Fix app initialization race when issuing annotation search query

If the initial annotation search query was constructed
before the user's session state had been retrieved,
the groups list was empty and groups.focused() returned null
in WidgetController._loadAnnotationsFrom

This commit resolves the issue by adding a 'groups.ready()'
function which returns a promise once the groups list is ready.

It currently just returns the session.load().$promise.

Fixes #2590

h/static/scripts/groups.js

@@ -31,7 +31,15 @@ function groups(localStorage, session, $rootScope, features) {
     }
   };
 
+  /** Returns a promise which resolves once the list of groups
+   * has been loaded.
+   */
+  function ready() {
+    return session.load().$promise;
+  }
+
   return {
+    ready: ready,
     all: all,
     get: get,
 

h/static/scripts/test/widget-controller-test.coffee

@@ -1,5 +1,7 @@
 {module, inject} = angular.mock
 
+Promise = require('core-js/library/es6/promise')
+
 describe 'WidgetController', ->
   $scope = null
   fakeAnnotationMapper = null
@@ -60,7 +62,8 @@ describe 'WidgetController', ->
     }
 
     fakeGroups = {
-      focused: -> {id: 'foo'}
+      focused: -> {id: 'foo'},
+      ready: -> Promise.resolve(),
     }
 
     $provide.value 'annotationMapper', fakeAnnotationMapper
@@ -92,3 +95,16 @@ describe 'WidgetController', ->
       assert.calledWith(loadSpy, [40..59])
       assert.calledWith(loadSpy, [60..79])
       assert.calledWith(loadSpy, [80..99])
+
+    it.only 'should defer loading annotations until groups service is ready', ->
+      ready = null
+      groupsReady = new Promise((resolve) -> ready = resolve)
+      fakeGroups.ready = -> groupsReady
+
+      fakeCrossFrame.frames.push({uri: 'http://example.com'})
+      $scope.$digest()
+      assert.callCount(fakeAnnotationMapper.loadAnnotations, 0)
+      ready()
+      groupsReady.then(->
+        assert.callCount(fakeAnnotationMapper.loadAnnotations, 1)
+      )

h/static/scripts/widget-controller.coffee

@@ -17,21 +17,25 @@ module.exports = class WidgetController
     loaded = []
 
     _loadAnnotationsFrom = (query, offset) =>
-      queryCore =
-        limit: @chunkSize
-        offset: offset
-        sort: 'created'
-        order: 'asc'
-        group: groups.focused().id
-      q = angular.extend(queryCore, query)
-
-      store.SearchResource.get q, (results) ->
-        total = results.total
-        offset += results.rows.length
-        if offset < total
-          _loadAnnotationsFrom query, offset
-
-        annotationMapper.loadAnnotations(results.rows)
+      groups.ready().then( ->
+        queryCore =
+          limit: @chunkSize
+          offset: offset
+          sort: 'created'
+          order: 'asc'
+          group: groups.focused().id
+        q = angular.extend(queryCore, query)
+
+        store.SearchResource.get q, (results) ->
+          total = results.total
+          offset += results.rows.length
+          if offset < total
+            _loadAnnotationsFrom query, offset
+
+          annotationMapper.loadAnnotations(results.rows)
+      ).catch((e) ->
+        throw e
+      )
 
     loadAnnotations = (frames) ->
       for f in frames