} True if the drop was valid, else false
     * @template
     */
    onNodeDrop : function(n, dd, e, data){
        return false;
    },

    /**
     * Called while the DropZone determines that a {@link Ext.dd.DragSource} is being dragged over it,
     * but not over any of its registered drop nodes.  The default implementation returns this.dropNotAllowed, so
     * it should be overridden to provide the proper feedback if necessary.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {String} status The CSS class that communicates the drop status back to the source so that the
     * underlying {@link Ext.dd.StatusProxy} can be updated
     * @template
     */
    onContainerOver : function(dd, e, data){
        return this.dropNotAllowed;
    },

    /**
     * Called when the DropZone determines that a {@link Ext.dd.DragSource} has been dropped on it,
     * but not on any of its registered drop nodes.  The default implementation returns false, so it should be
     * overridden to provide the appropriate processing of the drop event if you need the drop zone itself to
     * be able to accept drops.  It should return true when valid so that the drag source's repair action does not run.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {Boolean} True if the drop was valid, else false
     * @template
     */
    onContainerDrop : function(dd, e, data){
        return false;
    },

    /**
     * The function a {@link Ext.dd.DragSource} calls once to notify this drop zone that the source is now over
     * the zone.  The default implementation returns this.dropNotAllowed and expects that only registered drop
     * nodes can process drag drop operations, so if you need the drop zone itself to be able to process drops
     * you should override this method and provide a custom implementation.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {String} status The CSS class that communicates the drop status back to the source so that the
     * underlying {@link Ext.dd.StatusProxy} can be updated
     * @template
     */
    notifyEnter : function(dd, e, data){
        return this.dropNotAllowed;
    },

    /**
     * The function a {@link Ext.dd.DragSource} calls continuously while it is being dragged over the drop zone.
     * This method will be called on every mouse movement while the drag source is over the drop zone.
     * It will call {@link #onNodeOver} while the drag source is over a registered node, and will also automatically
     * delegate to the appropriate node-specific methods as necessary when the drag source enters and exits
     * registered nodes ({@link #onNodeEnter}, {@link #onNodeOut}). If the drag source is not currently over a
     * registered node, it will call {@link #onContainerOver}.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {String} status The CSS class that communicates the drop status back to the source so that the
     * underlying {@link Ext.dd.StatusProxy} can be updated
     * @template
     */
    notifyOver : function(dd, e, data){
        var n = this.getTargetFromEvent(e);
        if(!n) { // not over valid drop target
            if(this.lastOverNode){
                this.onNodeOut(this.lastOverNode, dd, e, data);
                this.lastOverNode = null;
            }
            return this.onContainerOver(dd, e, data);
        }
        if(this.lastOverNode != n){
            if(this.lastOverNode){
                this.onNodeOut(this.lastOverNode, dd, e, data);
            }
            this.onNodeEnter(n, dd, e, data);
            this.lastOverNode = n;
        }
        return this.onNodeOver(n, dd, e, data);
    },

    /**
     * The function a {@link Ext.dd.DragSource} calls once to notify this drop zone that the source has been dragged
     * out of the zone without dropping.  If the drag source is currently over a registered node, the notification
     * will be delegated to {@link #onNodeOut} for node-specific handling, otherwise it will be ignored.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop target
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag zone
     * @template
     */
    notifyOut : function(dd, e, data){
        if(this.lastOverNode){
            this.onNodeOut(this.lastOverNode, dd, e, data);
            this.lastOverNode = null;
        }
    },

    /**
     * The function a {@link Ext.dd.DragSource} calls once to notify this drop zone that the dragged item has
     * been dropped on it.  The drag zone will look up the target node based on the event passed in, and if there
     * is a node registered for that event, it will delegate to {@link #onNodeDrop} for node-specific handling,
     * otherwise it will call {@link #onContainerDrop}.
     * @param {Ext.dd.DragSource} source The drag source that was dragged over this drop zone
     * @param {Event} e The event
     * @param {Object} data An object containing arbitrary data supplied by the drag source
     * @return {Boolean} False if the drop was invalid.
     * @template
     */
    notifyDrop : function(dd, e, data){
        if(this.lastOverNode){
            this.onNodeOut(this.lastOverNode, dd, e, data);
            this.lastOverNode = null;
        }
        var n = this.getTargetFromEvent(e);
        return n ?
            this.onNodeDrop(n, dd, e, data) :
            this.onContainerDrop(dd, e, data);
    },

    // private
    triggerCacheRefresh : function() {
        Ext.dd.DDM.refreshCache(this.groups);
    }
});