using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.IO.Ports;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Timers;
using System.Windows;
using AgroBase.Models;
using AgroBase.Services;
using OperationControl.Models;
using static AgroBase.Models.Enums;
using static OperationControl.Services.BaseFixService;
using Application = System.Windows.Application;

namespace OperationControl.Services
{
    /// <summary>
    /// Serviço do UM982 da base.
    ///
    /// Princípios desta implementação:
    /// 1) O callback serial apenas lê, separa e enfileira. Nunca publica na rede.
    /// 2) NMEA e RTCM são demultiplexados por uma única máquina de estados.
    /// 3) RTCM só é encaminhado após validação CRC24Q.
    /// 4) A fila RTCM mantém apenas a mensagem mais nova de cada tipo.
    /// 5) Mensagens RTCM antigas são descartadas antes da publicação.
    /// 6) Reconectar a USB não altera silenciosamente o papel do GNSS.
    /// 7) Todas as escritas no UM982 passam por um único lock.
    /// 8) O cliente NTRIP possui cancelamento real e não mistura StreamReader com dados binários.
    /// </summary>
    public sealed class GpsService : IDisposable
    {
        // =========================================================
        // CONFIGURAÇÃO GERAL
        // =========================================================

        private const int DefaultBaudRate = 115200;
        private static readonly TimeSpan SerialSilenceReconnectTimeout = TimeSpan.FromSeconds(15);
        private static readonly TimeSpan SerialReconnectGrace = TimeSpan.FromSeconds(10);
        private static readonly TimeSpan RtcmAssemblyTimeout = TimeSpan.FromSeconds(1.5);
        private static readonly TimeSpan NmeaAssemblyTimeout = TimeSpan.FromSeconds(2.0);
        private static readonly TimeSpan RtcmMaxQueueAge = TimeSpan.FromSeconds(2.5);

        private readonly System.Timers.Timer _tmrCheck = new(2000) { AutoReset = true };
        private readonly SemaphoreSlim _scanGate = new(1, 1);
        private readonly SemaphoreSlim _serialWriteGate = new(1, 1);
        private readonly object _portLock = new();
        private readonly object _parserLock = new();
        private readonly object _modelLock = new();
        private readonly object _rtcmQueueLock = new();
        private readonly object _ntripLock = new();

        private readonly CancellationTokenSource _lifetimeCts = new();
        private readonly SemaphoreSlim _rtcmSignal = new(0);
        private readonly Dictionary<int, RtcmEnvelope> _rtcmLatestByType = new();
        private readonly Task _rtcmPublisherTask;

        private int _timerRunning;
        private int _disposed;
        private int _uiUpdatePending;

        private double _serialConnectedMono;
        private double _lastSerialRxMono;
        private double _lastValidNmeaMono;
        private double _lastValidGgaMono;
        private double _lastValidRtcmMono;
        private double _lastForwardedRtcmMono;

        private long _ggaSequence;
        private long _rtcmSequence;

        public GpsService()
        {
            BaseFix = new BaseFixService(null, this);

            _rtcmPublisherTask = Task.Run(
                () => RtcmPublisherLoopAsync(_lifetimeCts.Token),
                _lifetimeCts.Token);

            _tmrCheck.Elapsed += (_, __) => _ = CheckConnectionAsync();
            _tmrCheck.Start();
        }

        // =========================================================
        // ESTADO PÚBLICO / COMPATIBILIDADE
        // =========================================================

        public SerialPort PortaGps { get; private set; }

        public bool IsConnected
        {
            get
            {
                lock (_portLock)
                    return PortaGps != null && PortaGps.IsOpen;
            }
        }

        public string PortName
        {
            get
            {
                lock (_portLock)
                    return PortaGps?.PortName;
            }
        }

        private bool InverterHeading = false;
        private volatile bool CorrecaoRTK_Ntrip = false;
        private int TempoSurveryIn = 120;

        public volatile bool Ntrip_Conectado = false;
        public int TaxaAmostragemHz = 5;
        private int rtk_timeout = 60;
        public GPSModel UltimaLeitura = new GPSModel();
        public BaseFixService BaseFix;
        public GeoLeverArm LeverArm = new GeoLeverArm();

        /// <summary>
        /// Configure usuário e senha por variável de ambiente ou externamente.
        /// Nunca mantenha a senha NTRIP no código-fonte.
        /// </summary>
        public string NtripHost { get; set; } = "gps-ntrip.ibge.gov.br";
        public int NtripPort { get; set; } = 2101;
        public string NtripMountpoint { get; set; } = "EESC0";
        public string NtripUsername { get; set; } = "Zendion"; // Environment.GetEnvironmentVariable("AGRO_NTRIP_USERNAME") ?? string.Empty;
        public string NtripPassword { get; set; } = "kY3zd$*5"; //Environment.GetEnvironmentVariable("AGRO_NTRIP_PASSWORD") ?? string.Empty;

        private GnssExpectedRole _expectedRole = GnssExpectedRole.PreserveCurrentConfiguration;
        private BaseFixedConfiguration _lastBaseConfiguration;

        // =========================================================
        // MÉTRICAS
        // =========================================================

        private long _serialBytesReceived;
        private long _serialReadErrors;
        private long _nmeaValid;
        private long _nmeaInvalid;
        private long _nmeaChecksumErrors;
        private long _rtcmValid;
        private long _rtcmCrcErrors;
        private long _rtcmInvalidLength;
        private long _rtcmResyncs;
        private long _rtcmQueued;
        private long _rtcmReplaced;
        private long _rtcmDroppedStale;
        private long _rtcmForwarded;
        private long _rtcmPublishErrors;
        private long _serialReconnects;
        private long _ntripBytesReceived;
        private long _ntripReconnects;
        private long _ntripErrors;

        public GpsTransportMetrics GetTransportMetrics()
        {
            int queueDepth;
            double oldestQueueAgeMs = 0;

            lock (_rtcmQueueLock)
            {
                queueDepth = _rtcmLatestByType.Count;
                if (queueDepth > 0)
                {
                    double now = MonotonicNow();
                    oldestQueueAgeMs = _rtcmLatestByType.Values
                        .Max(x => Math.Max(0, (now - x.ReceivedMono) * 1000.0));
                }
            }

            double nowMono = MonotonicNow();

            return new GpsTransportMetrics
            {
                SerialConnected = IsConnected,
                PortName = PortName,
                SerialLastRxAgeMs = AgeMs(nowMono, _lastSerialRxMono),
                LastValidNmeaAgeMs = AgeMs(nowMono, _lastValidNmeaMono),
                LastValidGgaAgeMs = AgeMs(nowMono, _lastValidGgaMono),
                LastValidRtcmAgeMs = AgeMs(nowMono, _lastValidRtcmMono),
                LastForwardedRtcmAgeMs = AgeMs(nowMono, _lastForwardedRtcmMono),
                SerialBytesReceived = Interlocked.Read(ref _serialBytesReceived),
                SerialReadErrors = Interlocked.Read(ref _serialReadErrors),
                NmeaValid = Interlocked.Read(ref _nmeaValid),
                NmeaInvalid = Interlocked.Read(ref _nmeaInvalid),
                NmeaChecksumErrors = Interlocked.Read(ref _nmeaChecksumErrors),
                RtcmValid = Interlocked.Read(ref _rtcmValid),
                RtcmCrcErrors = Interlocked.Read(ref _rtcmCrcErrors),
                RtcmInvalidLength = Interlocked.Read(ref _rtcmInvalidLength),
                RtcmResyncs = Interlocked.Read(ref _rtcmResyncs),
                RtcmQueued = Interlocked.Read(ref _rtcmQueued),
                RtcmReplaced = Interlocked.Read(ref _rtcmReplaced),
                RtcmDroppedStale = Interlocked.Read(ref _rtcmDroppedStale),
                RtcmForwarded = Interlocked.Read(ref _rtcmForwarded),
                RtcmPublishErrors = Interlocked.Read(ref _rtcmPublishErrors),
                RtcmQueueDepth = queueDepth,
                RtcmOldestQueueAgeMs = oldestQueueAgeMs,
                SerialReconnects = Interlocked.Read(ref _serialReconnects),
                NtripConnected = Ntrip_Conectado,
                NtripBytesReceived = Interlocked.Read(ref _ntripBytesReceived),
                NtripReconnects = Interlocked.Read(ref _ntripReconnects),
                NtripErrors = Interlocked.Read(ref _ntripErrors),
                ExpectedRole = _expectedRole.ToString(),
            };
        }

        // =========================================================
        // DESCOBERTA / RECONEXÃO SERIAL
        // =========================================================

        private async Task CheckConnectionAsync()
        {
            if (Interlocked.CompareExchange(ref _timerRunning, 1, 0) != 0)
                return;

            try
            {
                if (Volatile.Read(ref _disposed) != 0)
                    return;

                bool connected = IsConnected;
                double now = MonotonicNow();

                if (connected)
                {
                    bool graceEnded =
                        _serialConnectedMono > 0 &&
                        (now - _serialConnectedMono) >= SerialReconnectGrace.TotalSeconds;

                    double lastActivity = _lastSerialRxMono > 0
                        ? _lastSerialRxMono
                        : _serialConnectedMono;

                    bool silentTooLong =
                        lastActivity > 0 &&
                        (now - lastActivity) >= SerialSilenceReconnectTimeout.TotalSeconds;

                    if (!graceEnded || !silentTooLong)
                        return;

                    Models.Variaveis.MostrarLog(
                        $"GNSS sem dados há {(now - _lastSerialRxMono):F1}s. Reiniciando conexão serial.");

                    DisconnectInternal();
                }

                bool found = await ScanAndConnectAsync(
                    timeoutPorPortaMs: 1500,
                    ct: _lifetimeCts.Token).ConfigureAwait(false);

                if (found)
                {
                    Models.Variaveis.MostrarLog($"GPS conectado na porta {PortName}");
                    await RestoreExpectedRoleAfterReconnectAsync(_lifetimeCts.Token).ConfigureAwait(false);
                }
                else
                {
                    Models.Variaveis.MostrarLog("Nenhum GPS UM982 encontrado.");
                }
            }
            catch (OperationCanceledException)
            {
            }
            catch (Exception ex)
            {
                Models.Variaveis.MostrarLog($"Erro ao verificar conexão do GNSS: {ex.Message}");
            }
            finally
            {
                Interlocked.Exchange(ref _timerRunning, 0);
            }
        }

        public async Task<bool> ScanAndConnectAsync(
            int timeoutPorPortaMs = 1500,
            CancellationToken ct = default)
        {
            if (IsConnected)
                return true;

            await _scanGate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                if (IsConnected)
                    return true;

                string[] portas = SerialPort.GetPortNames()
                    .OrderBy(p => p)
                    .ToArray();

                foreach (string portName in portas)
                {
                    ct.ThrowIfCancellationRequested();

                    if (await TryConnectOnPortAsync(portName, timeoutPorPortaMs, ct)
                        .ConfigureAwait(false))
                    {
                        Interlocked.Increment(ref _serialReconnects);
                        return true;
                    }
                }

                return false;
            }
            finally
            {
                _scanGate.Release();
            }
        }

        private async Task<bool> TryConnectOnPortAsync(
            string portName,
            int timeoutMs,
            CancellationToken ct)
        {
            SerialPort porta = null;

            try
            {
                porta = new SerialPort(portName, DefaultBaudRate)
                {
                    ReadTimeout = timeoutMs,
                    WriteTimeout = timeoutMs,
                    NewLine = "\n",
                    DtrEnable = false,
                    RtsEnable = false,
                    ReadBufferSize = 64 * 1024,
                    WriteBufferSize = 16 * 1024,
                };

                porta.Open();

                if (!await EhUm982PorVersionAsync(porta, timeoutMs, ct).ConfigureAwait(false))
                {
                    // Fallback não persistente: pede apenas GGA para confirmar que é GNSS.
                    byte[] nmea = Encoding.ASCII.GetBytes("gngga com2 1\r\n");
                    porta.Write(nmea, 0, nmea.Length);
                    await Task.Delay(200, ct).ConfigureAwait(false);

                    string sample = await LerAmostraAsync(porta, timeoutMs, ct).ConfigureAwait(false);
                    if (!EhGpsUm982OuNmea(sample))
                    {
                        porta.Close();
                        porta.Dispose();
                        return false;
                    }
                }

                RegisterConnectedPort(porta);
                return true;
            }
            catch (OperationCanceledException)
            {
                try { porta?.Close(); } catch { }
                try { porta?.Dispose(); } catch { }
                throw;
            }
            catch
            {
                try { porta?.Close(); } catch { }
                try { porta?.Dispose(); } catch { }
                return false;
            }
        }

        private void RegisterConnectedPort(SerialPort porta)
        {
            DisconnectInternal();

            lock (_portLock)
            {
                PortaGps = porta;
                PortaGps.DataReceived -= PortaGPS_DataReceived;
                PortaGps.DataReceived += PortaGPS_DataReceived;
            }

            ResetParsers();
            _serialConnectedMono = MonotonicNow();
            _lastSerialRxMono = 0;
        }

        private async Task<string> LerAmostraAsync(
            SerialPort porta,
            int timeoutMs,
            CancellationToken ct)
        {
            double start = MonotonicNow();
            StringBuilder buffer = new();

            while ((MonotonicNow() - start) * 1000.0 < timeoutMs)
            {
                ct.ThrowIfCancellationRequested();

                try
                {
                    int available = porta.BytesToRead;
                    if (available > 0)
                    {
                        byte[] temp = new byte[available];
                        int read = porta.Read(temp, 0, temp.Length);
                        if (read > 0)
                        {
                            buffer.Append(Encoding.ASCII.GetString(temp, 0, read));
                            string text = buffer.ToString();

                            if (text.Contains("UM982", StringComparison.OrdinalIgnoreCase) ||
                                text.Contains("$GP", StringComparison.OrdinalIgnoreCase) ||
                                text.Contains("$GN", StringComparison.OrdinalIgnoreCase))
                            {
                                break;
                            }
                        }
                    }
                }
                catch
                {
                    break;
                }

                await Task.Delay(50, ct).ConfigureAwait(false);
            }

            return buffer.ToString();
        }

        private static bool EhGpsUm982OuNmea(string recebido)
        {
            if (string.IsNullOrEmpty(recebido))
                return false;

            return recebido.Contains("UM982", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPTXT", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPRMC", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPGGA", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPGLL", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GNGGA", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPVTG", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GPGSV", StringComparison.OrdinalIgnoreCase) ||
                   recebido.Contains("$GNTHS", StringComparison.OrdinalIgnoreCase);
        }

        private async Task<bool> EhUm982PorVersionAsync(
            SerialPort porta,
            int timeoutMs,
            CancellationToken ct)
        {
            try
            {
                porta.DiscardInBuffer();
                byte[] cmd = Encoding.ASCII.GetBytes("version\r\n");
                porta.Write(cmd, 0, cmd.Length);

                await Task.Delay(100, ct).ConfigureAwait(false);
                string response = await LerAmostraAsync(porta, timeoutMs, ct).ConfigureAwait(false);

                return !string.IsNullOrEmpty(response) &&
                       response.Contains("UM982", StringComparison.OrdinalIgnoreCase);
            }
            catch
            {
                return false;
            }
        }

        public void Disconnect()
        {
            DisconnectInternal();
        }

        private void DisconnectInternal()
        {
            SerialPort port;

            lock (_portLock)
            {
                port = PortaGps;
                PortaGps = null;
            }

            if (port == null)
                return;

            try { port.DataReceived -= PortaGPS_DataReceived; } catch { }
            try { if (port.IsOpen) port.Close(); } catch { }
            try { port.Dispose(); } catch { }
        }

        private async Task RestoreExpectedRoleAfterReconnectAsync(CancellationToken ct)
        {
            // A regra mais importante é: uma reconexão nunca muda o papel do módulo
            // para rover por conta própria.
            if (_expectedRole == GnssExpectedRole.BaseFixed && _lastBaseConfiguration != null)
            {
                Models.Variaveis.MostrarLog("Restaurando configuração conhecida da base fixa após reconexão.");
                await BaseFix.AplicarBaseFixAsync(
                    _lastBaseConfiguration.PortaUsb,
                    _lastBaseConfiguration.PortaSaida,
                    _lastBaseConfiguration.BaseId,
                    _lastBaseConfiguration.Latitude,
                    _lastBaseConfiguration.Longitude,
                    _lastBaseConfiguration.AltitudeElipsoidal,
                    ct).ConfigureAwait(false);
            }
            else if (_expectedRole == GnssExpectedRole.RoverTemporary)
            {
                Models.Variaveis.MostrarLog("Restaurando modo rover temporário após reconexão.");
                await BaseFix.ConfigurarComoRoverParadoAsync("com2", "com2", ct)
                    .ConfigureAwait(false);
            }
            // PreserveCurrentConfiguration: não envia unlog, mode rover ou saveconfig.
        }

        // =========================================================
        // ESCRITA SERIAL SERIALIZADA
        // =========================================================

        internal async Task WriteSerialAsync(
            byte[] data,
            CancellationToken ct = default)
        {
            if (data == null || data.Length == 0)
                return;

            await _serialWriteGate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                SerialPort port;
                lock (_portLock)
                    port = PortaGps;

                if (port == null || !port.IsOpen)
                    throw new IOException("Porta do GNSS não está conectada.");

                port.Write(data, 0, data.Length);
            }
            finally
            {
                _serialWriteGate.Release();
            }
        }

        internal Task WriteSerialCommandAsync(
            string command,
            CancellationToken ct = default)
        {
            return WriteSerialAsync(Encoding.ASCII.GetBytes(command), ct);
        }

        internal async Task SendCommandsAsync(
            IEnumerable<string> commands,
            int delayMs,
            CancellationToken ct = default)
        {
            foreach (string command in commands)
            {
                ct.ThrowIfCancellationRequested();
                await WriteSerialCommandAsync(command, ct).ConfigureAwait(false);
                if (delayMs > 0)
                    await Task.Delay(delayMs, ct).ConfigureAwait(false);
            }
        }

        // =========================================================
        // CONFIGURAÇÃO DO MÓDULO
        // =========================================================

        public async Task ConfigurarModulo(
            bool fixar,
            MetodoFixacaoBase metodo = MetodoFixacaoBase.Ntrip,
            double? lat = null,
            double? lon = null,
            double? alt = null,
            bool? offset = false)
        {
            Models.Variaveis.MostrarLog("Iniciando configuração do módulo GPS...");

            BaseFix ??= new BaseFixService(PortaGps, this);
            BaseFix.FixLiberado = fixar;

            const string portaUsb = "com2";
            const string portaSaida = "com2";
            const string portaEntrada = "com2";
            const string baseId = "957";

            if (!fixar)
            {
                Models.Variaveis.MostrarLog(
                    "Configurando explicitamente o módulo como rover parado."
                );


                await BaseFix
                    .ConfigurarComoRoverParadoAsync(
                        portaUsb,
                        portaEntrada,
                        _lifetimeCts.Token
                    )
                    .ConfigureAwait(false);


                DefinirPapelEsperado(
                    GnssExpectedRole.RoverTemporary
                );


                return;
            }

            /*
             * Vamos iniciar uma configuração de BASE.
             *
             * Se estávamos fazendo levantamento móvel
             * com NTRIP, encerramos a injeção RTCM antes
             * de começar a enviar os comandos da base.
             *
             * No método NTRIP, FixarBaseViaNtripAsync()
             * iniciará novamente a correção no momento
             * correto.
             */
            await StopNtripAsync().ConfigureAwait(false);

            bool sucesso = false;
            string mensagem;

            try
            {
                BaseFix.fimProcesso = null;
                BaseFix.inicioProcesso = DateTime.UtcNow;
                BaseFix.inicioFix = DateTime.UtcNow;
                BaseFix.CorrecaoEmAndamento = true;

                Models.Variaveis.MostrarLog($"Aplicando posição fixa da base com o método {metodo}...");

                switch (metodo)
                {
                    case MetodoFixacaoBase.Ntrip:
                        BaseFix.DefinirTempos(
                            segsFixEstavel: TempoSurveryIn,
                            segsJanelaSegs: 600,
                            metodo: metodo);

                        sucesso = await BaseFix.FixarBaseViaNtripAsync(
                            portaUsb: portaUsb,
                            portaSaida: portaSaida,
                            portaEntrada: portaEntrada,
                            baseId: baseId,
                            startNtrip: StartNtripAsync,
                            stopNtrip: StopNtripAsync,
                            ct: _lifetimeCts.Token).ConfigureAwait(false);
                        break;

                    case MetodoFixacaoBase.SurveyIn:
                        BaseFix.DefinirTempos(
                            segsFixEstavel: TempoSurveryIn,
                            segsJanelaSegs: TempoSurveryIn + 30,
                            metodo: metodo);

                        await ConfigurarModuloBase(
                            tempo_fixacao: TempoSurveryIn,
                            porta_usb: portaUsb,
                            porta_saida: portaSaida,
                            ct: _lifetimeCts.Token).ConfigureAwait(false);

                        DateTime surveyDeadline = DateTime.UtcNow.AddSeconds(TempoSurveryIn + 30);
                        while (DateTime.UtcNow < surveyDeadline &&
                               GetFixQualitySnapshot() != TiposCorrecaoGPS.BaseFix)
                        {
                            await Task.Delay(500, _lifetimeCts.Token).ConfigureAwait(false);
                        }

                        sucesso = GetFixQualitySnapshot() == TiposCorrecaoGPS.BaseFix;
                        break;

                    case MetodoFixacaoBase.Manual:
                        if (lat.HasValue && lon.HasValue && alt.HasValue)
                        {
                            BaseFix.DefinirTempos(10, 10, metodo);
                            await BaseFix.AplicarBaseFixAsync(
                                portaUsb,
                                portaSaida,
                                baseId,
                                lat.Value,
                                lon.Value,
                                alt.Value,
                                _lifetimeCts.Token).ConfigureAwait(false);
                            sucesso = true;
                        }
                        break;
                }

                if (sucesso)
                {
                    DateTime deadline = DateTime.UtcNow.AddSeconds(10);
                    while (DateTime.UtcNow < deadline &&
                           GetFixQualitySnapshot() != TiposCorrecaoGPS.BaseFix)
                    {
                        await Task.Delay(500, _lifetimeCts.Token).ConfigureAwait(false);
                    }

                    sucesso = GetFixQualitySnapshot() == TiposCorrecaoGPS.BaseFix;
                }
            }
            catch (OperationCanceledException)
            {
                sucesso = false;
            }
            catch (Exception ex)
            {
                sucesso = false;
                Models.Variaveis.MostrarLog($"Erro ao definir posição da base: {ex.Message}");
            }
            finally
            {
                BaseFix.fimProcesso = DateTime.UtcNow;
                BaseFix.FixLiberado = false;
                BaseFix.CorrecaoEmAndamento = false;

                if (sucesso)
                {
                    var snapshot = GetPositionSnapshot();
                    DefinirPapelEsperado(
                        GnssExpectedRole.BaseFixed
                    );
                    _lastBaseConfiguration = new BaseFixedConfiguration
                    {
                        PortaUsb = portaUsb,
                        PortaSaida = portaSaida,
                        BaseId = baseId,
                        Latitude = snapshot.Latitude,
                        Longitude = snapshot.Longitude,
                        AltitudeElipsoidal = snapshot.AltitudeElipsoidal,
                    };

                    if (!(offset ?? false))
                    {
                        BaseFix.LatitudeFix = snapshot.Latitude;
                        BaseFix.LongitudeFix = snapshot.Longitude;
                        BaseFix.AltitudeElpsoidalFix = snapshot.AltitudeElipsoidal;
                        BaseFix.OrientacaoFix = snapshot.Orientacao;
                    }
                }

                if (!(offset ?? false) &&
                    AppShell.Mock &&
                    lat.HasValue && lon.HasValue && alt.HasValue)
                {
                    lock (_modelLock)
                    {
                        UltimaLeitura.Latitude = lat.Value;
                        UltimaLeitura.Longitude = lon.Value;
                        UltimaLeitura.AltitudeElipsoidal = alt.Value;
                    }
                    AtualizarCoordenadasGPS();
                    sucesso = true;
                }

                mensagem = sucesso
                    ? $"Posição da base aplicada com sucesso com o método {metodo}."
                    : $"Falha ao aplicar posição da base com o método {metodo}.";

                Models.Variaveis.MostrarLog(mensagem);
                Models.Variaveis.Dock?._vm?.FinalizarFixacaoBase(sucesso, mensagem);
            }
        }

        private async Task ConfigurarModuloBase(
            string porta_usb = "com3",
            string porta_saida = "com2",
            int tempo_fixacao = 60,
            CancellationToken ct = default)
        {
            const string baseId = "957";
            const string distanciaMin = "0";

            string[] commands =
            {
                "config com1 115200\r\n",
                "config com2 115200\r\n",
                "config com3 115200\r\n",
                "unlog com1\r\n",
                "unlog com2\r\n",
                "unlog com3\r\n",
                $"mode base {baseId} time {tempo_fixacao} {distanciaMin}\r\n",
                $"RTCM1006 {porta_saida} 10\r\n",
                $"RTCM1033 {porta_saida} 30\r\n",
                $"RTCM1074 {porta_saida} 1\r\n",
                $"RTCM1084 {porta_saida} 1\r\n",
                $"RTCM1094 {porta_saida} 1\r\n",
                $"RTCM1124 {porta_saida} 1\r\n",
                $"RTCM1230 {porta_saida} 10\r\n",
                $"gngga {porta_usb} 1\r\n",
                "saveconfig\r\n",
            };

            await Task.Delay(1000, ct).ConfigureAwait(false);
            await SendCommandsAsync(commands, 300, ct).ConfigureAwait(false);
            
            if (AppShell.Mock)
                _expectedRole = GnssExpectedRole.BaseFixed;
        }

        public async Task ConfigurarComoMovelParaLevantamentoAsync(bool usarNtrip = true)
        {
            if (!IsConnected)
            {
                throw new InvalidOperationException(
                    "O GNSS não está conectado."
                );
            }


            if (
                BaseFix?.CorrecaoEmAndamento ==
                true
            )
            {
                throw new InvalidOperationException(
                    "Existe uma fixação da base em andamento."
                );
            }


            Models.Variaveis.MostrarLog(
                "[GNSS][PAPEL] " +
                "Alterando para modo móvel / levantamento..."
            );


            /*
             * Se existia uma sessão NTRIP anterior,
             * encerramos antes de enviar comandos ASCII.
             *
             * Isso evita RTCM binário concorrendo com
             * configuração do UM982.
             */
            await StopNtripAsync()
                .ConfigureAwait(false);


            BaseFix?.ReiniciarFix();


            /*
             * ConfigurarModulo(false):
             *
             * - unlog
             * - mode rover uav
             * - GGA
             * - heading
             * - papel esperado = RoverTemporary
             */
            await ConfigurarModulo(
                fixar: false
            )
            .ConfigureAwait(false);


            /*
             * Para levantamento queremos precisão RTK.
             *
             * Portanto o receptor volta a receber
             * correções do caster depois de estar em
             * modo rover.
             */
            if (usarNtrip)
            {
                await StartNtripAsync()
                    .ConfigureAwait(false);
            }


            Models.Variaveis.MostrarLog(
                "[GNSS][PAPEL] " +
                $"Modo móvel ativo | " +
                $"NTRIP={(usarNtrip ? "SOLICITADO" : "NÃO")}"
            );
        }

        // =========================================================
        // LEITURA SERIAL E DEMULTIPLEXAÇÃO
        // =========================================================

        private ParserMode _parserMode = ParserMode.Idle;
        private readonly List<byte> _rtcmBuffer = new(1100);
        private readonly List<byte> _nmeaBuffer = new(256);
        private int _rtcmExpectedBytes = -1;
        private double _frameStartedMono;

        private void PortaGPS_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            try
            {
                SerialPort port;
                lock (_portLock)
                    port = PortaGps;

                if (port == null || !port.IsOpen)
                    return;

                int available = port.BytesToRead;
                if (available <= 0)
                    return;

                byte[] buffer = new byte[available];
                int bytesRead = port.Read(buffer, 0, buffer.Length);
                if (bytesRead <= 0)
                    return;

                double now = MonotonicNow();
                _lastSerialRxMono = now;
                Interlocked.Add(ref _serialBytesReceived, bytesRead);

                List<string> nmeaLines = new();
                List<byte[]> rtcmMessages = new();

                lock (_parserLock)
                {
                    for (int i = 0; i < bytesRead; i++)
                    {
                        ProcessIncomingByte(buffer[i], nmeaLines, rtcmMessages);
                    }
                }

                foreach (string line in nmeaLines)
                    ProcessNmeaSafely(line);

                foreach (byte[] message in rtcmMessages)
                    EnqueueRtcm(message);

                lock (_modelLock)
                {
                    UltimaLeitura.Momento = DateTime.Now;
                    UltimaLeitura.Inicializado = true;
                }
            }
            catch (Exception ex)
            {
                Interlocked.Increment(ref _serialReadErrors);
                Models.Variaveis.MostrarLog($"Erro ao processar dados da porta serial: {ex.Message}");
            }
        }

        private void ProcessIncomingByte(
            byte b,
            List<string> nmeaLines,
            List<byte[]> rtcmMessages)
        {
            double now = MonotonicNow();

            if (_parserMode == ParserMode.Rtcm &&
                (now - _frameStartedMono) > RtcmAssemblyTimeout.TotalSeconds)
            {
                ResetParserState();
                Interlocked.Increment(ref _rtcmResyncs);
            }
            else if (_parserMode == ParserMode.Nmea &&
                     (now - _frameStartedMono) > NmeaAssemblyTimeout.TotalSeconds)
            {
                ResetParserState();
                Interlocked.Increment(ref _nmeaInvalid);
            }

            switch (_parserMode)
            {
                case ParserMode.Idle:
                    StartFrameIfApplicable(b, now);
                    break;

                case ParserMode.Nmea:
                    // Uma sentença quebrada não pode esconder um RTCM novo.
                    if (b == 0xD3)
                    {
                        Interlocked.Increment(ref _nmeaInvalid);
                        StartRtcm(now);
                        return;
                    }

                    if (b == (byte)'$')
                    {
                        // Reinicia na sentença NMEA mais recente.
                        StartNmea(now);
                        return;
                    }

                    if (b == (byte)'\n')
                    {
                        _nmeaBuffer.Add(b);
                        string line = Encoding.ASCII.GetString(_nmeaBuffer.ToArray()).Trim();
                        ResetParserState();
                        if (!string.IsNullOrWhiteSpace(line))
                            nmeaLines.Add(line);
                        return;
                    }

                    if (b == (byte)'\r' || (b >= 0x20 && b <= 0x7E))
                    {
                        _nmeaBuffer.Add(b);
                    }
                    else
                    {
                        ResetParserState();
                        Interlocked.Increment(ref _nmeaInvalid);
                        StartFrameIfApplicable(b, now);
                        return;
                    }

                    if (_nmeaBuffer.Count > 512)
                    {
                        ResetParserState();
                        Interlocked.Increment(ref _nmeaInvalid);
                    }
                    break;

                case ParserMode.Rtcm:
                    _rtcmBuffer.Add(b);

                    if (_rtcmBuffer.Count == 3)
                    {
                        // Os seis bits superiores do byte 1 são reservados e devem ser zero.
                        if ((_rtcmBuffer[1] & 0xFC) != 0)
                        {
                            Interlocked.Increment(ref _rtcmInvalidLength);
                            ResetAndResyncFromCurrentBuffer(now);
                            return;
                        }

                        int payloadLength = ((_rtcmBuffer[1] & 0x03) << 8) | _rtcmBuffer[2];
                        _rtcmExpectedBytes = 3 + payloadLength + 3;

                        if (payloadLength <= 0 || _rtcmExpectedBytes > 1029)
                        {
                            Interlocked.Increment(ref _rtcmInvalidLength);
                            ResetAndResyncFromCurrentBuffer(now);
                            return;
                        }
                    }

                    if (_rtcmExpectedBytes > 0 && _rtcmBuffer.Count == _rtcmExpectedBytes)
                    {
                        byte[] message = _rtcmBuffer.ToArray();
                        ResetParserState();

                        if (ValidateRtcmCrc24Q(message))
                        {
                            Interlocked.Increment(ref _rtcmValid);
                            _lastValidRtcmMono = now;
                            rtcmMessages.Add(message);
                        }
                        else
                        {
                            Interlocked.Increment(ref _rtcmCrcErrors);
                            Interlocked.Increment(ref _rtcmResyncs);
                        }
                    }
                    else if (_rtcmExpectedBytes > 0 && _rtcmBuffer.Count > _rtcmExpectedBytes)
                    {
                        Interlocked.Increment(ref _rtcmResyncs);
                        ResetAndResyncFromCurrentBuffer(now);
                    }
                    break;
            }
        }

        private void StartFrameIfApplicable(byte b, double now)
        {
            if (b == 0xD3)
                StartRtcm(now);
            else if (b == (byte)'$')
                StartNmea(now);
        }

        private void StartNmea(double now)
        {
            ResetParserState();
            _parserMode = ParserMode.Nmea;
            _frameStartedMono = now;
            _nmeaBuffer.Add((byte)'$');
        }

        private void StartRtcm(double now)
        {
            ResetParserState();
            _parserMode = ParserMode.Rtcm;
            _frameStartedMono = now;
            _rtcmBuffer.Add(0xD3);
        }

        private void ResetAndResyncFromCurrentBuffer(double now)
        {
            byte[] candidate = _rtcmBuffer.Skip(1).ToArray();
            ResetParserState();
            Interlocked.Increment(ref _rtcmResyncs);

            foreach (byte b in candidate)
            {
                if (_parserMode == ParserMode.Idle)
                {
                    if (b == 0xD3)
                    {
                        StartRtcm(now);
                    }
                    else if (b == (byte)'$')
                    {
                        StartNmea(now);
                    }
                }
                else if (_parserMode == ParserMode.Rtcm)
                {
                    _rtcmBuffer.Add(b);
                    if (_rtcmBuffer.Count == 3)
                    {
                        int len = ((_rtcmBuffer[1] & 0x03) << 8) | _rtcmBuffer[2];
                        _rtcmExpectedBytes = 3 + len + 3;
                    }
                }
                else if (_parserMode == ParserMode.Nmea)
                {
                    if (b == (byte)'\n')
                    {
                        ResetParserState();
                    }
                    else if (b == (byte)'\r' || (b >= 0x20 && b <= 0x7E))
                    {
                        _nmeaBuffer.Add(b);
                    }
                }
            }
        }

        private void ResetParsers()
        {
            lock (_parserLock)
                ResetParserState();
        }

        private void ResetParserState()
        {
            _parserMode = ParserMode.Idle;
            _rtcmBuffer.Clear();
            _nmeaBuffer.Clear();
            _rtcmExpectedBytes = -1;
            _frameStartedMono = 0;
        }

        // =========================================================
        // RTCM: VALIDAÇÃO, FILA E PUBLICAÇÃO
        // =========================================================

        private void EnqueueRtcm(byte[] message)
        {
            int type = GetRtcmMessageType(message);
            if (type < 0)
            {
                Interlocked.Increment(ref _rtcmInvalidLength);
                return;
            }

            RtcmEnvelope envelope = new()
            {
                Type = type,
                Data = message,
                ReceivedMono = MonotonicNow(),
                Sequence = Interlocked.Increment(ref _rtcmSequence),
            };

            bool shouldSignal;

            lock (_rtcmQueueLock)
            {
                shouldSignal = _rtcmLatestByType.Count == 0;

                if (_rtcmLatestByType.ContainsKey(type))
                    Interlocked.Increment(ref _rtcmReplaced);

                _rtcmLatestByType[type] = envelope;
                Interlocked.Increment(ref _rtcmQueued);
            }

            if (shouldSignal)
            {
                try { _rtcmSignal.Release(); } catch (SemaphoreFullException) { }
            }
        }

        private async Task RtcmPublisherLoopAsync(CancellationToken ct)
        {
            while (!ct.IsCancellationRequested)
            {
                try
                {
                    await _rtcmSignal.WaitAsync(ct).ConfigureAwait(false);
                }
                catch (OperationCanceledException)
                {
                    break;
                }

                while (!ct.IsCancellationRequested)
                {
                    List<RtcmEnvelope> batch;

                    lock (_rtcmQueueLock)
                    {
                        if (_rtcmLatestByType.Count == 0)
                            break;

                        batch = _rtcmLatestByType.Values
                            .OrderBy(x => x.Sequence)
                            .ToList();

                        _rtcmLatestByType.Clear();
                    }

                    foreach (RtcmEnvelope item in batch)
                    {
                        if (ct.IsCancellationRequested)
                            break;

                        double age = MonotonicNow() - item.ReceivedMono;
                        if (age > RtcmMaxQueueAge.TotalSeconds)
                        {
                            Interlocked.Increment(ref _rtcmDroppedStale);
                            continue;
                        }

                        try
                        {
                            // A chamada externa fica isolada neste worker. Se MQTT bloquear,
                            // a serial continua lendo e a fila mantém somente o RTCM mais novo por tipo.
                            VariaveisControleOperacao.EnviarDadosCorrecaoRTCM(item.Data);
                            _lastForwardedRtcmMono = MonotonicNow();
                            Interlocked.Increment(ref _rtcmForwarded);
                        }
                        catch (Exception ex)
                        {
                            Interlocked.Increment(ref _rtcmPublishErrors);
                            Models.Variaveis.MostrarLog(
                                $"Erro ao encaminhar RTCM tipo {item.Type}: {ex.Message}");
                        }
                    }
                }
            }
        }

        private static int GetRtcmMessageType(byte[] message)
        {
            if (message == null || message.Length < 8 || message[0] != 0xD3)
                return -1;

            return (message[3] << 4) | (message[4] >> 4);
        }

        private static bool ValidateRtcmCrc24Q(byte[] message)
        {
            if (message == null || message.Length < 6)
                return false;

            uint calculated = ComputeCrc24Q(message, 0, message.Length - 3);
            uint received =
                ((uint)message[^3] << 16) |
                ((uint)message[^2] << 8) |
                message[^1];

            return calculated == received;
        }

        private static uint ComputeCrc24Q(byte[] data, int offset, int count)
        {
            uint crc = 0;

            for (int i = offset; i < offset + count; i++)
            {
                crc ^= (uint)data[i] << 16;

                for (int bit = 0; bit < 8; bit++)
                {
                    crc <<= 1;
                    if ((crc & 0x1000000) != 0)
                        crc ^= 0x1864CFB;
                }
            }

            return crc & 0xFFFFFF;
        }

        // =========================================================
        // NMEA
        // =========================================================

        private void ProcessNmeaSafely(string sentence)
        {
            if (string.IsNullOrWhiteSpace(sentence))
                return;

            try
            {
                if (!TryValidateNmeaChecksum(sentence, out bool checksumPresent))
                {
                    Interlocked.Increment(ref _nmeaChecksumErrors);
                    Interlocked.Increment(ref _nmeaInvalid);
                    return;
                }

                ProcessarDadosNMEA(sentence);
                _lastValidNmeaMono = MonotonicNow();
                Interlocked.Increment(ref _nmeaValid);

                if (sentence.StartsWith("$GNGGA", StringComparison.Ordinal) ||
                    sentence.StartsWith("$GPGGA", StringComparison.Ordinal) ||
                    sentence.StartsWith("$GLGGA", StringComparison.Ordinal))
                {
                    _lastValidGgaMono = MonotonicNow();
                    Interlocked.Increment(ref _ggaSequence);
                }
            }
            catch (Exception ex)
            {
                Interlocked.Increment(ref _nmeaInvalid);
                Models.Variaveis.MostrarLog($"Sentença NMEA inválida descartada: {ex.Message}");
            }
        }

        private static bool TryValidateNmeaChecksum(string sentence, out bool checksumPresent)
        {
            checksumPresent = false;

            if (string.IsNullOrWhiteSpace(sentence) || sentence[0] != '$')
                return false;

            int star = sentence.IndexOf('*');
            if (star < 0)
            {
                // Alguns comandos/respostas do fabricante podem não trazer checksum.
                return true;
            }

            checksumPresent = true;
            if (star + 2 >= sentence.Length)
                return false;

            byte checksum = 0;
            for (int i = 1; i < star; i++)
                checksum ^= (byte)sentence[i];

            string expectedText = sentence.Substring(star + 1, 2);
            return byte.TryParse(
                       expectedText,
                       NumberStyles.HexNumber,
                       CultureInfo.InvariantCulture,
                       out byte expected) &&
                   checksum == expected;
        }

        private void ProcessarDadosNMEA(string sentenca)
        {
            DateTime agora = DateTime.Now;

            if (sentenca.StartsWith("$GPGGA", StringComparison.Ordinal))
            {
                ProcessarGPGGA(sentenca);
                AtualizarCoordenadasGPS();
            }
            else if (sentenca.StartsWith("$GNGGA", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GLGGA", StringComparison.Ordinal))
            {
                ProcessarGNGGA(sentenca);
                AtualizarCoordenadasGPS();
            }
            else if (sentenca.StartsWith("$GNRMC", StringComparison.Ordinal))
            {
                ProcessarGxRMC(sentenca);
            }
            else if (sentenca.StartsWith("$GNVTG", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GPVTG", StringComparison.Ordinal))
            {
                ProcessarGNVTG(sentenca);
            }
            else if (sentenca.StartsWith("$GPGSV", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GLGSV", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GBGSV", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GAGSV", StringComparison.Ordinal))
            {
                ProcessarGSV(sentenca);
            }
            else if (sentenca.StartsWith("$GNTHS", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GPTHS", StringComparison.Ordinal) ||
                     sentenca.StartsWith("$GATHS", StringComparison.Ordinal))
            {
                ProcessarGNTHS(sentenca);
            }
            else if (sentenca.Length > 6 &&
                     sentenca[3] == 'G' && sentenca[4] == 'L' && sentenca[5] == 'L')
            {
                ProcessarGNGLL(sentenca);
            }
            else if (sentenca.Length > 6 &&
                     sentenca[3] == 'G' && sentenca[4] == 'S' && sentenca[5] == 'A')
            {
                ProcessarGxGSA(sentenca);
            }
            else if (sentenca.Length > 6 &&
                     sentenca[3] == 'R' && sentenca[4] == 'M' && sentenca[5] == 'C')
            {
                ProcessarGxRMC(sentenca);
            }

            lock (_modelLock)
                UltimaLeitura.UltimoComandoRespondido = agora;
        }

        private void ProcessarGPGGA(string sentenca)
        {
            string[] parts = sentenca.Split(',');
            if (parts.Length < 10)
                throw new FormatException("GPGGA incompleta.");

            lock (_modelLock)
            {
                UltimaLeitura.TimestampPos.valor = Stopwatch.GetTimestamp() / (double)Stopwatch.Frequency;
                UltimaLeitura.Momento = DateTime.Now;

                if (!string.IsNullOrWhiteSpace(parts[2]) && !string.IsNullOrWhiteSpace(parts[3]))
                    UltimaLeitura.Latitude = GPSUtils.ConvertToDecimalDegrees(parts[2], parts[3], 2);

                if (!string.IsNullOrWhiteSpace(parts[4]) && !string.IsNullOrWhiteSpace(parts[5]))
                    UltimaLeitura.Longitude = GPSUtils.ConvertToDecimalDegrees(parts[4], parts[5], 3);

                UltimaLeitura.NumeroSatelites = ParseInt(parts[7], 0);
                UltimaLeitura.PrecisaoHorizontal = ParseDouble(parts[8], 0);
                UltimaLeitura.Altitude = ParseDouble(parts[9], 0);
            }
        }

        private void ProcessarGNGGA(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 15)
                throw new FormatException("GNGGA incompleta.");

            string horaUtc = campos[1];
            string latitudeRaw = campos[2];
            string hemisferioLat = campos[3];
            string longitudeRaw = campos[4];
            string hemisferioLon = campos[5];
            int fixCode = ParseInt(campos[6], 0);
            int satelites = ParseInt(campos[7], 0);
            double hdop = ParseDouble(campos[8], 99.9);
            double altMsl = ParseDouble(campos[9], 0);
            double geoidSep = ParseDouble(campos[11], 0);
            string idadeRaw = campos[13];
            string baseId = campos[14].Split('*')[0];

            double latitude = ParseDmm(latitudeRaw, hemisferioLat, 2);
            double longitude = ParseDmm(longitudeRaw, hemisferioLon, 3);
            double idadeCorrecao = -1;

            if (!string.IsNullOrWhiteSpace(idadeRaw) &&
                double.TryParse(
                    idadeRaw,
                    NumberStyles.Float,
                    CultureInfo.InvariantCulture,
                    out double parsedAge))
            {
                idadeCorrecao = parsedAge;
            }

            double altElipsoidal = altMsl + geoidSep;

            lock (_modelLock)
            {
                UltimaLeitura.TimestampPos.valor = Stopwatch.GetTimestamp() / (double)Stopwatch.Frequency;
                UltimaLeitura.Momento = DateTime.Now;

                if (!double.IsNaN(latitude))
                {
                    UltimaLeitura.LatitudeAnt = UltimaLeitura.Latitude;
                    UltimaLeitura.Latitude = latitude;
                }

                if (!double.IsNaN(longitude))
                {
                    UltimaLeitura.LongitudeAnt = UltimaLeitura.Longitude;
                    UltimaLeitura.Longitude = longitude;
                }

                UltimaLeitura.Altitude = altMsl;
                UltimaLeitura.AltitudeElipsoidal = altElipsoidal;
                UltimaLeitura.PrecisaoHorizontal = hdop;
                UltimaLeitura.NumeroSatelites = satelites;
                UltimaLeitura.QualidadeFix = (TiposCorrecaoGPS)fixCode;
                UltimaLeitura.IdadeCorrecao = idadeCorrecao;
                UltimaLeitura.BaseID = baseId;

                if (TryParseNmeaTime(horaUtc, out TimeSpan tod))
                    UltimaLeitura.DataHora = DateTime.UtcNow.Date.Add(tod).ToLocalTime();

                if (!UltimaLeitura.EnuOriginSet &&
                    UltimaLeitura.QualidadeFix == TiposCorrecaoGPS.RTKFixo &&
                    !double.IsNaN(latitude) &&
                    !double.IsNaN(longitude))
                {
                    UltimaLeitura.Lat0 = latitude;
                    UltimaLeitura.Lon0 = longitude;
                    UltimaLeitura.EnuOriginSet = true;
                }

                if (UltimaLeitura.EnuOriginSet &&
                    !double.IsNaN(latitude) &&
                    !double.IsNaN(longitude))
                {
                    (double latCor, double lonCor) = LeverArm.FixLeverArmLatLon_Fast(
                        latitude,
                        longitude,
                        UltimaLeitura.OrientacaoReal,
                        UltimaLeitura.TimestampOri.frequencia);

                    UltimaLeitura.Latitude = latCor;
                    UltimaLeitura.Longitude = lonCor;
                }
            }
        }

        private void ProcessarGNVTG(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 8)
                throw new FormatException("VTG incompleta.");

            double curso = ParseDouble(campos[1], 0);
            double velocidadeKmh = ParseDouble(campos[7].Split('*')[0], 0);

            lock (_modelLock)
            {
                UltimaLeitura.Momento = DateTime.Now;
                UltimaLeitura.CursoVerdadeiro = curso;
                UltimaLeitura.Velocidade = velocidadeKmh;
            }
        }

        private void ProcessarGSV(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 4 || sentenca.Length < 3)
                throw new FormatException("GSV incompleta.");

            string sistema = sentenca.Substring(1, 2);
            int total = ParseInt(campos[1], 0);
            int atual = ParseInt(campos[2], 0);
            int visiveis = ParseInt(campos[3], 0);

            lock (_modelLock)
            {
                UltimaLeitura.Momento = DateTime.Now;

                var leitura = UltimaLeitura.SatelitesEmVista
                    .FirstOrDefault(x => x.TipoSistema == sistema);

                if (leitura == null)
                {
                    leitura = new GPSSatelitesEmVistaModel
                    {
                        TipoSistema = sistema,
                        Sentencas = new List<GPSSatelitesEmVistaSentencaModel>(),
                    };
                    UltimaLeitura.SatelitesEmVista.Add(leitura);
                }

                var item = leitura.Sentencas.FirstOrDefault(x => x.SentencaAtual == atual);
                if (item == null)
                {
                    item = new GPSSatelitesEmVistaSentencaModel
                    {
                        SentencaAtual = atual,
                        SentencasTotal = total,
                        QuantidadeSatelites = visiveis,
                        Dados = new List<GPSSatelitesEmVistaDadosModel>(),
                    };
                    leitura.Sentencas.Add(item);
                }

                item.SentencasTotal = total;
                item.QuantidadeSatelites = visiveis;
                item.Dados = new List<GPSSatelitesEmVistaDadosModel>();

                for (int i = 4; i + 3 < campos.Length; i += 4)
                {
                    item.Dados.Add(new GPSSatelitesEmVistaDadosModel
                    {
                        PRN = campos[i],
                        Elevacao = ParseDouble(campos[i + 1], 0),
                        Azimute = ParseDouble(campos[i + 2], 0),
                        QualidadeSinal = ParseDouble(campos[i + 3].Split('*')[0], 0),
                    });
                }
            }
        }

        private void ProcessarGNTHS(string sentenca)
        {
            string[] campos = sentenca.TrimStart('$').Split(',');
            if (campos.Length < 3)
                throw new FormatException("THS incompleta.");

            string status = campos[2].Split('*')[0];
            bool headingValido = double.TryParse(
                campos[1],
                NumberStyles.Float,
                CultureInfo.InvariantCulture,
                out double heading);

            lock (_modelLock)
            {
                UltimaLeitura.TimestampOri.valor = Stopwatch.GetTimestamp() / (double)Stopwatch.Frequency;
                UltimaLeitura.Momento = DateTime.Now;
                UltimaLeitura.TipoOrientacao = status;

                if (headingValido)
                {
                    UltimaLeitura.OrientacaoReal = InverterHeading
                        ? GPSUtils.NormalizarAngulo(heading - 180.0)
                        : heading;
                }
                else
                {
                    // Mantém o último heading numérico, mas atualiza o status V/A.
                    // Assim a saúde consegue distinguir dado inválido de ausência de sentença.
                }
            }
        }

        private void ProcessarGNGLL(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 7)
                throw new FormatException("GLL incompleta.");

            string mode = campos.Length > 7 ? campos[7].Split('*')[0] : string.Empty;
            bool valido = campos[6] == "A" && mode != "N";

            lock (_modelLock)
            {
                if (valido)
                {
                    double lat = ParseDmm(campos[1], campos[2], 2);
                    double lon = ParseDmm(campos[3], campos[4], 3);

                    if (!double.IsNaN(lat)) UltimaLeitura.Latitude = lat;
                    if (!double.IsNaN(lon)) UltimaLeitura.Longitude = lon;
                }

                if (TryParseNmeaTime(campos[5], out TimeSpan tod))
                    UltimaLeitura.DataHora = DateTime.UtcNow.Date.Add(tod).ToLocalTime();

                ApplyModeToFixQuality(mode);
            }

            AtualizarCoordenadasGPS();
        }

        private void ProcessarGxGSA(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 17)
                throw new FormatException("GSA incompleta.");

            int satsUsados = 0;
            for (int i = 3; i <= 14 && i < campos.Length; i++)
                if (!string.IsNullOrWhiteSpace(campos[i])) satsUsados++;

            double pdop = ParseDouble(campos[15], double.NaN);
            double hdop = ParseDouble(campos[16], double.NaN);
            double vdop = campos.Length > 17
                ? ParseDouble(campos[17].Split('*')[0], double.NaN)
                : double.NaN;

            var fixDim = (TiposDimensaoCorrecaoGPS)ParseInt(campos[2], 1);

            lock (_modelLock)
            {
                if (!double.IsNaN(hdop)) UltimaLeitura.PrecisaoHorizontal = hdop;
                if (satsUsados > 0) UltimaLeitura.NumeroSatelites = Math.Max(UltimaLeitura.NumeroSatelites, satsUsados);
                if (!double.IsNaN(pdop)) UltimaLeitura.PDOP = pdop;
                if (!double.IsNaN(vdop)) UltimaLeitura.VDOP = vdop;
                UltimaLeitura.FixDimensao = fixDim;
            }
        }

        private void ProcessarGxRMC(string sentenca)
        {
            string[] campos = sentenca.Split(',');
            if (campos.Length < 12)
                throw new FormatException("RMC incompleta.");

            string mode = string.Empty;
            if (campos.Length > 12)
                mode = campos[12].Split('*')[0].Trim();

            bool valido = campos[2] == "A";

            lock (_modelLock)
            {
                if (valido)
                {
                    double lat = ParseDmm(campos[3], campos[4], 2);
                    double lon = ParseDmm(campos[5], campos[6], 3);
                    if (!double.IsNaN(lat)) UltimaLeitura.Latitude = lat;
                    if (!double.IsNaN(lon)) UltimaLeitura.Longitude = lon;
                }

                if (double.TryParse(campos[7], NumberStyles.Float, CultureInfo.InvariantCulture, out double speedKnots))
                    UltimaLeitura.Velocidade = speedKnots * 1.852; // km/h

                if (double.TryParse(campos[8], NumberStyles.Float, CultureInfo.InvariantCulture, out double course))
                    UltimaLeitura.CursoVerdadeiro = course;

                if (TryParseRmcDateTime(campos[1], campos[9], out DateTime dt))
                    UltimaLeitura.DataHora = dt.ToLocalTime();

                if (double.TryParse(campos[10], NumberStyles.Float, CultureInfo.InvariantCulture, out double magVar))
                {
                    if (campos[11].StartsWith("W", StringComparison.OrdinalIgnoreCase))
                        magVar = -magVar;
                    UltimaLeitura.VariacaoMagnetica = magVar;
                }

                ApplyModeToFixQuality(mode);
            }

            AtualizarCoordenadasGPS();
        }

        private void ApplyModeToFixQuality(string mode)
        {
            if (string.IsNullOrWhiteSpace(mode))
                return;

            UltimaLeitura.QualidadeFix = mode switch
            {
                "R" => TiposCorrecaoGPS.RTKFixo,
                "F" => TiposCorrecaoGPS.RTKFlutuante,
                "D" => TiposCorrecaoGPS.DGPS,
                "E" => TiposCorrecaoGPS.DeadReckoing,
                "A" => TiposCorrecaoGPS.Autonomo,
                "N" => TiposCorrecaoGPS.SemCorrecao,
                _ => UltimaLeitura.QualidadeFix,
            };
        }

        // =========================================================
        // NTRIP COM CANCELAMENTO REAL
        // =========================================================

        private CancellationTokenSource _ntripCts;
        private Task _ntripTask;
        private TcpClient _ntripClient;

        private Task StartNtripAsync()
        {
            lock (_ntripLock)
            {
                if (_ntripTask != null && !_ntripTask.IsCompleted)
                    return Task.CompletedTask;

                CorrecaoRTK_Ntrip = true;
                _ntripCts = CancellationTokenSource.CreateLinkedTokenSource(_lifetimeCts.Token);
                _ntripTask = Task.Run(
                    () => AplicarCorrecaoRTK_NtripAsync(_ntripCts.Token),
                    _ntripCts.Token);
            }

            return Task.CompletedTask;
        }

        private async Task StopNtripAsync()
        {
            Task task;
            TcpClient client;

            lock (_ntripLock)
            {
                CorrecaoRTK_Ntrip = false;
                _ntripCts?.Cancel();
                client = _ntripClient;
                task = _ntripTask;
            }

            try { client?.Close(); } catch { }

            if (task != null)
            {
                try { await task.ConfigureAwait(false); }
                catch (OperationCanceledException) { }
                catch { }
            }

            lock (_ntripLock)
            {
                _ntripClient = null;
                _ntripTask = null;
                _ntripCts?.Dispose();
                _ntripCts = null;
                Ntrip_Conectado = false;
            }
        }

        private async Task AplicarCorrecaoRTK_NtripAsync(CancellationToken ct)
        {
            if (!IsConnected || !APIService.HasInternet)
                return;

            double backoffSeconds = 1.0;

            while (!ct.IsCancellationRequested && CorrecaoRTK_Ntrip)
            {
                if (!APIService.HasInternet)
                {
                    Ntrip_Conectado = false;
                    await Task.Delay(TimeSpan.FromSeconds(2), ct).ConfigureAwait(false);
                    continue;
                }

                TcpClient client = null;

                try
                {
                    client = new TcpClient();
                    lock (_ntripLock)
                        _ntripClient = client;

                    await ConnectTcpWithTimeoutAsync(
                        client,
                        NtripHost,
                        NtripPort,
                        TimeSpan.FromSeconds(8),
                        ct).ConfigureAwait(false);

                    using NetworkStream stream = client.GetStream();

                    string credentials = string.IsNullOrWhiteSpace(NtripUsername)
                        ? string.Empty
                        : Convert.ToBase64String(
                            Encoding.ASCII.GetBytes($"{NtripUsername}:{NtripPassword}"));

                    string request =
                        $"GET /{NtripMountpoint} HTTP/1.0\r\n" +
                        "User-Agent: NTRIP AgroBase/1.0\r\n" +
                        "Accept: */*\r\n" +
                        "Connection: keep-alive\r\n" +
                        (!string.IsNullOrEmpty(credentials)
                            ? $"Authorization: Basic {credentials}\r\n"
                            : string.Empty) +
                        "\r\n";

                    byte[] requestBytes = Encoding.ASCII.GetBytes(request);
                    await stream.WriteAsync(requestBytes, 0, requestBytes.Length, ct).ConfigureAwait(false);
                    await stream.FlushAsync(ct).ConfigureAwait(false);

                    (string header, byte[] firstBodyBytes) =
                        await ReadHttpHeaderAsync(stream, 16 * 1024, ct).ConfigureAwait(false);

                    string firstLine = header
                        .Split(new[] { "\r\n" }, StringSplitOptions.None)
                        .FirstOrDefault() ?? string.Empty;

                    bool accepted =
                        firstLine.Contains("200 OK", StringComparison.OrdinalIgnoreCase) ||
                        firstLine.StartsWith("ICY 200", StringComparison.OrdinalIgnoreCase);

                    if (!accepted)
                        throw new IOException($"NTRIP recusou conexão: {firstLine}");

                    Ntrip_Conectado = true;
                    backoffSeconds = 1.0;
                    Models.Variaveis.MostrarLog("Conexão NTRIP estabelecida.");

                    if (firstBodyBytes.Length > 0)
                    {
                        await WriteSerialAsync(firstBodyBytes, ct).ConfigureAwait(false);
                        Interlocked.Add(ref _ntripBytesReceived, firstBodyBytes.Length);
                    }

                    byte[] buffer = new byte[4096];

                    while (!ct.IsCancellationRequested && CorrecaoRTK_Ntrip)
                    {
                        int read = await stream.ReadAsync(buffer, 0, buffer.Length, ct).ConfigureAwait(false);
                        if (read <= 0)
                            throw new IOException("Caster NTRIP encerrou a conexão.");

                        byte[] serialChunk = new byte[read];
                        Buffer.BlockCopy(buffer, 0, serialChunk, 0, read);
                        await WriteSerialAsync(serialChunk, ct).ConfigureAwait(false);
                        Interlocked.Add(ref _ntripBytesReceived, read);
                    }
                }
                catch (OperationCanceledException) when (ct.IsCancellationRequested)
                {
                    break;
                }
                catch (Exception ex)
                {
                    Ntrip_Conectado = false;
                    Interlocked.Increment(ref _ntripErrors);
                    Models.Variaveis.MostrarLog($"Erro na conexão NTRIP: {ex.Message}");
                }
                finally
                {
                    Ntrip_Conectado = false;
                    try { client?.Close(); } catch { }

                    lock (_ntripLock)
                    {
                        if (ReferenceEquals(_ntripClient, client))
                            _ntripClient = null;
                    }
                }

                if (!ct.IsCancellationRequested && CorrecaoRTK_Ntrip)
                {
                    Interlocked.Increment(ref _ntripReconnects);
                    double jitter = ((uint)Environment.TickCount % 500) / 1000.0;
                    await Task.Delay(
                        TimeSpan.FromSeconds(backoffSeconds + jitter),
                        ct).ConfigureAwait(false);
                    backoffSeconds = Math.Min(20.0, backoffSeconds * 1.8);
                }
            }

            Ntrip_Conectado = false;
        }

        private static async Task ConnectTcpWithTimeoutAsync(
            TcpClient client,
            string host,
            int port,
            TimeSpan timeout,
            CancellationToken ct)
        {
            Task connectTask = client.ConnectAsync(host, port);
            Task timeoutTask = Task.Delay(timeout, ct);
            Task completed = await Task.WhenAny(connectTask, timeoutTask).ConfigureAwait(false);

            if (completed != connectTask)
            {
                ct.ThrowIfCancellationRequested();
                throw new TimeoutException($"Timeout conectando em {host}:{port}.");
            }

            await connectTask.ConfigureAwait(false);
        }

        private static async Task<(string Header, byte[] FirstBodyBytes)> ReadHttpHeaderAsync(
            NetworkStream stream,
            int maxHeaderBytes,
            CancellationToken ct)
        {
            List<byte> data = new(1024);
            byte[] temp = new byte[512];
            int headerEnd = -1;
            int delimiterLength = 0;

            while (headerEnd < 0)
            {
                int read = await stream.ReadAsync(temp, 0, temp.Length, ct).ConfigureAwait(false);
                if (read <= 0)
                    throw new IOException("Conexão encerrada antes do cabeçalho NTRIP.");

                for (int i = 0; i < read; i++)
                    data.Add(temp[i]);

                if (data.Count > maxHeaderBytes)
                    throw new InvalidDataException("Cabeçalho NTRIP excedeu o limite.");

                (headerEnd, delimiterLength) = FindNtripHeaderEnd(data);
            }

            byte[] all = data.ToArray();
            string header = Encoding.ASCII.GetString(all, 0, headerEnd);
            int bodyStart = headerEnd + delimiterLength;
            byte[] body = bodyStart < all.Length
                ? all.Skip(bodyStart).ToArray()
                : Array.Empty<byte>();

            return (header, body);
        }

        private static (int HeaderEnd, int DelimiterLength) FindNtripHeaderEnd(List<byte> data)
        {
            // Resposta HTTP/NTRIP v2: cabeçalho termina em CRLF CRLF.
            for (int i = 0; i <= data.Count - 4; i++)
            {
                if (data[i] == '\r' && data[i + 1] == '\n' &&
                    data[i + 2] == '\r' && data[i + 3] == '\n')
                {
                    return (i, 4);
                }
            }

            // Alguns casters NTRIP v1 respondem apenas "ICY 200 OK\r\n"
            // e iniciam o corpo binário imediatamente depois.
            if (data.Count >= 3 &&
                data[0] == (byte)'I' && data[1] == (byte)'C' && data[2] == (byte)'Y')
            {
                for (int i = 0; i <= data.Count - 2; i++)
                {
                    if (data[i] == '\r' && data[i + 1] == '\n')
                        return (i, 2);
                }
            }

            return (-1, 0);
        }

        // =========================================================
        // SNAPSHOTS E UI
        // =========================================================

        internal long GetGgaSequence() => Interlocked.Read(ref _ggaSequence);

        internal bool TryGetGgaSnapshot(long afterSequence, out long sequence, out GgaFix snapshot)
        {
            sequence = Interlocked.Read(ref _ggaSequence);
            snapshot = default;

            if (sequence <= afterSequence)
                return false;

            lock (_modelLock)
            {
                snapshot = new GgaFix(
                    tsUtc: UltimaLeitura.DataHora.ToUniversalTime(),
                    latDeg: UltimaLeitura.Latitude,
                    lonDeg: UltimaLeitura.Longitude,
                    altElipsoidalM: UltimaLeitura.AltitudeElipsoidal,
                    headingDeg: UltimaLeitura.OrientacaoReal,
                    fixQuality: UltimaLeitura.QualidadeFix);
            }

            return true;
        }

        private TiposCorrecaoGPS GetFixQualitySnapshot()
        {
            lock (_modelLock)
                return UltimaLeitura.QualidadeFix;
        }

        private PositionSnapshot GetPositionSnapshot()
        {
            lock (_modelLock)
            {
                return new PositionSnapshot
                {
                    Latitude = UltimaLeitura.Latitude,
                    Longitude = UltimaLeitura.Longitude,
                    AltitudeElipsoidal = UltimaLeitura.AltitudeElipsoidal,
                    Orientacao = UltimaLeitura.OrientacaoReal,
                };
            }
        }

        private void AtualizarCoordenadasGPS()
        {
            lock (_modelLock)
            {
                UltimaLeitura.AnguloCarroDefinido = UltimaLeitura.OrientacaoReal;
                UltimaLeitura.Ntrip_ativado = CorrecaoRTK_Ntrip;
                UltimaLeitura.Heartbeat = (UltimaLeitura.Heartbeat + 1) % 10;
            }

            if (Interlocked.CompareExchange(ref _uiUpdatePending, 1, 0) != 0)
                return;

            Application.Current?.Dispatcher?.BeginInvoke(new Action(() =>
            {
                try
                {
                    Models.Variaveis.Dock?._vm?.AtualizarDadosGnss(UltimaLeitura);
                }
                catch (Exception ex)
                {
                    Models.Variaveis.MostrarLog($"Erro ao atualizar UI GNSS: {ex.Message}");
                }
                finally
                {
                    Interlocked.Exchange(ref _uiUpdatePending, 0);
                }
            }));
        }

        // =========================================================
        // HELPERS
        // =========================================================

        private static double MonotonicNow() =>
            Stopwatch.GetTimestamp() / (double)Stopwatch.Frequency;

        private static double AgeMs(double now, double timestamp)
        {
            if (timestamp <= 0)
                return -1;
            return Math.Max(0, (now - timestamp) * 1000.0);
        }

        private static int ParseInt(string text, int fallback)
        {
            return int.TryParse(text, NumberStyles.Integer, CultureInfo.InvariantCulture, out int value)
                ? value
                : fallback;
        }

        private static double ParseDouble(string text, double fallback)
        {
            return double.TryParse(text, NumberStyles.Float, CultureInfo.InvariantCulture, out double value)
                ? value
                : fallback;
        }

        private static double ParseDmm(string raw, string hemisphere, int degreeDigits)
        {
            if (string.IsNullOrWhiteSpace(raw) || raw.Length <= degreeDigits)
                return double.NaN;

            if (!double.TryParse(
                    raw.Substring(0, degreeDigits),
                    NumberStyles.Float,
                    CultureInfo.InvariantCulture,
                    out double degrees) ||
                !double.TryParse(
                    raw.Substring(degreeDigits),
                    NumberStyles.Float,
                    CultureInfo.InvariantCulture,
                    out double minutes))
            {
                return double.NaN;
            }

            double value = degrees + minutes / 60.0;
            if (hemisphere.Equals("S", StringComparison.OrdinalIgnoreCase) ||
                hemisphere.Equals("W", StringComparison.OrdinalIgnoreCase))
            {
                value = -value;
            }

            return value;
        }

        private static bool TryParseNmeaTime(string text, out TimeSpan value)
        {
            value = default;
            if (string.IsNullOrWhiteSpace(text) || text.Length < 6)
                return false;

            if (!int.TryParse(text.Substring(0, 2), out int hh) ||
                !int.TryParse(text.Substring(2, 2), out int mm) ||
                !double.TryParse(
                    text.Substring(4),
                    NumberStyles.Float,
                    CultureInfo.InvariantCulture,
                    out double seconds))
            {
                return false;
            }

            int ss = (int)Math.Floor(seconds);
            int ms = (int)Math.Round((seconds - ss) * 1000.0);

            if (ms >= 1000)
            {
                ss++;
                ms = 0;
            }

            try
            {
                value = new TimeSpan(0, hh, mm, ss, ms);
                return true;
            }
            catch
            {
                return false;
            }
        }

        private static bool TryParseRmcDateTime(
            string timeText,
            string dateText,
            out DateTime utc)
        {
            utc = default;

            if (!TryParseNmeaTime(timeText, out TimeSpan tod) ||
                string.IsNullOrWhiteSpace(dateText) ||
                dateText.Length != 6)
            {
                return false;
            }

            if (!int.TryParse(dateText.Substring(0, 2), out int day) ||
                !int.TryParse(dateText.Substring(2, 2), out int month) ||
                !int.TryParse(dateText.Substring(4, 2), out int yy))
            {
                return false;
            }

            try
            {
                utc = new DateTime(2000 + yy, month, day, 0, 0, 0, DateTimeKind.Utc).Add(tod);
                return true;
            }
            catch
            {
                return false;
            }
        }

        public void Dispose()
        {
            if (Interlocked.Exchange(ref _disposed, 1) != 0)
                return;

            _tmrCheck.Stop();
            _tmrCheck.Dispose();

            try { StopNtripAsync().GetAwaiter().GetResult(); } catch { }

            _lifetimeCts.Cancel();
            try { _rtcmSignal.Release(); } catch { }
            try { _rtcmPublisherTask.Wait(TimeSpan.FromSeconds(2)); } catch { }

            DisconnectInternal();

            _scanGate.Dispose();
            _serialWriteGate.Dispose();
            _rtcmSignal.Dispose();
            _lifetimeCts.Dispose();
        }

        private enum ParserMode
        {
            Idle,
            Nmea,
            Rtcm,
        }

        private enum GnssExpectedRole
        {
            PreserveCurrentConfiguration,
            RoverTemporary,
            BaseFixed,
        }


        public enum GnssPapelEstacao
        {
            Indefinido = 0,

            Movel = 1,

            BaseFixa = 2
        }

        public GnssPapelEstacao PapelEstacaoAtual
        {
            get
            {
                return _expectedRole switch
                {
                    GnssExpectedRole.RoverTemporary =>
                        GnssPapelEstacao.Movel,

                    GnssExpectedRole.BaseFixed =>
                        GnssPapelEstacao.BaseFixa,

                    /*
                     * Quando acabamos de abrir o programa,
                     * ainda podemos estar em Preserve.
                     *
                     * Se o próprio UM982 estiver reportando
                     * BASE FIX, conseguimos reconhecer que
                     * ele está funcionando como base.
                     */
                    _ when
                        GetFixQualitySnapshot() ==
                        TiposCorrecaoGPS.BaseFix =>
                            GnssPapelEstacao.BaseFixa,

                    _ =>
                        GnssPapelEstacao.Indefinido
                };
            }
        }

        private void DefinirPapelEsperado(GnssExpectedRole papel)
        {
            _expectedRole = papel;
        }


        private sealed class RtcmEnvelope
        {
            public int Type { get; init; }
            public byte[] Data { get; init; }
            public double ReceivedMono { get; init; }
            public long Sequence { get; init; }
        }

        private sealed class BaseFixedConfiguration
        {
            public string PortaUsb { get; init; }
            public string PortaSaida { get; init; }
            public string BaseId { get; init; }
            public double Latitude { get; init; }
            public double Longitude { get; init; }
            public double AltitudeElipsoidal { get; init; }
        }

        private sealed class PositionSnapshot
        {
            public double Latitude { get; init; }
            public double Longitude { get; init; }
            public double AltitudeElipsoidal { get; init; }
            public double Orientacao { get; init; }
        }
    }

    // =============================================================
    // BASE FIX SERVICE
    // =============================================================

    public class BaseFixService
    {
        public BaseFixService(SerialPort porta, GpsService service)
        {
            // O SerialPort recebido é mantido apenas por compatibilidade de assinatura.
            // As escritas usam sempre o GpsService para não reter uma porta antiga após reconexão.
            gpsService = service ?? throw new ArgumentNullException(nameof(service));
        }

        private readonly GpsService gpsService;
        private long _lastGgaSequence;

        public List<GgaFix> amostras_pos = new(1000);
        public DateTime? inicioProcesso = null;
        public DateTime? inicioFix = null;
        public DateTime? fimProcesso = null;

        private int segundosFixEstavel = 120;
        private int maxJanelaSegundos = 120;
        private MetodoFixacaoBase metodo = MetodoFixacaoBase.Ntrip;

        public double Progresso
        {
            get
            {
                if (inicioFix is null)
                    return 0;
                if (fimProcesso != null)
                    return 100;

                return Math.Clamp(
                    (DateTime.UtcNow - inicioFix.Value).TotalSeconds /
                    Math.Max(1, segundosFixEstavel) * 100.0,
                    0,
                    100);
            }
        }

        public double ProgressoGeral
        {
            get
            {
                if (inicioProcesso is null)
                    return 0;

                return Math.Clamp(
                    (DateTime.UtcNow - inicioProcesso.Value).TotalSeconds /
                    Math.Max(1, maxJanelaSegundos) * 100.0,
                    0,
                    100);
            }
        }

        public string ProgressoStr
        {
            get
            {
                if (CorrecaoEmAndamento)
                    return $"Recebendo correção RTK via {metodo}. Progresso geral: {ProgressoGeral:F2}%, progresso da correção: {Progresso:F2}%";

                if (PosicaoBaseFixada && CorrecaoAbsoluta && inicioProcesso.HasValue && fimProcesso.HasValue)
                    return $"Correção absoluta concluída com {amostras_pos.Count} amostras em {(fimProcesso.Value - inicioProcesso.Value).TotalSeconds:F2} segundos";

                if (PosicaoBaseFixada && !CorrecaoAbsoluta)
                    return $"Correção relativa concluída em {segundosFixEstavel} segundos";

                if (inicioProcesso.HasValue && fimProcesso.HasValue)
                    return $"Correção absoluta falhou com {amostras_pos.Count} amostras em {(fimProcesso.Value - inicioProcesso.Value).TotalSeconds:F2} segundos";

                return "Correção absoluta não realizada";
            }
        }

        public bool PosicaoBaseFixada =>
            gpsService.UltimaLeitura.QualidadeFix == TiposCorrecaoGPS.BaseFix;

        public bool CorrecaoAbsoluta = false;
        public bool CorrecaoEmAndamento = false;
        public bool FixLiberado = false;
        public double LatitudeFix { get; set; }
        public double LongitudeFix { get; set; }
        public double AltitudeElpsoidalFix { get; set; }
        public double OrientacaoFix { get; set; }

        public void DefinirTempos(
            int segsFixEstavel,
            int segsJanelaSegs,
            MetodoFixacaoBase metodo)
        {
            segundosFixEstavel = Math.Max(1, segsFixEstavel);
            maxJanelaSegundos = Math.Max(segundosFixEstavel, segsJanelaSegs);
            this.metodo = metodo;
        }

        public void ReiniciarFix()
        {
            CorrecaoEmAndamento = false;
            CorrecaoAbsoluta = false;
            inicioFix = null;
            inicioProcesso = null;
            fimProcesso = null;
            FixLiberado = false;
            amostras_pos.Clear();
        }

        public async Task<bool> FixarBaseViaNtripAsync(
            string portaUsb = "com3",
            string portaEntrada = "com2",
            string portaSaida = "com2",
            string baseId = "957",
            double madK = 3.5,
            Func<Task> startNtrip = null,
            Func<Task> stopNtrip = null,
            CancellationToken ct = default)
        {
            if (!APIService.HasInternetNow())
                return false;

            await ConfigurarComoRoverParadoAsync(portaUsb, portaEntrada, ct)
                .ConfigureAwait(false);

            if (startNtrip != null)
                await startNtrip().ConfigureAwait(false);

            try
            {
                List<GgaFix> samples = await EsperarFixEAmostrarAsync(ct).ConfigureAwait(false);

                if (samples.Count < 10)
                {
                    Models.Variaveis.MostrarLog(
                        "Poucas amostras de RTK FIX coletadas. Verifique NTRIP e sinais GNSS.");
                    CorrecaoAbsoluta = false;
                    return false;
                }

                var (lat, lon, h, heading, count) = FiltrarEAgrupar(samples, madK);
                if (count < 5 ||
                    double.IsNaN(lat) ||
                    double.IsNaN(lon) ||
                    double.IsNaN(h))
                {
                    Models.Variaveis.MostrarLog("Filtro da posição da base não produziu amostras suficientes.");
                    CorrecaoAbsoluta = false;
                    return false;
                }

                // Para de injetar RTCM NTRIP e aguarda o socket realmente fechar
                // antes de enviar comandos ASCII de configuração ao UM982.
                if (stopNtrip != null)
                    await stopNtrip().ConfigureAwait(false);

                await AplicarBaseFixAsync(
                    portaUsb,
                    portaSaida,
                    baseId,
                    lat,
                    lon,
                    h,
                    ct).ConfigureAwait(false);

                Models.Variaveis.MostrarLog(
                    $"[BASE/FIX] Coordenadas aplicadas (n={count}): lat={lat:0.000000000}, lon={lon:0.000000000}, h={h:0.000}, heading={heading:0.00}");

                CorrecaoAbsoluta = true;
                return true;
            }
            finally
            {
                if (stopNtrip != null)
                {
                    try { await stopNtrip().ConfigureAwait(false); }
                    catch { }
                }
            }
        }

        public async Task ConfigurarComoRoverParadoAsync(
            string portaUsb,
            string portaEntrada,
            CancellationToken ct = default)
        {
            Models.Variaveis.MostrarLog("Configurando GNSS temporariamente como rover parado...");

            string[] commands =
            {
                $"config {portaUsb} 115200\r\n",
                $"config {portaEntrada} 115200\r\n",
                "unlog com1\r\n",
                "unlog com2\r\n",
                "unlog com3\r\n",
                "mode rover uav\r\n",
                $"gngga {portaUsb} 1\r\n",
                $"gpths {portaUsb} 1\r\n",
                // Não salva a configuração rover temporária.
            };

            await gpsService.SendCommandsAsync(commands, 250, ct).ConfigureAwait(false);
        }

        private async Task<List<GgaFix>> EsperarFixEAmostrarAsync(CancellationToken ct)
        {
            Models.Variaveis.MostrarLog("Iniciando coleta de dados para fixação da base...");

            amostras_pos = new List<GgaFix>(1000);
            inicioProcesso = DateTime.UtcNow;
            inicioFix = null;
            _lastGgaSequence = gpsService.GetGgaSequence();

            DateTime noFixDeadline = DateTime.UtcNow.AddMinutes(2);

            while (ProgressoGeral < 100 && FixLiberado)
            {
                ct.ThrowIfCancellationRequested();

                if (inicioFix is null && DateTime.UtcNow >= noFixDeadline)
                {
                    Models.Variaveis.MostrarLog("Timeout aguardando RTK FIX via NTRIP.");
                    break;
                }

                GgaFix gga = await LerProximoGgaAsync(5000, ct).ConfigureAwait(false);
                if (gga is null)
                    continue;

                bool valid = gga.FixQuality == TiposCorrecaoGPS.RTKFixo;
                if (!valid &&
                    inicioProcesso.HasValue &&
                    (DateTime.UtcNow - inicioProcesso.Value).TotalSeconds > 120)
                {
                    valid = gga.FixQuality == TiposCorrecaoGPS.RTKFlutuante;
                }

                if (!FixLiberado || !valid)
                {
                    inicioFix = null;
                    amostras_pos.Clear();
                    continue;
                }

                if (inicioFix is null)
                {
                    Models.Variaveis.MostrarLog("RTK válido definido. Iniciando janela de coleta estável...");
                    inicioFix = DateTime.UtcNow;
                    amostras_pos.Clear();
                }

                amostras_pos.Add(gga);

                if (Progresso >= 100)
                    break;
            }

            return amostras_pos;
        }

        private async Task<GgaFix> LerProximoGgaAsync(
            int timeoutMs = 5000,
            CancellationToken ct = default)
        {
            Stopwatch sw = Stopwatch.StartNew();

            while (!ct.IsCancellationRequested && sw.ElapsedMilliseconds < timeoutMs)
            {
                if (gpsService.TryGetGgaSnapshot(
                        _lastGgaSequence,
                        out long sequence,
                        out GgaFix snapshot))
                {
                    _lastGgaSequence = sequence;
                    return snapshot;
                }

                await Task.Delay(50, ct).ConfigureAwait(false);
            }

            return null;
        }

        private (double lat, double lon, double h, double hdg, int n) FiltrarEAgrupar(
            List<GgaFix> samples,
            double madK = 3.5)
        {
            Models.Variaveis.MostrarLog("Filtrando dados aferidos...");

            if (samples == null || samples.Count == 0)
                return (double.NaN, double.NaN, double.NaN, double.NaN, 0);

            double medLat = Median(samples.Select(x => x.LatDeg));
            double medLon = Median(samples.Select(x => x.LonDeg));
            double medH = Median(samples.Select(x => x.AltElipsoidalM));

            double[] validHeadings = samples
                .Select(x => x.HeadingDeg)
                .Where(x => !double.IsNaN(x) && !double.IsInfinity(x))
                .ToArray();

            bool useHeadingFilter = validHeadings.Length >= Math.Max(5, samples.Count / 2);
            double medHeading = useHeadingFilter
                ? CircularMedian(validHeadings)
                : double.NaN;

            double madLat = Math.Max(1e-12, Median(samples.Select(x => Math.Abs(x.LatDeg - medLat))));
            double madLon = Math.Max(1e-12, Median(samples.Select(x => Math.Abs(x.LonDeg - medLon))));
            double madH = Math.Max(1e-9, Median(samples.Select(x => Math.Abs(x.AltElipsoidalM - medH))));
            double madHeading = useHeadingFilter
                ? Math.Max(0.01, Median(validHeadings.Select(x => AngularDistanceDegrees(x, medHeading))))
                : 1.0;

            List<GgaFix> filtered = samples.Where(x =>
                    Math.Abs(x.LatDeg - medLat) / madLat <= madK &&
                    Math.Abs(x.LonDeg - medLon) / madLon <= madK &&
                    Math.Abs(x.AltElipsoidalM - medH) / madH <= madK &&
                    (!useHeadingFilter ||
                     AngularDistanceDegrees(x.HeadingDeg, medHeading) / madHeading <= madK))
                .ToList();

            if (filtered.Count == 0)
                return (double.NaN, double.NaN, double.NaN, double.NaN, 0);

            double heading = CircularMean(
                filtered
                    .Select(x => x.HeadingDeg)
                    .Where(x => !double.IsNaN(x) && !double.IsInfinity(x)));

            return (
                filtered.Average(x => x.LatDeg),
                filtered.Average(x => x.LonDeg),
                filtered.Average(x => x.AltElipsoidalM),
                heading,
                filtered.Count);
        }

        public async Task AplicarBaseFixAsync(
            string portaUsb,
            string portaSaida,
            string baseId,
            double latDeg,
            double lonDeg,
            double hEllipsM,
            CancellationToken ct = default)
        {
            Models.Variaveis.MostrarLog("Aplicando dados de correção da base...");

            string lat = latDeg.ToString("0.000000000", CultureInfo.InvariantCulture);
            string lon = lonDeg.ToString("0.000000000", CultureInfo.InvariantCulture);
            string h = hEllipsM.ToString("0.000", CultureInfo.InvariantCulture);

            string[] commands =
            {
                "unlog com1\r\n",
                "unlog com2\r\n",
                "unlog com3\r\n",
                $"mode base {baseId} {lat} {lon} {h}\r\n",
                $"RTCM1006 {portaSaida} 10\r\n",
                $"RTCM1033 {portaSaida} 30\r\n",
                $"RTCM1074 {portaSaida} 1\r\n",
                $"RTCM1084 {portaSaida} 1\r\n",
                $"RTCM1094 {portaSaida} 1\r\n",
                $"RTCM1124 {portaSaida} 1\r\n",
                $"RTCM1230 {portaSaida} 10\r\n",
                $"gngga {portaUsb} 1\r\n",
                $"gpths {portaUsb} 1\r\n",
                "saveconfig\r\n",
            };

            await gpsService.SendCommandsAsync(commands, 200, ct).ConfigureAwait(false);
        }

        private static double Median(IEnumerable<double> values)
        {
            double[] ordered = values
                .Where(x => !double.IsNaN(x) && !double.IsInfinity(x))
                .OrderBy(x => x)
                .ToArray();

            if (ordered.Length == 0)
                return double.NaN;

            int middle = ordered.Length / 2;
            return ordered.Length % 2 == 1
                ? ordered[middle]
                : (ordered[middle - 1] + ordered[middle]) / 2.0;
        }

        private static double CircularMean(IEnumerable<double> headings)
        {
            double[] valid = headings
                .Where(x => !double.IsNaN(x) && !double.IsInfinity(x))
                .ToArray();

            if (valid.Length == 0)
                return double.NaN;

            double sin = valid.Sum(x => Math.Sin(x * Math.PI / 180.0));
            double cos = valid.Sum(x => Math.Cos(x * Math.PI / 180.0));
            double angle = Math.Atan2(sin, cos) * 180.0 / Math.PI;
            return (angle + 360.0) % 360.0;
        }

        private static double CircularMedian(IEnumerable<double> headings)
        {
            double[] valid = headings
                .Where(x => !double.IsNaN(x) && !double.IsInfinity(x))
                .Select(x => (x % 360.0 + 360.0) % 360.0)
                .ToArray();

            if (valid.Length == 0)
                return double.NaN;

            return valid
                .OrderBy(candidate => valid.Sum(x => AngularDistanceDegrees(x, candidate)))
                .First();
        }

        private static double AngularDistanceDegrees(double a, double b)
        {
            double diff = Math.Abs(((a - b + 540.0) % 360.0) - 180.0);
            return diff;
        }

        public enum MetodoFixacaoBase
        {
            Ntrip = 0,
            SurveyIn = 1,
            Manual = 2,
        }
    }

    public sealed class GpsTransportMetrics
    {
        public bool SerialConnected { get; init; }
        public string PortName { get; init; }
        public double SerialLastRxAgeMs { get; init; }
        public double LastValidNmeaAgeMs { get; init; }
        public double LastValidGgaAgeMs { get; init; }
        public double LastValidRtcmAgeMs { get; init; }
        public double LastForwardedRtcmAgeMs { get; init; }
        public long SerialBytesReceived { get; init; }
        public long SerialReadErrors { get; init; }
        public long NmeaValid { get; init; }
        public long NmeaInvalid { get; init; }
        public long NmeaChecksumErrors { get; init; }
        public long RtcmValid { get; init; }
        public long RtcmCrcErrors { get; init; }
        public long RtcmInvalidLength { get; init; }
        public long RtcmResyncs { get; init; }
        public long RtcmQueued { get; init; }
        public long RtcmReplaced { get; init; }
        public long RtcmDroppedStale { get; init; }
        public long RtcmForwarded { get; init; }
        public long RtcmPublishErrors { get; init; }
        public int RtcmQueueDepth { get; init; }
        public double RtcmOldestQueueAgeMs { get; init; }
        public long SerialReconnects { get; init; }
        public bool NtripConnected { get; init; }
        public long NtripBytesReceived { get; init; }
        public long NtripReconnects { get; init; }
        public long NtripErrors { get; init; }
        public string ExpectedRole { get; init; }
    }
}