feat: Jump to last read event

assets/l10n/intl_en.arb

@@ -2526,5 +2526,6 @@
         "placeholders": {
             "path": {}
         }
-    }
+    },
+    "jumpToLastReadMessage": "Jump to last read message"
 }

lib/pages/chat/chat.dart

@@ -132,6 +132,11 @@ class ChatController extends State<Chat> {
 
   bool showEmojiPicker = false;
 
+  bool get lastReadEventVisible =>
+      timeline == null ||
+      room!.fullyRead.isEmpty ||
+      timeline!.events.any((event) => event.eventId == room!.fullyRead);
+
   void recreateChat() async {
     final room = this.room;
     final userId = room?.directChatMatrixID;
@@ -190,9 +195,13 @@ class ChatController extends State<Chat> {
   }
 
   void requestFuture() async {
-    if (!timeline!.canRequestFuture) return;
+    final timeline = this.timeline;
+    if (timeline == null) return;
+    if (!timeline.canRequestFuture) return;
     try {
-      await timeline!.requestFuture(historyCount: _loadHistoryCount);
+      final mostRecentEventId = timeline.events.first.eventId;
+      await timeline.requestFuture(historyCount: _loadHistoryCount);
+      setReadMarker(eventId: mostRecentEventId);
     } catch (err) {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
@@ -280,20 +289,30 @@ class ChatController extends State<Chat> {
 
   Future<void>? _setReadMarkerFuture;
 
-  void setReadMarker([_]) {
-    if (_setReadMarkerFuture == null &&
-        (room!.hasNewMessages || room!.notificationCount > 0) &&
-        timeline != null &&
-        timeline!.events.isNotEmpty &&
-        Matrix.of(context).webHasFocus) {
-      Logs().v('Set read marker...');
+  void setReadMarker({String? eventId}) {
+    if (_setReadMarkerFuture != null) return;
+    if (lastReadEventVisible &&
+        !room!.hasNewMessages &&
+        room!.notificationCount == 0) {
+      return;
+    }
+    if (!Matrix.of(context).webHasFocus) return;
+
+    final timeline = this.timeline;
+    if (timeline == null || timeline.events.isEmpty) return;
+
+    if (eventId == null && !lastReadEventVisible) {
+      return;
+    }
+
+    eventId ??= timeline.events.first.eventId;
+    Logs().v('Set read marker...', eventId);
     // ignore: unawaited_futures
-      _setReadMarkerFuture = timeline!.setReadMarker().then((_) {
+    _setReadMarkerFuture = timeline.setReadMarker(eventId).then((_) {
       _setReadMarkerFuture = null;
     });
     room!.client.updateIosBadge();
   }
-  }
 
   @override
   void dispose() {
@@ -759,6 +778,7 @@ class ChatController extends State<Chat> {
         timeline = null;
       });
       await getTimeline();
+      setReadMarker(eventId: timeline!.events.first.eventId);
     }
     scrollController.jumpTo(0);
   }

lib/pages/chat/chat_view.dart

@@ -174,7 +174,7 @@ class ChatView extends StatelessWidget {
         }
       },
       child: GestureDetector(
-        onTapDown: controller.setReadMarker,
+        onTapDown: (_) => controller.setReadMarker(),
         behavior: HitTestBehavior.opaque,
         child: StreamBuilder(
           stream: controller.room!.onUpdate.stream
@@ -351,6 +351,31 @@ class ChatView extends StatelessWidget {
                           ],
                         ),
                       ),
+                      if (!controller.lastReadEventVisible)
+                        Positioned(
+                          top: 16,
+                          left: 0,
+                          right: 0,
+                          child: Center(
+                            child: FloatingActionButton.extended(
+                              icon: const Icon(Icons.arrow_upward_outlined),
+                              onPressed: () => controller
+                                  .scrollToEventId(controller.room!.fullyRead),
+                              label: Row(
+                                mainAxisSize: MainAxisSize.min,
+                                children: [
+                                  Text(L10n.of(context)!.jumpToLastReadMessage),
+                                  IconButton(
+                                    onPressed: () => controller.setReadMarker(
+                                      eventId: controller.room!.fullyRead,
+                                    ),
+                                    icon: const Icon(Icons.close),
+                                  ),
+                                ],
+                              ),
+                            ),
+                          ),
+                        ),
                       if (controller.dragging)
                         Container(
                           color: Theme.of(context)