using System;
using System.Threading;
using System.Threading.Tasks;
using HC_APTBS.Models;

namespace HC_APTBS.Services.Impl
{
    /// <summary>
    /// Linear state-machine orchestrator for the Dashboard "Connect &amp; Auto Test"
    /// button. Coordinates existing services (<see cref="IKwpService"/>,
    /// <see cref="ICanService"/>, <see cref="IBenchService"/>, <see cref="IUnlockService"/>,
    /// <see cref="IConfigurationService"/>) rather than re-implementing any protocol.
    ///
    /// <para>Behavioural contract:</para>
    /// <list type="bullet">
    ///   <item>Linear phases: <see cref="AutoTestState.Preflight"/> →
    ///         <see cref="AutoTestState.ConnectingKLine"/> →
    ///         <see cref="AutoTestState.ReadingPump"/> →
    ///         <see cref="AutoTestState.Unlocking"/> →
    ///         <see cref="AutoTestState.TurningOnBench"/> →
    ///         <see cref="AutoTestState.StartingOilPump"/> →
    ///         <see cref="AutoTestState.StartingTest"/> →
    ///         <see cref="AutoTestState.Running"/> →
    ///         <see cref="AutoTestState.Completed"/> or <see cref="AutoTestState.Aborted"/>.</item>
    ///   <item>Connecting/Reading are skipped when the K-Line is already open and a pump
    ///         is already selected (fast-path for "re-run on the same pump").</item>
    ///   <item>Unlocking is skipped when the selected pump's
    ///         <see cref="PumpDefinition.UnlockType"/> is 0.</item>
    ///   <item>When the oil-pump leak-check confirmation has not been disabled via
    ///         <see cref="AppSettings.AutoTestSkipsOilPumpConfirm"/>, the sequence aborts
    ///         with <see cref="AutoTestFailureReason.OilPumpNotConfirmed"/> before the
    ///         relay is energised.</item>
    ///   <item>Failure past <see cref="AutoTestStateExtensions.IsPastBenchOn(AutoTestState)"/>
    ///         triggers <see cref="IBenchService.RequestEmergencyStop"/>; earlier failures
    ///         close the K-Line and exit cleanly.</item>
    /// </list>
    /// </summary>
    public sealed class AutoTestOrchestrator : IAutoTestOrchestrator
    {
        private readonly IKwpService _kwp;
        private readonly ICanService _can;
        private readonly IBenchService _bench;
        private readonly IUnlockService _unlock;
        private readonly IConfigurationService _config;
        private readonly IAppLogger _log;
        private readonly Func<IAutoTestHost> _hostFactory;
        private const string LogId = "AutoTestOrch";

        private CancellationTokenSource? _autoCts;
        private AutoTestState _state = AutoTestState.Idle;

        /// <summary>Latest test-phase name observed from <see cref="IBenchService.PhaseChanged"/>.</summary>
        private string? _latestPhaseDetail;

        /// <summary>Raised once a failure has been reported; guards against duplicate emits.</summary>
        private bool _failureReported;

        /// <inheritdoc/>
        public AutoTestState State => _state;

        /// <inheritdoc/>
        public event Action<AutoTestState, string?>? StateChanged;

        /// <inheritdoc/>
        public event Action<AutoTestFailureReason, string>? Failed;

        /// <summary>
        /// Creates an orchestrator wired to the core services. The <paramref name="hostFactory"/>
        /// resolves the <see cref="IAutoTestHost"/> lazily so that the orchestrator can be
        /// constructed by the DI container at the same time as <c>MainViewModel</c> (which
        /// implements <see cref="IAutoTestHost"/>) without creating a construction-order cycle.
        /// </summary>
        public AutoTestOrchestrator(
            IKwpService kwp,
            ICanService can,
            IBenchService bench,
            IUnlockService unlock,
            IConfigurationService config,
            IAppLogger log,
            Func<IAutoTestHost> hostFactory)
        {
            _kwp = kwp;
            _can = can;
            _bench = bench;
            _unlock = unlock;
            _config = config;
            _log = log;
            _hostFactory = hostFactory;
        }

        /// <inheritdoc/>
        public void Cancel() => _autoCts?.Cancel();

        /// <inheritdoc/>
        public async Task<bool> RunAsync(CancellationToken ct)
        {
            if (_state.IsRunning())
            {
                _log.Warning(LogId, "RunAsync called while a sequence is already in progress");
                return false;
            }

            _failureReported = false;
            _latestPhaseDetail = null;

            _autoCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
            var token = _autoCts.Token;

            // ── Abort watchers ────────────────────────────────────────────────────
            // Subscribe these up-front so any mid-sequence hardware drop-out trips
            // the CTS immediately. Unsubscribed in the finally block.

            void OnBenchLiveness(bool alive)
            {
                if (alive) return;
                if (_state == AutoTestState.Idle || _state == AutoTestState.Preflight) return;
                ReportFailure(AutoTestFailureReason.BenchCanLost, "Bench CAN liveness lost");
                _autoCts?.Cancel();
            }

            void OnKLineState(KLineConnectionState st)
            {
                if (st != KLineConnectionState.Failed) return;
                // Only treat as loss when K-Line is actually required by the current phase.
                if (_state is AutoTestState.ConnectingKLine
                    or AutoTestState.ReadingPump
                    or AutoTestState.Unlocking)
                {
                    ReportFailure(AutoTestFailureReason.KLineLost, "K-Line session dropped");
                    _autoCts?.Cancel();
                }
            }

            // Snapshot the alarm mask on entry; any transition that flips a critical bit
            // to "set" aborts the run. Uses the bench alarm parameter directly so we stay
            // decoupled from DashboardAlarmsViewModel.
            int initialMask = ReadAlarmMask();
            int criticalMask = BuildCriticalAlarmBitmask();

            _can.BenchLivenessChanged += OnBenchLiveness;
            _kwp.KLineStateChanged += OnKLineState;
            _bench.PhaseChanged += OnPhaseChanged;

            using var alarmWatch = StartAlarmWatchdog(token, initialMask, criticalMask);

            try
            {
                // ── Preflight ────────────────────────────────────────────────────
                SetState(AutoTestState.Preflight);
                if (!_can.IsConnected)
                {
                    ReportFailure(AutoTestFailureReason.PreflightDenied, "CAN bus not connected");
                    return false;
                }
                if ((ReadAlarmMask() & criticalMask) != 0)
                {
                    ReportFailure(AutoTestFailureReason.PreflightDenied, "Critical alarm already active");
                    return false;
                }

                token.ThrowIfCancellationRequested();

                var host = _hostFactory();

                bool klineAlreadyOpen =
                    _kwp.KLineState == KLineConnectionState.Connected &&
                    host.CurrentPump != null;

                // ── ConnectingKLine ──────────────────────────────────────────────
                if (!klineAlreadyOpen)
                {
                    SetState(AutoTestState.ConnectingKLine);
                    string? port = _kwp.DetectKLinePort();
                    if (string.IsNullOrEmpty(port))
                    {
                        ReportFailure(AutoTestFailureReason.KLineConnectFailed,
                            "FTDI adapter not found");
                        return false;
                    }

                    // ConnectAsync opens the session and starts the keep-alive loop.
                    // If the session is already open the service returns immediately.
                    try
                    {
                        await _kwp.ConnectAsync(port, token).ConfigureAwait(true);
                    }
                    catch (OperationCanceledException) { throw; }
                    catch (Exception ex)
                    {
                        ReportFailure(AutoTestFailureReason.KLineConnectFailed,
                            $"ConnectAsync failed: {ex.Message}");
                        return false;
                    }
                }

                // ── ReadingPump ──────────────────────────────────────────────────
                if (!klineAlreadyOpen)
                {
                    SetState(AutoTestState.ReadingPump);
                    int version = host.CurrentPump?.KwpVersion ?? 0;
                    string? port = _kwp.ConnectedPort ?? _kwp.DetectKLinePort();
                    if (string.IsNullOrEmpty(port))
                    {
                        ReportFailure(AutoTestFailureReason.KLineConnectFailed,
                            "FTDI adapter disappeared before read");
                        return false;
                    }

                    // Forward ReadAllInfoAsync percentage ticks to the snackbar.
                    void OnProgress(int pct, string _) =>
                        RaiseStateChanged(AutoTestState.ReadingPump, pct.ToString());
                    _kwp.ProgressChanged += OnProgress;

                    System.Collections.Generic.Dictionary<string, string> info;
                    try
                    {
                        info = await _kwp.ReadAllInfoAsync(port, version, token).ConfigureAwait(true);
                    }
                    catch (OperationCanceledException) { throw; }
                    catch (Exception ex)
                    {
                        ReportFailure(AutoTestFailureReason.ReadFailed,
                            $"ReadAllInfoAsync threw: {ex.Message}");
                        return false;
                    }
                    finally
                    {
                        _kwp.ProgressChanged -= OnProgress;
                    }

                    if (!info.TryGetValue(KlineKeys.Result, out var result) || result != "1")
                    {
                        ReportFailure(AutoTestFailureReason.ReadFailed,
                            info.TryGetValue(KlineKeys.ConnectError, out var err) ? err : "Read result=0");
                        return false;
                    }

                    // The KwpService.PumpIdentified event fires mid-read on the background
                    // thread and is marshalled to the UI thread by PumpIdentificationViewModel,
                    // which sets SelectedPumpId → CurrentPump via a synchronous side-effect
                    // chain. After await completes, CurrentPump is therefore populated —
                    // unless the K-Line pump ID was not in pumps.xml.
                    if (host.CurrentPump == null)
                    {
                        ReportFailure(AutoTestFailureReason.PumpNotRecognized,
                            info.TryGetValue(KlineKeys.PumpId, out var kid)
                                ? $"Pump ID '{kid}' not in database"
                                : "Pump ID not recognised");
                        return false;
                    }
                }

                var pump = host.CurrentPump;
                if (pump == null)
                {
                    ReportFailure(AutoTestFailureReason.PumpNotRecognized, "No pump selected");
                    return false;
                }

                token.ThrowIfCancellationRequested();

                // ── Unlocking ────────────────────────────────────────────────────
                // When the pump was auto-selected during the read, MainViewModel.OnPumpChanged
                // already started UnlockService.UnlockAsync AND the 1 s observer in the
                // background. We wait on whichever fires first:
                //   - PumpUnlocked (observer confirmed the CAN TestUnlock param flipped),
                //   - UnlockCompleted (the service's own UnlockAsync finished).
                // The observer race-guards against the case where the pump auto-unlocks
                // (fast unlock shortcut or an external manual unlock) before we subscribe.
                if (pump.UnlockType != 0)
                {
                    SetState(AutoTestState.Unlocking);

                    // Race-guard short-circuit: if the observer already latched an
                    // unlocked state (fast unlock finished while we were still doing
                    // the K-Line read), skip straight past the Unlocking wait.
                    if (_unlock.IsPumpUnlocked)
                    {
                        RaiseStateChanged(AutoTestState.Unlocking, "Pump already unlocked");
                    }
                    else
                    {
                        var unlockTcs = new TaskCompletionSource<bool>(
                            TaskCreationOptions.RunContinuationsAsynchronously);

                        void OnUnlockStatus(string msg) =>
                            RaiseStateChanged(AutoTestState.Unlocking, msg);
                        void OnUnlockCompleted(bool success) => unlockTcs.TrySetResult(success);
                        // Observer fires as soon as the CAN TestUnlock parameter reports
                        // unlocked — this covers fast unlock and external unlocks that
                        // would otherwise only be observed when UnlockAsync itself finishes.
                        void OnPumpUnlocked() => unlockTcs.TrySetResult(true);

                        _unlock.StatusChanged += OnUnlockStatus;
                        _unlock.UnlockCompleted += OnUnlockCompleted;
                        _unlock.PumpUnlocked += OnPumpUnlocked;

                        using var ctReg = token.Register(() => unlockTcs.TrySetCanceled());

                        bool unlocked;
                        try
                        {
                            // Re-check after subscribing to close the subscribe-vs-fire race.
                            if (_unlock.IsPumpUnlocked)
                                unlockTcs.TrySetResult(true);

                            unlocked = await unlockTcs.Task.ConfigureAwait(true);
                        }
                        finally
                        {
                            _unlock.StatusChanged -= OnUnlockStatus;
                            _unlock.UnlockCompleted -= OnUnlockCompleted;
                            _unlock.PumpUnlocked -= OnPumpUnlocked;
                        }

                        if (!unlocked)
                        {
                            ReportFailure(AutoTestFailureReason.UnlockFailed, "Unlock verification failed");
                            return false;
                        }
                    }
                }

                token.ThrowIfCancellationRequested();

                // ── TurningOnBench ───────────────────────────────────────────────
                // Past this point any failure must request an emergency stop.
                SetState(AutoTestState.TurningOnBench);
                _bench.SetRelay(RelayNames.Electronic, true);
                _bench.SetRpm(0);

                token.ThrowIfCancellationRequested();

                // ── StartingOilPump ──────────────────────────────────────────────
                // Delegate to the UI host: handles already-on short-circuit, the
                // autoskip setting, and the leak-check dialog. Returns false only
                // when the operator actively cancels the confirmation dialog.
                SetState(AutoTestState.StartingOilPump);
                bool oilPumpReady = await _hostFactory()
                    .EnsureOilPumpOnAsync(_config.Settings.AutoTestSkipsOilPumpConfirm)
                    .ConfigureAwait(true);
                if (!oilPumpReady)
                {
                    ReportFailure(AutoTestFailureReason.OilPumpNotConfirmed,
                        string.Empty);
                    return false;
                }

                token.ThrowIfCancellationRequested();

                // ── StartingTest / Running ───────────────────────────────────────
                SetState(AutoTestState.StartingTest);

                var testTcs = new TaskCompletionSource<(bool interrupted, bool success)>(
                    TaskCreationOptions.RunContinuationsAsynchronously);

                void OnTestStarted() => SetState(AutoTestState.Running, _latestPhaseDetail);
                void OnTestFinished(bool interrupted, bool success)
                    => testTcs.TrySetResult((interrupted, success));
                void OnVerbose(string msg) => RaiseStateChanged(AutoTestState.Running, msg);

                _bench.TestStarted += OnTestStarted;
                _bench.TestFinished += OnTestFinished;
                _bench.VerboseMessage += OnVerbose;

                try
                {
                    // RunTestsAsync runs its sequence on a background task internally;
                    // we wait on TestFinished so we observe success/interruption state.
                    await _bench.RunTestsAsync(pump, token).ConfigureAwait(true);

                    // RunTestsAsync returns once the background task completes, but the
                    // TestFinished event is the authoritative source for interrupted/success.
                    var result = await testTcs.Task.ConfigureAwait(true);

                    if (result.interrupted)
                    {
                        ReportFailure(AutoTestFailureReason.TestInterrupted, "Test interrupted");
                        return false;
                    }
                    if (!result.success)
                    {
                        ReportFailure(AutoTestFailureReason.TestFailed, "Test failed");
                        return false;
                    }
                }
                finally
                {
                    _bench.TestStarted -= OnTestStarted;
                    _bench.TestFinished -= OnTestFinished;
                    _bench.VerboseMessage -= OnVerbose;
                }

                SetState(AutoTestState.Completed);
                return true;
            }
            catch (OperationCanceledException)
            {
                if (!_failureReported)
                    ReportFailure(AutoTestFailureReason.UserCancelled, "Cancelled");
                return false;
            }
            catch (Exception ex)
            {
                _log.Error(LogId, $"Unexpected exception: {ex}");
                if (!_failureReported)
                    ReportFailure(AutoTestFailureReason.Unexpected, ex.Message);
                return false;
            }
            finally
            {
                _can.BenchLivenessChanged -= OnBenchLiveness;
                _kwp.KLineStateChanged -= OnKLineState;
                _bench.PhaseChanged -= OnPhaseChanged;

                // E-stop only if we failed past bench-on.
                if (_state.IsPastBenchOn() && _state != AutoTestState.Completed)
                {
                    try { _bench.RequestEmergencyStop("Auto-test aborted"); }
                    catch (Exception ex) { _log.Error(LogId, $"E-stop failed: {ex.Message}"); }
                }

                if (_state != AutoTestState.Completed && _state != AutoTestState.Aborted)
                    SetState(AutoTestState.Aborted);

                _autoCts?.Dispose();
                _autoCts = null;
            }
        }

        // ── Helpers ──────────────────────────────────────────────────────────────

        private void SetState(AutoTestState next, string? detail = null)
        {
            _state = next;
            RaiseStateChanged(next, detail);
        }

        private void RaiseStateChanged(AutoTestState s, string? detail)
            => StateChanged?.Invoke(s, detail);

        private void ReportFailure(AutoTestFailureReason reason, string message)
        {
            if (_failureReported) return;
            _failureReported = true;
            _log.Warning(LogId, $"Failed: {reason} — {message}");
            Failed?.Invoke(reason, message);
        }

        private void OnPhaseChanged(string phaseName)
        {
            _latestPhaseDetail = phaseName;
            if (_state == AutoTestState.Running)
                RaiseStateChanged(AutoTestState.Running, phaseName);
        }

        private int ReadAlarmMask()
        {
            try { return (int)_bench.ReadBenchParameter(BenchParameterNames.Alarms); }
            catch { return 0; }
        }

        private int BuildCriticalAlarmBitmask()
        {
            int mask = 0;
            foreach (var a in _config.Settings.Alarms)
                if (a.IsCritical) mask |= 1 << a.Bit;
            return mask;
        }

        /// <summary>
        /// Starts a lightweight task that polls the bench alarm word and aborts the
        /// run if any critical bit transitions from clear to set.
        /// </summary>
        private IDisposable StartAlarmWatchdog(CancellationToken token, int initialMask, int criticalMask)
        {
            var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
            int lastMask = initialMask;

            _ = Task.Run(async () =>
            {
                try
                {
                    while (!cts.IsCancellationRequested)
                    {
                        await Task.Delay(250, cts.Token).ConfigureAwait(false);
                        int now = ReadAlarmMask();
                        int newlySet = now & ~lastMask;
                        lastMask = now;
                        if ((newlySet & criticalMask) != 0)
                        {
                            ReportFailure(AutoTestFailureReason.AlarmTriggered,
                                "Critical alarm transitioned active");
                            _autoCts?.Cancel();
                            return;
                        }
                    }
                }
                catch (OperationCanceledException) { /* expected */ }
            }, cts.Token);

            return new Disposer(cts);
        }

        private sealed class Disposer : IDisposable
        {
            private readonly CancellationTokenSource _cts;
            public Disposer(CancellationTokenSource cts) { _cts = cts; }
            public void Dispose()
            {
                try { _cts.Cancel(); } catch { }
                _cts.Dispose();
            }
        }
    }
}