Can update admin status of a user

lib/helpers/conversations_helper.dart

@@ -67,6 +67,16 @@ class ConversationsHelper {
           .addInt("userID", userID)
           .execWithThrow();
 
+  /// Update admin status of a user in a conversation
+  ///
+  /// Throws in case of failure
+  static Future<void> setAdmin(int convID, int userID, bool admin) async =>
+      await APIRequest.withLogin("conversations/setAdmin")
+          .addInt("convID", convID)
+          .addInt("userID", userID)
+          .addBool("setAdmin", admin)
+          .execWithThrow();
+
   /// Update an existing conversation
   ///
   /// Throws in case of failure

lib/models/conversation.dart

@@ -66,6 +66,9 @@ class Conversation extends SerializableElement<Conversation> {
   /// Check if the last message has been seen or not
   bool get sawLastMessage => lastActivity <= membership.lastAccessTime;
 
+  /// Check out whether a conversation is managed or not
+  bool get isManaged => groupID != null;
+
   Conversation.fromJson(Map<String, dynamic> map)
       : id = map["id"],
         name = map["name"],

lib/ui/screens/update_conversation_screen.dart

@@ -63,7 +63,9 @@ class _UpdateConversationScreen extends State<UpdateConversationScreen> {
 
   get isAdmin => !isUpdating || _conversation.isAdmin;
 
-  bool get _canAddMembers => isAdmin || _conversation.canEveryoneAddMembers;
+  bool get _canAddMembers =>
+      (isAdmin || _conversation.canEveryoneAddMembers) &&
+      (!isUpdating || !_conversation.isManaged);
 
   get _isValid => _members.length > 0;
 
@@ -221,7 +223,7 @@ class _UpdateConversationScreen extends State<UpdateConversationScreen> {
         break;
 
       case _MembersMenuChoices.TOGGLE_ADMIN_STATUS:
-        // TODO: Handle this case.
+        _toggleAdminStatus(user);
         break;
     }
   }
@@ -255,6 +257,23 @@ class _UpdateConversationScreen extends State<UpdateConversationScreen> {
     }
   }
 
+  void _toggleAdminStatus(User user) async {
+    try {
+      final setAdmin = !_admins.contains(user.id);
+      await ConversationsHelper.setAdmin(_conversation.id, user.id, setAdmin);
+
+      setState(() {
+        if (!setAdmin)
+          _admins.remove(user.id);
+        else
+          _admins.add(user.id);
+      });
+    } catch (e, s) {
+      logError(e, s);
+      snack(context, tr("Failed to toggle admin status of user!"));
+    }
+  }
+
   /// Submit the conversation
   Future<void> _submitForm() async {
     try {