/*******************************************************************************
 * 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.core.commands.operations;

import org.eclipse.core.runtime.IAdaptable;
import org.eclipse.core.runtime.IStatus;

/**
 * <p>
 * IOperationApprover defines an interface for approving the undo or redo of a
 * particular operation within an operation history. Operations that are
 * candidates for undo or redo have already been validated against their current
 * state and according to the rules of the history.
 * </p>
 * <p>
 * By the time an IOperationApprover is consulted, the undo has already been
 * requested. Approvers should return an <code>IStatus</code> object with
 * severity <code>OK</code> if the operation should proceed, and any other
 * severity if it should not. When an operation is not approved, it is expected
 * that the object not allowing the operation has already consulted the user if
 * necessary or otherwise provided any necessary information to the user about
 * the fact that the operation is not approved.
 * </p>
 * <p>
 * Operation approvers must be prepared to receive the approval messages from a
 * background thread. Any UI access occurring inside the implementation must be
 * properly synchronized using the techniques specified by the client's widget
 * library.
 * </p>
 * 
 * @since 3.1
 */
public interface IOperationApprover {

	/**
	 * Return a status indicating whether the specified operation should be
	 * redone. Any status that does not have severity <code>IStatus.OK</code>
	 * will not be approved. Implementers should not assume that the redo will
	 * be performed when the status is <code>OK</code>, since other operation
	 * approvers may veto the redo.
	 * 
	 * @param operation 
	 *            the operation to be redone
	 * @param history 
	 *            the history redoing 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. Even if UI
	 *            information is provided, the implementation of this method
	 *            must be prepared for being called from a background thread.
	 *            Any UI access must be properly synchronized using the
	 *            techniques specified by the client's widget library.
	 * @return the IStatus describing whether the operation is approved. The
	 *         redo will not proceed if the status severity is not
	 *         <code>OK</code>, and the caller requesting the redo will be
	 *         returned the status that caused the rejection. Any other status
	 *         severities will not be interpreted by the history.
	 */
	IStatus proceedRedoing(IUndoableOperation operation,
			IOperationHistory history, IAdaptable info);

	/**
	 * Return a status indicating whether the specified operation should be
	 * undone. Any status that does not have severity <code>IStatus.OK</code>
	 * will not be approved. Implementers should not assume that the undo will
	 * be performed when the status is <code>OK</code>, since other operation
	 * approvers can veto the undo.
	 * 
	 * @param operation 
	 *            the operation to be undone
	 * @param history 
	 *            the history undoing 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. Even if UI
	 *            information is provided, the implementation of this method
	 *            must be prepared for being called from a background thread.
	 *            Any UI access must be properly synchronized using the
	 *            techniques specified by the client's widget library.
	 * @return the IStatus describing whether the operation is approved. The
	 *         undo will not proceed if the status severity is not
	 *         <code>OK</code>, and the caller requesting the undo will be
	 *         returned the status that caused the rejection. Any other status
	 *         severities will not be interpreted by the history.
	 */
	IStatus proceedUndoing(IUndoableOperation operation,
			IOperationHistory history, IAdaptable info);

}