ulapp/FieldLogger/ViewModels/DeviceScanViewModel.cs

using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using FieldLogger.Models;
using FieldLogger.Services;
using FieldLogger.Services.Ble;

namespace FieldLogger.ViewModels;

[QueryProperty(nameof(KindName), "kind")]
public sealed partial class DeviceScanViewModel : ObservableObject
{
    private readonly BleScanner _scanner;
    private readonly DeviceConnectionManager _manager;
    private CancellationTokenSource? _scanCts;

    [ObservableProperty]
    private string _kindName = nameof(DeviceKind.Locator);

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(ScanButtonText))]
    private bool _isScanning;

    [ObservableProperty]
    private string _title = "Select Device";

    [ObservableProperty]
    private string _hint = "";

    public ObservableCollection<DiscoveredDevice> Devices { get; } = new();

    public DeviceKind Kind => Enum.TryParse<DeviceKind>(KindName, out var k) ? k : DeviceKind.Locator;

    public string ScanButtonText => IsScanning ? "Scanning…" : "Scan Again";

    public DeviceScanViewModel(BleScanner scanner, DeviceConnectionManager manager)
    {
        _scanner = scanner;
        _manager = manager;
        _scanner.DeviceDiscovered += OnDeviceDiscovered;
    }

    partial void OnKindNameChanged(string value)
    {
        Title = Kind == DeviceKind.Locator ? "Select Locating Receiver" : "Select RTK GPS Receiver";
        Hint = Kind == DeviceKind.Locator
            ? "Looking for UM receivers (UMRX / DT100). Make sure Bluetooth is enabled on the receiver."
            : "Looking for Maglink RTK receivers. Make sure the receiver is powered on.";
    }

    [RelayCommand]
    public async Task ScanAsync()
    {
        if (IsScanning)
            return;

        Devices.Clear();
        IsScanning = true;
        _scanCts = new CancellationTokenSource();
        try
        {
            await _scanner.ScanAsync(TimeSpan.FromSeconds(12), _scanCts.Token);
        }
        catch (Exception ex)
        {
            await Shell.Current.DisplayAlert("Scan Failed", ex.Message, "OK");
        }
        finally
        {
            IsScanning = false;
            _scanCts?.Dispose();
            _scanCts = null;
        }
    }

    public void StopScan() => _scanCts?.Cancel();

    [RelayCommand]
    private async Task SelectAsync(DiscoveredDevice device)
    {
        StopScan();
        await _manager.UseDeviceAsync(Kind, device.Id, device.Name);
        await Shell.Current.GoToAsync("..");
    }

    private void OnDeviceDiscovered(object? sender, DiscoveredDevice device)
    {
        // Filter by device name prefix based on device type.
        if (Kind == DeviceKind.Locator && !UmReceiverService.IsUmReceiverName(device.Name))
            return;
        if (Kind == DeviceKind.RtkGps && !MaglinkService.IsMaglinkName(device.Name))
            return;

        MainThread.BeginInvokeOnMainThread(() =>
        {
            var existing = Devices.FirstOrDefault(d => d.Id == device.Id);
            if (existing is not null)
                Devices.Remove(existing);

            // Keep the list sorted by signal strength.
            var index = 0;
            while (index < Devices.Count && Devices[index].Rssi >= device.Rssi)
                index++;
            Devices.Insert(index, device);
        });
    }
}