/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla 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/MPL/
 *
 * 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 the Mozilla browser.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications, Inc.
 * Portions created by the Initial Developer are Copyright (C) 1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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 * decision by deleting the provisions above and replace them with the notice
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 * the provisions above, a recipient may use your version of this file under
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 * ***** END LICENSE BLOCK ***** */

#include "nsISupports.idl"

interface nsIURI;

/**
 * nsISHistoryListener defines the interface one can implement to receive
 * notifications about activities in session history and to be able to
 * cancel them.
 *
 * A session history listener will be notified when pages are added, removed
 * and loaded from session history. It can prevent any action (except adding
 * a new session history entry) from happening by returning false from the
 * corresponding callback method.
 *
 * A session history listener can be registered on a particular nsISHistory
 * instance via the nsISHistory::addSHistoryListener() method.
 *
 * @status FROZEN
 */
[scriptable, uuid(3b07f591-e8e1-11d4-9882-00c04fa02f40)]
interface nsISHistoryListener : nsISupports 
{
  /**
   * Called when a new document is added to session history. New documents are
   * added to session history by docshell when new pages are loaded in a frame
   * or content area, for example via nsIWebNavigation::loadURI()
   *
   * @param aNewURI     The URI of the document to be added to session history.
   */
   void OnHistoryNewEntry(in nsIURI aNewURI);

  /**
   * Called when navigating to a previous session history entry, for example
   * due to a nsIWebNavigation::goBack() call.
   *
   * @param aBackURI    The URI of the session history entry being navigated to.
   * @return            Whether the operation can proceed.
   */
   boolean OnHistoryGoBack(in nsIURI aBackURI);

  /**
   * Called when navigating to a next session history entry, for example
   * due to a nsIWebNavigation::goForward() call.
   *
   * @param aForwardURI   The URI of the session history entry being navigated to.
   * @return              Whether the operation can proceed.
   */
   boolean OnHistoryGoForward(in nsIURI aForwardURI);

  /** 
   * Called when the current document is reloaded, for example due to a
   * nsIWebNavigation::reload() call.
   *
   * @param aReloadURI    The URI of the document to be reloaded.
   * @param aReloadFlags  Flags that indicate how the document is to be 
   *                      refreshed. See constants on the nsIWebNavigation
   *                      interface.
   * @return              Whether the operation can proceed.
   *
   * @see  nsIWebNavigation
   */
   boolean OnHistoryReload(in nsIURI aReloadURI, in unsigned long aReloadFlags);

  /**
   * Called when navigating to a session history entry by index, for example,
   * when nsIWebNavigation::gotoIndex() is called.
   *
   * @param aIndex        The index in session history of the entry to be loaded.
   * @param aGotoURI      The URI of the session history entry to be loaded.
   * @return              Whether the operation can proceed.
   */
   boolean OnHistoryGotoIndex(in long aIndex, in nsIURI aGotoURI);

  /**
   * Called when entries are removed from session history. Entries can be
   * removed from session history for various reasons, for example to control
   * the memory usage of the browser, to prevent users from loading documents
   * from history, to erase evidence of prior page loads, etc.
   *
   * To purge documents from session history call nsISHistory::PurgeHistory()
   *
   * @param aNumEntries   The number of entries to be removed from session history.
   * @return              Whether the operation can proceed.
   */
   boolean OnHistoryPurge(in long aNumEntries);
};