// modify the reservation that is selected
        private void modifyButton_Click(object sender, EventArgs e)
        {
            if (reservationComboBox.SelectedIndex == -1)
            {
                MessageBox.Show("Please select a reservation.");
            }
            else
            {
                // retrieve the reservation from the user input information
                ParkingReservation selectedReservation = reservationComboBox.SelectedItem as ParkingReservation;
                ModifyReservationForm modifyForm = new ModifyReservationForm(this, Database, selectedReservation, CustomerClock, Mailer);
                int indexOfChange = reservationComboBox.SelectedIndex;

                // show the form for modifying a reservation
                this.Visible = false;
                modifyForm.ShowDialog();

                // update the details view based on any changes made
                List<ParkingReservation> res = Database.GetCurrentAndFutureReservations(Customer.CustomerID);
                Reservations[indexOfChange].Date = res[indexOfChange].Date;
                Reservations[indexOfChange].DurationMinutes = res[indexOfChange].DurationMinutes;
                Reservations[indexOfChange].ReservationVehicle = res[indexOfChange].ReservationVehicle;
                Reservations[indexOfChange].ParkingSpotID = res[indexOfChange].ParkingSpotID;
                UpdateDetails();
            }
        }
        // modify the reservation that has been selected, if any exist
        private void modifyButton_Click(object sender, EventArgs e)
        {
            Garage.ParkingSpot selectedSpot = parkingSpotComboBox.SelectedItem as Garage.ParkingSpot;
            ParkingReservation currentReservation = Database.GetRelevantReservation(selectedSpot.ParkingSpotID);
            if (currentReservation == null)
            {
                MessageBox.Show("No reservation to modify.");
            }
            else
            {
                // show the form for modifying a reservation
                ModifyReservationForm modifyForm = new ModifyReservationForm(this, Database, currentReservation, OverviewClock, Mailer);
                this.Visible = false;
                modifyForm.ShowDialog();

                // update the details view
                currentReservation = Database.GetRelevantReservation(selectedSpot.ParkingSpotID);
                FillReservationDetails(currentReservation);
            }
        }