ulapp/FieldLogger/Services/MaglinkService.cs

using FieldLogger.Models;
using FieldLogger.Services.Ble;
using Microsoft.Extensions.Logging;

namespace FieldLogger.Services;

/// <summary>
/// Manages the connection to the Maglink (H11) RTK GNSS receiver: parses the
/// $GNPOS / $GNDEV custom NMEA stream and sends AT configuration commands.
/// </summary>
public sealed class MaglinkService : IAsyncDisposable
{
    public static readonly Guid ServiceUuid = Guid.Parse("0000fff0-0000-1000-8000-00805f9b34fb");
    public static readonly Guid NotifyUuid = Guid.Parse("0000fff2-0000-1000-8000-00805f9b34fb");
    public static readonly Guid WriteUuid = Guid.Parse("0000fff2-0000-1000-8000-00805f9b34fb");

    private readonly BleSerialClient _client = new();
    private readonly ILogger<MaglinkService> _logger;

    public GnssFix? LatestFix { get; private set; }
    public GnssDeviceInfo? DeviceInfo { get; private set; }
    public bool IsConnected => _client.IsConnected;
    public string? DeviceName => _client.DeviceName;

    public event EventHandler<GnssFix>? FixReceived;
    public event EventHandler<GnssDeviceInfo>? DeviceInfoReceived;
    public event EventHandler? Disconnected;

    /// <summary>Device-name filter for scan results (ML-*).</summary>
    public static bool IsMaglinkName(string? name) =>
        name is not null && name.StartsWith("ML-", StringComparison.OrdinalIgnoreCase);

    public MaglinkService(ILogger<MaglinkService> logger)
    {
        _logger = logger;
        _client.LineReceived += OnLineReceived;
        _client.Disconnected += (_, _) => Disconnected?.Invoke(this, EventArgs.Empty);
    }

    public async Task ConnectAsync(Guid deviceId, CancellationToken cancellationToken = default)
    {
        await _client.ConnectAsync(deviceId, ServiceUuid, NotifyUuid, WriteUuid, cancellationToken);

        // Custom mode with GNPOS + GNDEV only - everything the app needs, minimal traffic.
        await SendCommandAsync("AT+BT_OUT=SET,1,0,1,1,0,0,0,0,0,0", cancellationToken);
    }

    /// <summary>Sends an AT command (terminator appended automatically).</summary>
    public Task SendCommandAsync(string command, CancellationToken cancellationToken = default)
        => _client.WriteLineAsync(command, cancellationToken);

    public Task DisconnectAsync() => _client.DisconnectAsync();

    /// <summary>A fix received within the last few seconds, or null if the stream has gone stale.</summary>
    public GnssFix? FreshFix(TimeSpan? maxAge = null)
    {
        var fix = LatestFix;
        if (fix is null)
            return null;
        return DateTime.UtcNow - fix.ReceivedUtc <= (maxAge ?? TimeSpan.FromSeconds(5)) ? fix : null;
    }

    private void OnLineReceived(object? sender, string line)
    {
        if (line.StartsWith("$GNPOS,", StringComparison.Ordinal))
        {
            if (!NmeaSentence.VerifyChecksum(line))
            {
                _logger.LogWarning("GNPOS checksum failed: {Line}", line);
                return;
            }
            var fix = GnssFix.TryParse(line);
            if (fix is not null)
            {
                LatestFix = fix;
                FixReceived?.Invoke(this, fix);
            }
        }
        else if (line.StartsWith("$GNDEV,", StringComparison.Ordinal))
        {
            if (!NmeaSentence.VerifyChecksum(line))
                return;
            var info = GnssDeviceInfo.TryParse(line);
            if (info is not null)
            {
                DeviceInfo = info;
                DeviceInfoReceived?.Invoke(this, info);
            }
        }
        else
        {
            // AT command responses and anything else.
            _logger.LogDebug("Maglink rx: {Line}", line);
        }
    }

    public ValueTask DisposeAsync() => _client.DisposeAsync();
}