public static void GenerateSpecificUserSummary(int userID)
        {
            List <Reservation> userPastReservations = ReservationCalendar.GetSpecificUserPastReservations(userID);

            List <string> output = new List <string>();
            string        currentlyLoggedUsername = CurrentlyLoggedUser.GetSpecificUserUsername();
            string        filePath  = $"{currentlyLoggedUsername}Summary.txt";
            string        firstLine = $"Reservation summary for client {currentlyLoggedUsername}:";

            output.Add(firstLine);
            int totalSpentSum = 0;
            int totalRentDays = 0;

            foreach (var reservation in userPastReservations)
            {
                DateTime pickUp            = Convert.ToDateTime(reservation.rentedFrom);
                DateTime dropOff           = Convert.ToDateTime(reservation.rentedTo);
                int      numberOfRentDays  = (dropOff.Date - pickUp.Date).Days;
                int      oneReservationSum = CarList.getSpecificCarRentPrice(reservation.carId) * numberOfRentDays;
                totalSpentSum += oneReservationSum;
                totalRentDays += numberOfRentDays;

                output.Add($"Car {CarList.getSpecificCarName(reservation.carId)} rented from {reservation.rentedFrom} to {reservation.rentedTo} ({numberOfRentDays} days)" +
                           $" for total of {oneReservationSum}PLN");
            }
            string lastLine = $"Total sum spent: {totalSpentSum}PLN, total rent days: {totalRentDays}";

            output.Add(lastLine);
            File.WriteAllLines(filePath, output);
        }
        private void Login_Button_Click(object sender, RoutedEventArgs e)
        {
            string inputPassword = password.Password;
            string inputUsername = username.Text;

            bool switcher = true;

            if (string.IsNullOrEmpty(inputUsername))
            {
                System.Windows.MessageBox.Show("Username box is empty");
                switcher = false;
            }
            else if (string.IsNullOrEmpty(inputPassword))
            {
                System.Windows.MessageBox.Show("Password box is empty");
                switcher = false;
            }

            if (switcher)
            {
                if (AdminList.isOnTheList(inputUsername, inputPassword))
                {
                    System.Windows.MessageBox.Show("You are successfully logged in as an admin!");
                    Admin_ControlPanel admin_ControlPanel = new Admin_ControlPanel(this.Left, this.Top);
                    admin_ControlPanel.Show();
                    Close();
                }
                else if (UserList.isOnTheList(inputUsername, inputPassword))
                {
                    CurrentlyLoggedUser.InitilizeCurrentyLoggedUser(UserList.GetId(inputUsername, inputPassword));
                    System.Windows.MessageBox.Show("You are successfully logged in as an user!");
                    User_ControlPanel user_ControlPanel = new User_ControlPanel(this.Left, this.Top);
                    user_ControlPanel.Show();
                    Close();
                }
                else
                {
                    System.Windows.MessageBox.Show("Account does not exist! Click REGISTER button in order to register.");
                }
            }
        }