api: Update ChannelDeleteEvent to match new API changes

There are new changes made to `stream op: delete` event in server-10:
  - The `streams` field which used to be an array of the just-deleted
    channel objects is now an array of objects which only contains ID
    of the just-deleted channels (this would crash the app before
    this commit).
  - The same `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

@@ -616,9 +616,24 @@ class ChannelDeleteEvent extends ChannelEvent {
   @JsonKey(includeToJson: true)
   String get op => 'delete';
 
-  final List<ZulipStream> streams;
+  @JsonKey(readValue: _readChannelIds)
+  final List<int> channelIds;
+
+  // TODO(server-10) simplify away; rely on stream_ids
+  static List<int> _readChannelIds(Map<dynamic, dynamic> json, String key) {
+    final channelIds = json['stream_ids'] as List<int>?;
+    if (channelIds != null) return channelIds;
 
-  ChannelDeleteEvent({required super.id, required this.streams});
+    final channels = json['streams'] as List<dynamic>;
+    return channels
+      .map((c) => (c as Map<String, dynamic>)['stream_id'] as int)
+      .toList();
+  }
+
+  ChannelDeleteEvent({
+    required super.id,
+    required this.channelIds,
+  });
 
   factory ChannelDeleteEvent.fromJson(Map<String, dynamic> json) =>
     _$ChannelDeleteEventFromJson(json);

lib/api/model/events.g.dart

@@ -398,13 +398,15 @@ 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);
+        for (final channelId in event.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, channelIds: [stream.streamId]),
       ], queueId: null).toJson());
     }
 

test/model/store_test.dart

@@ -340,7 +340,8 @@ void main() {
 
         testWidgets('unknown channel', (tester) async {
           await prepare();
-          await store.handleEvent(ChannelDeleteEvent(id: 1, streams: [someChannel]));
+          await store.handleEvent(ChannelDeleteEvent(id: 1,
+            channelIds: [someChannel.streamId]));
           check(store.streams[someChannel.streamId]).isNull();
           await showFromTopicListAppBar(tester);
           check(findInHeader(find.byType(Icon))).findsNothing();