/*******************************************************************************
 * Copyright (c) 2005 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.ui.operations;

import org.eclipse.core.commands.ExecutionException;
import org.eclipse.core.commands.operations.IUndoContext;
import org.eclipse.core.commands.operations.IUndoableOperation;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.ui.ISharedImages;
import org.eclipse.ui.IWorkbenchPartSite;
import org.eclipse.ui.PlatformUI;
import org.eclipse.ui.internal.WorkbenchMessages;


/**
 * <p>
 * UndoActionHandler provides common behavior for performing an undo, as
 * well as enabling and labelling the undo menu item.  This class may be
 * instantiated by clients.
 * </p>
 * 
 * @since 3.1
 */
public final class UndoActionHandler extends OperationHistoryActionHandler {

	/**
	 * Construct an action handler that handles the labelling and enabling of
	 * the undo action for a specified operation context.
	 * 
	 * @param site 
	 *            the workbench part site that created the action.
	 * @param context 
	 *            the context to be used for the undo
	 */
	public UndoActionHandler(IWorkbenchPartSite site, IUndoContext context) {
		super(site, context);
        setImageDescriptor(PlatformUI.getWorkbench().getSharedImages()
                .getImageDescriptor(ISharedImages.IMG_TOOL_UNDO));
	}

	void flush() {
		getHistory().dispose(undoContext, true, false, false);
	}

	String getCommandString() {
		return WorkbenchMessages.Workbench_undo;
	}

	IUndoableOperation getOperation() {
		return getHistory().getUndoOperation(undoContext);

	}

	IStatus runCommand(IProgressMonitor pm) throws ExecutionException  {
		return getHistory().undo(undoContext, pm, this);
	}

	boolean shouldBeEnabled() {
		// if a context was not supplied, do not enable.
		if (undoContext == null)
			return false;
		return getHistory().canUndo(undoContext);
	}
}
