/*******************************************************************************
 * Copyright (c) 2005, 2006 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.core.commands.operations;

import org.eclipse.core.commands.ExecutionException;
import org.eclipse.core.internal.commands.operations.GlobalUndoContext;
import org.eclipse.core.runtime.IAdaptable;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;

/**
 * <p>
 * IOperationHistory tracks a history of operations that can be undone or
 * redone. Operations are added to the history once they have been initially
 * executed. Clients may choose whether to have the operations history perform
 * the initial execution or to simply add an already-executed operation to the
 * history.
 * </p>
 * <p>
 * Once operations are added to the history, the methods
 * {@link #canRedo(IUndoContext)} and {@link #canUndo(IUndoContext)} are used to
 * determine whether there is an operation available for undo and redo in a
 * given undo context. The context-based protocol implies that there is only one
 * operation that can be undone or redone at a given time in a given context.
 * This is typical of a linear undo model, when only the most recently executed
 * operation is available for undo. When this protocol is used, a linear model
 * is enforced by the history.
 * </p>
 * <p>
 * It is up to clients to determine how to maintain a history that is invalid or
 * stale. For example, when the most recent operation for a context cannot be
 * performed, clients may wish to dispose the history for that context.
 * </p>
 * <p>
 * Additional protocol allows direct undo and redo of a specified operation,
 * regardless of its position in the history. When a more flexible undo model is
 * supported, these methods can be implemented to undo and redo directly
 * specified operations. If an implementer of IOperationHistory does not allow
 * direct undo and redo, these methods can return a status indicating that it is
 * not allowed.
 * </p>
 * <p>
 * Listeners ({@link IOperationHistoryListener}) can listen for notifications
 * about changes in the history (operations added or removed), and for
 * notification before and after any operation is executed, undone or redone.
 * Notification of operation execution only occurs when clients direct the
 * history to execute the operation. If the operation is added after it is
 * executed, there can be no notification of its execution.
 * </p>
 * <p>
 * {@link IOperationApprover} defines an interface for approving an undo or redo
 * before it occurs. This is useful for injecting policy-decisions into the undo
 * model - whether direct undo and redo are supported, or warning the user about
 * certain kinds of operations. It can also be used when clients maintain state
 * related to an operation and need to determine whether an undo or redo will
 * cause any conflicts with their local state.
 * </p>
 * 
 * @since 3.1
 */
public interface IOperationHistory {

	/**
	 * An operation is to be opened or closed for execution. (value is 1).
	 */
	public static final int EXECUTE = 1;

	/**
	 * An operation is to be opened for undo. (value is 2).
	 */
	public static final int UNDO = 2;

	/**
	 * An operation is to be opened for redo. (value is 3).
	 */
	public static final int REDO = 3;

	/**
	 * An undo context that can be used to refer to the global undo history.
	 * This context is not intended to be assigned to operations. Instead, it is
	 * used for querying the history or performing an undo or redo on the entire
	 * history, regardless of each operation's undo contexts.
	 */
	public static final IUndoContext GLOBAL_UNDO_CONTEXT = new GlobalUndoContext();

	/**
	 * An operation info status describing the condition that there is no
	 * available operation for redo.
	 */
	public static final IStatus NOTHING_TO_REDO_STATUS = new OperationStatus(
			IStatus.INFO, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.NOTHING_TO_REDO, "No operation to redo", null); //$NON-NLS-1$

	/**
	 * An operation info status describing the condition that there is no
	 * available operation for undo.
	 */
	public static final IStatus NOTHING_TO_UNDO_STATUS = new OperationStatus(
			IStatus.INFO, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.NOTHING_TO_UNDO, "No operation to undo", null); //$NON-NLS-1$

	/**
	 * An operation error status describing the condition that the operation
	 * available for execution, undo or redo is not in a valid state for the
	 * action to be performed.
	 */
	public static final IStatus OPERATION_INVALID_STATUS = new OperationStatus(
			IStatus.ERROR, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.OPERATION_INVALID, "Operation is not valid", null); //$NON-NLS-1$

	/**
	 * <p>
	 * Add the specified operation to the history without executing it. The
	 * operation should have already been executed by the time it is added to
	 * the history. Listeners will be notified that the operation was added to
	 * the history (<code>OPERATION_ADDED</code>).
	 * </p>
	 * 
	 * @param operation
	 *            the operation to be added to the history
	 */
	void add(IUndoableOperation operation);

	/**
	 * <p>
	 * Add the specified approver to the list of operation approvers consulted
	 * by the operation history before an undo or redo is attempted.
	 * </p>
	 * 
	 * @param approver
	 *            the IOperationApprover to be added as an approver.the instance
	 *            to remove. Must not be <code>null</code>. If an attempt is
	 *            made to register an instance which is already registered with
	 *            this instance, this method has no effect.
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationApprover
	 */
	void addOperationApprover(IOperationApprover approver);

	/**
	 * <p>
	 * Add the specified listener to the list of operation history listeners
	 * that are notified about changes in the history or operations that are
	 * executed, undone, or redone.
	 * </p>
	 * 
	 * @param listener
	 *            the IOperationHistoryListener to be added as a listener. Must
	 *            not be <code>null</code>. If an attempt is made to register
	 *            an instance which is already registered with this instance,
	 *            this method has no effect.
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationHistoryListener
	 * @see org.eclipse.core.commands.operations.OperationHistoryEvent
	 */
	void addOperationHistoryListener(IOperationHistoryListener listener);

	/**
	 * <p>
	 * Close the current operation. If the operation has successfully completed,
	 * send listeners a <code>DONE</code>, <code>UNDONE</code>, or
	 * <code>REDONE</code> notification, depending on the mode. Otherwise send
	 * an <code>OPERATION_NOT_OK</code> notification. Add the operation to the
	 * history if specified and send an <code>OPERATION_ADDED</code>
	 * notification.
	 * </p>
	 * <p>
	 * Any operations that are executed and added after this operation is closed
	 * will no longer be considered part of this operation.
	 * </p>
	 * <p>
	 * This method has no effect if the caller has not previously called
	 * {@link #openOperation}.
	 * </p>
	 * 
	 * @param operationOK
	 *            <code>true</code> if the operation successfully completed.
	 *            Listeners should be notified with <code>DONE</code>,
	 *            <code>UNDONE</code>, or <code>REDONE</code>.
	 *            <code>false</code> if the operation did not successfully
	 *            complete. Listeners should be notified with
	 *            <code>OPERATION_NOT_OK</code>.
	 * @param addToHistory
	 *            <code>true</code> if the operation should be added to the
	 *            history, <code>false</code> if it should not. If the
	 *            <code>operationOK</code> parameter is <code>false</code>,
	 *            the operation will never be added to the history.
	 * @param mode
	 *            the mode the operation was opened in. Can be one of
	 *            <code>EXECUTE</code>, <code>UNDO</code>, or
	 *            <code>REDO</code>. This determines what notifications are
	 *            sent.
	 */
	void closeOperation(boolean operationOK, boolean addToHistory, int mode);

	/**
	 * <p>
	 * Return whether there is a valid redoable operation available in the given
	 * context.
	 * </p>
	 * 
	 * @param context
	 *            the context to be checked
	 * @return <code>true</code> if there is a redoable operation,
	 *         <code>false</code> otherwise.
	 */

	boolean canRedo(IUndoContext context);

	/**
	 * <p>
	 * Return whether there is a valid undoable operation available in the given
	 * context
	 * </p>
	 * 
	 * @param context
	 *            the context to be checked
	 * @return <code>true</code> if there is an undoable operation,
	 *         <code>false</code> otherwise.
	 */
	boolean canUndo(IUndoContext context);

	/**
	 * <p>
	 * Dispose of the specified context in the history. All operations that have
	 * only the given context will be disposed. References to the context in
	 * operations that have more than one context will also be removed. A
	 * history notification for the removal of each operation being disposed
	 * will be sent.
	 * </p>
	 * 
	 * @param context
	 *            the context to be disposed
	 * @param flushUndo
	 *            <code>true</code> if the context should be flushed from the
	 *            undo history, <code>false</code> if it should not
	 * @param flushRedo
	 *            <code>true</code> if the context should be flushed from the
	 *            redo history, <code>false</code> if it should not.
	 * @param flushContext
	 *            <code>true</code> if the context is no longer in use and
	 *            references to it should be flushed.
	 */
	void dispose(IUndoContext context, boolean flushUndo, boolean flushRedo,
			boolean flushContext);

	/**
	 * <p>
	 * Execute the specified operation and add it to the operations history if
	 * successful. This method is used by clients who wish operation history
	 * listeners to receive notifications before and after the execution of the
	 * operation. Execution of the operation is subject to approval by any
	 * registered {@link IOperationApprover2}. If execution is approved,
	 * listeners will be notified before (<code>ABOUT_TO_EXECUTE</code>) and
	 * after (<code>DONE</code> or <code>OPERATION_NOT_OK</code>).
	 * </p>
	 * <p>
	 * If the operation successfully executes, an additional notification that
	 * the operation has been added to the history (<code>OPERATION_ADDED</code>)
	 * will be sent.
	 * </p>
	 * 
	 * @param operation
	 *            the operation to be executed and then added to the history
	 * 
	 * @param monitor
	 *            the progress monitor to be used (or <code>null</code>)
	 *            during the operation.
	 * 
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.
	 * 
	 * @return the IStatus indicating whether the execution succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it was added to the history. <code>OK</code>
	 * severity indicates that the execute operation was successful and that the
	 * operation has been added to the history. Listeners will receive
	 * notifications about the operation's success (<code>DONE</code>) and
	 * about the operation being added to the history (<code>OPERATION_ADDED</code>).
	 * </p>
	 * <p>
	 * <code>CANCEL</code> severity indicates that the user cancelled the
	 * operation and that the operation was not added to the history.
	 * <code>ERROR</code> severity indicates that the operation did not
	 * successfully execute and that it was not added to the history. Any other
	 * severity code is not specifically interpreted by the history, and the
	 * operation will not be added to the history. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>DONE</code> notification if the execution was approved and
	 * attempted.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during execution.
	 * 
	 */
	IStatus execute(IUndoableOperation operation, IProgressMonitor monitor,
			IAdaptable info) throws ExecutionException;

	/**
	 * <p>
	 * Return the limit on the undo and redo history for a particular context.
	 * </p>
	 * 
	 * @param context
	 *            the context whose limit is requested
	 * 
	 * @return the undo and redo history limit for the specified context.
	 */
	int getLimit(IUndoContext context);

	/**
	 * <p>
	 * Get the array of operations in the redo history for a the specified undo
	 * context. The operations are in the order that they were added to the
	 * history, with the most recently undone operation appearing last in the
	 * array. This history is used LIFO (last in, first out) when successive
	 * "Redo" commands are invoked.
	 * 
	 * </p>
	 * 
	 * @param context
	 *            the context for the redo
	 * @return the array of operations in the history
	 */
	IUndoableOperation[] getRedoHistory(IUndoContext context);

	/**
	 * <p>
	 * Get the operation that will next be redone in the given undo context.
	 * </p>
	 * 
	 * @param context
	 *            the context for the redo
	 * @return the operation to be redone or <code>null</code> if there is no
	 *         operation available. There is no guarantee that the returned
	 *         operation is valid for redo.
	 */
	IUndoableOperation getRedoOperation(IUndoContext context);

	/**
	 * <p>
	 * Get the array of operations in the undo history for the specified undo
	 * context. The operations are in the order that they were added to the
	 * history, with the most recently added operation appearing last in the
	 * array. This history is used LIFO (last in, first out) when successive
	 * "Undo" commands are invoked.
	 * </p>
	 * 
	 * @param context
	 *            the context for the undo
	 * @return the array of operations in the history
	 */
	IUndoableOperation[] getUndoHistory(IUndoContext context);

	/**
	 * <p>
	 * Open this composite operation and consider it an operation that contains
	 * other related operations. Consider all operations that are subsequently
	 * executed or added to be part of this operation. When an operation is
	 * opened, listeners will immediately receive a notification for the opened
	 * operation. The specific notification depends on the mode in which the
	 * operation is opened (<code>ABOUT_TO_EXECUTE</code>,
	 * <code>ABOUT_TO_UNDO</code>, <code>ABOUT_TO_REDO</code>).
	 * Notifications for any other execute or add while this operation is open
	 * will not occur. Instead, those operations will be added to the current
	 * operation.
	 * </p>
	 * <p>
	 * Note: This method is intended to be used by legacy undo frameworks that
	 * do not expect related undo operations to appear in the same undo history
	 * as the triggering undo operation. When an operation is open, any
	 * subsequent requests to execute, add, undo, or redo another operation will
	 * result in that operation being added to the open operation. Once the
	 * operation is closed, the composite will be considered an atomic
	 * operation. Clients should not modify the composite directly (by adding
	 * and removing children) while it is open.
	 * </p>
	 * <p>
	 * When a composite is open, operations that are added to the history will
	 * be considered part of the open operation instead. Operations that are
	 * executed while a composite is open will first be executed and then added
	 * to the composite.
	 * </p>
	 * <p>
	 * Open operations cannot be nested. If this method is called when a
	 * different operation is open, it is presumed to be an application coding
	 * error and this method will throw an IllegalStateException.
	 * </p>
	 * 
	 * @param operation
	 *            the composite operation to be considered as the parent for all
	 *            subsequent operations.
	 * @param mode
	 *            the mode the operation is executing in. Can be one of
	 *            <code>EXECUTE</code>, <code>UNDO</code>, or
	 *            <code>REDO</code>. This determines what notifications are
	 *            sent.
	 */
	void openOperation(ICompositeOperation operation, int mode);

	/**
	 * <p>
	 * The specified operation has changed in some way since it was added to the
	 * operation history. Notify listeners with an OPERATION_CHANGED event.
	 * </p>
	 * 
	 * @param operation
	 *            the operation that has changed.
	 * 
	 */
	void operationChanged(IUndoableOperation operation);

	/**
	 * <p>
	 * Get the operation that will next be undone in the given undo context.
	 * </p>
	 * 
	 * @param context
	 *            the context for the undo
	 * @return the operation to be undone or <code>null</code> if there is no
	 *         operation available. There is no guarantee that the available
	 *         operation is valid for the undo.
	 */
	IUndoableOperation getUndoOperation(IUndoContext context);

	/**
	 * <p>
	 * Redo the most recently undone operation in the given context. The redo of
	 * the operation is subject to approval by any registered
	 * {@link IOperationApprover} before it is attempted.
	 * </p>
	 * 
	 * @param context
	 *            the context to be redone
	 * @param monitor
	 *            the progress monitor to be used for the redo, or
	 *            <code>null</code> if no progress monitor is provided.
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.
	 * @return the IStatus indicating whether the redo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the redo operation was successful and (since
	 * release 3.2), that the operation will be placed in the undo history.
	 * (Prior to 3.2, a successfully redone operation would not be placed on the
	 * undo history if it could not be undone. Since 3.2, this is relaxed, and
	 * all successfully redone operations are placed in the undo history.)
	 * Listeners will receive the <code>REDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>,
	 * <code>INFO</code>, etc.) are not specifically interpreted by the
	 * history. The operation will remain in the history and the returned status
	 * is simply passed back to the caller. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>REDONE</code> notification if the redo was approved and
	 * attempted.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during redo.
	 * 
	 */
	IStatus redo(IUndoContext context, IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;

	/**
	 * <p>
	 * Redo the specified operation. The redo of the operation is subject to
	 * approval by any registered {@link IOperationApprover} before it is
	 * attempted.
	 * </p>
	 * 
	 * @param operation
	 *            the operation to be redone
	 * @param monitor
	 *            the progress monitor to be used for the redo, or code>null</code>
	 *            if no progress monitor is provided
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not <code>null</code>,
	 *            it should minimally contain an adapter for the
	 *            org.eclipse.swt.widgets.Shell.class.
	 * 
	 * @return the IStatus indicating whether the redo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the redo operation was successful, and (since
	 * release 3.2), that the operation will be placed in the undo history.
	 * (Prior to 3.2, a successfully redone operation would not be placed on the
	 * undo history if it could not be undone. Since 3.2, this is relaxed, and
	 * all successfully redone operations are placed in the undo history.)
	 * Listeners will receive the <code>REDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>,
	 * <code>INFO</code>, etc.) are not specifically interpreted by the
	 * history. The operation will remain in the history and the returned status
	 * is simply passed back to the caller. For all severities other than <code>OK</code>,
	 * listeners will receive the <code>OPERATION_NOT_OK</code> notification
	 * instead of the <code>REDONE</code> notification if the redo was
	 * approved and attempted.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during redo.
	 */
	IStatus redoOperation(IUndoableOperation operation,
			IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;

	/**
	 * <p>
	 * Remove the specified operation approver from the list of operation
	 * approvers that are consulted before an operation is undone or redone.
	 * </p>
	 * 
	 * @param approver
	 *            the IOperationApprover to be removed. Must not be
	 *            <code>null</code>. If an attempt is made to remove an
	 *            instance which is not already registered with this instance,
	 *            this method has no effect.
	 */
	void removeOperationApprover(IOperationApprover approver);

	/**
	 * <p>
	 * Remove the specified listener from the list of operation history
	 * listeners.
	 * </p>
	 * 
	 * @param listener
	 *            The IOperationHistoryListener to be removed. Must not be
	 *            <code>null</code>. If an attempt is made to remove an
	 *            instance which is not already registered with this instance,
	 *            this method has no effect.
	 */
	void removeOperationHistoryListener(IOperationHistoryListener listener);

	/**
	 * <p>
	 * Replace the specified operation in the undo or redo history with the
	 * provided list of replacements. This protocol is typically used when a
	 * composite is broken up into its atomic parts. The replacements will be
	 * inserted so that the first replacement will be the first of the
	 * replacements to be undone or redone. Listeners will be notified about the
	 * removal of the replaced element and the addition of each replacement.
	 * </p>
	 * 
	 * @param operation
	 *            The IUndoableOperation to be replaced
	 * @param replacements
	 *            the array of IUndoableOperation to replace the first operation
	 */
	void replaceOperation(IUndoableOperation operation,
			IUndoableOperation[] replacements);

	/**
	 * <p>
	 * Set the limit on the undo and redo history for a particular context.
	 * </p>
	 * 
	 * @param context
	 *            the context whose limit is being set.
	 * 
	 * @param limit
	 *            the maximum number of operations that should be kept in the
	 *            undo or redo history for the specified context. Must not be
	 *            negative.
	 */
	void setLimit(IUndoContext context, int limit);

	/**
	 * <p>
	 * Undo the most recently executed operation in the given context. The undo
	 * of the operation is subject to approval by any registered
	 * {@link IOperationApprover} before it is attempted.
	 * </p>
	 * 
	 * @param context
	 *            the context to be undone
	 * @param monitor
	 *            the progress monitor to be used for the undo, or
	 *            <code>null</code> if no progress monitor is provided.
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.
	 * 
	 * @return the IStatus indicating whether the undo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the undo operation was successful, and (since
	 * release 3.2), that the operation will be placed on the redo history.
	 * (Prior to 3.2, a successfully undone operation would not be placed on the
	 * redo history if it could not be redone. Since 3.2, this is relaxed, and
	 * all successfully undone operations are placed in the redo history.)
	 * Listeners will receive the <code>UNDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>,
	 * <code>INFO</code>, etc.) are not specifically interpreted by the
	 * history. The operation will remain in the history and the returned status
	 * is simply passed back to the caller. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>UNDONE</code> notification if the undo was approved and
	 * attempted.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during undo.
	 */

	IStatus undo(IUndoContext context, IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;

	/**
	 * <p>
	 * Undo the specified operation. The undo of the operation is subject to
	 * approval by any registered {@link IOperationApprover} before it is
	 * attempted.
	 * </p>
	 * 
	 * @param operation
	 *            the operation to be undone
	 * @param monitor
	 *            the progress monitor to be used for the undo, or
	 *            <code>null</code> if no progress monitor is provided
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.
	 * 
	 * @return the IStatus indicating whether the undo succeeded.
	 * 
	 * <p>
	 * The severity code in the returned status describes whether the operation
	 * succeeded and whether it remains in the history. <code>OK</code>
	 * severity indicates that the undo operation was successful, and (since
	 * release 3.2), that the operation will be placed on the redo history.
	 * (Prior to 3.2, a successfully undone operation would not be placed on the
	 * redo history if it could not be redone. Since 3.2, this is relaxed, and
	 * all successfully undone operations are placed in the redo history.)
	 * Listeners will receive the <code>UNDONE</code> notification.
	 * </p>
	 * <p>
	 * Other severity codes (<code>CANCEL</code>, <code>ERROR</code>,
	 * <code>INFO</code>, etc.) are not specifically interpreted by the
	 * history. The operation will remain in the history and the returned status
	 * is simply passed back to the caller. For all severities other than
	 * <code>OK</code>, listeners will receive the
	 * <code>OPERATION_NOT_OK</code> notification instead of the
	 * <code>UNDONE</code> notification if the undo was approved and
	 * attempted.
	 * </p>
	 * 
	 * @throws ExecutionException
	 *             if an exception occurred during undo.
	 */
	IStatus undoOperation(IUndoableOperation operation,
			IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;

}