/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (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.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s): 
 */

#include "nsISupports.idl"

/*
 * The nsITransaction interface.
 * <P>
 * This interface is implemented by an object that needs to
 * execute some behavior that must be tracked by the transaction manager.
 */
[scriptable, uuid(58e330c1-7b48-11d2-98b9-00805f297d89)]
interface nsITransaction : nsISupports
{
  /**
   * Executes the transaction.
   */
  void doTransaction();

  /**
   * Restores the state to what it was before the transaction was executed.
   */
  void undoTransaction();

  /**
   * Executes the transaction again. Can only be called on a transaction that
   * was previously undone.
   * <P>
   * In most cases, the redoTransaction() method will actually call the
   * doTransaction() method to execute the transaction again.
   */
  void redoTransaction();

  /**
   * The transaction's transient state. This attribute is checked by
   * the transaction manager after the transaction's Execute() method is called.
   * If the transient state is false, a reference to the transaction is
   * held by the transaction manager so that the transactions' undoTransaction()
   * and redoTransaction() methods can be called. If the transient state is
   * true, the transaction manager returns immediately after the transaction's
   * doTransaction() method is called, no references to the transaction are
   * maintained. Transient transactions cannot be undone or redone by the
   * transaction manager.
   */
  readonly attribute boolean isTransient;

  /**
   * Attempts to merge a transaction into "this" transaction. Both transactions
   * must be in their undo state, doTransaction() methods already called. The
   * transaction manager calls this method to coalesce a new transaction with
   * the transaction on the top of the undo stack.
   * This method returns a boolean value that indicates the merge result.
   * A true value indicates that the transactions were merged successfully,
   * a false value if the merge was not possible or failed. If true,
   * the transaction manager will Release() the new transacton instead of
   * pushing it on the undo stack.
   * @param aTransaction the previously executed transaction to merge.
   */
  boolean merge(in nsITransaction aTransaction);
};

