implemented backward pagination for chat history with on-scroll prefetching

lib/api/marianumcloud/talk/chat/get_chat_cache.dart

@@ -16,7 +16,10 @@ class GetChatCache extends SimpleCache<GetChatResponse> {
            GetChatParams(
              lookIntoFuture: GetChatParamsSwitch.off,
              setReadMarker: GetChatParamsSwitch.on,
-             limit: 200,
+             // Small initial page; also the per-chat offline snapshot written to
+             // localstore. Older messages are paged in on scroll-up via
+             // GetChatHistory. Keep in sync with ChatBloc's _kInitialPageSize.
+             limit: 50,
            ),
          ).run(),
          fromJson: GetChatResponse.fromJson,

lib/api/marianumcloud/talk/chat/get_chat_history.dart

@@ -0,0 +1,56 @@
+import 'package:http/http.dart' as http;
+
+import '../../../errors/server_exception.dart';
+import '../../../http_errors.dart';
+import '../../nextcloud_ocs.dart';
+import 'get_chat_params.dart';
+import 'get_chat_response.dart';
+
+/// Backwards-paging variant of GetChat (`lookIntoFuture=0` + `lastKnownMessageId`)
+/// that fetches the page of messages *older* than a given id. Bypasses [TalkApi]
+/// because that layer treats non-2xx as errors, and the server answers HTTP 304
+/// when there are no older messages left — a normal "start of chat" outcome here.
+/// `setReadMarker=off` so paging into history never moves the read cursor.
+class GetChatHistory {
+  final String chatToken;
+  final int lastKnownMessageId;
+  final int limit;
+
+  GetChatHistory({
+    required this.chatToken,
+    required this.lastKnownMessageId,
+    required this.limit,
+  });
+
+  /// Returns the older page, or `null` on HTTP 304 (no older messages).
+  Future<GetChatResponse?> run() async {
+    final params = GetChatParams(
+      lookIntoFuture: GetChatParamsSwitch.off,
+      lastKnownMessageId: lastKnownMessageId,
+      includeLastKnown: GetChatParamsSwitch.off,
+      setReadMarker: GetChatParamsSwitch.off,
+      limit: limit,
+    );
+    final uri = NextcloudOcs.uri(
+      'apps/spreed/api/v1/chat/$chatToken',
+      queryParameters: params.toJson(),
+    );
+    final headers = NextcloudOcs.headers();
+
+    final response = (await sendGuarded(
+      'GetChatHistory $uri',
+      () => http.get(uri, headers: headers),
+    ))!;
+
+    final status = response.statusCode;
+    if (status == 304) return null;
+    if (status >= 200 && status < 300) {
+      return GetChatResponse.fromJson(NextcloudOcs.decode(response.body))
+        ..headers = response.headers;
+    }
+    throw ServerException(
+      statusCode: status,
+      technicalDetails: 'GetChatHistory $uri: HTTP $status',
+    );
+  }
+}

lib/state/app/modules/chat/bloc/chat_bloc.dart

@@ -4,6 +4,7 @@ import 'dart:math' as math;
 
 import 'package:flutter/widgets.dart';
 
+import '../../../../../api/marianumcloud/talk/chat/get_chat_history.dart';
 import '../../../../../api/marianumcloud/talk/chat/get_chat_response.dart';
 import '../../../../../api/marianumcloud/talk/chat/long_poll_chat.dart';
 import '../../../../../api/marianumcloud/talk/room/get_room_response.dart';
@@ -56,7 +57,22 @@ class ChatBloc
   ChatState fromStorage(Map<String, dynamic> json) => ChatState.fromJson(json);
 
   @override
-  Map<String, dynamic>? toStorage(ChatState state) => state.toJson();
+  Map<String, dynamic>? toStorage(ChatState state) {
+    final response = state.chatResponse;
+    if (response == null ||
+        response.data.length <= _kMaxPersistedMessages) {
+      return state.toJson();
+    }
+    // Keep only the newest N; trimming drops older messages, so there is
+    // definitely more history to page back in after a restart.
+    final newest = response
+        .sortByTimestamp()
+        .reversed
+        .take(_kMaxPersistedMessages)
+        .toSet();
+    final trimmed = GetChatResponse(newest)..headers = response.headers;
+    return state.copyWith(chatResponse: trimmed, hasMoreOld: true).toJson();
+  }
 
   @override
   Future<void> gatherData() async {
@@ -75,7 +91,16 @@ class ChatBloc
       return;
     }
     _stopLongPoll();
-    add(Emit((s) => s.copyWith(currentToken: token, chatResponse: null)));
+    add(
+      Emit(
+        (s) => s.copyWith(
+          currentToken: token,
+          chatResponse: null,
+          hasMoreOld: true,
+          isLoadingOlder: false,
+        ),
+      ),
+    );
     add(RefetchStarted<ChatState>());
     _scheduleLoad(token);
   }
@@ -100,6 +125,40 @@ class ChatBloc
     _stopLongPoll();
   }
 
+  /// Pages in the next block of messages older than the oldest currently held.
+  /// No-ops when nothing more can be loaded or a load is already in flight.
+  Future<void> loadOlder() async {
+    final state = innerState;
+    if (state == null) return;
+    final token = state.currentToken;
+    if (token.isEmpty) return;
+    if (state.isLoadingOlder || !state.hasMoreOld) return;
+    final response = state.chatResponse;
+    if (response == null) return;
+    final oldestId = _minMessageId(response);
+    if (oldestId <= 0) return;
+
+    add(Emit((s) => s.copyWith(isLoadingOlder: true)));
+    try {
+      final older = await GetChatHistory(
+        chatToken: token,
+        lastKnownMessageId: oldestId,
+        limit: _kOlderPageSize,
+      ).run();
+      if (isClosed) return;
+      if ((innerState?.currentToken ?? '') != token) return;
+      if (older == null || older.data.isEmpty) {
+        add(Emit((s) => s.copyWith(hasMoreOld: false, isLoadingOlder: false)));
+        return;
+      }
+      _applyOlderResponse(older);
+    } on Object catch (e) {
+      log('Load older messages for $token failed: $e');
+      if (isClosed) return;
+      add(Emit((s) => s.copyWith(isLoadingOlder: false)));
+    }
+  }
+
   Future<void> sendServerReadMarker(String token, int messageId) async {
     try {
       await SetReadMarker(
@@ -245,7 +304,15 @@ class ChatBloc
   void _applyChatResponse(GetChatResponse incoming) {
     final current = innerState?.chatResponse;
     if (current == null) {
-      add(DataGathered((s) => s.copyWith(chatResponse: incoming)));
+      // Initial load: a short first page means there is nothing older to page in.
+      add(
+        DataGathered(
+          (s) => s.copyWith(
+            chatResponse: incoming,
+            hasMoreOld: incoming.data.length >= _kInitialPageSize,
+          ),
+        ),
+      );
       return;
     }
     final byId = <int, GetChatResponseObject>{};
@@ -260,6 +327,32 @@ class ChatBloc
     add(DataGathered((s) => s.copyWith(chatResponse: merged)));
   }
 
+  /// Merges an older history page. Unlike [_applyChatResponse] it keeps the
+  /// current headers — the older page's `x-chat-last-common-read` would regress
+  /// the read-status shown for already-visible messages.
+  void _applyOlderResponse(GetChatResponse older) {
+    final current = innerState?.chatResponse;
+    if (current == null) return;
+    final byId = <int, GetChatResponseObject>{};
+    for (final m in current.data) {
+      byId[m.id] = m;
+    }
+    for (final m in older.data) {
+      byId.putIfAbsent(m.id, () => m);
+    }
+    final merged = GetChatResponse(byId.values.toSet())
+      ..headers = current.headers;
+    add(
+      DataGathered(
+        (s) => s.copyWith(
+          chatResponse: merged,
+          hasMoreOld: older.data.length >= _kOlderPageSize,
+          isLoadingOlder: false,
+        ),
+      ),
+    );
+  }
+
   int _maxMessageId(GetChatResponse? response) {
     if (response == null) return 0;
     var max = 0;
@@ -269,6 +362,16 @@ class ChatBloc
     return max;
   }
 
+  int _minMessageId(GetChatResponse? response) {
+    if (response == null) return 0;
+    var min = 0;
+    for (final m in response.data) {
+      if (m.id <= 0) continue; // skip dummies
+      if (min == 0 || m.id < min) min = m.id;
+    }
+    return min;
+  }
+
   /// Mirrors the server's own `lastMessage` selection (comments + voice only).
   GetChatResponseObject? _pickDisplayMessage(GetChatResponse response) {
     GetChatResponseObject? best;
@@ -288,3 +391,16 @@ class ChatBloc
 }
 
 const _kLongPollLastGivenHeader = 'x-chat-last-given';
+
+/// Small first page shown on open (keeps the initial request cheap). Must match
+/// the `limit` in GetChatCache (get_chat_cache.dart).
+const _kInitialPageSize = 50;
+
+/// Upper bound on how many messages are persisted via HydratedBloc. The full
+/// scrolled history stays in memory at runtime; only the newest this-many
+/// survive a restart (older ones are re-fetchable via scroll-up).
+const _kMaxPersistedMessages = 500;
+
+/// Larger block fetched per scroll-up so paging back through history needs
+/// fewer round trips.
+const _kOlderPageSize = 200;

lib/state/app/modules/chat/bloc/chat_state.dart

@@ -11,6 +11,8 @@ abstract class ChatState with _$ChatState {
     @Default('') String currentToken,
     GetChatResponse? chatResponse,
     int? referenceMessageId,
+    @Default(true) bool hasMoreOld,
+    @Default(false) bool isLoadingOlder,
   }) = _ChatState;
 
   factory ChatState.fromJson(Map<String, Object?> json) =>

lib/state/app/modules/chat/bloc/chat_state.freezed.dart

@@ -15,7 +15,7 @@ T _$identity<T>(T value) => value;
 /// @nodoc
 mixin _$ChatState {
 
- String get currentToken; GetChatResponse? get chatResponse; int? get referenceMessageId;
+ String get currentToken; GetChatResponse? get chatResponse; int? get referenceMessageId; bool get hasMoreOld; bool get isLoadingOlder;
 /// Create a copy of ChatState
 /// with the given fields replaced by the non-null parameter values.
 @JsonKey(includeFromJson: false, includeToJson: false)
@@ -28,16 +28,16 @@ $ChatStateCopyWith<ChatState> get copyWith => _$ChatStateCopyWithImpl<ChatState>
 
 @override
 bool operator ==(Object other) {
-  return identical(this, other) || (other.runtimeType == runtimeType&&other is ChatState&&(identical(other.currentToken, currentToken) || other.currentToken == currentToken)&&(identical(other.chatResponse, chatResponse) || other.chatResponse == chatResponse)&&(identical(other.referenceMessageId, referenceMessageId) || other.referenceMessageId == referenceMessageId));
+  return identical(this, other) || (other.runtimeType == runtimeType&&other is ChatState&&(identical(other.currentToken, currentToken) || other.currentToken == currentToken)&&(identical(other.chatResponse, chatResponse) || other.chatResponse == chatResponse)&&(identical(other.referenceMessageId, referenceMessageId) || other.referenceMessageId == referenceMessageId)&&(identical(other.hasMoreOld, hasMoreOld) || other.hasMoreOld == hasMoreOld)&&(identical(other.isLoadingOlder, isLoadingOlder) || other.isLoadingOlder == isLoadingOlder));
 }
 
 @JsonKey(includeFromJson: false, includeToJson: false)
 @override
-int get hashCode => Object.hash(runtimeType,currentToken,chatResponse,referenceMessageId);
+int get hashCode => Object.hash(runtimeType,currentToken,chatResponse,referenceMessageId,hasMoreOld,isLoadingOlder);
 
 @override
 String toString() {
-  return 'ChatState(currentToken: $currentToken, chatResponse: $chatResponse, referenceMessageId: $referenceMessageId)';
+  return 'ChatState(currentToken: $currentToken, chatResponse: $chatResponse, referenceMessageId: $referenceMessageId, hasMoreOld: $hasMoreOld, isLoadingOlder: $isLoadingOlder)';
 }
 
 
@@ -48,7 +48,7 @@ abstract mixin class $ChatStateCopyWith<$Res>  {
   factory $ChatStateCopyWith(ChatState value, $Res Function(ChatState) _then) = _$ChatStateCopyWithImpl;
 @useResult
 $Res call({
- String currentToken, GetChatResponse? chatResponse, int? referenceMessageId
+ String currentToken, GetChatResponse? chatResponse, int? referenceMessageId, bool hasMoreOld, bool isLoadingOlder
 });
 
 
@@ -65,12 +65,14 @@ class _$ChatStateCopyWithImpl<$Res>
 
 /// Create a copy of ChatState
 /// with the given fields replaced by the non-null parameter values.
-@pragma('vm:prefer-inline') @override $Res call({Object? currentToken = null,Object? chatResponse = freezed,Object? referenceMessageId = freezed,}) {
+@pragma('vm:prefer-inline') @override $Res call({Object? currentToken = null,Object? chatResponse = freezed,Object? referenceMessageId = freezed,Object? hasMoreOld = null,Object? isLoadingOlder = null,}) {
   return _then(_self.copyWith(
 currentToken: null == currentToken ? _self.currentToken : currentToken // ignore: cast_nullable_to_non_nullable
 as String,chatResponse: freezed == chatResponse ? _self.chatResponse : chatResponse // ignore: cast_nullable_to_non_nullable
 as GetChatResponse?,referenceMessageId: freezed == referenceMessageId ? _self.referenceMessageId : referenceMessageId // ignore: cast_nullable_to_non_nullable
-as int?,
+as int?,hasMoreOld: null == hasMoreOld ? _self.hasMoreOld : hasMoreOld // ignore: cast_nullable_to_non_nullable
+as bool,isLoadingOlder: null == isLoadingOlder ? _self.isLoadingOlder : isLoadingOlder // ignore: cast_nullable_to_non_nullable
+as bool,
   ));
 }
 
@@ -155,10 +157,10 @@ return $default(_that);case _:
 /// }
 /// ```
 
-@optionalTypeArgs TResult maybeWhen<TResult extends Object?>(TResult Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId)?  $default,{required TResult orElse(),}) {final _that = this;
+@optionalTypeArgs TResult maybeWhen<TResult extends Object?>(TResult Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId,  bool hasMoreOld,  bool isLoadingOlder)?  $default,{required TResult orElse(),}) {final _that = this;
 switch (_that) {
 case _ChatState() when $default != null:
-return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);case _:
+return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId,_that.hasMoreOld,_that.isLoadingOlder);case _:
   return orElse();
 
 }
@@ -176,10 +178,10 @@ return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);
 /// }
 /// ```
 
-@optionalTypeArgs TResult when<TResult extends Object?>(TResult Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId)  $default,) {final _that = this;
+@optionalTypeArgs TResult when<TResult extends Object?>(TResult Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId,  bool hasMoreOld,  bool isLoadingOlder)  $default,) {final _that = this;
 switch (_that) {
 case _ChatState():
-return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);case _:
+return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId,_that.hasMoreOld,_that.isLoadingOlder);case _:
   throw StateError('Unexpected subclass');
 
 }
@@ -196,10 +198,10 @@ return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);
 /// }
 /// ```
 
-@optionalTypeArgs TResult? whenOrNull<TResult extends Object?>(TResult? Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId)?  $default,) {final _that = this;
+@optionalTypeArgs TResult? whenOrNull<TResult extends Object?>(TResult? Function( String currentToken,  GetChatResponse? chatResponse,  int? referenceMessageId,  bool hasMoreOld,  bool isLoadingOlder)?  $default,) {final _that = this;
 switch (_that) {
 case _ChatState() when $default != null:
-return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);case _:
+return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId,_that.hasMoreOld,_that.isLoadingOlder);case _:
   return null;
 
 }
@@ -211,12 +213,14 @@ return $default(_that.currentToken,_that.chatResponse,_that.referenceMessageId);
 @JsonSerializable()
 
 class _ChatState implements ChatState {
-  const _ChatState({this.currentToken = '', this.chatResponse, this.referenceMessageId});
+  const _ChatState({this.currentToken = '', this.chatResponse, this.referenceMessageId, this.hasMoreOld = true, this.isLoadingOlder = false});
   factory _ChatState.fromJson(Map<String, dynamic> json) => _$ChatStateFromJson(json);
 
 @override@JsonKey() final  String currentToken;
 @override final  GetChatResponse? chatResponse;
 @override final  int? referenceMessageId;
+@override@JsonKey() final  bool hasMoreOld;
+@override@JsonKey() final  bool isLoadingOlder;
 
 /// Create a copy of ChatState
 /// with the given fields replaced by the non-null parameter values.
@@ -231,16 +235,16 @@ Map<String, dynamic> toJson() {
 
 @override
 bool operator ==(Object other) {
-  return identical(this, other) || (other.runtimeType == runtimeType&&other is _ChatState&&(identical(other.currentToken, currentToken) || other.currentToken == currentToken)&&(identical(other.chatResponse, chatResponse) || other.chatResponse == chatResponse)&&(identical(other.referenceMessageId, referenceMessageId) || other.referenceMessageId == referenceMessageId));
+  return identical(this, other) || (other.runtimeType == runtimeType&&other is _ChatState&&(identical(other.currentToken, currentToken) || other.currentToken == currentToken)&&(identical(other.chatResponse, chatResponse) || other.chatResponse == chatResponse)&&(identical(other.referenceMessageId, referenceMessageId) || other.referenceMessageId == referenceMessageId)&&(identical(other.hasMoreOld, hasMoreOld) || other.hasMoreOld == hasMoreOld)&&(identical(other.isLoadingOlder, isLoadingOlder) || other.isLoadingOlder == isLoadingOlder));
 }
 
 @JsonKey(includeFromJson: false, includeToJson: false)
 @override
-int get hashCode => Object.hash(runtimeType,currentToken,chatResponse,referenceMessageId);
+int get hashCode => Object.hash(runtimeType,currentToken,chatResponse,referenceMessageId,hasMoreOld,isLoadingOlder);
 
 @override
 String toString() {
-  return 'ChatState(currentToken: $currentToken, chatResponse: $chatResponse, referenceMessageId: $referenceMessageId)';
+  return 'ChatState(currentToken: $currentToken, chatResponse: $chatResponse, referenceMessageId: $referenceMessageId, hasMoreOld: $hasMoreOld, isLoadingOlder: $isLoadingOlder)';
 }
 
 
@@ -251,7 +255,7 @@ abstract mixin class _$ChatStateCopyWith<$Res> implements $ChatStateCopyWith<$Re
   factory _$ChatStateCopyWith(_ChatState value, $Res Function(_ChatState) _then) = __$ChatStateCopyWithImpl;
 @override @useResult
 $Res call({
- String currentToken, GetChatResponse? chatResponse, int? referenceMessageId
+ String currentToken, GetChatResponse? chatResponse, int? referenceMessageId, bool hasMoreOld, bool isLoadingOlder
 });
 
 
@@ -268,12 +272,14 @@ class __$ChatStateCopyWithImpl<$Res>
 
 /// Create a copy of ChatState
 /// with the given fields replaced by the non-null parameter values.
-@override @pragma('vm:prefer-inline') $Res call({Object? currentToken = null,Object? chatResponse = freezed,Object? referenceMessageId = freezed,}) {
+@override @pragma('vm:prefer-inline') $Res call({Object? currentToken = null,Object? chatResponse = freezed,Object? referenceMessageId = freezed,Object? hasMoreOld = null,Object? isLoadingOlder = null,}) {
   return _then(_ChatState(
 currentToken: null == currentToken ? _self.currentToken : currentToken // ignore: cast_nullable_to_non_nullable
 as String,chatResponse: freezed == chatResponse ? _self.chatResponse : chatResponse // ignore: cast_nullable_to_non_nullable
 as GetChatResponse?,referenceMessageId: freezed == referenceMessageId ? _self.referenceMessageId : referenceMessageId // ignore: cast_nullable_to_non_nullable
-as int?,
+as int?,hasMoreOld: null == hasMoreOld ? _self.hasMoreOld : hasMoreOld // ignore: cast_nullable_to_non_nullable
+as bool,isLoadingOlder: null == isLoadingOlder ? _self.isLoadingOlder : isLoadingOlder // ignore: cast_nullable_to_non_nullable
+as bool,
   ));
 }
 

lib/state/app/modules/chat/bloc/chat_state.g.dart

@@ -12,6 +12,8 @@ _ChatState _$ChatStateFromJson(Map<String, dynamic> json) => _ChatState(
       ? null
       : GetChatResponse.fromJson(json['chatResponse'] as Map<String, dynamic>),
   referenceMessageId: (json['referenceMessageId'] as num?)?.toInt(),
+  hasMoreOld: json['hasMoreOld'] as bool? ?? true,
+  isLoadingOlder: json['isLoadingOlder'] as bool? ?? false,
 );
 
 Map<String, dynamic> _$ChatStateToJson(_ChatState instance) =>
@@ -19,4 +21,6 @@ Map<String, dynamic> _$ChatStateToJson(_ChatState instance) =>
       'currentToken': instance.currentToken,
       'chatResponse': instance.chatResponse,
       'referenceMessageId': instance.referenceMessageId,
+      'hasMoreOld': instance.hasMoreOld,
+      'isLoadingOlder': instance.isLoadingOlder,
     };

lib/view/pages/talk/chat_view.dart

@@ -42,9 +42,15 @@ class ChatView extends StatefulWidget {
 
 class _ChatViewState extends State<ChatView> with RouteAware {
   final ItemScrollController _itemScrollController = ItemScrollController();
+  final ItemPositionsListener _positionsListener =
+      ItemPositionsListener.create();
   final TextEditingController _searchTextController = TextEditingController();
   final Map<int, int> _matchIndices = {};
 
+  // Number of rows currently rendered; kept in sync in build so the scroll
+  // listener can tell when the oldest row (highest index, reverse list) nears.
+  int _itemCount = 0;
+
   bool _searchActive = false;
   String _searchQuery = '';
   List<ChatSearchMatch> _matches = const [];
@@ -63,9 +69,24 @@ class _ChatViewState extends State<ChatView> with RouteAware {
     super.initState();
     _chatBlocRef = context.read<ChatBloc>();
     _chatListBlocRef = context.read<ChatListBloc>();
+    _positionsListener.itemPositions.addListener(_onScrollPositions);
     NotificationTasks.clearNotificationsForChat(widget.room.token);
   }
 
+  /// Loads the next older block once the top of the list comes into view.
+  void _onScrollPositions() {
+    final positions = _positionsListener.itemPositions.value;
+    if (positions.isEmpty) return;
+    // reverse:true → the highest index is the oldest message (top of screen).
+    // Prefetch ~a screenful ahead so the next block is usually already merged
+    // before the user reaches the top — the load stays invisible.
+    final maxIndex = positions.map((p) => p.index).reduce(math.max);
+    if (maxIndex < _itemCount - _kLoadOlderPrefetchRows) return;
+    final data = _chatBlocRef?.state.data;
+    if (data == null || !data.hasMoreOld || data.isLoadingOlder) return;
+    _chatBlocRef?.loadOlder();
+  }
+
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
@@ -93,6 +114,7 @@ class _ChatViewState extends State<ChatView> with RouteAware {
     if (_subscribedRoute != null) {
       AppRoutes.chatRouteObserver.unsubscribe(this);
     }
+    _positionsListener.itemPositions.removeListener(_onScrollPositions);
     _markAsReadFinal();
     _chatBlocRef?.leaveChat(widget.room.token);
     _searchTextController.dispose();
@@ -281,22 +303,6 @@ class _ChatViewState extends State<ChatView> with RouteAware {
       );
     }
 
-    if (response.data.length >= 200) {
-      messages.insert(
-        0,
-        ChatBubble(
-          isSender: false,
-          bubbleData: GetChatResponseObject.getTextDummy(
-            'Zurzeit können in dieser App nur die letzten 200 vergangenen Nachrichten angezeigt werden. '
-            'Um ältere Nachrichten abzurufen verwende die Webversion unter https://cloud.marianum-fulda.de',
-          ),
-          chatData: widget.room,
-          refetch: ({bool renew = false}) => _refresh(),
-        ),
-      );
-      chronologicalMatchIndex.updateAll((_, v) => v + 1);
-    }
-
     final total = messages.length;
     _matchIndices
       ..clear()
@@ -373,9 +379,27 @@ class _ChatViewState extends State<ChatView> with RouteAware {
                     final items = _buildMessages(
                       state.chatResponse!,
                     ).reversed.toList();
+                    // reverse:true renders index 0 at the bottom, so the top
+                    // marker (spinner / start-of-chat) goes at the end.
+                    if (state.isLoadingOlder) {
+                      items.add(const _LoadingOlderIndicator());
+                    } else if (!state.hasMoreOld) {
+                      items.add(
+                        ChatBubble(
+                          isSender: false,
+                          bubbleData: GetChatResponseObject.getTextDummy(
+                            'Anfang des Chats',
+                          ),
+                          chatData: widget.room,
+                          refetch: ({bool renew = false}) => _refresh(),
+                        ),
+                      );
+                    }
+                    _itemCount = items.length;
                     return ScrollablePositionedList.builder(
                       reverse: true,
                       itemScrollController: _itemScrollController,
+                      itemPositionsListener: _positionsListener,
                       itemCount: items.length,
                       itemBuilder: (ctx, idx) => items[idx],
                     );
@@ -405,3 +429,22 @@ class _ChatViewState extends State<ChatView> with RouteAware {
     );
   }
 }
+
+/// How many rows before the oldest one the older-history prefetch kicks in.
+const _kLoadOlderPrefetchRows = 15;
+
+class _LoadingOlderIndicator extends StatelessWidget {
+  const _LoadingOlderIndicator();
+
+  @override
+  Widget build(BuildContext context) => const Padding(
+    padding: EdgeInsets.symmetric(vertical: 12),
+    child: Center(
+      child: SizedBox(
+        width: 22,
+        height: 22,
+        child: CircularProgressIndicator(strokeWidth: 2),
+      ),
+    ),
+  );
+}