unreads: Handle updates when there are moved messages

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

lib/model/unreads.dart

@@ -8,6 +8,7 @@ import '../api/model/model.dart';
 import '../api/model/events.dart';
 import '../log.dart';
 import 'algorithms.dart';
+import 'message.dart';
 import 'narrow.dart';
 import 'channel.dart';
 
@@ -296,13 +297,37 @@ class Unreads extends ChangeNotifier {
         madeAnyUpdate |= mentions.add(messageId);
     }
 
-    // TODO(#901) handle moved messages
+    madeAnyUpdate |= _handleMessageMove(event);
 
     if (madeAnyUpdate) {
       notifyListeners();
     }
   }
 
+  bool _handleMessageMove(UpdateMessageEvent event) {
+    // TODO(#901) handle moved messages
+    final messageMove = UpdateMessageMoveData.tryParseFromEvent(event);
+    if (messageMove == null) {
+      // No moved messages or malformed event.
+      return false;
+    }
+
+    final topics = streams[messageMove.origStreamId];
+    if (topics == null || topics[messageMove.origTopic] == null) {
+      // No known unreads affected by move; nothing to do.
+      return false;
+    }
+
+    final messageIdsToMove = _removeAllInStreamTopic(
+      event.messageIds.toSet(),
+      messageMove.origStreamId, messageMove.origTopic);
+    assert(isSortedWithoutDuplicates(messageIdsToMove));
+    _addAllInStreamTopic(
+      messageIdsToMove..sort(),
+      messageMove.newStreamId, messageMove.newTopic);
+    return true;
+  }
+
   void handleDeleteMessageEvent(DeleteMessageEvent event) {
     mentions.removeAll(event.messageIds);
     final messageIdsSet = Set.of(event.messageIds);

test/model/unreads_test.dart

@@ -469,6 +469,32 @@ void main() {
         }
       }
     });
+
+    group('moves', () {
+      test('unknown message move', () {
+
+      });
+
+      test('tolerates unsorted event.messageIds', () {
+
+      });
+
+      test('move read message from known topic to unknown topic', () {
+
+      });
+
+      test('move unread message from known topic to known topic', () {
+
+      });
+
+      test('move unread from unknown to unknown', () {
+
+      });
+
+      test('move unread from unknown to known', () {
+
+      });
+    });
   });