/*
# 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/.
*/

/**
# * Session Storage and Restoration
# *
# * Overview
# * This service reads user's session file at startup, and makes a determination
# * as to whether the session should be restored. It will restore the session
# * under the circumstances described below.  If the auto-start Private Browsing
# * mode is active, however, the session is never restored.
# *
# * Crash Detection
# * The session file stores a session.state property, that
# * indicates whether the browser is currently running. When the browser shuts
# * down, the field is changed to "stopped". At startup, this field is read, and
# * if its value is "running", then it's assumed that the browser had previously
# * crashed, or at the very least that something bad happened, and that we should
# * restore the session.
# *
# * Forced Restarts
# * In the event that a restart is required due to application update or extension
# * installation, set the browser.sessionstore.resume_session_once pref to true,
# * and the session will be restored the next time the browser starts.
# *
# * Always Resume
# * This service will always resume the session if the integer pref
# * browser.startup.page is set to 3.
*/

/* :::::::: Constants and Helpers ::::::::::::::: */

const Cc = Components.classes;
const Ci = Components.interfaces;
const Cr = Components.results;
const Cu = Components.utils;
Cu.import("resource://gre/modules/XPCOMUtils.jsm");
Cu.import("resource://gre/modules/Services.jsm");
Cu.import("resource://gre/modules/TelemetryStopwatch.jsm");

const STATE_RUNNING_STR = "running";
const MAX_FILE_SIZE = 100 * 1024 * 1024; // 100 megabytes

function debug(aMsg) {
  aMsg = ("SessionStartup: " + aMsg).replace(/\S{80}/g, "$&\n");
  Services.console.logStringMessage(aMsg);
}

/* :::::::: The Service ::::::::::::::: */

function SessionStartup() {
}

SessionStartup.prototype = {

  // the state to restore at startup
  _initialState: null,
  _sessionType: Ci.nsISessionStartup.NO_SESSION,

/* ........ Global Event Handlers .............. */

  /**
   * Initialize the component
   */
  init: function sss_init() {
    // do not need to initialize anything in auto-started private browsing sessions
    let pbs = Cc["@mozilla.org/privatebrowsing;1"].
              getService(Ci.nsIPrivateBrowsingService);
    if (pbs.autoStarted || pbs.lastChangedByCommandLine)
      return;

    let prefBranch = Cc["@mozilla.org/preferences-service;1"].
                     getService(Ci.nsIPrefService).getBranch("browser.");

    // get file references
    var dirService = Cc["@mozilla.org/file/directory_service;1"].
                     getService(Ci.nsIProperties);
    let sessionFile = dirService.get("ProfD", Ci.nsILocalFile);
    sessionFile.append("sessionstore.js");

    let doResumeSessionOnce = prefBranch.getBoolPref("sessionstore.resume_session_once");
    let doResumeSession = doResumeSessionOnce ||
                          prefBranch.getIntPref("startup.page") == 3;

    // only continue if the session file exists
    if (!sessionFile.exists())
      return;

    // get string containing session state
    let iniString = this._readStateFile(sessionFile);
    if (!iniString)
      return;

    // parse the session state into a JS object
    // remove unneeded braces (added for compatibility with Firefox 2.0 and 3.0)
    if (iniString.charAt(0) == '(')
      iniString = iniString.slice(1, -1);
    let corruptFile = false;
    try {
      this._initialState = JSON.parse(iniString);
    }
    catch (ex) {
      debug("The session file contained un-parse-able JSON: " + ex);
      // Try to eval.
      // evalInSandbox will throw if iniString is not parse-able.
      try {
        var s = new Cu.Sandbox("about:blank", {sandboxName: 'nsSessionStartup'});
        this._initialState = Cu.evalInSandbox("(" + iniString + ")", s);
      } catch(ex) {
        debug("The session file contained un-eval-able JSON: " + ex);
        corruptFile = true;
      }
    }
    Services.telemetry.getHistogramById("FX_SESSION_RESTORE_CORRUPT_FILE").add(corruptFile);

    // If this is a normal restore then throw away any previous session
    if (!doResumeSessionOnce)
      delete this._initialState.lastSessionState;

    let resumeFromCrash = prefBranch.getBoolPref("sessionstore.resume_from_crash");
    let lastSessionCrashed =
      this._initialState && this._initialState.session &&
      this._initialState.session.state &&
      this._initialState.session.state == STATE_RUNNING_STR;

    // Report shutdown success via telemetry. Shortcoming here are
    // being-killed-by-OS-shutdown-logic, shutdown freezing after
    // session restore was written, etc.
    Services.telemetry.getHistogramById("SHUTDOWN_OK").add(!lastSessionCrashed);

    // set the startup type
    if (lastSessionCrashed && resumeFromCrash)
      this._sessionType = Ci.nsISessionStartup.RECOVER_SESSION;
    else if (!lastSessionCrashed && doResumeSession)
      this._sessionType = Ci.nsISessionStartup.RESUME_SESSION;
    else if (this._initialState)
      this._sessionType = Ci.nsISessionStartup.DEFER_SESSION;
    else
      this._initialState = null; // reset the state

    // wait for the first browser window to open
    // Don't reset the initial window's default args (i.e. the home page(s))
    // if all stored tabs are pinned.
    if (this.doRestore() &&
        (!this._initialState.windows ||
        !this._initialState.windows.every(function (win)
           win.tabs.every(function (tab) tab.pinned))))
      Services.obs.addObserver(this, "domwindowopened", true);

    Services.obs.addObserver(this, "sessionstore-windows-restored", true);

    if (this._sessionType != Ci.nsISessionStartup.NO_SESSION)
      Services.obs.addObserver(this, "browser:purge-session-history", true);
  },

  /**
   * Handle notifications
   */
  observe: function sss_observe(aSubject, aTopic, aData) {
    switch (aTopic) {
    case "app-startup":
      Services.obs.addObserver(this, "final-ui-startup", true);
      Services.obs.addObserver(this, "quit-application", true);
      break;
    case "final-ui-startup":
      Services.obs.removeObserver(this, "final-ui-startup");
      Services.obs.removeObserver(this, "quit-application");
      this.init();
      break;
    case "quit-application":
      // no reason for initializing at this point (cf. bug 409115)
      Services.obs.removeObserver(this, "final-ui-startup");
      Services.obs.removeObserver(this, "quit-application");
      if (this._sessionType != Ci.nsISessionStartup.NO_SESSION)
        Services.obs.removeObserver(this, "browser:purge-session-history");
      break;
    case "domwindowopened":
      var window = aSubject;
      var self = this;
      window.addEventListener("load", function() {
        self._onWindowOpened(window);
        window.removeEventListener("load", arguments.callee, false);
      }, false);
      break;
    case "sessionstore-windows-restored":
      Services.obs.removeObserver(this, "sessionstore-windows-restored");
      // free _initialState after nsSessionStore is done with it
      this._initialState = null;
      break;
    case "browser:purge-session-history":
      Services.obs.removeObserver(this, "browser:purge-session-history");
      // reset all state on sanitization
      this._sessionType = Ci.nsISessionStartup.NO_SESSION;
      break;
    }
  },

  /**
   * Removes the default arguments from the first browser window
   * (and removes the "domwindowopened" observer afterwards).
   */
  _onWindowOpened: function sss_onWindowOpened(aWindow) {
    var wType = aWindow.document.documentElement.getAttribute("windowtype");
    if (wType != "navigator:browser")
      return;

    /**
     * Note: this relies on the fact that nsBrowserContentHandler will return
     * a different value the first time its getter is called after an update,
     * due to its needHomePageOverride() logic. We don't want to remove the
     * default arguments in the update case, since they include the "What's
     * New" page.
     *
     * Since we're garanteed to be at least the second caller of defaultArgs
     * (nsBrowserContentHandler calls it to determine which arguments to pass
     * at startup), we know that if the window's arguments don't match the
     * current defaultArguments, we're either in the update case, or we're
     * launching a non-default browser window, so we shouldn't remove the
     * window's arguments.
     */
    var defaultArgs = Cc["@mozilla.org/browser/clh;1"].
                      getService(Ci.nsIBrowserHandler).defaultArgs;
    if (aWindow.arguments && aWindow.arguments[0] &&
        aWindow.arguments[0] == defaultArgs)
      aWindow.arguments[0] = null;

    try {
      Services.obs.removeObserver(this, "domwindowopened");
    } catch (e) {
      // This might throw if we're removing the observer multiple times,
      // but this is safe to ignore.
    }
  },

/* ........ Public API ................*/

  /**
   * Get the session state as a jsval
   */
  get state() {
    return this._initialState;
  },

  /**
   * Determine whether there is a pending session restore.
   * @returns bool
   */
  doRestore: function sss_doRestore() {
    return this._sessionType == Ci.nsISessionStartup.RECOVER_SESSION ||
           this._sessionType == Ci.nsISessionStartup.RESUME_SESSION;
  },

  /**
   * Get the type of pending session store, if any.
   */
  get sessionType() {
    return this._sessionType;
  },

/* ........ Storage API .............. */

  /**
   * Reads a session state file into a string and lets
   * observers modify the state before it's being used
   *
   * @param aFile is any nsIFile
   * @returns a session state string
   */
  _readStateFile: function sss_readStateFile(aFile) {
    TelemetryStopwatch.start("FX_SESSION_RESTORE_READ_FILE_MS");
    var stateString = Cc["@mozilla.org/supports-string;1"].
                        createInstance(Ci.nsISupportsString);
    stateString.data = this._readFile(aFile) || "";
    TelemetryStopwatch.finish("FX_SESSION_RESTORE_READ_FILE_MS");

    Services.obs.notifyObservers(stateString, "sessionstore-state-read", "");

    return stateString.data;
  },

  /**
   * reads a file into a string
   * @param aFile
   *        nsIFile
   * @returns string
   */
  _readFile: function sss_readFile(aFile) {
    try {
      var stream = Cc["@mozilla.org/network/file-input-stream;1"].
                   createInstance(Ci.nsIFileInputStream);
      stream.init(aFile, 0x01, 0, 0);
      var cvstream = Cc["@mozilla.org/intl/converter-input-stream;1"].
                     createInstance(Ci.nsIConverterInputStream);

      var fileSize = stream.available();
      if (fileSize > MAX_FILE_SIZE)
        throw "SessionStartup: sessionstore.js was not processed because it was too large.";

      cvstream.init(stream, "UTF-8", fileSize, Ci.nsIConverterInputStream.DEFAULT_REPLACEMENT_CHARACTER);
      var data = {};
      cvstream.readString(fileSize, data);
      var content = data.value;
      cvstream.close();

      return content.replace(/\r\n?/g, "\n");
    }
    catch (ex) { Cu.reportError(ex); }

    return null;
  },

  /* ........ QueryInterface .............. */
  QueryInterface : XPCOMUtils.generateQI([Ci.nsIObserver,
                                          Ci.nsISupportsWeakReference,
                                          Ci.nsISessionStartup]),
  classID:          Components.ID("{ec7a6c20-e081-11da-8ad9-0800200c9a66}"),
};

var NSGetFactory = XPCOMUtils.generateNSGetFactory([SessionStartup]);