practice/practiceApplicaiton/BookingEditPage.xaml.cs

namespace practiceApplicaiton;

public partial class BookingEditPage : ContentPage
{
    private readonly Booking? _booking;
    private List<Client> _clients = [];
    private List<Room> _rooms = [];

    public BookingEditPage(Booking? booking)
    {
        InitializeComponent();
        _booking = booking;
        Title = booking == null ? "Новое бронирование" : "Редактировать бронирование";
    }

    protected override async void OnAppearing()
    {
        base.OnAppearing();
        _clients = await Repository.GetClientsAsync();
        _rooms   = await Repository.GetRoomsAsync();

        ClientPicker.ItemsSource = _clients.Select(c => c.FullName).ToList();
        RoomPicker.ItemsSource   = _rooms.Select(r => $"{r.RoomNumber} ({r.TypeName})").ToList();

        if (_booking != null)
        {
            var ci = _clients.FindIndex(c => c.ClientId == _booking.ClientId);
            var ri = _rooms.FindIndex(r => r.RoomId == _booking.RoomId);
            ClientPicker.SelectedIndex  = ci;
            RoomPicker.SelectedIndex    = ri;
            CheckInPicker.Date          = _booking.CheckInDate;
            CheckOutPicker.Date         = _booking.CheckOutDate;
            PriceEntry.Text             = _booking.PricePerNight.ToString();
        }
        else
        {
            CheckInPicker.Date  = DateTime.Today;
            CheckOutPicker.Date = DateTime.Today.AddDays(3);
        }
    }

    private async void OnSaveClicked(object sender, EventArgs e)
    {
        if (ClientPicker.SelectedIndex < 0 || RoomPicker.SelectedIndex < 0)
        {
            await DisplayAlert("Ошибка", "Выберите клиента и комнату", "OK");
            return;
        }
        if (!decimal.TryParse(PriceEntry.Text, out var price) || price <= 0)
        {
            await DisplayAlert("Ошибка", "Введите корректную цену", "OK");
            return;
        }
        if (CheckOutPicker.Date <= CheckInPicker.Date)
        {
            await DisplayAlert("Ошибка", "Дата выезда должна быть позже заезда", "OK");
            return;
        }

        try
        {
            var client = _clients[ClientPicker.SelectedIndex];
            var room   = _rooms[RoomPicker.SelectedIndex];

            if (_booking == null)
                await Repository.CreateBookingAsync(client.ClientId, room.RoomId,
                    (DateTime)CheckInPicker.Date, (DateTime)CheckOutPicker.Date, price);
            else
                await Repository.UpdateBookingAsync(_booking.BookingId,
                    (DateTime)CheckInPicker.Date, (DateTime)CheckOutPicker.Date, price);

            await Navigation.PopAsync();
        }
        catch (Exception ex)
        {
            await DisplayAlert("Ошибка", ex.Message, "OK");
        }
    }
}