api: Change streamPostPolicy to JsonEnum

lib/api/model/model.dart

@@ -249,8 +249,8 @@ class ZulipStream {
   final bool historyPublicToSubscribers;
   final int? messageRetentionDays;
 
-  final int streamPostPolicy; // TODO enum
-  // final bool isAnnouncementOnly; // deprecated; ignore
+  final StreamPostPolicy streamPostPolicy;
+  // final bool isAnnouncementOnly; // deprecated for `streamPostPolicy`; ignore
 
   final int? canRemoveSubscribersGroupId; // TODO(server-6)
 
@@ -275,6 +275,27 @@ class ZulipStream {
   Map<String, dynamic> toJson() => _$ZulipStreamToJson(this);
 }
 
+/// Policy for which users can post to the stream.
+///
+/// For docs, search for "stream_post_policy"
+/// in <https://zulip.com/api/get-stream-by-id>
+@JsonEnum(valueField: 'apiValue')
+enum StreamPostPolicy{
+  any(apiValue: 1),
+  admin(apiValue: 2),
+  member(apiValue: 3),
+  moderator(apiValue: 4),
+  unknown(apiValue: null);
+
+  const StreamPostPolicy({
+    required this.apiValue,
+  });
+
+  final int? apiValue;
+
+  int? toJson() => apiValue;
+}
+
 /// As in `subscriptions` in the initial snapshot.
 ///
 /// For docs, search for "subscriptions:"

test/example_data.dart

@@ -103,7 +103,7 @@ ZulipStream stream({
   bool? isWebPublic,
   bool? historyPublicToSubscribers,
   int? messageRetentionDays,
-  int? streamPostPolicy,
+  StreamPostPolicy? streamPostPolicy,
   int? canRemoveSubscribersGroupId,
 }) {
   return ZulipStream(
@@ -117,7 +117,7 @@ ZulipStream stream({
     isWebPublic: isWebPublic ?? false,
     historyPublicToSubscribers: historyPublicToSubscribers ?? true,
     messageRetentionDays: messageRetentionDays,
-    streamPostPolicy: streamPostPolicy ?? 1,
+    streamPostPolicy: streamPostPolicy ?? StreamPostPolicy.any,
     canRemoveSubscribersGroupId: canRemoveSubscribersGroupId ?? 123,
   );
 }