private async void OnUsersChanged(object sender, UserChangedEventArgs args)
        {
            UserChangedNotification notification = new UserChangedNotification();

            notification.Type    = NotificationType.UserChanged;
            notification.NewUser = args.NewUser;
            notification.OldUser = args.OldUser;

            await BroadcastAsync(notification);
        }
        private void OnUserAddedToDataStore(object sender, UserChangedEventArgs args)
        {
            _stream.PauseStream();

            if (args.NewUser != null)
            {
                _stream.AddFollow(args.NewUser.Id);
            }

            if (args.OldUser != null)
            {
                _stream.RemoveFollow(args.OldUser.Id);
            }

            _stream.ResumeStream();
        }