api: Update ChannelDeleteEvent to match new API changes

There are new changes made to `stream op: delete` event in server-10:
  - The `streams` field used to be an array of just-deleted channel
    objects, but now it is an array of objects each containing only ID
    of the just-deleted channels (this would crash the app).
  - The `streams` field is also deprecated and will be removed in a
    future release.
  - As a replacement to `streams`, `stream_ids` is introduced which is
    an array of the just-deleted channel IDs.

Author: sm-sayedi

lib/api/model/events.dart

@@ -609,9 +609,14 @@ class ChannelDeleteEvent extends ChannelEvent {
   @JsonKey(includeToJson: true)
   String get op => 'delete';
 
-  final List<ZulipStream> streams;
+  final List<ZulipStreamId>? streams; // TODO(server-10): remove
+  final List<int>? streamIds; // TODO(server-10): remove nullability
 
-  ChannelDeleteEvent({required super.id, required this.streams});
+  ChannelDeleteEvent({
+    required super.id,
+    this.streams,
+    required this.streamIds,
+  }) : assert(streams != null || streamIds != null);
 
   factory ChannelDeleteEvent.fromJson(Map<String, dynamic> json) =>
     _$ChannelDeleteEventFromJson(json);
@@ -620,6 +625,18 @@ class ChannelDeleteEvent extends ChannelEvent {
   Map<String, dynamic> toJson() => _$ChannelDeleteEventToJson(this);
 }
 
+@JsonSerializable(fieldRename: FieldRename.snake)
+class ZulipStreamId {
+  final int streamId;
+
+  ZulipStreamId({required this.streamId});
+
+  factory ZulipStreamId.fromJson(Map<String, dynamic> json) =>
+    _$ZulipStreamIdFromJson(json);
+
+  Map<String, dynamic> toJson() => _$ZulipStreamIdToJson(this);
+}
+
 /// A [ChannelEvent] with op `update`: https://zulip.com/api/get-events#stream-update
 @JsonSerializable(fieldRename: FieldRename.snake)
 class ChannelUpdateEvent extends ChannelEvent {

lib/api/model/events.g.dart

@@ -370,13 +370,16 @@ class ChannelStoreImpl extends HasUserStore with ChannelStore {
         // details will come in a later `subscription` event.)
 
       case ChannelDeleteEvent():
-        for (final stream in event.streams) {
-          assert(identical(streams[stream.streamId], streamsByName[stream.name]));
-          assert(subscriptions[stream.streamId] == null
-            || identical(subscriptions[stream.streamId], streams[stream.streamId]));
-          streams.remove(stream.streamId);
-          streamsByName.remove(stream.name);
-          subscriptions.remove(stream.streamId);
+        final channelIds = event.streamIds ?? event.streams!.map((e) => e.streamId);
+        for (final channelId in channelIds) {
+          final channel = streams[channelId];
+          if (channel == null) break;
+          assert(identical(streams[channel.streamId], streamsByName[channel.name]));
+          assert(subscriptions[channelId] == null
+            || identical(subscriptions[channelId], streams[channelId]));
+          streams.remove(channel.streamId);
+          streamsByName.remove(channel.name);
+          subscriptions.remove(channel.streamId);
         }
 
       case ChannelUpdateEvent():

lib/model/channel.dart

@@ -862,7 +862,7 @@ void main() {
       // Then prepare an event on which handleEvent will throw
       // because it hits that broken invariant.
       connection.prepare(json: GetEventsResult(events: [
-        ChannelDeleteEvent(id: 1, streams: [stream]),
+        ChannelDeleteEvent(id: 1, streamIds: [stream.streamId]),
       ], queueId: null).toJson());
     }