public RedirectToRouteResult AddTariffToCheckout(Checkout order, int TariffId, string returnUrl)
 {
     Tariff chosenTariff = tariffRepo.Tariffs
     .FirstOrDefault(p => p.Id == TariffId);
     if (chosenTariff != null)
     {
         order.InitCalc(new ValueCalculator());
         order.SetTariff(chosenTariff);
     }
     return RedirectToAction("Index", new { returnUrl });
 }