UndoManager.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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();
}