api: Add route subscribeToChannels

Author: Khader-1

lib/api/route/channels.dart

@@ -1,6 +1,7 @@
 import 'package:json_annotation/json_annotation.dart';
 
 import '../core.dart';
+import '../model/model.dart';
 part 'channels.g.dart';
 
 /// https://zulip.com/api/get-stream-topics
@@ -38,3 +39,27 @@ class GetStreamTopicsEntry {
 
   Map<String, dynamic> toJson() => _$GetStreamTopicsEntryToJson(this);
 }
+
+/// https://zulip.com/api/subscribe
+Future<SubscribeToChannelsResult> subscribeToChannels(ApiConnection connection, List<ZulipStream> streams) {
+  return connection.post('subscribe', SubscribeToChannelsResult.fromJson,
+    'users/me/subscriptions', {'subscriptions': streams.map((e) => {'name': e.name}).toList()});
+}
+
+@JsonSerializable(fieldRename: FieldRename.snake)
+class SubscribeToChannelsResult {
+  final Map<String, List<String>> subscribed;
+  final Map<String, List<String>> alreadySubscribed;
+  final List<String>? unauthorized;
+
+  SubscribeToChannelsResult({
+    required this.subscribed,
+    required this.alreadySubscribed,
+    this.unauthorized,
+  });
+
+  factory SubscribeToChannelsResult.fromJson(Map<String, dynamic> json) =>
+    _$SubscribeToChannelsResultFromJson(json);
+
+  Map<String, dynamic> toJson() => _$SubscribeToChannelsResultToJson(this);
+}