Issue 4131 - Simplify UI initialization logic

lib/ui.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 259 matching lines @@
  */
 let notificationTimer = null;
 
 let UI = exports.UI =
 {
   /**
    * Gets called on startup, initializes UI integration.
    */
   init: function()
   {
-    // We should call initDone once both overlay and filters are loaded
-    let overlayLoaded = false;
-    let filtersLoaded = false;
-    let sessionRestored = false;
+    // We have to wait for multiple events before running start-up actions
+    let prerequisites = [];
 
     // Start loading overlay
-    let request = new XMLHttpRequest();
-    request.mozBackgroundRequest = true;
-    request.open("GET", "chrome://adblockplus/content/ui/overlay.xul");
-    request.channel.owner = Utils.systemPrincipal;
-    request.addEventListener("load", function(event)
+    prerequisites.push(new Promise((resolve, reject) =>
     {
-      if (onShutdown.done)
-        return;
+      let request = new XMLHttpRequest();
+      request.mozBackgroundRequest = true;
+      request.open("GET", "chrome://adblockplus/content/ui/overlay.xul");
+      request.channel.owner = Utils.systemPrincipal;
+      request.addEventListener("load", event =>
+      {
+        if (onShutdown.done)
+          return;
 
-      this.processOverlay(request.responseXML.documentElement);
+        this.processOverlay(request.responseXML.documentElement);
 
-      // Don't wait for the rest of the startup sequence, add icon already
-      this.addToolbarButton();
+        // Don't wait for the rest of the startup sequence, add icon already
+        this.addToolbarButton();
 
-      overlayLoaded = true;
-      if (overlayLoaded && filtersLoaded && sessionRestored)
-        this.initDone();
-    }.bind(this), false);
-    request.send(null);
+        resolve();
+      }, false);
+
+      request.addEventListener("error", event =>
+      {
+        reject(new Error("Unexpected: Failed to load overlay.xul"));
+      });
+
+      request.send(null);
+    }));
 
     // Wait for filters to load
     if (FilterStorage._loading)
+      prerequisites.push(FilterNotifier.once("load"));
+
+    // Wait for session to be restored
+    prerequisites.push(new Promise((resolve, reject) =>
     {
-      let listener = function(action)
+      let window = this.currentWindow;
+      if (!window && "nsISessionStore" in Ci)
       {
-        if (action != "load")
-          return;
+        // No application windows yet, the application must be starting up. Wait
+        // for session to be restored before initializing our UI.
+        new SessionRestoreObserver(resolve);
+      }
+      else
+        resolve();
+    }));
 
-        FilterNotifier.removeListener(listener);
-        filtersLoaded = true;
-        if (overlayLoaded && filtersLoaded && sessionRestored)
-          this.initDone();
-      }.bind(this);
-      FilterNotifier.addListener(listener);
-    }
-    else
-      filtersLoaded = true;
-
-    // Initialize UI after the session is restored
-    let window = this.currentWindow;
-    if (!window && "nsISessionStore" in Ci)
-    {
-      // No application windows yet, the application must be starting up. Wait
-      // for session to be restored before initializing our UI.
-      new SessionRestoreObserver(function()
-      {
-        sessionRestored = true;
-        if (overlayLoaded && filtersLoaded && sessionRestored)
-          this.initDone();
-      }.bind(this));
-    }
-    else
-      sessionRestored = true;
+    Promise.all(prerequisites).then(() => this.initDone())
+        .catch(e => Cu.reportError(e));
   },
 
   /**
    * Provesses overlay document data and initializes overlay property.
    */
   processOverlay: function(/**Element*/ root)
   {
     Utils.splitAllLabels(root);
 
     let specialElements = {"abp-status-popup": true, "abp-status": true, "abp-toolbarbutton": true, "abp-menuitem": true, "abp-bottombar-container": true};
@@ skipping 1547 matching lines @@
   ["abp-command-contribute-hide", "command", UI.hideContributeButton.bind(UI)],
   ["abp-command-toggleshownotifications", "command", Notification.toggleIgnoreCategory.bind(Notification, "*", null)]
 ];
 
 onShutdown.add(function()
 {
   for (let window of UI.applicationWindows)
     if (UI.isBottombarOpen(window))
       UI.toggleBottombar(window);
 });