improved performance and battery usage on older devices

lib/state/app/modules/chat_list/bloc/chat_list_bloc.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:convert';
 import 'dart:developer';
 
 import 'package:flutter_app_badge/flutter_app_badge.dart';
@@ -6,6 +7,7 @@ import 'package:flutter_app_badge/flutter_app_badge.dart';
 import '../../../../../api/marianumcloud/talk/actions/talk_actions.dart';
 import '../../../../../api/marianumcloud/talk/chat/get_chat_response.dart';
 import '../../../../../api/marianumcloud/talk/room/get_room_response.dart';
+import '../../../../../utils/session_single_flight.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc_event.dart';
 import '../repository/chat_list_repository.dart';
@@ -74,13 +76,32 @@ class ChatListBloc
       renew: renew,
       onError: (e) => capturedError = e,
     );
+    _lastRoomsJson = null;
     add(DataGathered((s) => s.copyWith(rooms: rooms)));
     _updateAppBadge(rooms);
 
     if (capturedError != null) throw capturedError!;
   }
 
-  Future<void> refresh({bool renew = true, bool silent = false}) async {
+  final SessionSingleFlight _refreshFlight = SessionSingleFlight();
+
+  /// Concurrent callers (tab switch, poll, push, resume) join the running
+  /// refresh instead of each fetching and re-emitting the full room list.
+  Future<void> refresh({bool renew = true, bool silent = false}) =>
+      _refreshFlight.run(() => _refresh(renew: renew, silent: silent));
+
+  /// Skips the refresh when the list was fetched within [maxAge].
+  Future<void> refreshIfOlderThan(Duration maxAge) {
+    final lastFetch = state.lastFetch;
+    if (lastFetch != null &&
+        DateTime.now().millisecondsSinceEpoch - lastFetch <
+            maxAge.inMilliseconds) {
+      return Future.value();
+    }
+    return refresh();
+  }
+
+  Future<void> _refresh({required bool renew, required bool silent}) async {
     if (!silent) add(RefetchStarted<ChatListState>());
     Object? capturedError;
     try {
@@ -88,6 +109,11 @@ class ChatListBloc
         renew: renew,
         onError: (e) => capturedError = e,
       );
+      if (silent) {
+        if (_isUnchanged(rooms)) return;
+      } else {
+        _lastRoomsJson = null;
+      }
       add(DataGathered((s) => s.copyWith(rooms: rooms)));
       _updateAppBadge(rooms);
     } catch (e) {
@@ -96,6 +122,23 @@ class ChatListBloc
     if (capturedError != null) addLoadingError(capturedError!);
   }
 
+  // Encoded room data of the last applied poll result; response headers are
+  // left out because they differ on every request.
+  String? _lastRoomsJson;
+
+  /// A background poll that returns the same rooms would otherwise rebuild the
+  /// list and re-persist the whole state every 15 s.
+  bool _isUnchanged(GetRoomResponse rooms) {
+    final encoded = jsonEncode(rooms.data);
+    final unchanged =
+        encoded == _lastRoomsJson &&
+        innerState?.rooms != null &&
+        state.error == null &&
+        !state.isLoading;
+    _lastRoomsJson = encoded;
+    return unchanged;
+  }
+
   /// Creates (or resolves) a 1:1 chat and returns its room token, or null in
   /// demo mode. Refreshes the list so the room shows up.
   Future<String?> createDirectChat(String invite) async {
@@ -171,6 +214,7 @@ class ChatListBloc
     }).toSet();
     if (!changed) return;
     final newRooms = GetRoomResponse(updated)..headers = rooms.headers;
+    _lastRoomsJson = null;
     add(Emit((s) => s.copyWith(rooms: newRooms)));
     _updateAppBadge(newRooms);
   }