model: Refactor Subscription to extend from ZulipStream

The properties of Subscription are a superset of ZulipStream
properties. Unfortunately this means there are duplicate
fields (such as the stream name) that live in two places and
there is no mechanism yet to synchronize them (that is work
left for zulip#182). This change makes is clearer which
properties of Subscription are specific to subscriptions.

lib/api/model/model.dart

@@ -252,7 +252,17 @@ class ZulipStream {
   final StreamPostPolicy streamPostPolicy;
   // final bool isAnnouncementOnly; // deprecated for `streamPostPolicy`; ignore
 
-  final int? canRemoveSubscribersGroupId; // TODO(server-6)
+  // TODO(server-6): `canRemoveSubscribersGroupId` added in FL 142
+  // TODO(server-8): in FL 197 renamed to `canRemoveSubscribersGroup`
+  @JsonKey(readValue: _readCanRemoveSubscribersGroup)
+  final int? canRemoveSubscribersGroup;
+
+  // TODO(server-8): added in FL 199, was previously only on [Subscription] objects
+  final int? streamWeeklyTraffic;
+
+  static int _readCanRemoveSubscribersGroup(Map json, String key) {
+    return json[key] ?? json['can_remove_subscribers_group_id'];
+  }
 
   ZulipStream({
     required this.streamId,
@@ -266,7 +276,8 @@ class ZulipStream {
     required this.historyPublicToSubscribers,
     required this.messageRetentionDays,
     required this.streamPostPolicy,
-    required this.canRemoveSubscribersGroupId,
+    required this.canRemoveSubscribersGroup,
+    required this.streamWeeklyTraffic,
   });
 
   factory ZulipStream.fromJson(Map<String, dynamic> json) =>
@@ -301,75 +312,54 @@ enum StreamPostPolicy{
 /// For docs, search for "subscriptions:"
 /// in <https://zulip.com/api/register-queue>.
 @JsonSerializable(fieldRename: FieldRename.snake)
-class Subscription {
-  // First, fields that are about the stream and not the user's relation to it.
-  // These are largely the same as in [ZulipStream].
-
-  final int streamId;
-  final String name;
-  final String description;
-  final String renderedDescription;
-
-  final int dateCreated;
-  final int? firstMessageId;
-  final int? streamWeeklyTraffic;
-
-  final bool inviteOnly;
-  final bool? isWebPublic; // TODO(server-??): doc doesn't say when added
-  final bool historyPublicToSubscribers;
-  final int? messageRetentionDays;
-  // final List<int> subscribers; // we register with includeSubscribers false
+class Subscription extends ZulipStream {
+  List<int>? subscribers;
 
-  final int streamPostPolicy; // TODO enum
-  // final bool? isAnnouncementOnly; // deprecated; ignore
-  final String emailAddress;
+  bool? desktopNotifications;
+  bool? emailNotifications;
+  bool? wildcardMentionsNotify;
+  bool? pushNotifications;
+  bool? audibleNotifications;
 
-  final int? canRemoveSubscribersGroupId; // TODO(server-6)
+  bool pinToTop;
 
-  // Then, fields that are specific to the subscription,
-  // i.e. the user's relationship to the stream.
-
-  final bool? desktopNotifications;
-  final bool? emailNotifications;
-  final bool? wildcardMentionsNotify;
-  final bool? pushNotifications;
-  final bool? audibleNotifications;
-
-  final bool pinToTop;
-
-  final bool isMuted;
+  bool isMuted;
   // final bool? inHomeView; // deprecated; ignore
 
-  final String color;
+  String color;
+  String emailAddress;
 
   Subscription({
-    required this.streamId,
-    required this.name,
-    required this.description,
-    required this.renderedDescription,
-    required this.dateCreated,
-    required this.inviteOnly,
+    required super.streamId,
+    required super.name,
+    required super.description,
+    required super.renderedDescription,
+    required super.dateCreated,
+    required super.firstMessageId,
+    required super.inviteOnly,
+    required super.isWebPublic,
+    required super.historyPublicToSubscribers,
+    required super.messageRetentionDays,
+    required super.streamPostPolicy,
+    required super.canRemoveSubscribersGroup,
+    required super.streamWeeklyTraffic,
+
+    required this.subscribers,
     required this.desktopNotifications,
     required this.emailNotifications,
     required this.wildcardMentionsNotify,
     required this.pushNotifications,
     required this.audibleNotifications,
     required this.pinToTop,
-    required this.emailAddress,
     required this.isMuted,
-    required this.isWebPublic,
     required this.color,
-    required this.streamPostPolicy,
-    required this.messageRetentionDays,
-    required this.historyPublicToSubscribers,
-    required this.firstMessageId,
-    required this.streamWeeklyTraffic,
-    required this.canRemoveSubscribersGroupId,
+    required this.emailAddress,
   });
 
   factory Subscription.fromJson(Map<String, dynamic> json) =>
     _$SubscriptionFromJson(json);
 
+  @override
   Map<String, dynamic> toJson() => _$SubscriptionToJson(this);
 }
 

test/example_data.dart

@@ -104,7 +104,8 @@ ZulipStream stream({
   bool? historyPublicToSubscribers,
   int? messageRetentionDays,
   StreamPostPolicy? streamPostPolicy,
-  int? canRemoveSubscribersGroupId,
+  int? canRemoveSubscribersGroup,
+  int? streamWeeklyTraffic,
 }) {
   return ZulipStream(
     streamId: streamId ?? 123, // TODO generate example IDs
@@ -118,7 +119,8 @@ ZulipStream stream({
     historyPublicToSubscribers: historyPublicToSubscribers ?? true,
     messageRetentionDays: messageRetentionDays,
     streamPostPolicy: streamPostPolicy ?? StreamPostPolicy.any,
-    canRemoveSubscribersGroupId: canRemoveSubscribersGroupId ?? 123,
+    canRemoveSubscribersGroup: canRemoveSubscribersGroup ?? 123,
+    streamWeeklyTraffic: streamWeeklyTraffic,
   );
 }
 const _stream = stream;