add thread support

Fixes #129

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,
+  };
+}