/*
 * Copyright 2009 Fred Sauer
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package com.allen_sauer.gwt.dnd.client;

import com.google.gwt.user.client.ui.AbsolutePanel;
import com.google.gwt.user.client.ui.Widget;

import com.allen_sauer.gwt.dnd.client.drop.DropController;

import java.util.ArrayList;
import java.util.List;

/**
 * Container class for context information about the current drag operation.
 */
public class DragContext {

  /**
   * The boundary panel for this drag controller.
   * 
   * TODO replace context.dragController.getBoundaryPanel() with context.boundaryPanel
   */
  public final AbsolutePanel boundaryPanel;

  /**
   * Desired x coordinate of draggable due to mouse dragging.
   */
  public int desiredDraggableX;

  /**
   * Desired y coordinate of draggable due to mouse dragging.
   */
  public int desiredDraggableY;

  /**
   * The DragController for which this context exists.
   */
  public final DragController dragController;

  /**
   * The primary widget currently being dragged or <code>null</code> when not dragging.
   */
  public Widget draggable;

  /**
   * The currently engaged drop controller or <code>null</code> when not dragging, or when the drag
   * controller does not utilize drop controllers.
   */
  public DropController dropController;

  /**
   * The drop controller which participated in the final drop, or <code>null</code> before the final
   * drop has occurred, or when the drag controller does not utilize drop controllers.
   * 
   * TODO use setter methods to handle the finalDropController/vetoException dependencies
   */
  public DropController finalDropController;

  /**
   * Current mouse x coordinate.
   */
  public int mouseX;

  /**
   * Current mouse y coordinate.
   */
  public int mouseY;

  /**
   * List of currently selected widgets. List will contain at most one widget when
   * {@link DragController#setBehaviorMultipleSelection(boolean)} is disabled.
   */
  public List<Widget> selectedWidgets = new ArrayList<Widget>();

  /**
   * At the end of a drag operation this fields will contain either the {@link VetoDragException}
   * which caused the drag to be cancelled, or <code>null</code> if the drag was successful. Note
   * that while the value of this field will still be <code>null</code> in
   * {@link DragHandler#onPreviewDragEnd(DragEndEvent)}, the value will be available in
   * {@link DragHandler#onDragEnd(DragEndEvent)}.
   */
  public Exception vetoException;

  DragContext(DragController dragController) {
    this.dragController = dragController;
    boundaryPanel = dragController.getBoundaryPanel();
  }

  /**
   * Called by {@link MouseDragHandler#dragEndCleanup} at the end of a drag operation to cleanup
   * state.
   */
  public void dragEndCleanup() {
    dropController = null;
    draggable = null;
  }

  /**
   * Called by {@link MouseDragHandler#startDragging} at the start of a drag operation to initialize
   * state.
   */
  public void dragStartCleanup() {
    assert dropController == null;
    finalDropController = null;
    vetoException = null;
  }
}