store: Update streams and subscriptions on stream-create/delete events

lib/api/model/events.dart

@@ -25,6 +25,14 @@ abstract class Event {
           case 'update': return RealmUserUpdateEvent.fromJson(json);
           default: return UnexpectedEvent.fromJson(json);
         }
+      case 'stream':
+        final op = json['op'] as String;
+        switch (op) {
+          case 'create': return StreamCreateEvent.fromJson(json);
+          case 'delete': return StreamDeleteEvent.fromJson(json);
+          // TODO(#182): case 'update': …
+          default: return UnexpectedEvent.fromJson(json);
+        }
       case 'message': return MessageEvent.fromJson(json);
       case 'heartbeat': return HeartbeatEvent.fromJson(json);
       // TODO add many more event types
@@ -179,6 +187,54 @@ class RealmUserUpdateEvent extends RealmUserEvent {
   Map<String, dynamic> toJson() => _$RealmUserUpdateEventToJson(this);
 }
 
+/// A Zulip event of type `stream`.
+abstract class StreamEvent extends Event {
+  @override
+  @JsonKey(includeToJson: true)
+  String get type => 'stream';
+
+  String get op;
+
+  StreamEvent({required super.id});
+}
+
+/// A [StreamEvent] with op `create`: https://zulip.com/api/get-events#stream-create
+@JsonSerializable(fieldRename: FieldRename.snake)
+class StreamCreateEvent extends StreamEvent {
+  @override
+  String get op => 'create';
+
+  final List<ZulipStream> streams;
+
+  StreamCreateEvent({required super.id, required this.streams});
+
+  factory StreamCreateEvent.fromJson(Map<String, dynamic> json) =>
+    _$StreamCreateEventFromJson(json);
+
+  @override
+  Map<String, dynamic> toJson() => _$StreamCreateEventToJson(this);
+}
+
+/// A [StreamEvent] with op `delete`: https://zulip.com/api/get-events#stream-delete
+@JsonSerializable(fieldRename: FieldRename.snake)
+class StreamDeleteEvent extends StreamEvent {
+  @override
+  String get op => 'delete';
+
+  final List<ZulipStream> streams;
+
+  StreamDeleteEvent({required super.id, required this.streams});
+
+  factory StreamDeleteEvent.fromJson(Map<String, dynamic> json) =>
+    _$StreamDeleteEventFromJson(json);
+
+  @override
+  Map<String, dynamic> toJson() => _$StreamDeleteEventToJson(this);
+}
+
+// TODO(#182) StreamUpdateEvent, for a [StreamEvent] with op `update`:
+//   https://zulip.com/api/get-events#stream-update
+
 /// A Zulip event of type `message`.
 // TODO use [JsonSerializable] here too, using its customization features,
 //   in order to skip the boilerplate in [fromJson] and [toJson].

lib/model/store.dart

@@ -239,6 +239,19 @@ class PerAccountStore extends ChangeNotifier {
       }
       autocompleteViewManager.handleRealmUserUpdateEvent(event);
       notifyListeners();
+    } else if (event is StreamCreateEvent) {
+      assert(debugLog("server event: stream/create"));
+      streams.addEntries(event.streams.map((stream) => MapEntry(stream.streamId, stream)));
+      // (Don't touch `subscriptions`. If the user is subscribed to the stream,
+      // details will come in a later `subscription` event.)
+      notifyListeners();
+    } else if (event is StreamDeleteEvent) {
+      assert(debugLog("server event: stream/delete"));
+      for (final stream in event.streams) {
+        streams.remove(stream.streamId);
+        subscriptions.remove(stream.streamId);
+      }
+      notifyListeners();
     } else if (event is MessageEvent) {
       assert(debugLog("server event: message ${jsonEncode(event.message.toJson())}"));
       for (final view in _messageListViews) {

test/model/test_store.dart

@@ -68,4 +68,12 @@ extension PerAccountStoreTestExtension on PerAccountStore {
       addUser(user);
     }
   }
+
+  void addStream(ZulipStream stream) {
+    addStreams([stream]);
+  }
+
+  void addStreams(List<ZulipStream> streams) {
+    handleEvent(StreamCreateEvent(id: 1, streams: streams));
+  }
 }