/* -*- 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 (for reloads) to be
 * able to cancel them.
 *
 * A session history listener will be notified when pages are added, removed
 * and loaded from session history. In the case of reloads, it can prevent them
 * 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.
 *
 * Listener methods should not alter the session history. Things are likely to
 * go haywire if they do.
 */
[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 before the current document is reloaded, for example due to a
   * nsIWebNavigation::reload() call.
   */
  boolean OnHistoryReload();

  /**
   * Called before navigating to a session history entry by index, for example,
   * when nsIWebNavigation::gotoIndex() is called.
   */
  void OnHistoryGotoIndex();

  /**
   * Called before entries are removed from the start of 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 being removed.
   */
  void OnHistoryPurge(in long aNumEntries);

  /**
   * Called before entries are removed from the end of session history. This
   * occurs when navigating to a new page while on a previous session entry.
   *
   * @param aNumEntries  The number of entries being removed.
   */
  void OnHistoryTruncate(in long aNumEntries);

  /**
   * Called before 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.
   */
  void OnHistoryReplaceEntry();


  /**
   * Called whenever a content viewer is evicted. A content viewer is evicted
   * whenever a bfcache entry has timed out or the number of total content
   * viewers has exceeded the global max. This is used for testing only.
   *
   * @param aNumEvicted - number of content viewers evicted
   */
  void OnDocumentViewerEvicted(in unsigned long aNumEvicted);
};