/**
 * Copyright 2010 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;

import org.waveprotocol.wave.model.util.Pair;

/**
 * An <code>UndoManager</code> that provides versions of the undo and redo
 * methods which return more information.
 *
 *
 * @param <T> The type of operations.
 */
public interface UndoManagerPlus<T> extends UndoManager<T> {

  /**
   * Effects an undo. Returns null if there are no operations to undo.
   *
   * NOTE(user): Warning. This interface method may change.
   *
   * @return a pair containing the operation that will effect an undo and the
   *         relevant transformed non-undoable operation (which may be null if
   *         no such operation exists)
   *
   * NOTE(user): Returning null is probably slightly harder to use than
   * returning an operation that does nothing.
   */
  Pair<T, T> undoPlus();

  /**
   * Effects a redo. Returns null if there are no operations to redo.
   *
   * NOTE(user): Warning. This interface method may change.
   *
   * @return a pair containing the operation that will effect a redo and the
   *         relevant transformed non-undoable operation (which may be null if
   *         no such operation exists)
   *
   * NOTE(user): Returning null is probably slightly harder to use than
   * returning an operation that does nothing.
   */
  Pair<T, T> redoPlus();

}
