private async Task <Room> FindAvailableRoom(ReservationDTO res)
{
var reservationsInProgress = await _repository.AllInProgressByLocal(res.LocalId, res.Starttime, res.Endtime);
var allRoomsInALocal = await _roomsRepository.GetAllByLocalId(res.LocalId);
var takenRoomIdsUnique = reservationsInProgress.Select(x => x.RoomId).Distinct().ToList();
var availableRoomIds = allRoomsInALocal.Select(x => x.Id).Except(takenRoomIdsUnique).ToList();
return(_roomsRepository.GetByID(availableRoomIds.FirstOrDefault()));
}