content: /*******************************************************************************
   * Copyright (c) 2000, 2007 IBM Corporation and others.
   * All rights reserved. This program and the accompanying materials
   * are made available under the terms of the Eclipse Public License v1.0
   * which accompanies this distribution, and is available at
   * http://www.eclipse.org/legal/epl-v10.html
   *
   * Contributors:
   *     IBM Corporation - initial API and implementation
   *******************************************************************************/
  package org.eclipse.wst.jsdt.internal.ui.dnd;
  
  import org.eclipse.core.runtime.Assert;
  import org.eclipse.core.runtime.SafeRunner;
  import org.eclipse.jface.util.SafeRunnable;
  import org.eclipse.jface.util.TransferDropTargetListener;
  import org.eclipse.swt.dnd.DND;
  import org.eclipse.swt.dnd.DropTargetEvent;
  import org.eclipse.swt.dnd.DropTargetListener;
  import org.eclipse.swt.dnd.Transfer;
  import org.eclipse.swt.dnd.TransferData;
  
  /**
   * A delegating drop adapter negotiates between a set of
   * <code>TransferDropTargetListener</code> s On <code>dragEnter</code> the
   * adapter determines the listener to be used for any further <code>drag*</code>
   * callback.
   */
  public class DelegatingDropAdapter implements DropTargetListener {
  
  	private TransferDropTargetListener[] fListeners;
  	private TransferDropTargetListener fCurrentListener;
  	private int fOriginalDropType;
  
  	/**
  	 * Creates a new delegating drop adapter.
  	 * 
  	 * @param listeners an array of potential listeners
  	 */
  	public DelegatingDropAdapter(TransferDropTargetListener[] listeners) {
  		Assert.isNotNull(listeners);
  		fListeners= listeners;
  	}
  
  	/**
  	 * The cursor has entered the drop target boundaries. The current listener
  	 * is updated, and <code>#dragEnter()</code> is forwarded to the current
  	 * listener.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#dragEnter(DropTargetEvent)
  	 */
  	public void dragEnter(DropTargetEvent event) {
  		fOriginalDropType= event.detail;
  		updateCurrentListener(event);
  	}
  
  	/**
  	 * The cursor has left the drop target boundaries. The event is forwarded to
  	 * the current listener.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#dragLeave(DropTargetEvent)
  	 */
  	public void dragLeave(final DropTargetEvent event) {
  		setCurrentListener(null, event);
  	}
  
  	/**
  	 * The operation being performed has changed (usually due to the user
  	 * changing a drag modifier key while dragging). Updates the current
  	 * listener and forwards this event to that listener.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#dragOperationChanged(DropTargetEvent)
  	 */
  	public void dragOperationChanged(final DropTargetEvent event) {
  		fOriginalDropType= event.detail;
  		TransferDropTargetListener oldListener= getCurrentListener();
  		updateCurrentListener(event);
  		final TransferDropTargetListener newListener= getCurrentListener();
  		// only notify the current listener if it hasn't changed based on the
  		// operation change. otherwise the new listener would get a dragEnter
  		// followed by a dragOperationChanged with the exact same event.
  		if (newListener != null && newListener == oldListener) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					newListener.dragOperationChanged(event);
  				}
  			});
  		}
  	}
  
  	/**
  	 * The cursor is moving over the drop target. Updates the current listener
  	 * and forwards this event to that listener. If no listener can handle the
  	 * drag operation the <code>event.detail</code> field is set to
  	 * <code>DND.DROP_NONE</code> to indicate an invalid drop.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#dragOver(DropTargetEvent)
  	 */
  	public void dragOver(final DropTargetEvent event) {
  		TransferDropTargetListener oldListener= getCurrentListener();
  		updateCurrentListener(event);
  		final TransferDropTargetListener newListener= getCurrentListener();
  
  		// only notify the current listener if it hasn't changed based on the
  		// drag over. otherwise the new listener would get a dragEnter
  		// followed by a dragOver with the exact same event.
  		if (newListener != null && newListener == oldListener) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					newListener.dragOver(event);
  				}
  			});
  		}
  	}
  
  	/**
  	 * Forwards this event to the current listener, if there is one. Sets the
  	 * current listener to <code>null</code> afterwards.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#drop(DropTargetEvent)
  	 */
  	public void drop(final DropTargetEvent event) {
  		updateCurrentListener(event);
  		if (getCurrentListener() != null) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					getCurrentListener().drop(event);
  				}
  			});
  		}
  		setCurrentListener(null, event);
  	}
  
  	/**
  	 * Forwards this event to the current listener if there is one.
  	 * 
  	 * @param event the drop target event
  	 * @see DropTargetListener#dropAccept(DropTargetEvent)
  	 */
  	public void dropAccept(final DropTargetEvent event) {
  		if (getCurrentListener() != null) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					getCurrentListener().dropAccept(event);
  				}
  			});
  		}
  	}
  
  	/**
  	 * Returns the listener which currently handles drop events.
  	 * 
  	 * @return the <code>TransferDropTargetListener</code> which currently
  	 *         handles drop events.
  	 */
  	private TransferDropTargetListener getCurrentListener() {
  		return fCurrentListener;
  	}
  
  	/**
  	 * Returns the transfer data type supported by the given listener. Returns
  	 * <code>null</code> if the listener does not support any of the specified
  	 * data types.
  	 * 
  	 * @param dataTypes available data types
  	 * @param listener <code>TransferDropTargetListener</code> to use for
  	 *        testing supported data types.
  	 * @return the transfer data type supported by the given listener or
  	 *         <code>null</code>.
  	 */
  	private TransferData getSupportedTransferType(TransferData[] dataTypes, TransferDropTargetListener listener) {
  		for (int i= 0; i < dataTypes.length; i++) {
  			if (listener.getTransfer().isSupportedType(dataTypes[i])) {
  				return dataTypes[i];
  			}
  		}
  		return null;
  	}
  
  	/**
  	 * Returns the combined set of <code>Transfer</code> types of all
  	 * <code>TransferDropTargetListeners</code>.
  	 * 
  	 * @return the combined set of <code>Transfer</code> types
  	 */
  	public Transfer[] getTransfers() {
  		Transfer[] types= new Transfer[fListeners.length];
  		for (int i= 0; i < fListeners.length; i++) {
  			types[i]= fListeners[i].getTransfer();
  		}
  		return types;
  	}
  
  	/**
  	 * Sets the current listener to <code>listener</code>. Sends the given
  	 * <code>DropTargetEvent</code> if the current listener changes.
  	 * 
  	 * @return <code>true</code> if the new listener is different than the
  	 *         previous <code>false</code> otherwise
  	 */
  	private boolean setCurrentListener(TransferDropTargetListener listener, final DropTargetEvent event) {
  		if (fCurrentListener == listener)
  			return false;
  		if (fCurrentListener != null) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					fCurrentListener.dragLeave(event);
  				}
  			});
  		}
  		fCurrentListener= listener;
  		if (fCurrentListener != null) {
  			SafeRunner.run(new SafeRunnable() {
  				public void run() throws Exception {
  					fCurrentListener.dragEnter(event);
  				}
  			});
  		}
  		return true;
  	}
  
  	/**
  	 * Updates the current listener to one that can handle the drop. There can
  	 * be many listeners and each listener may be able to handle many
  	 * <code>TransferData</code> types. The first listener found that can
  	 * handle a drop of one of the given <code>TransferData</code> types will
  	 * be selected. If no listener can handle the drag operation the
  	 * <code>event.detail</code> field is set to <code>DND.DROP_NONE</code>
  	 * to indicate an invalid drop.
  	 * 
  	 * @param event the drop target event
  	 */
  	private void updateCurrentListener(DropTargetEvent event) {
  		int originalDetail= event.detail;
  		// Revert the detail to the "original" drop type that the User
  		// indicated. This is necessary because the previous listener 
  		// may have changed the detail to something other than what the 
  		// user indicated.
  		event.detail= fOriginalDropType;
  
  		for (int i= 0; i < fListeners.length; i++) {
  			TransferDropTargetListener listener= fListeners[i];
  			TransferData dataType= getSupportedTransferType(event.dataTypes, listener);
  			if (dataType != null) {
  				TransferData originalDataType= event.currentDataType;
  				// set the data type supported by the drop listener
  				event.currentDataType= dataType;
  				if (listener.isEnabled(event)) {
  					// if the listener stays the same, set its previously
  					// determined
  					// event detail
  					if (!setCurrentListener(listener, event))
  						event.detail= originalDetail;
  					return;
  				} else {
  					event.currentDataType= originalDataType;
  				}
  			}
  		}
  		setCurrentListener(null, event);
  		event.detail= DND.DROP_NONE;
  	}
  }
  