fix: timeline pagination

lib/controllers/room_chat.dart

@@ -17,27 +17,30 @@ import "package:nexus/models/room.dart";
 
 class RoomChatController extends AsyncNotifier<IList<Event>?> {
   final String roomId;
+  Future<bool>? _loadingOlder;
   RoomChatController(this.roomId);
 
   @override
   Future<IList<Event>?> build() async {
     final client = ref.watch(ClientController.provider.notifier);
-    final room = ref.watch(
+    final initialRoom = ref.watch(
       RoomsController.provider.select((rooms) => rooms[roomId]),
     );
 
-    if (room == null) return null;
+    if (initialRoom == null) return null;
+    Room room = initialRoom;
 
     if (!room.hasFetchedState) {
       final state = await client.getRoomState(.new(roomId: roomId));
 
       await ref.read(RoomsController.provider.notifier).addState(roomId, state);
+      room = ref.read(RoomsController.provider)[roomId] ?? room;
     }
 
-    // While there are under 20 events, try to load more
-    // until there's no more or the conditions are met.
+    // Load one more page when the initial timeline is short.
     if (room.hasMore && room.timeline.length < 20) {
-      loadOlder();
+      await loadOlder();
+      room = ref.read(RoomsController.provider)[roomId] ?? room;
     }
 
     return room.timeline
@@ -74,18 +77,22 @@ class RoomChatController extends AsyncNotifier<IList<Event>?> {
         ),
       );
 
-  Future<bool> loadOlder() async {
-    final timelineKeys = ref
-        .read(RoomsController.provider.select((value) => value[roomId]))
-        ?.timeline
-        .keys;
+  Future<bool> loadOlder() => _loadingOlder ??= _loadOlder().whenComplete(() {
+    _loadingOlder = null;
+  });
+
+  Future<bool> _loadOlder() async {
+    final room = ref.read(RoomsController.provider)[roomId];
+    if (room == null || !room.hasMore) return false;
+
+    final timelineKeys = room.timeline.keys;
     final response = await ref
         .watch(ClientController.provider.notifier)
         .paginate(
           .new(
             roomId: roomId,
-            maxTimelineId: timelineKeys?.isNotEmpty == true
-                ? timelineKeys?.reduce(min)
+            maxTimelineId: timelineKeys.isNotEmpty
+                ? timelineKeys.reduce(min)
                 : null,
           ),
         );