autocomplete: Use topic data from store in topic autocomplete

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -6,7 +6,6 @@ import 'package:unorm_dart/unorm_dart.dart' as unorm;
 
 import '../api/model/events.dart';
 import '../api/model/model.dart';
-import '../api/route/channels.dart';
 import '../generated/l10n/zulip_localizations.dart';
 import '../widgets/compose_box.dart';
 import 'algorithms.dart';
@@ -1175,10 +1174,8 @@ class TopicAutocompleteView extends AutocompleteView<TopicAutocompleteQuery, Top
   Future<void> _fetch() async {
      assert(!_isFetching);
     _isFetching = true;
-    final result = await getStreamTopics(store.connection, streamId: streamId,
-      allowEmptyTopicName: true,
-    );
-    _topics = result.topics.map((e) => e.name);
+    await store.fetchTopics(streamId);
+    _topics = store.getChannelTopics(streamId)!.map((e) => e.name);
     _isFetching = false;
     return _startSearch();
   }

test/model/autocomplete_test.dart

@@ -1277,19 +1277,28 @@ void main() {
     check(done).isTrue();
   });
 
-  test('TopicAutocompleteView getStreamTopics request', () async {
+  test('TopicAutocompleteView fetch topics once for a channel', () async {
     final store = eg.store();
     final connection = store.connection as FakeApiConnection;
 
     connection.prepare(json: GetStreamTopicsResult(
-      topics: [eg.getStreamTopicsEntry(name: '')],
+      topics: [eg.getStreamTopicsEntry(name: 'topic')],
     ).toJson());
-    TopicAutocompleteView.init(store: store, streamId: 1000,
-      query: TopicAutocompleteQuery('foo'));
-    check(connection.lastRequest).isA<http.Request>()
+    final view = TopicAutocompleteView.init(store: store, streamId: 1000,
+      query: TopicAutocompleteQuery(''));
+    check(connection.takeRequests()).last.isA<http.Request>()
       ..method.equals('GET')
       ..url.path.equals('/api/v1/users/me/1000/topics')
       ..url.queryParameters['allow_empty_topic_name'].equals('true');
+    await Future(() {});
+
+    view.query = TopicAutocompleteQuery('top');
+    check(connection.takeRequests()).isEmpty();
+    view.dispose();
+
+    TopicAutocompleteView.init(store: store, streamId: 1000,
+      query: TopicAutocompleteQuery('topic'));
+    check(connection.takeRequests()).isEmpty();
   });
 
   group('TopicAutocompleteQuery.testTopic', () {