public string CheckWasReturnDelayed(Book book) { var currentDate = DateTime.Now; var borrowDate = book.Customer.BorrowDate; int daysBookWasBorrowed = (currentDate - borrowDate).Days; if (daysBookWasBorrowed > 60) { return(_errorService.ReturnDelayedReturnErrorMessage()); } throw new Exception("You returned the book with dalay"); }