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/* 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/. */

"use strict";

var EXPORTED_SYMBOLS = ["SessionSaver"];

ChromeUtils.import("resource://gre/modules/Timer.jsm", this);
ChromeUtils.import("resource://gre/modules/Services.jsm", this);
ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm", this);

XPCOMUtils.defineLazyModuleGetters(this, {
  AppConstants: "resource://gre/modules/AppConstants.jsm",
  PrivacyFilter: "resource://gre/modules/sessionstore/PrivacyFilter.jsm",
  RunState: "resource:///modules/sessionstore/RunState.jsm",
  SessionStore: "resource:///modules/sessionstore/SessionStore.jsm",
  SessionFile: "resource:///modules/sessionstore/SessionFile.jsm",
  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
});

/*
 * Minimal interval between two save operations (in milliseconds).
 *
 * To save system resources, we generally do not save changes immediately when
 * a change is detected. Rather, we wait a little to see if this change is
 * followed by other changes, in which case only the last write is necessary.
 * This delay is defined by "browser.sessionstore.interval".
 *
 * Furthermore, when the user is not actively using the computer, webpages
 * may still perform changes that require (re)writing to sessionstore, e.g.
 * updating Session Cookies or DOM Session Storage, or refreshing, etc. We
 * expect that these changes are much less critical to the user and do not
 * need to be saved as often. In such cases, we increase the delay to
 *  "browser.sessionstore.interval.idle".
 *
 * When the user returns to the computer, if a save is pending, we reschedule
 * it to happen soon, with "browser.sessionstore.interval".
 */
const PREF_INTERVAL_ACTIVE = "browser.sessionstore.interval";
const PREF_INTERVAL_IDLE = "browser.sessionstore.interval.idle";
const PREF_IDLE_DELAY = "browser.sessionstore.idleDelay";

// Notify observers about a given topic with a given subject.
function notify(subject, topic) {
  Services.obs.notifyObservers(subject, topic);
}

// TelemetryStopwatch helper functions.
function stopWatch(method) {
  return function(...histograms) {
    for (let hist of histograms) {
      TelemetryStopwatch[method]("FX_SESSION_RESTORE_" + hist);
    }
  };
}

var stopWatchStart = stopWatch("start");
var stopWatchFinish = stopWatch("finish");

/**
 * The external API implemented by the SessionSaver module.
 */
var SessionSaver = Object.freeze({
  /**
   * Immediately saves the current session to disk.
   */
  run() {
    return SessionSaverInternal.run();
  },

  /**
   * Saves the current session to disk delayed by a given amount of time. Should
   * another delayed run be scheduled already, we will ignore the given delay
   * and state saving may occur a little earlier.
   */
  runDelayed() {
    SessionSaverInternal.runDelayed();
  },

  /**
   * Sets the last save time to the current time. This will cause us to wait for
   * at least the configured interval when runDelayed() is called next.
   */
  updateLastSaveTime() {
    SessionSaverInternal.updateLastSaveTime();
  },

  /**
   * Cancels all pending session saves.
   */
  cancel() {
    SessionSaverInternal.cancel();
  },
});

/**
 * The internal API.
 */
var SessionSaverInternal = {
  /**
   * The timeout ID referencing an active timer for a delayed save. When no
   * save is pending, this is null.
   */
  _timeoutID: null,

  /**
   * The idle callback ID referencing an active idle callback. When no idle
   * callback is pending, this is null.
   * */
  _idleCallbackID: null,

  /**
   * A timestamp that keeps track of when we saved the session last. We will
   * this to determine the correct interval between delayed saves to not deceed
   * the configured session write interval.
   */
  _lastSaveTime: 0,

  /**
   * `true` if the user has been idle for at least
   * `SessionSaverInternal._intervalWhileIdle` ms. Idleness is computed
   * with `nsIIdleService`.
   */
  _isIdle: false,

  /**
   * `true` if the user was idle when we last scheduled a delayed save.
   * See `_isIdle` for details on idleness.
   */
  _wasIdle: false,

  /**
   * Minimal interval between two save operations (in ms), while the user
   * is active.
   */
  _intervalWhileActive: null,

  /**
   * Minimal interval between two save operations (in ms), while the user
   * is idle.
   */
  _intervalWhileIdle: null,

  /**
   * How long before we assume that the user is idle (ms).
   */
  _idleDelay: null,

  /**
   * Immediately saves the current session to disk.
   */
  run() {
    return this._saveState(true /* force-update all windows */);
  },

  /**
   * Saves the current session to disk delayed by a given amount of time. Should
   * another delayed run be scheduled already, we will ignore the given delay
   * and state saving may occur a little earlier.
   *
   * @param delay (optional)
   *        The minimum delay in milliseconds to wait for until we collect and
   *        save the current session.
   */
  runDelayed(delay = 2000) {
    // Bail out if there's a pending run.
    if (this._timeoutID) {
      return;
    }

    // Interval until the next disk operation is allowed.
    let interval = this._isIdle
      ? this._intervalWhileIdle
      : this._intervalWhileActive;
    delay = Math.max(this._lastSaveTime + interval - Date.now(), delay, 0);

    // Schedule a state save.
    this._wasIdle = this._isIdle;
    this._timeoutID = setTimeout(() => {
      // Execute _saveStateAsync when we have enough idle time. Otherwise,
      // another idle request is made to schedule _saveStateAsync again.
      let saveStateAsyncWhenIdle = deadline => {
        // When looking at the telemetry data, the time it takes to execute
        // _saveStateAsync is around 5.9ms (median). Therefore,
        // we'll not execute the function when the idle time is less than 5ms.
        if (deadline.timeRemaining() < 5) {
          this._idleCallbackID = requestIdleCallback(saveStateAsyncWhenIdle);
          return;
        }
        this._saveStateAsync();
      };

      this._idleCallbackID = requestIdleCallback(saveStateAsyncWhenIdle);
    }, delay);
  },

  /**
   * Sets the last save time to the current time. This will cause us to wait for
   * at least the configured interval when runDelayed() is called next.
   */
  updateLastSaveTime() {
    this._lastSaveTime = Date.now();
  },

  /**
   * Cancels all pending session saves.
   */
  cancel() {
    clearTimeout(this._timeoutID);
    this._timeoutID = null;
    cancelIdleCallback(this._idleCallbackID);
    this._idleCallbackID = null;
  },

  /**
   * Observe idle/ active notifications.
   */
  observe(subject, topic, data) {
    switch (topic) {
      case "idle":
        this._isIdle = true;
        break;
      case "active":
        this._isIdle = false;
        if (this._timeoutID && this._wasIdle) {
          // A state save has been scheduled while we were idle.
          // Replace it by an active save.
          clearTimeout(this._timeoutID);
          this._timeoutID = null;
          this.runDelayed();
        }
        break;
      default:
        throw new Error(`Unexpected change value ${topic}`);
    }
  },

  /**
   * Saves the current session state. Collects data and writes to disk.
   *
   * @param forceUpdateAllWindows (optional)
   *        Forces us to recollect data for all windows and will bypass and
   *        update the corresponding caches.
   */
  _saveState(forceUpdateAllWindows = false) {
    // Cancel any pending timeouts.
    this.cancel();

    if (PrivateBrowsingUtils.permanentPrivateBrowsing) {
      // Don't save (or even collect) anything in permanent private
      // browsing mode

      this.updateLastSaveTime();
      return Promise.resolve();
    }

    stopWatchStart("COLLECT_DATA_MS");
    let state = SessionStore.getCurrentState(forceUpdateAllWindows);
    PrivacyFilter.filterPrivateWindowsAndTabs(state);

    // Make sure we only write worth saving tabs to disk.
    SessionStore.keepOnlyWorthSavingTabs(state);

    // Make sure that we keep the previous session if we started with a single
    // private window and no non-private windows have been opened, yet.
    if (state.deferredInitialState) {
      state.windows = state.deferredInitialState.windows || [];
      delete state.deferredInitialState;
    }

    if (AppConstants.platform != "macosx") {
      // We want to restore closed windows that are marked with _shouldRestore.
      // We're doing this here because we want to control this only when saving
      // the file.
      while (state._closedWindows.length) {
        let i = state._closedWindows.length - 1;

        if (!state._closedWindows[i]._shouldRestore) {
          // We only need to go until _shouldRestore
          // is falsy since we're going in reverse.
          break;
        }

        delete state._closedWindows[i]._shouldRestore;
        state.windows.unshift(state._closedWindows.pop());
      }
    }

    // Clear cookies and storage on clean shutdown.
    this._maybeClearCookiesAndStorage(state);

    stopWatchFinish("COLLECT_DATA_MS");
    return this._writeState(state);
  },

  /**
   * Purges cookies and DOMSessionStorage data from the session on clean
   * shutdown, only if requested by the user's preferences.
   */
  _maybeClearCookiesAndStorage(state) {
    // Only do this on shutdown.
    if (!RunState.isClosing) {
      return;
    }

    // Don't clear when restarting.
    if (
      Services.prefs.getBoolPref("browser.sessionstore.resume_session_once")
    ) {
      return;
    }

    let expireCookies =
      Services.prefs.getIntPref("network.cookie.lifetimePolicy") ==
      Services.cookies.QueryInterface(Ci.nsICookieService).ACCEPT_SESSION;
    let sanitizeCookies =
      Services.prefs.getBoolPref("privacy.sanitize.sanitizeOnShutdown") &&
      Services.prefs.getBoolPref("privacy.clearOnShutdown.cookies");

    if (expireCookies || sanitizeCookies) {
      // Remove cookies.
      delete state.cookies;

      // Remove DOMSessionStorage data.
      for (let window of state.windows) {
        for (let tab of window.tabs) {
          delete tab.storage;
        }
      }
    }
  },

  /**
   * Saves the current session state. Collects data asynchronously and calls
   * _saveState() to collect data again (with a cache hit rate of hopefully
   * 100%) and write to disk afterwards.
   */
  _saveStateAsync() {
    // Allow scheduling delayed saves again.
    this._timeoutID = null;

    // Write to disk.
    this._saveState();
  },

  /**
   * Write the given state object to disk.
   */
  _writeState(state) {
    // We update the time stamp before writing so that we don't write again
    // too soon, if saving is requested before the write completes. Without
    // this update we may save repeatedly if actions cause a runDelayed
    // before writing has completed. See Bug 902280
    this.updateLastSaveTime();

    // Write (atomically) to a session file, using a tmp file. Once the session
    // file is successfully updated, save the time stamp of the last save and
    // notify the observers.
    return SessionFile.write(state).then(() => {
      this.updateLastSaveTime();
      notify(null, "sessionstore-state-write-complete");
    }, console.error);
  },
};

XPCOMUtils.defineLazyPreferenceGetter(
  SessionSaverInternal,
  "_intervalWhileActive",
  PREF_INTERVAL_ACTIVE,
  15000 /* 15 seconds */,
  () => {
    // Cancel any pending runs and call runDelayed() with
    // zero to apply the newly configured interval.
    SessionSaverInternal.cancel();
    SessionSaverInternal.runDelayed(0);
  }
);

XPCOMUtils.defineLazyPreferenceGetter(
  SessionSaverInternal,
  "_intervalWhileIdle",
  PREF_INTERVAL_IDLE,
  3600000 /* 1 h */
);

XPCOMUtils.defineLazyPreferenceGetter(
  SessionSaverInternal,
  "_idleDelay",
  PREF_IDLE_DELAY,
  180000 /* 3 minutes */,
  (key, previous, latest) => {
    // Update the idle observer for the new `PREF_IDLE_DELAY` value. Here we need
    // to re-fetch the service instead of the original one in use; This is for a
    // case that the Mock service in the unit test needs to be fetched to
    // replace the original one.
    var idleService = Cc["@mozilla.org/widget/idleservice;1"].getService(
      Ci.nsIIdleService
    );
    if (previous != undefined) {
      idleService.removeIdleObserver(SessionSaverInternal, previous);
    }
    if (latest != undefined) {
      idleService.addIdleObserver(SessionSaverInternal, latest);
    }
  }
);

var idleService = Cc["@mozilla.org/widget/idleservice;1"].getService(
  Ci.nsIIdleService
);
idleService.addIdleObserver(
  SessionSaverInternal,
  SessionSaverInternal._idleDelay
);