add thread support

Fixes #129

gomuks

@@ -1 +1 @@
-Subproject commit 9e6254b703a841d1e9ee64dbaf90d5a1b798696e
+Subproject commit 46ab9e9afa54c12f585cbbf559c395b9c2dcb545

lib/controllers/attachment.dart

@@ -4,9 +4,10 @@ import "package:nexus/controllers/client.dart";
 import "package:nexus/controllers/rooms.dart";
 import "package:nexus/models/content/content.dart";
 import "package:nexus/models/content/message.dart";
+import "package:nexus/models/composer_params.dart";
 import "package:path/path.dart";
 
-class AttachmentController(final String roomId)
+class AttachmentController(final ComposerParams composer)
     extends Notifier<(String, MessageContent?)?> {
   @override
   Null build() => null;
@@ -18,7 +19,10 @@ class AttachmentController(final String roomId)
     final isEncrypted = ref.read(
       RoomsController.provider.select(
         (value) =>
-            value[roomId]?.state[EventType.encryption.type]?.isNotEmpty == true,
+            value[composer.roomId]
+                ?.state[EventType.encryption.type]
+                ?.isNotEmpty ==
+            true,
       ),
     );
 
@@ -32,7 +36,9 @@ class AttachmentController(final String roomId)
   void set((String, MessageContent?)? attachment) => state = attachment;
 
   static final provider = NotifierProvider.family
-      .autoDispose<AttachmentController, (String, MessageContent?)?, String>(
-        AttachmentController.new,
-      );
+      .autoDispose<
+        AttachmentController,
+        (String, MessageContent?)?,
+        ComposerParams
+      >(AttachmentController.new);
 }

lib/controllers/bot_argument_suggestions.dart

@@ -8,16 +8,17 @@ import "package:nexus/helpers/extensions/get_localpart.dart";
 import "package:nexus/helpers/extensions/weighted_search.dart";
 import "package:nexus/models/bot_argument_suggestion.dart";
 import "package:nexus/models/bot_command_draft.dart";
+import "package:nexus/models/composer_params.dart";
 import "package:nexus/models/content/bot_command_description.dart";
 import "package:nexus/models/content/membership.dart";
 import "package:nexus/models/event.dart";
 import "package:nexus/models/room.dart";
 
-class BotArgumentSuggestionsController(final String roomId)
+class BotArgumentSuggestionsController(final ComposerParams composer)
     extends Notifier<IList<BotArgumentSuggestion>> {
   @override
   IList<BotArgumentSuggestion> build() {
-    final draft = ref.watch(BotCommandDraftController.provider(roomId));
+    final draft = ref.watch(BotCommandDraftController.provider(composer));
     final (parameter, text) = switch (draft) {
       BotCommandDraft(focusedParameter: final parameter?, :final texts) => (
         parameter,
@@ -38,7 +39,7 @@ class BotArgumentSuggestionsController(final String roomId)
         ? ref
                   .watch(
                     MembersByStatusController.provider(
-                      .new(roomId: roomId, status: .join),
+                      .new(roomId: composer.roomId, status: .join),
                     ),
                   )
                   .value ??
@@ -102,7 +103,7 @@ class BotArgumentSuggestionsController(final String roomId)
   }
 
   void pick(BotArgumentSuggestion suggestion) => ref
-      .read(BotCommandDraftController.provider(roomId).notifier)
+      .read(BotCommandDraftController.provider(composer).notifier)
       .pick(
         suggestion,
         via: switch (suggestion.room) {
@@ -112,7 +113,7 @@ class BotArgumentSuggestionsController(final String roomId)
       );
 
   bool pickTop() {
-    final draft = ref.read(BotCommandDraftController.provider(roomId));
+    final draft = ref.read(BotCommandDraftController.provider(composer));
     if (state.firstOrNull case final suggestion?
         when draft != null && !draft.arguments.containsKey(draft.focused)) {
       pick(suggestion);
@@ -125,6 +126,6 @@ class BotArgumentSuggestionsController(final String roomId)
       .family<
         BotArgumentSuggestionsController,
         IList<BotArgumentSuggestion>,
-        String
+        ComposerParams
       >(BotArgumentSuggestionsController.new);
 }

lib/controllers/bot_command_draft.dart

@@ -4,9 +4,10 @@ import "package:flutter_riverpod/flutter_riverpod.dart";
 import "package:nexus/models/bot_argument_suggestion.dart";
 import "package:nexus/models/bot_command.dart";
 import "package:nexus/models/bot_command_draft.dart";
+import "package:nexus/models/composer_params.dart";
 import "package:nexus/models/content/bot_command_description.dart";
 
-class BotCommandDraftController(final String roomId)
+class BotCommandDraftController(final ComposerParams composer)
     extends Notifier<BotCommandDraft?> {
   @override
   BotCommandDraft? build() => null;
@@ -14,7 +15,7 @@ class BotCommandDraftController(final String roomId)
   void start(BotCommand command, {String text = ""}) {
     state = BotCommandDraft(
       command: command,
-      roomId: roomId,
+      composer: composer,
       texts: .fromEntries(
         command.description.parameters
             .where((parameter) => !parameter.optional)
@@ -97,7 +98,7 @@ class BotCommandDraftController(final String roomId)
   void clear() => state = null;
 
   static final provider = NotifierProvider.autoDispose
-      .family<BotCommandDraftController, BotCommandDraft?, String>(
+      .family<BotCommandDraftController, BotCommandDraft?, ComposerParams>(
         BotCommandDraftController.new,
       );
 }

lib/controllers/client.dart

@@ -12,6 +12,7 @@ import "package:nexus/controllers/active_account.dart";
 import "package:nexus/controllers/client_state.dart";
 import "package:nexus/controllers/settings.dart";
 import "package:nexus/helpers/extensions/gomuks_buffer.dart";
+import "package:nexus/helpers/extensions/thread_events.dart";
 import "package:nexus/main.dart";
 import "package:nexus/models/content/bot_command_description.dart";
 import "package:nexus/models/account.dart";
@@ -37,6 +38,7 @@ import "package:nexus/models/requests/get_room_state.dart";
 import "package:nexus/models/requests/get_specific_room_state.dart";
 import "package:nexus/models/requests/get_space_hierarchy.dart";
 import "package:nexus/models/requests/get_room_directory.dart";
+import "package:nexus/models/requests/get_threads.dart";
 import "package:nexus/models/requests/join_room.dart";
 import "package:nexus/models/profile_response.dart";
 import "package:nexus/models/push_notification.dart";
@@ -367,6 +369,9 @@ class ClientController(final String? accountId) extends AsyncNotifier<int> {
   Future<Paginate> paginate(PaginateRequest request) async =>
       .fromJson(await _sendCommand("paginate", request.toJson()));
 
+  Future<PaginateManual> getThreads(GetThreadsRequest request) async =>
+      .fromJson(await _sendCommand("get_threads", request.toJson()));
+
   Future<PaginateManual> paginateManual(PaginateManualRequest request) async =>
       .fromJson(await _sendCommand("paginate_manual", request.toJson()));
 
@@ -438,10 +443,16 @@ class ClientController(final String? accountId) extends AsyncNotifier<int> {
     {"room_id": roomId, "timeout": timeout.inMilliseconds},
   );
 
-  Future<void> markRead(Room room) async {
-    if (room.timeline.isEmpty || room.metadata == null) return;
-    final eventRowId = room.timeline[room.timeline.keys.reduce(max)];
-    final event = eventRowId == null ? null : room.events[eventRowId];
+  Future<void> markRead(Room room, {String? threadRoot}) async {
+    if (room.metadata == null) return;
+    final event = switch (threadRoot) {
+      final threadRoot? => room.latestThreadEvent(threadRoot),
+      null when room.timeline.isEmpty => null,
+      null => switch (room.timeline[room.timeline.keys.reduce(max)]) {
+        final rowId? => room.events[rowId],
+        null => null,
+      },
+    };
 
     if (event == null) return;
 
@@ -454,6 +465,7 @@ class ClientController(final String? accountId) extends AsyncNotifier<int> {
       "room_id": room.metadata!.id,
       "receipt_type": sendPublic ? "m.read" : "m.read.private",
       "event_id": event.eventId,
+      "thread_id": ?threadRoot,
     });
   }
 

lib/controllers/event.dart

@@ -1,25 +1,20 @@
 import "package:flutter_riverpod/flutter_riverpod.dart";
 import "package:nexus/controllers/client.dart";
 import "package:nexus/controllers/rooms.dart";
-import "package:nexus/models/event.dart";
 import "package:nexus/models/requests/get_event.dart";
 
+/// The row ID of an event, fetching it if it isn't stored yet.
 class EventController(final GetEventRequest request)
-    extends AsyncNotifier<Event?> {
+    extends AsyncNotifier<int?> {
   @override
-  Future<Event?> build() async {
-    final event = ref.watch(
-      RoomsController.provider.select((rooms) {
-        final room = rooms[request.roomId];
-
-        return switch (room?.eventIds[request.eventId]) {
-          final rowId? => room?.events[rowId],
-          null => null,
-        };
-      }),
+  Future<int?> build() async {
+    final rowId = ref.watch(
+      RoomsController.provider.select(
+        (rooms) => rooms[request.roomId]?.eventIds[request.eventId],
+      ),
     );
 
-    if (event != null) return event;
+    if (rowId != null) return rowId;
 
     final link = ref.keepAlive();
     final fetchedEvent = await ref
@@ -44,11 +39,9 @@ class EventController(final GetEventRequest request)
       );
     }
 
-    return fetchedEvent;
+    return fetchedEvent?.rowId;
   }
 
   static final provider = AsyncNotifierProvider.family
-      .autoDispose<EventController, Event?, GetEventRequest>(
-        EventController.new,
-      );
+      .autoDispose<EventController, int?, GetEventRequest>(EventController.new);
 }

lib/controllers/pinned_events.dart

@@ -13,7 +13,7 @@ class PinnedEventsController(final String roomId)
       pinIds.map(
         (eventId) => ref.watch(
           EventController.provider(.new(eventId: eventId, roomId: roomId))
-              .selectAsync((data) => data?.rowId),
+              .future,
         ),
       ),
     )).nonNulls.toIList();

lib/controllers/read_receipts.dart

@@ -32,7 +32,12 @@ class ReadReceiptsController(final ChatParams chat)
     final room = ref.watch(
       RoomsController.provider.select(
         (rooms) => switch (rooms[chat.roomId]) {
-          final room? => (events: room.events, receipts: room.receipts),
+          final room? => (
+            events: room.events,
+            eventIds: room.eventIds,
+            receipts: room.receipts,
+            timeline: room.timeline,
+          ),
           null => null,
         },
       ),
@@ -50,15 +55,48 @@ class ReadReceiptsController(final ChatParams chat)
         .toIList();
     final messageIndexes = messages.map((entry) => entry.$1).toList();
 
+    final positions = IMap.fromEntries(
+      room.timeline.entries
+          .map(
+            (entry) => switch (entry.value) {
+              final rowId? => MapEntry(rowId, entry.key),
+              null => null,
+            },
+          )
+          .nonNulls,
+    );
+    final placed = events.indexed
+        .map(
+          (entry) => switch (positions[entry.$2.rowId]) {
+            final position? => (index: entry.$1, position: position),
+            null => null,
+          },
+        )
+        .nonNulls
+        .toList();
+    final placedPositions = placed.map((entry) => entry.position).toList();
+
+    int? indexOf(String eventId) {
+      if (indexes[eventId] case final index?) return index;
+
+      final position = switch (room.eventIds[eventId]) {
+        final rowId? => positions[rowId],
+        null => null,
+      };
+      if (position == null) return null;
+
+      final before = lowerBound(placedPositions, position + 1) - 1;
+      return before < 0 ? null : placed[before].index;
+    }
+
     return room.receipts.values.flattened
         .where(
           (receipt) =>
               receipt.userId != userId &&
-              // Receipts in threads are for the thread, not the timeline
-              receipt.thread == "main",
+              receipt.thread == (chat.threadRoot ?? "main"),
         )
         .map(
-          (receipt) => switch (indexes[receipt.eventId]) {
+          (receipt) => switch (indexOf(receipt.eventId)) {
             final index? => (
               receipt: receipt,
               message: lowerBound(messageIndexes, index + 1) - 1,

lib/controllers/room_chat.dart

@@ -7,10 +7,14 @@ import "package:flutter_riverpod/flutter_riverpod.dart";
 import "package:fluttertagger/fluttertagger.dart";
 import "package:nexus/controllers/attachment.dart";
 import "package:nexus/controllers/client.dart";
+import "package:nexus/controllers/event.dart";
 import "package:nexus/controllers/rooms.dart";
+import "package:nexus/controllers/thread_replies.dart";
 import "package:nexus/helpers/extensions/is_media.dart";
 import "package:nexus/helpers/extensions/send_failed.dart";
+import "package:nexus/helpers/extensions/thread_events.dart";
 import "package:nexus/models/bot_command_draft.dart";
+import "package:nexus/models/composer_params.dart";
 import "package:nexus/models/content/bot_command.dart";
 import "package:nexus/models/content/content.dart";
 import "package:nexus/models/content/image_pack.dart";
@@ -21,6 +25,7 @@ import "package:nexus/models/content/reaction.dart";
 import "package:nexus/models/content/sticker.dart";
 import "package:nexus/models/direction.dart";
 import "package:nexus/models/event.dart";
+import "package:nexus/models/paginate_manual.dart";
 import "package:nexus/models/requests/redact_event.dart";
 import "package:nexus/models/relation_type.dart";
 import "package:nexus/models/content/message.dart";
@@ -28,7 +33,11 @@ import "package:nexus/models/requests/send_message.dart";
 import "package:nexus/models/room.dart";
 import "package:nexus/models/room_chat.dart";
 
-typedef ChatParams = ({String roomId, int? contextualEvent});
+typedef ChatParams = ({
+  String roomId,
+  int? contextualEvent,
+  String? threadRoot,
+});
 
 class RoomChatController(final ChatParams info)
     extends AsyncNotifier<RoomChat?> {
@@ -47,19 +56,41 @@ class RoomChatController(final ChatParams info)
       ref.read(RoomsController.provider.notifier).addState(info.roomId, state);
     }
 
+    if (info.threadRoot case final threadRoot?
+        when info.contextualEvent == null) {
+      final nextBatch = await ref.watch(
+        ThreadRepliesController.provider((
+          roomId: info.roomId,
+          threadRoot: threadRoot,
+        )).future,
+      );
+
+      return .new(
+        timeline: ref.watch(RoomsController.provider.select(threadTimeline)),
+        hasMoreBackward: nextBatch != null,
+        hasMoreForward: false,
+      );
+    }
+
+    if (info.threadRoot == null) {
       final timeline = room.timeline
           .toEntryIList(compare: (a, b) => (a?.key ?? 0).compareTo(b?.key ?? 0))
           .map((e) => e.value)
           .toIList()
           .addAll(room.clientSticky)
           .nonNulls
+          // Threads are shown from their root instead
+          .where((rowId) => room.events[rowId]?.threadRoot == null)
           .toIList();
+
       if (info.contextualEvent == null ||
           timeline.contains(info.contextualEvent)) {
         ref.watch(
           RoomsController.provider.select(
-          (rooms) =>
-              (rooms[info.roomId]?.timeline, rooms[info.roomId]?.clientSticky),
+            (rooms) => (
+              rooms[info.roomId]?.timeline,
+              rooms[info.roomId]?.clientSticky,
+            ),
           ),
         );
 
@@ -68,7 +99,9 @@ class RoomChatController(final ChatParams info)
           hasMoreBackward: room.hasMore,
           hasMoreForward: false,
         );
-    } else {
+      }
+    }
+
     final context = await client.getEventContext(
       .new(
         roomId: info.roomId,
@@ -76,22 +109,119 @@ class RoomChatController(final ChatParams info)
       ),
     );
 
-      // `before` is in reverse chronological order
-      final events = context.before.reversed
+    final contextEvents = context.before.reversed
         .toIList()
         .add(context.event)
         .addAll(context.after);
     ref
         .read(RoomsController.provider.notifier)
-          .storeEvents(events.addAll(context.relatedEvents));
+        .storeEvents(contextEvents.addAll(context.relatedEvents));
+
+    if (info.threadRoot case final threadRoot?) {
+      final (older, newer) = await (
+        client.paginateManual(
+          .new(
+            roomId: info.roomId,
+            threadRoot: threadRoot,
+            since: context.start,
+            direction: .backward,
+          ),
+        ),
+        client.paginateManual(
+          .new(
+            roomId: info.roomId,
+            threadRoot: threadRoot,
+            since: context.end,
+            direction: .forward,
+          ),
+        ),
+      ).wait;
+      final rootRowId = await threadRootBefore(older);
+      ref
+          .read(RoomsController.provider.notifier)
+          .storeEvents(
+            older.events
+                .addAll(older.relatedEvents)
+                .addAll(newer.events)
+                .addAll(newer.relatedEvents),
+          );
+
       return .new(
-        timeline: .new(events.map((element) => element.rowId)),
+        timeline: .new([?rootRowId])
+            .addAll(
+              // Paginating backwards gives the newest first
+              older.events.reversed
+                  .addAll(
+                    contextEvents.where(
+                      (event) => event.threadRoot == threadRoot,
+                    ),
+                  )
+                  .addAll(newer.events)
+                  .map((event) => event.rowId),
+            )
+            .removeDuplicates(),
+        hasMoreBackward: older.nextBatch != null,
+        hasMoreForward: newer.nextBatch != null,
+        historicalData: .new(
+          start: older.nextBatch ?? "",
+          end: newer.nextBatch ?? "",
+        ),
+      );
+    }
+
+    return .new(
+      timeline: .new(
+        contextEvents
+            .where((event) => event.threadRoot == null)
+            .map((event) => event.rowId),
+      ),
       hasMoreBackward: true,
       hasMoreForward: true,
       historicalData: .new(start: context.start, end: context.end),
     );
   }
-  }
+
+  /// The thread's root, which comes before all of its events, if paginating
+  /// backwards to [older] reached the start of the thread.
+  Future<int?> threadRootBefore(PaginateManual older) async =>
+      switch (info.threadRoot) {
+        final threadRoot? when older.nextBatch == null => await ref.read(
+          EventController.provider(
+            .new(roomId: info.roomId, eventId: threadRoot),
+          ).future,
+        ),
+        _ => null,
+      };
+
+  /// The thread's root, then its events, if this is a thread's chat.
+  IList<int> threadTimeline(IMap<String, Room> rooms) =>
+      switch ((rooms[info.roomId], info.threadRoot)) {
+        (final room?, final threadRoot?) => .new([
+          ?room.eventIds[threadRoot],
+          ...room.threadEvents(threadRoot).map((event) => event.rowId),
+        ]),
+        _ => const .empty(),
+      };
+
+  Relation? replyRelation(Event? replied) =>
+      switch (info.threadRoot ?? replied?.threadRoot) {
+        null =>
+          replied == null
+              ? null
+              : .new(eventId: replied.eventId, relationType: .reply),
+        final threadRoot => .new(
+          eventId:
+              replied?.eventId ??
+              ref
+                  .read(RoomsController.provider)[info.roomId]
+                  ?.latestThreadEvent(threadRoot)
+                  ?.eventId ??
+              threadRoot,
+          relationType: .reply,
+          threadRoot: threadRoot,
+          isFallingBack: replied == null,
+        ),
+      };
 
   Future<void> deleteMessage(Event event, {String? reason}) => ref
       .read(ClientController.provider.notifier)
@@ -133,13 +263,28 @@ class RoomChatController(final ChatParams info)
       return;
     }
 
+    if ((info.threadRoot, chat) case (final threadRoot?, final chat?)
+        when chat.historicalData == null) {
+      return ref
+          .read(
+            ThreadRepliesController.provider((
+              roomId: info.roomId,
+              threadRoot: threadRoot,
+            )).notifier,
+          )
+          .loadOlder();
+    }
+
     state = .loading();
 
     final client = ref.read(ClientController.provider.notifier);
 
+    try {
       if (chat?.historicalData == null) {
         final timelineKeys = ref
-          .read(RoomsController.provider.select((value) => value[info.roomId]))
+            .read(
+              RoomsController.provider.select((value) => value[info.roomId]),
+            )
             ?.timeline
             .keys;
         final response = await client.paginate(
@@ -158,16 +303,18 @@ class RoomChatController(final ChatParams info)
         ref
             .read(RoomsController.provider.notifier)
             .update(
-            IMap({
-              info.roomId: Room(
-                events: IMap.fromIterable(
+              .new({
+                info.roomId: .new(
+                  // ignore: unused_result - I am using it you donkey
+                  events: .fromIterable(
                     response.events.addAll(response.relatedEvents),
                     keyMapper: (event) => event.rowId,
                     valueMapper: (event) => event,
                   ),
                   hasMore: response.hasMore,
                   receipts: response.receipts,
-                timeline: IMap.fromIterable(
+                  // ignore: unused_result - I am using it you donkey
+                  timeline: .fromIterable(
                     response.events,
                     keyMapper: (event) => event.timelineRowId,
                     valueMapper: (event) => event.rowId,
@@ -179,6 +326,7 @@ class RoomChatController(final ChatParams info)
         final paginationResponse = await client.paginateManual(
           .new(
             roomId: info.roomId,
+            threadRoot: info.threadRoot,
             direction: direction,
             since: direction == .forward
                 ? chat!.historicalData!.end
@@ -189,15 +337,22 @@ class RoomChatController(final ChatParams info)
         ref
             .read(RoomsController.provider.notifier)
             .storeEvents(
-            paginationResponse.events.addAll(paginationResponse.relatedEvents),
+              paginationResponse.events.addAll(
+                paginationResponse.relatedEvents,
+              ),
             );
 
-      final eventRowIds =
-          (direction == .forward
+        final rootRowId = direction == .backward
+            ? await threadRootBefore(paginationResponse)
+            : null;
+        final eventRowIds = [
+          ?rootRowId,
+          ...(direction == .forward
                   ? paginationResponse.events
                   : paginationResponse.events.reversed)
-              .map((element) => element.rowId)
-              .toIList();
+              .where((event) => event.threadRoot == info.threadRoot)
+              .map((element) => element.rowId),
+        ].lock;
 
         state = .data(
           .new(
@@ -219,12 +374,18 @@ class RoomChatController(final ChatParams info)
                       : null) ??
                   chat.historicalData!.start,
               end:
-                (direction == .forward ? paginationResponse.nextBatch : null) ??
+                  (direction == .forward
+                      ? paginationResponse.nextBatch
+                      : null) ??
                   chat.historicalData!.end,
             ),
           ),
         );
       }
+    } catch (_) {
+      state = .data(chat);
+      rethrow;
+    }
   }
 
   Future<void> send(
@@ -239,7 +400,11 @@ class RoomChatController(final ChatParams info)
         ? null
         : events?[relatedEventRowId];
 
-    final attachmentProvider = AttachmentController.provider(info.roomId);
+    final ComposerParams composer = (
+      roomId: info.roomId,
+      threadRoot: info.threadRoot,
+    );
+    final attachmentProvider = AttachmentController.provider(composer);
     final attachment = ref.read(attachmentProvider)?.$2;
     ref.invalidate(attachmentProvider);
 
@@ -275,9 +440,9 @@ class RoomChatController(final ChatParams info)
           room: taggedMessage.contains("@room"),
         ),
         text: taggedMessage,
-        relation: relatedEvent == null
-            ? null
-            : .new(eventId: relatedEvent.eventId, relationType: relationType),
+        relation: relationType == .edit && relatedEvent != null
+            ? .new(eventId: relatedEvent.eventId, relationType: .edit)
+            : replyRelation(relatedEvent),
       ),
     );
 
@@ -384,7 +549,7 @@ class RoomChatController(final ChatParams info)
                 if (shouldMention && repliedEvent != null) repliedEvent.sender,
               ].toIList(),
             ),
-            replyTo: repliedEvent?.eventId,
+            reply: replyRelation(repliedEvent),
           ),
         );
 
@@ -451,9 +616,7 @@ class RoomChatController(final ChatParams info)
               command: draft.input,
             ),
             mentions: .new(userIds: [draft.command.sender].lock),
-            relation: repliedEvent == null
-                ? null
-                : .new(eventId: repliedEvent.eventId, relationType: .reply),
+            relation: replyRelation(repliedEvent),
           ),
         );
 

lib/controllers/thread_list.dart

@@ -0,0 +1,37 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/client.dart";
+import "package:nexus/controllers/rooms.dart";
+
+class ThreadListController(final String roomId) extends AsyncNotifier<String?> {
+  @override
+  Future<String?> build() => fetch(null);
+
+  Future<String?> fetch(String? since) async {
+    final threads = await ref
+        .read(ClientController.provider.notifier)
+        .getThreads(.new(roomId: roomId, since: since));
+    ref
+        .read(RoomsController.provider.notifier)
+        .storeEvents(threads.events.addAll(threads.relatedEvents));
+
+    return threads.nextBatch;
+  }
+
+  Future<void> loadMore() async {
+    final since = await future;
+    if (state.isLoading || since == null) return;
+
+    state = .loading();
+    try {
+      state = .data(await fetch(since));
+    } catch (_) {
+      state = .data(since);
+      rethrow;
+    }
+  }
+
+  static final provider = AsyncNotifierProvider.family
+      .autoDispose<ThreadListController, String?, String>(
+        ThreadListController.new,
+      );
+}

lib/controllers/thread_replies.dart

@@ -0,0 +1,49 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/client.dart";
+import "package:nexus/controllers/rooms.dart";
+
+typedef ThreadParams = ({String roomId, String threadRoot});
+
+/// Loads a thread's replies from the server, newest first, storing them. Its
+/// state is the token for older replies, or null if there are none.
+class ThreadRepliesController(final ThreadParams thread)
+    extends AsyncNotifier<String?> {
+  @override
+  Future<String?> build() => fetch(null);
+
+  Future<String?> fetch(String? since) async {
+    final response = await ref
+        .read(ClientController.provider.notifier)
+        .paginateManual(
+          .new(
+            roomId: thread.roomId,
+            threadRoot: thread.threadRoot,
+            since: since,
+            direction: .backward,
+          ),
+        );
+    ref
+        .read(RoomsController.provider.notifier)
+        .storeEvents(response.events.addAll(response.relatedEvents));
+
+    return response.nextBatch;
+  }
+
+  Future<void> loadOlder() async {
+    final since = await future;
+    if (state.isLoading || since == null) return;
+
+    state = .loading();
+    try {
+      state = .data(await fetch(since));
+    } catch (_) {
+      state = .data(since);
+      rethrow;
+    }
+  }
+
+  static final provider = AsyncNotifierProvider.family
+      .autoDispose<ThreadRepliesController, String?, ThreadParams>(
+        ThreadRepliesController.new,
+      );
+}

lib/helpers/extensions/build_event_options.dart

@@ -26,6 +26,7 @@ extension BuildEventOptions on Event {
     required String roomId,
     required String userId,
     required void Function(int, RelationType) onRelation,
+    void Function(String threadRoot)? onStartThread,
   }) {
     final theme = Theme.of(context);
     final danger = theme.colorScheme.error;
@@ -34,11 +35,15 @@ extension BuildEventOptions on Event {
     final notifier = RoomChatController.provider((
       roomId: roomId,
       contextualEvent: null,
+      threadRoot: null,
     )).notifier;
 
     final isPinned = ref
         .read(PinnedIdsController.provider(roomId))
         .contains(eventId);
+    final canSend = ref.read(
+      PowerLevelController.provider(.new(eventType: .message, roomId: roomId)),
+    );
 
     void showReasonSheet({
       required String title,
@@ -170,11 +175,7 @@ extension BuildEventOptions on Event {
           ),
         ),
 
-      if (ref.read(
-        PowerLevelController.provider(
-          .new(eventType: .message, roomId: roomId),
-        ),
-      ))
+      if (canSend)
         PopupMenuItem(
           onTap: () => onRelation(rowId, .reply),
           child: const ListTile(
@@ -183,6 +184,18 @@ extension BuildEventOptions on Event {
           ),
         ),
 
+      if (onStartThread != null &&
+          threadCount == 0 &&
+          canSend &&
+          relatesTo == null)
+        PopupMenuItem(
+          onTap: () => onStartThread(eventId),
+          child: const ListTile(
+            leading: Icon(Icons.forum),
+            title: Text("Start Thread"),
+          ),
+        ),
+
       if (sender == userId &&
           switch (content) {
             LocationMessageContent() ||

lib/helpers/extensions/open_link_info.dart

@@ -32,7 +32,7 @@ extension OpenLinkInfo on WidgetRef {
         : await read(
             EventController.provider(
               .new(roomId: summary.roomId, eventId: linkInfo.eventId!),
-            ).selectAsync((data) => data?.rowId),
+            ).future,
           ).onError((_, _) => null);
 
     if (await focusRoom(summary.roomId, eventRowId) || !context.mounted) return;

lib/helpers/extensions/thread_events.dart

@@ -0,0 +1,50 @@
+import "package:collection/collection.dart";
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:nexus/helpers/extensions/event_id_is_fake.dart";
+import "package:nexus/models/event.dart";
+import "package:nexus/models/room.dart";
+
+typedef ThreadInfo = ({int count, Event? latest});
+typedef Thread = ({Event root, ThreadInfo info});
+
+extension ThreadEvents on Room {
+  /// The threads in the loaded events, most recently active first.
+  IList<Thread> get threads {
+    DateTime lastActive(Thread thread) =>
+        thread.info.latest?.timestamp ?? thread.root.timestamp;
+
+    return events.values
+        .where((event) => event.threadCount > 0)
+        .map((root) => (root: root, info: thread(root)))
+        .sorted((a, b) => lastActive(b).compareTo(lastActive(a)))
+        .toIList();
+  }
+
+  /// The events in the thread from [threadRoot], oldest first, without the
+  /// root itself.
+  IList<Event> threadEvents(String threadRoot) =>
+      (relations[threadRoot] ?? const .empty())
+          .map((rowId) => events[rowId])
+          .nonNulls
+          .where(
+            (event) =>
+                event.threadRoot == threadRoot &&
+                (!event.eventId.isFake || clientSticky.contains(event.rowId)),
+          )
+          .sorted((a, b) => a.timestamp.compareTo(b.timestamp))
+          .toIList();
+
+  /// How many replies the thread from [root] has, and its latest event, from
+  /// gomuks' aggregate on it
+  ThreadInfo thread(Event root) =>
+      (count: root.threadCount, latest: events[root.threadLatestRowId]);
+
+  /// The latest event in the thread from [threadRoot], if it's loaded.
+  Event? latestThreadEvent(String threadRoot) => switch (eventIds[threadRoot]) {
+    final rowId? => switch (events[rowId]) {
+      final root? => thread(root).latest,
+      null => null,
+    },
+    null => null,
+  };
+}

lib/helpers/hooks/chat_composer.dart

@@ -0,0 +1,40 @@
+import "package:flutter/services.dart";
+import "package:flutter_hooks/flutter_hooks.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/models/relation_type.dart";
+
+final class ChatComposer({
+  required final ValueNotifier<int?> relatedEvent,
+  required final ValueNotifier<RelationType> relationType,
+  required final FocusNode node,
+}) {
+  factory use() {
+    final relatedEvent = useState<int?>(null);
+    final relationType = useState(RelationType.reply);
+    final node = useFocusNode(
+      onKeyEvent: (_, event) {
+        if (event is KeyDownEvent && event.logicalKey == .escape) {
+          relatedEvent.value = null;
+          return .handled;
+        }
+
+        return .ignored;
+      },
+    );
+
+    return .new(
+      relatedEvent: relatedEvent,
+      relationType: relationType,
+      node: node,
+    );
+  }
+
+  int? get repliedEventRowId =>
+      relationType.value == .reply ? relatedEvent.value : null;
+
+  void relate(int rowId, RelationType type) {
+    relatedEvent.value = rowId;
+    relationType.value = type;
+    node.requestFocus();
+  }
+}

lib/helpers/hooks/chat_scroll.dart

@@ -15,6 +15,8 @@ final class ChatScroll({
   required final GlobalKey centerKey,
   required final ScrollController scrollController,
   required final bool atBottom,
+  required final int? highlightedEvent,
+
   required final JumpToEvent jumpToEvent,
   required final Future<void> Function() jumpToBottom,
   required final GlobalKey Function(int eventRowId) keyFor,
@@ -28,6 +30,8 @@ final class ChatScroll({
     final anchorId = useState<int?>(null);
     final atBottom = useState(true);
     final pendingJump = useState<int?>(null);
+    final highlightedEvent = useState<int?>(null);
+    final hookContext = useContext();
     final pendingJumpDone = useRef<Completer<void>?>(null);
     void finishPendingJump() {
       pendingJumpDone.value?.complete();
@@ -95,15 +99,14 @@ final class ChatScroll({
 
       final anchorIndex = items.indexOf(anchor);
 
-      if (anchorIndex == -1) return (history: const .empty(), live: items);
-
+      final historyLength = anchorIndex == -1 ? items.length : anchorIndex + 1;
       return (
-        history: items.take(anchorIndex).toIList().reversed.toIList(),
-        live: items.skip(anchorIndex).toIList(),
+        history: items.take(historyLength).toIList().reversed.toIList(),
+        live: items.skip(historyLength).toIList(),
       );
     }, [controllerData, anchorId.value]);
 
-    final lastRowId = split.live.lastOrNull;
+    final lastRowId = controllerData.value?.timeline.lastOrNull;
     final previousLastRowId = useRef<int?>(null);
 
     useEffect(() {
@@ -118,7 +121,8 @@ final class ChatScroll({
       WidgetsBinding.instance.addPostFrameCallback((_) {
         if (!scrollController.hasClients) return;
 
-        scrollController.jumpTo(scrollController.position.minScrollExtent);
+        anchorId.value = lastRowId;
+        scrollController.position.correctPixels(0);
       });
 
       return null;
@@ -173,14 +177,7 @@ final class ChatScroll({
       ],
     );
 
-    return .new(
-      historyRows: split.history,
-      liveRows: split.live,
-      centerKey: centerKey,
-      scrollController: scrollController,
-      atBottom: atBottom.value,
-      keyFor: keyFor,
-      jumpToEvent: (int rowId) async {
+    Future<void> scrollToEvent(int rowId) async {
       if (!scrollController.hasClients) return;
 
       final context = keyFor(rowId).currentContext;
@@ -204,6 +201,25 @@ final class ChatScroll({
         contextualEvent.value = rowId;
       }
       await done.future;
+    }
+
+    return .new(
+      historyRows: split.history,
+      liveRows: split.live,
+      centerKey: centerKey,
+      scrollController: scrollController,
+      atBottom: atBottom.value,
+      highlightedEvent: highlightedEvent.value,
+      keyFor: keyFor,
+      jumpToEvent: (int rowId) async {
+        highlightedEvent.value = rowId;
+
+        await scrollToEvent(rowId);
+        await Future.delayed(Durations.extralong1, () {
+          if (hookContext.mounted && highlightedEvent.value == rowId) {
+            highlightedEvent.value = null;
+          }
+        });
       },
       jumpToBottom: () async {
         finishPendingJump();

lib/models/bot_command_draft.dart

@@ -2,6 +2,7 @@ import "package:collection/collection.dart";
 import "package:fast_immutable_collections/fast_immutable_collections.dart";
 import "package:freezed_annotation/freezed_annotation.dart";
 import "package:nexus/models/bot_command.dart";
+import "package:nexus/models/composer_params.dart";
 import "package:nexus/models/content/bot_command.dart";
 import "package:nexus/models/content/bot_command_description.dart";
 
@@ -10,7 +11,7 @@ part "bot_command_draft.freezed.dart";
 @Freezed(toJson: false, fromJson: false)
 class const BotCommandDraft({
   required final BotCommand command,
-  required final String roomId,
+  required final ComposerParams composer,
   final IMap<String, String> texts = const .empty(),
 
   // The servers to join rooms picked from suggestions through, by room ID
@@ -33,8 +34,9 @@ class const BotCommandDraft({
   BotParameter? get focusedParameter => command.description.parameters
       .firstWhereOrNull((parameter) => parameter.key == focused);
 
-  ({Object? value, String? error}) parse(BotParameter parameter) =>
-      parameter.schema.parseText(texts[parameter.key] ?? "", roomId: roomId);
+  ({Object? value, String? error}) parse(BotParameter parameter) => parameter
+      .schema
+      .parseText(texts[parameter.key] ?? "", roomId: composer.roomId);
 
   IMap<String, Object> get arguments => .fromEntries(
     shown

lib/models/composer_params.dart

@@ -0,0 +1 @@
+typedef ComposerParams = ({String roomId, String? threadRoot});

lib/models/event.dart

@@ -29,6 +29,8 @@ class const Event({
   final String? sendError,
   final IMap<String, int> reactions = const .empty(),
   @JsonKey(name: "last_edit_rowid") final int lastEditRowId = 0,
+  final int threadCount = 0,
+  @JsonKey(name: "thread_latest_rowid") final int threadLatestRowId = 0,
   final UnreadType? unreadType,
   final Profile? pmp,
   required final Content content,
@@ -36,6 +38,8 @@ class const Event({
 }) with _$Event {
   Map<String, Object?> toJson() => _$EventToJson(this);
 
+  String? get threadRoot => relationType == "m.thread" ? relatesTo : null;
+
   static String typeJsonFromJson(Map<dynamic, dynamic> json, _) =>
       json["decrypted_type"] ?? json["type"];
 
@@ -47,7 +51,15 @@ class const Event({
 
   static String? replyToFromJson(Map<dynamic, dynamic> json) {
     try {
-      return json["m.relates_to"]?["m.in_reply_to"]?["event_id"];
+      final relatesTo = json["m.relates_to"];
+
+      // Thread fallbacks are only for clients without thread support
+      if (relatesTo?["rel_type"] == "m.thread" &&
+          relatesTo?["is_falling_back"] == true) {
+        return null;
+      }
+
+      return relatesTo?["m.in_reply_to"]?["event_id"];
     } catch (_) {
       return null;
     }

lib/models/requests/get_threads.dart

@@ -0,0 +1,17 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+
+part "get_threads.freezed.dart";
+part "get_threads.g.dart";
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const GetThreadsRequest({
+  required final String roomId,
+  final String? since,
+  final int limit = 20,
+}) with _$GetThreadsRequest {
+  Map<String, Object?> toJson() => _$GetThreadsRequestToJson(this);
+
+  factory GetThreadsRequest.fromJson(Map<String, Object?> json) =>
+      _$GetThreadsRequestFromJson(json);
+}