Add filtersLoaded and filterLoadListener to AdblockPlusApi

adblockplus/Api.jsm

Index: adblockplus/Api.jsm
===================================================================
--- a/adblockplus/Api.jsm
+++ b/adblockplus/Api.jsm
@@ -32,12 +32,20 @@
   return result.exports;
 }
 
+let {FilterNotifier} = require("filterNotifier");
 let {FilterStorage} = require("filterStorage");
 let {Prefs} = require("prefs");
 let {UI} = require("ui");
 
+let filtersLoaded = false;
+
 var AdblockPlusApi =
 {
+  get filtersLoaded()
+  {
+    return filtersLoaded;

[Wladimir Palant, 2015/03/20 16:38:20]

return FilterStorage._loading?

[Felix Dahlke, 2015/03/20 16:54:57]

What we want to know here is whether the filters have been loaded. How I see it,
_loading is false initially, true while filters are being loaded, then false
again. So we could return !FilterStorage._loading - assuming
FilterStorage.loadFromDisk is always called before this getter. Seems like
asking for trouble to me.

[Felix Dahlke, 2015/03/20 21:13:02]

Well actually, you're right. Api.jsm is not necessarily executed before
FilterStorage.loadFromDisk, so we're quite likely to miss "load" events in the
listener below... Compared to that, the risk of accessing filtersLoaded before
FilterStorage.loadFromDisk is first called seems negligible in comparison.

+  },
+  filterLoadListener: null,
   get acceptableAdsEnabled()
   {
     return FilterStorage.subscriptions.some(
@@ -49,3 +57,14 @@
       UI.toggleAcceptableAds();
   }
 };
+
+FilterNotifier.addListener(function(action)
+{
+  if (action != "load")
+    return;
+
+  filtersLoaded = true;

[Wladimir Palant, 2015/03/20 16:38:20]

This listener should be removed after the first call rather than staying in
memory and being called for each change.

[Felix Dahlke, 2015/03/20 16:54:57]

Done.

[Felix Dahlke, 2015/03/20 17:13:06]

Well, NOW it's done. Misunderstood you, unregistered the filter listener now.
I've reverted the part about setting filterLoadListener to null here. Don't have
a strong opinion on this, but it seems like something the client should do.

+  if ("filterLoadListener" in AdblockPlusApi &&
+      typeof AdblockPlusApi.filterLoadListener == "function")

[Wladimir Palant, 2015/03/20 16:38:20]

Using typeof is sufficient, "filterLoadListener" in AdblockPlusApi is mostly
equivalent to typeof AdblockPlusApi.filterLoadListener != "undefined".

[Felix Dahlke, 2015/03/20 16:54:57]

Ouch, getting rusty...

+    AdblockPlusApi.filterLoadListener();
+});