channel: Ensure SubscriptionRemoveEvent updates all collections

Author: Khader-1

lib/api/model/model.dart

@@ -489,6 +489,24 @@ class Subscription extends ZulipStream {
 
   @override
   Map<String, dynamic> toJson() => _$SubscriptionToJson(this);
+
+  /// Returns a plain `ZulipStream` with same values as `this`
+  ///
+  /// This is helpful when unsubscribing from a stream.
+  ZulipStream toStream() => ZulipStream(
+    streamId: streamId,
+    name: name,
+    description: description,
+    renderedDescription: renderedDescription,
+    dateCreated: dateCreated,
+    firstMessageId: firstMessageId,
+    inviteOnly: inviteOnly,
+    isWebPublic: isWebPublic,
+    historyPublicToSubscribers: historyPublicToSubscribers,
+    messageRetentionDays: messageRetentionDays,
+    channelPostPolicy: channelPostPolicy,
+    canRemoveSubscribersGroup: canRemoveSubscribersGroup,
+    streamWeeklyTraffic: streamWeeklyTraffic);
 }
 
 @JsonEnum(fieldRename: FieldRename.snake, valueField: "apiValue")

lib/model/channel.dart

@@ -268,6 +268,9 @@ class ChannelStoreImpl with ChannelStore {
           }
           assert(streamsByName[subscription.name] is Subscription);
           assert(subscriptions.containsKey(streamId));
+          final unsubscribedStream = subscription.toStream();
+          streams[streamId] = unsubscribedStream;
+          streamsByName[subscription.name] = unsubscribedStream;
           subscriptions.remove(streamId);
         }
 

test/model/channel_test.dart

@@ -114,6 +114,17 @@ void main() {
         value: false));
       check(store.subscriptions[stream.streamId]!.isMuted).isTrue();
     });
+
+    test('SubscriptionRemoveEvent updates streams and streamsByName', () async {
+      final store = eg.store(initialSnapshot: eg.initialSnapshot(
+        streams: [eg.subscription(stream)],
+        subscriptions: [eg.subscription(stream)],
+      ));
+
+      check(store.streams[stream.streamId] is Subscription).isTrue();
+      await store.handleEvent(SubscriptionRemoveEvent(id: 1, streamIds: [stream.streamId]));
+      check(store.streams[stream.streamId] is Subscription).isFalse();
+    });
   });
 
   group('topic visibility', () {