/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#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.
 */
[scriptable, uuid(125c0833-746a-400e-9b89-d2d18545c08a)]
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.
   * @param aOldIndex   The index of the current history item before the operation.
   */
   void OnHistoryNewEntry(in nsIURI aNewURI, in long aOldIndex);

  /**
   * 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);

  /**
   * Called when an entry is replaced in the session history. Entries are
   * replaced when navigating away from non-persistent history entries (such as
   * about pages) and when history.replaceState is called.
   *
   * @param aIndex        The index in session history of the entry being
  *                       replaced
   */
   void OnHistoryReplaceEntry(in long aIndex);

   /**
    * Called when nsISHistory::count has been updated. Unlike OnHistoryNewEntry
    * and OnHistoryPurge which happen before the modifications are actually done
    * and maybe cancellable, this function is called after these modifications.
    */
   void OnLengthChange(in long aCount);
};