model: Add view-model for typing status.

Using SendableNarrow as the key covers the narrows where typing
notifications are supported (topics and dms). Consumers of the typing
status will only be notified if a typist has been added or removed from
any of the narrows.

At the moment, getTypistIdsInNarrow is unused. It will get exercised by
the UI code that implements the typing indicator.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/model/store.dart

@@ -24,6 +24,7 @@ import 'message.dart';
 import 'message_list.dart';
 import 'recent_dm_conversations.dart';
 import 'stream.dart';
+import 'typing_status.dart';
 import 'unreads.dart';
 
 export 'package:drift/drift.dart' show Value;
@@ -251,6 +252,12 @@ class PerAccountStore extends ChangeNotifier with StreamStore, MessageStore {
       ),
       recentDmConversationsView: RecentDmConversationsView(
         initial: initialSnapshot.recentPrivateConversations, selfUserId: account.userId),
+      typingStatus: TypingStatus(
+        selfUserId: account.userId,
+        typingStartedExpiryPeriod: Duration(milliseconds: initialSnapshot.serverTypingStartedExpiryPeriodMilliseconds),
+        typingStoppedWaitPeriod: Duration(milliseconds: initialSnapshot.serverTypingStoppedWaitPeriodMilliseconds),
+        typingStartedWaitPeriod: Duration(milliseconds: initialSnapshot.serverTypingStartedWaitPeriodMilliseconds),
+      )
     );
   }
 
@@ -270,6 +277,7 @@ class PerAccountStore extends ChangeNotifier with StreamStore, MessageStore {
     required MessageStoreImpl messages,
     required this.unreads,
     required this.recentDmConversationsView,
+    required this.typingStatus,
   }) : assert(selfUserId == globalStore.getAccount(accountId)!.userId),
        assert(realmUrl == globalStore.getAccount(accountId)!.realmUrl),
        assert(realmUrl == connection.realmUrl),
@@ -361,6 +369,8 @@ class PerAccountStore extends ChangeNotifier with StreamStore, MessageStore {
 
   final RecentDmConversationsView recentDmConversationsView;
 
+  final TypingStatus typingStatus;
+
   ////////////////////////////////
   // Other digests of data.
 
@@ -485,6 +495,9 @@ class PerAccountStore extends ChangeNotifier with StreamStore, MessageStore {
       assert(debugLog("server event: update_message_flags/${event.op} ${event.flag.toJson()}"));
       _messages.handleUpdateMessageFlagsEvent(event);
       unreads.handleUpdateMessageFlagsEvent(event);
+    } else if (event is TypingEvent) {
+      assert(debugLog("server event: typing/${event.op} ${event.messageType}"));
+      typingStatus.handleTypingEvent(event);
     } else if (event is ReactionEvent) {
       assert(debugLog("server event: reaction/${event.op}"));
       _messages.handleReactionEvent(event);

lib/model/typing_status.dart

@@ -0,0 +1,73 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+
+import '../api/model/events.dart';
+import 'narrow.dart';
+
+/// The view-model for tracking the typing status organized by narrows.
+class TypingStatus extends ChangeNotifier {
+  @visibleForTesting
+  final Map<SendableNarrow, Map<int, Timer>> typistIdsByNarrow = {};
+
+  final int selfUserId;
+  final Duration typingStartedExpiryPeriod;
+  final Duration typingStoppedWaitPeriod;
+  final Duration typingStartedWaitPeriod;
+
+  TypingStatus({
+    required this.selfUserId,
+    required this.typingStartedExpiryPeriod,
+    required this.typingStoppedWaitPeriod,
+    required this.typingStartedWaitPeriod,
+  });
+
+  bool _addTypist(SendableNarrow narrow, int typistUserId, void Function() callback) {
+    final narrowTimerMap = typistIdsByNarrow[narrow] ??= {};
+    final typistTimer = narrowTimerMap[typistUserId];
+    final isNewTypist = typistTimer == null;
+    typistTimer?.cancel();
+    narrowTimerMap[typistUserId] = Timer(typingStartedExpiryPeriod, callback);
+    return isNewTypist;
+  }
+
+  bool _removeTypist(SendableNarrow narrow, int typistUserId) {
+    final narrowTimerMap = typistIdsByNarrow[narrow];
+    final typistTimer = narrowTimerMap?[typistUserId];
+    if (narrowTimerMap == null || typistTimer == null) {
+      return false;
+    }
+    typistTimer.cancel();
+    narrowTimerMap.remove(typistUserId);
+    if (narrowTimerMap.isEmpty) typistIdsByNarrow.remove(narrow);
+    return true;
+  }
+
+  Iterable<int> getTypistIdsInNarrow(SendableNarrow narrow) {
+    return typistIdsByNarrow[narrow]?.keys ?? [];
+  }
+
+  void handleTypingEvent(TypingEvent event) {
+    SendableNarrow narrow = switch (event.messageType) {
+      MessageType.private => DmNarrow(
+        allRecipientIds: event.recipientIds!..sort(), selfUserId: selfUserId),
+      MessageType.stream => TopicNarrow(event.streamId!, event.topic!),
+    };
+
+    bool hasUpdate = false;
+    switch (event.op) {
+      case TypingOp.start:
+        hasUpdate = _addTypist(narrow, event.senderId, () {
+          if (_removeTypist(narrow, event.senderId)) {
+            notifyListeners();
+          }
+        });
+      case TypingOp.stop:
+        hasUpdate = _removeTypist(narrow, event.senderId);
+    }
+
+    if (hasUpdate) {
+      notifyListeners();
+    }
+  }
+}