refactor: Implement on history received in timeline

In order to make delta updates
for GUIs displaying the
timeline events easier, the
onHistoryReceived callback
has been introduced.

lib/src/room.dart

@@ -983,7 +983,8 @@ class Room {
   /// Request more previous events from the server. [historyCount] defines how much events should
   /// be received maximum. When the request is answered, [onHistoryReceived] will be triggered **before**
   /// the historical events will be published in the onEvent stream.
-  Future<void> requestHistory(
+  /// Returns the actual count of received timeline events.
+  Future<int> requestHistory(
       {int historyCount = defaultHistoryCount,
       void Function()? onHistoryReceived}) async {
     final prev_batch = this.prev_batch;
@@ -1044,6 +1045,8 @@ class Room {
     } else {
       await loadFn();
     }
+
+    return resp.chunk?.length ?? 0;
   }
 
   /// Sets this room as a direct chat for this user if not already.
@@ -1131,12 +1134,13 @@ class Room {
   /// Creates a timeline from the store. Returns a [Timeline] object. If you
   /// just want to update the whole timeline on every change, use the [onUpdate]
   /// callback. For updating only the parts that have changed, use the
-  /// [onChange], [onRemove] and the [onInsert] callbacks.
+  /// [onChange], [onRemove], [onInsert] and the [onHistoryReceived] callbacks.
   Future<Timeline> getTimeline({
     void Function(int index)? onChange,
     void Function(int index)? onRemove,
     void Function(int insertID)? onInsert,
     void Function()? onUpdate,
+    void Function(int count)? onHistoryReceived,
   }) async {
     await postLoad();
     var events;
@@ -1166,6 +1170,7 @@ class Room {
       onRemove: onRemove,
       onInsert: onInsert,
       onUpdate: onUpdate,
+      onHistoryReceived: onHistoryReceived,
     );
     if (client.database == null) {
       await requestHistory(historyCount: 10);

lib/src/timeline.dart

@@ -36,6 +36,7 @@ class Timeline {
   final void Function(int index)? onChange;
   final void Function(int index)? onInsert;
   final void Function(int index)? onRemove;
+  final void Function(int count)? onHistoryReceived;
 
   StreamSubscription<EventUpdate>? sub;
   StreamSubscription<SyncUpdate>? roomSub;
@@ -86,19 +87,16 @@ class Timeline {
       );
       if (eventsFromStore != null && eventsFromStore.isNotEmpty) {
         events.addAll(eventsFromStore);
-        final startIndex = events.length - eventsFromStore.length;
+        onHistoryReceived?.call(eventsFromStore.length);
-        final endIndex = events.length;
-        for (var i = startIndex; i < endIndex; i++) {
-          onInsert?.call(i);
-        }
       } else {
         Logs().v('No more events found in the store. Request from server...');
-        await room.requestHistory(
+        final count = await room.requestHistory(
           historyCount: historyCount,
           onHistoryReceived: () {
             _collectHistoryUpdates = true;
           },
         );
+        onHistoryReceived?.call(count);
       }
     } finally {
       _collectHistoryUpdates = false;
@@ -114,6 +112,7 @@ class Timeline {
     this.onChange,
     this.onInsert,
     this.onRemove,
+    this.onHistoryReceived,
   }) : events = events ?? [] {
     sub = room.client.onEvent.stream.listen(_handleEventUpdate);
 
@@ -331,11 +330,10 @@ class Timeline {
           } else {
             index = events.firstIndexWhereNotError;
             events.insert(index, newEvent);
+            onInsert?.call(index);
           }
 
           addAggregatedEvent(newEvent);
-
-          onInsert?.call(index);
         }
       }
       if (update && !_collectHistoryUpdates) {