add jump to bottom button

lib/helpers/hooks/chat_scroll.dart

@@ -17,14 +17,15 @@ final class ChatScroll({
   required final ListController historyListController,
   required final ListController liveListController,
   required final ScrollController scrollController,
+  required final bool atBottom,
   required final Future<void> Function(String id) jumpToId,
+  required final Future<void> Function() jumpToBottom,
 }) {
   factory use({
     required AsyncValue<RoomChat?> controllerData,
     required Future<void> Function(Direction direction) paginate,
     required Future<void> Function() markRead,
-    required String? contextualEvent,
+    required ValueNotifier<String?> contextualEvent,
-    required void Function(String id) setContextualEvent,
   }) {
     final anchorId = useState<String?>(null);
 
@@ -35,6 +36,8 @@ final class ChatScroll({
     final scrollController = useScrollController();
     final centerKey = useMemoized(GlobalKey.new);
 
+    final atBottom = useState(true);
+
     final pendingAnchorTarget = useState<String?>(null);
     final anchorMountedCompleter = useRef<Completer<BuildContext>?>(null);
 
@@ -43,17 +46,17 @@ final class ChatScroll({
         if (controllerData case AsyncData(:final value?)
             when value.timeline.isNotEmpty) {
           final hasContextualEvent = value.timeline.any(
-            (event) => event.eventId == contextualEvent,
+            (event) => event.eventId == contextualEvent.value,
           );
 
           anchorId.value = hasContextualEvent
-              ? contextualEvent
+              ? contextualEvent.value
               : value.timeline.last.eventId;
         }
       }
 
       return null;
-    }, [controllerData, contextualEvent]);
+    }, [controllerData, contextualEvent.value]);
 
     useEffect(() {
       final target = pendingAnchorTarget.value;
@@ -115,7 +118,8 @@ final class ChatScroll({
       );
     }, [controllerData, anchorId.value]);
 
-    useEffect(() {
+    useEffect(
+      () {
         const loadThreshold = 500.0;
         const readThreshold = 50.0;
 
@@ -124,9 +128,12 @@ final class ChatScroll({
 
           final position = scrollController.position;
 
+          final isAtBottom = position.extentBefore <= readThreshold;
+          if (isAtBottom != atBottom.value) atBottom.value = isAtBottom;
+
           if (position.extentAfter <= loadThreshold) {
             await paginate(.backward);
-        } else if (contextualEvent != null &&
+          } else if (contextualEvent.value != null &&
               position.extentBefore <= loadThreshold) {
             await paginate(.forward);
           } else if (position.extentBefore <= readThreshold) {
@@ -139,7 +146,15 @@ final class ChatScroll({
         WidgetsBinding.instance.addPostFrameCallback((_) => checkPosition());
 
         return () => scrollController.removeListener(checkPosition);
-    }, [scrollController, controllerData, paginate, markRead, contextualEvent]);
+      },
+      [
+        scrollController,
+        controllerData,
+        paginate,
+        markRead,
+        contextualEvent.value,
+      ],
+    );
 
     double? resolveOffset(String itemId) {
       final historyIndex = split.history.indexWhere(
@@ -177,7 +192,7 @@ final class ChatScroll({
       final completer = Completer<BuildContext>();
       anchorMountedCompleter.value = completer;
       pendingAnchorTarget.value = itemId;
-      setContextualEvent(itemId);
+      contextualEvent.value = itemId;
 
       final context = await completer.future;
 
@@ -191,6 +206,21 @@ final class ChatScroll({
       }
     }
 
+    Future<void> jumpToBottom() async {
+      if (contextualEvent.value != null) {
+        anchorId.value = null;
+        contextualEvent.value = null;
+      }
+
+      if (!scrollController.hasClients) return;
+
+      await scrollController.animateTo(
+        scrollController.position.minScrollExtent,
+        duration: const .new(milliseconds: 700),
+        curve: Curves.easeInOut,
+      );
+    }
+
     return .new(
       historyItems: split.history,
       liveItems: split.live,
@@ -199,7 +229,9 @@ final class ChatScroll({
       historyListController: historyListController,
       liveListController: liveListController,
       scrollController: scrollController,
+      atBottom: atBottom.value,
       jumpToId: jumpToId,
+      jumpToBottom: jumpToBottom,
     );
   }
 }

lib/widgets/room_chat/room_chat.dart

@@ -74,8 +74,7 @@ final class const RoomChat({
     final scroll = ChatScroll.use(
       controllerData: controllerData,
       paginate: notifier.paginate,
-      contextualEvent: contextualEvent.value,
+      contextualEvent: contextualEvent,
-      setContextualEvent: (id) => contextualEvent.value = id,
       markRead: () async {
         final room = ref.read(
           RoomsController.provider.select((rooms) => rooms[roomId]),
@@ -159,6 +158,21 @@ final class const RoomChat({
                         ),
                       ),
                     ),
+                    Positioned(
+                      right: 16,
+                      bottom: composerSize.value,
+                      child: IgnorePointer(
+                        ignoring: scroll.atBottom,
+                        child: AnimatedOpacity(
+                          opacity: scroll.atBottom ? 0 : 1,
+                          duration: const Duration(milliseconds: 200),
+                          child: FloatingActionButton.small(
+                            onPressed: scroll.jumpToBottom,
+                            child: const Icon(Icons.keyboard_arrow_down),
+                          ),
+                        ),
+                      ),
+                    ),
                     Positioned(
                       bottom: 0,
                       left: 0,