/**
* Copyright 2009 Google Inc.
*
* 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 org.waveprotocol.wave.model.undo;
/**
* An undo manager.
*
*
* @param <T> The type of operations.
*/
public interface UndoManager<T> {
/**
* Places into the undo manager an operation that should be undone by undos.
*
* @param op the operation that should be undone by an appropriate undo
*/
void undoableOp(T op);
/**
* Places into the undo manager an operation that should not be undone by undos.
*
* @param op the operation that should not be undone by any undos
*/
void nonUndoableOp(T op);
/**
* Places an undo checkpoint.
*/
void checkpoint();
/**
* Effects an undo. Returns null if there are no operations to undo.
*
* @return the operation that will effect an undo
*/
T undo();
/**
* Effects a redo. Returns null if there are no operations to redo.
*
* @return the operation that will effect a redo
*/
T redo();
}