using Akka.Actor;
using Akka.Event;
using ZB.MOM.WW.OtOpcUa.Commons.Observability;
using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
using ZB.MOM.WW.OtOpcUa.Commons.Types;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;

// private timer key type — file-scoped so the name stays unique per-file
file sealed class HealthPollTick
{
    public static readonly HealthPollTick Instance = new();
    private HealthPollTick() { }
}

/// <summary>
/// Akka wrapper for a single <see cref="IDriver"/> instance. States:
///
/// <list type="bullet">
///   <item><c>Connecting</c> — calling <see cref="IDriver.InitializeAsync"/>.</item>
///   <item><c>Connected</c> — initialised; serving Read/Write/Subscribe requests.</item>
///   <item><c>Reconnecting</c> — disconnect observed; periodic retry of Initialize.</item>
///   <item><c>Failed</c> — terminal until parent restarts the actor.</item>
/// </list>
///
/// Engine wiring (subscriptions → AttributeValueUpdate publishes, ApplyDelta-driven Reinitialize,
/// per-tag write Asks) is staged for follow-up F7. This skeleton compiles + has a working
/// state machine so the Phase 6 control-plane integration tests can target it.
/// </summary>
public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
{
    public static readonly TimeSpan DefaultReconnectInterval = TimeSpan.FromSeconds(10);

    public sealed record InitializeRequested(string DriverConfigJson);
    public sealed record InitializeSucceeded;
    public sealed record InitializeFailed(string Reason);
    public sealed record DisconnectObserved(string Reason);
    public sealed record ApplyDelta(string DriverConfigJson, CorrelationId Correlation);
    public sealed record ApplyResult(bool Success, string? Reason, CorrelationId Correlation);
    public sealed record WriteAttribute(string TagId, object Value);
    public sealed record WriteAttributeResult(bool Success, string? Reason);
    public sealed record Subscribe(IReadOnlyList<string> FullReferences, TimeSpan PublishingInterval);
    public sealed record SubscriptionEstablished(string DiagnosticId, int ReferenceCount);
    public sealed record SubscriptionFailed(string Reason);
    public sealed record Unsubscribe;
    /// <summary>
    ///     Sent by <see cref="DriverHostActor"/> when the AdminUI issues a Reconnect operation.
    ///     Pushes the actor out of <c>Connected</c> into <c>Reconnecting</c> so the transport is
    ///     re-established without fully stopping and respawning the actor. Safe to send in any
    ///     state — a no-op when already Reconnecting or Connecting.
    /// </summary>
    public sealed record ForceReconnect;
    /// <summary>Published to the actor's parent whenever the subscribed IDriver fires
    /// <see cref="ISubscribable.OnDataChange"/>. The parent forwards to OpcUaPublishActor.</summary>
    public sealed record AttributeValuePublished(string FullReference, object? Value, OpcUaQuality Quality, DateTime TimestampUtc);
    private sealed record DataChangeForward(string FullReference, DataValueSnapshot Snapshot);
    public sealed class RetryConnect
    {
        public static readonly RetryConnect Instance = new();
        private RetryConnect() { }
    }

    /// <summary>Interval between periodic health-poll heartbeats sent to the snapshot store.</summary>
    public static readonly TimeSpan HealthPollInterval = TimeSpan.FromSeconds(30);

    private readonly IDriver _driver;
    private readonly string _driverInstanceId;
    private readonly string _clusterId;
    private readonly IDriverHealthPublisher _healthPublisher;
    private readonly TimeSpan _reconnectInterval;
    private readonly ILoggingAdapter _log = Context.GetLogger();
    private string? _currentConfigJson;

    /// <summary>Timestamps of recent Faulted-state transitions; used to compute the 5-minute error count.</summary>
    private readonly Queue<DateTime> _faultTimestamps = new();
    private readonly object _faultLock = new();

    /// <summary>Active subscription handle (null when not subscribed). Lifetime is one-per-actor —
    /// re-subscribe across reconnects is the consumer's responsibility today (subscribe-once
    /// semantics keep the actor simple; mux-driven re-subscribe is tracked as F8b/#113).</summary>
    private ISubscriptionHandle? _subscriptionHandle;
    private EventHandler<DataChangeEventArgs>? _dataChangeHandler;

    /// <summary>
    /// Gets or sets the timer scheduler for scheduling reconnection attempts.
    /// </summary>
    public ITimerScheduler Timers { get; set; } = null!;

    /// <summary>
    /// Creates a Props object for instantiating a <see cref="DriverInstanceActor"/>.
    /// </summary>
    /// <param name="driver">The driver instance to wrap.</param>
    /// <param name="reconnectInterval">Optional interval for reconnection attempts; defaults to 10 seconds.</param>
    /// <param name="startStubbed">If true, the actor starts in stub mode for testing or unavailable platforms.</param>
    /// <param name="healthPublisher">Optional health publisher; defaults to <see cref="NullDriverHealthPublisher"/> so tests and
    /// stub paths don't need to provide one.</param>
    /// <param name="clusterId">Optional cluster identifier forwarded in <see cref="DriverHealthChanged"/> messages;
    /// defaults to an empty string when not provided (e.g. in unit tests).</param>
    public static Props Props(
        IDriver driver,
        TimeSpan? reconnectInterval = null,
        bool startStubbed = false,
        IDriverHealthPublisher? healthPublisher = null,
        string? clusterId = null) =>
        Akka.Actor.Props.Create(() => new DriverInstanceActor(
            driver,
            reconnectInterval ?? DefaultReconnectInterval,
            startStubbed,
            healthPublisher ?? NullDriverHealthPublisher.Instance,
            clusterId ?? string.Empty));

    /// <summary>
    /// Returns true when the driver should boot in DEV-STUB mode based on host platform and
    /// configured roles. Only the v1 in-process types stay Windows-only:
    /// <list type="bullet">
    ///   <item><c>"Galaxy"</c> — legacy MXAccess COM proxy (retired in PR 7.2; gated for any
    ///         leftover DriverInstance rows that still reference the old type name).</item>
    ///   <item><c>"Historian.Wonderware"</c> — Wonderware Historian sidecar over Windows-only
    ///         named pipes.</item>
    /// </list>
    /// The v2 <c>"GalaxyMxGateway"</c> driver talks gRPC to an external mxaccessgw process,
    /// so it runs on any platform .NET 10 supports — Linux containers included. Not stubbed.
    /// </summary>
    /// <param name="driverType">The type identifier of the driver.</param>
    /// <param name="roles">Operational roles configured for this instance.</param>
    public static bool ShouldStub(string driverType, IEnumerable<string> roles)
    {
        var isWindowsOnly = driverType is "Galaxy" or "Historian.Wonderware";
        if (!OperatingSystem.IsWindows() && isWindowsOnly) return true;
        if (roles.Contains("dev") && isWindowsOnly) return true;
        return false;
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="DriverInstanceActor"/> class.
    /// </summary>
    /// <param name="driver">The driver instance to wrap and manage.</param>
    /// <param name="reconnectInterval">Interval between reconnection attempts.</param>
    /// <param name="startStubbed">If true, start in stub mode for testing or unavailable platforms.</param>
    /// <param name="healthPublisher">Sink for health-change notifications; must not be null.</param>
    /// <param name="clusterId">Cluster identifier forwarded in health snapshots.</param>
    public DriverInstanceActor(
        IDriver driver,
        TimeSpan reconnectInterval,
        bool startStubbed = false,
        IDriverHealthPublisher? healthPublisher = null,
        string? clusterId = null)
    {
        _driver = driver;
        _driverInstanceId = driver.DriverInstanceId;
        _clusterId = clusterId ?? string.Empty;
        _healthPublisher = healthPublisher ?? NullDriverHealthPublisher.Instance;
        _reconnectInterval = reconnectInterval;
        OtOpcUaTelemetry.DriverInstanceLifecycle.Add(1,
            new KeyValuePair<string, object?>("event", startStubbed ? "spawn_stub" : "spawn"),
            new KeyValuePair<string, object?>("driver_type", driver.DriverType));
        if (startStubbed)
        {
            Context.GetLogger().Info("[DEV-STUB] driver={Name} type={Type}",
                _driverInstanceId, driver.DriverType);
            Become(Stubbed);
        }
        else
        {
            Become(Connecting);
        }
    }

    /// <inheritdoc />
    protected override void PreStart()
    {
        // Warm up the snapshot store immediately so AdminUI sees current state as soon as the
        // actor starts, before any state transition fires. Also start the periodic heartbeat so
        // long-lived Healthy drivers keep their snapshot fresh for newly-joined SignalR clients.
        PublishHealthSnapshot();
        Timers.StartPeriodicTimer("health-poll", HealthPollTick.Instance, HealthPollInterval);
    }

    private void Stubbed()
    {
        // Stubbed drivers accept the standard message contracts but return deterministic
        // success without touching real hardware. Read returns null; Write succeeds.
        Receive<InitializeRequested>(_ => { /* no-op */ });
        Receive<ApplyDelta>(msg => Sender.Tell(new ApplyResult(true, "stubbed", msg.Correlation)));
        Receive<WriteAttribute>(_ => Sender.Tell(new WriteAttributeResult(true, "stubbed")));
        Receive<DisconnectObserved>(_ => { /* stubbed drivers don't disconnect */ });
        Receive<ForceReconnect>(_ => { /* stubbed drivers don't reconnect */ });
        Receive<HealthPollTick>(_ => PublishHealthSnapshot());
    }

    private void Connecting()
    {
        Receive<InitializeRequested>(msg => InitializeAsync(msg.DriverConfigJson));
        Receive<InitializeSucceeded>(_ =>
        {
            _log.Info("DriverInstance {Id}: connected", _driverInstanceId);
            Become(Connected);
            PublishHealthSnapshot();
        });
        Receive<InitializeFailed>(msg =>
        {
            _log.Warning("DriverInstance {Id}: initialize failed: {Reason}", _driverInstanceId, msg.Reason);
            RecordFault();
            Become(Reconnecting);
            PublishHealthSnapshot();
        });
        Receive<ForceReconnect>(_ => { /* already connecting — no-op */ });
        Receive<HealthPollTick>(_ => PublishHealthSnapshot());
    }

    private void Connected()
    {
        ReceiveAsync<ApplyDelta>(HandleApplyDeltaAsync);
        Receive<DisconnectObserved>(msg =>
        {
            _log.Warning("DriverInstance {Id}: disconnect observed ({Reason}); reconnecting",
                _driverInstanceId, msg.Reason);
            DetachSubscription();
            RecordFault();
            Become(Reconnecting);
            PublishHealthSnapshot();
        });
        Receive<ForceReconnect>(_ =>
        {
            _log.Info("DriverInstance {Id}: ForceReconnect requested by admin; re-entering Reconnecting", _driverInstanceId);
            DetachSubscription();
            Become(Reconnecting);
            PublishHealthSnapshot();
        });
        ReceiveAsync<WriteAttribute>(HandleWriteAsync);
        ReceiveAsync<Subscribe>(HandleSubscribeAsync);
        ReceiveAsync<Unsubscribe>(_ => UnsubscribeAsync());
        Receive<DataChangeForward>(OnDataChangeForward);
        Receive<HealthPollTick>(_ => PublishHealthSnapshot());
    }

    private void Reconnecting()
    {
        Receive<RetryConnect>(_ => InitializeAsync(_currentConfigJson ?? "{}"));
        Receive<InitializeSucceeded>(_ =>
        {
            Timers.Cancel("retry-connect");
            _log.Info("DriverInstance {Id}: reconnected", _driverInstanceId);
            Become(Connected);
            PublishHealthSnapshot();
        });
        Receive<InitializeFailed>(_ => { /* keep retrying via timer */ });
        Receive<ForceReconnect>(_ => { /* already reconnecting — no-op */ });
        Receive<HealthPollTick>(_ => PublishHealthSnapshot());
        Timers.StartPeriodicTimer("retry-connect", RetryConnect.Instance, _reconnectInterval);
    }

    private void InitializeAsync(string driverConfigJson)
    {
        _currentConfigJson = driverConfigJson;
        var self = Self;
        _ = Task.Run(async () =>
        {
            try
            {
                await _driver.InitializeAsync(driverConfigJson, CancellationToken.None);
                self.Tell(new InitializeSucceeded());
            }
            catch (Exception ex)
            {
                self.Tell(new InitializeFailed(ex.Message));
            }
        });
    }

    private async Task HandleApplyDeltaAsync(ApplyDelta msg)
    {
        var replyTo = Sender;
        try
        {
            await _driver.ReinitializeAsync(msg.DriverConfigJson, CancellationToken.None);
            _currentConfigJson = msg.DriverConfigJson;
            replyTo.Tell(new ApplyResult(true, null, msg.Correlation));
        }
        catch (Exception ex)
        {
            replyTo.Tell(new ApplyResult(false, ex.Message, msg.Correlation));
        }
    }

    private async Task HandleWriteAsync(WriteAttribute msg)
    {
        if (_driver is not IWritable writable)
        {
            Sender.Tell(new WriteAttributeResult(false, "Driver does not implement IWritable"));
            return;
        }

        var replyTo = Sender;
        var request = new[] { new WriteRequest(msg.TagId, msg.Value) };
        // Bound the write so a hung backend can't pin this actor forever — decision #44/#45 keeps
        // retry off by default, but a stalled call still needs an answer.
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
        try
        {
            var results = await writable.WriteAsync(request, cts.Token).ConfigureAwait(false);
            if (results is { Count: 1 } && IsGoodStatus(results[0].StatusCode))
            {
                replyTo.Tell(new WriteAttributeResult(true, null));
                return;
            }
            var status = results is { Count: > 0 } ? results[0].StatusCode : 0xFFFFFFFF;
            replyTo.Tell(new WriteAttributeResult(false, $"StatusCode=0x{status:X8}"));
        }
        catch (OperationCanceledException)
        {
            replyTo.Tell(new WriteAttributeResult(false, "write timeout"));
        }
        catch (Exception ex)
        {
            replyTo.Tell(new WriteAttributeResult(false, ex.Message));
        }
    }

    private async Task HandleSubscribeAsync(Subscribe msg)
    {
        if (_driver is not ISubscribable subscribable)
        {
            Sender.Tell(new SubscriptionFailed("Driver does not implement ISubscribable"));
            return;
        }
        if (_subscriptionHandle is not null)
        {
            // Subscribe-twice — drop the prior subscription before establishing the new one.
            await UnsubscribeAsync().ConfigureAwait(false);
        }

        var replyTo = Sender;
        var self = Self;
        try
        {
            _dataChangeHandler = (_, args) => self.Tell(new DataChangeForward(args.FullReference, args.Snapshot));
            subscribable.OnDataChange += _dataChangeHandler;

            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
            _subscriptionHandle = await subscribable
                .SubscribeAsync(msg.FullReferences, msg.PublishingInterval, cts.Token)
                .ConfigureAwait(false);

            replyTo.Tell(new SubscriptionEstablished(_subscriptionHandle.DiagnosticId, msg.FullReferences.Count));
            _log.Info("DriverInstance {Id}: subscribed to {Count} refs ({Diag})",
                _driverInstanceId, msg.FullReferences.Count, _subscriptionHandle.DiagnosticId);
        }
        catch (Exception ex)
        {
            DetachSubscription();
            _log.Warning(ex, "DriverInstance {Id}: subscribe failed", _driverInstanceId);
            replyTo.Tell(new SubscriptionFailed(ex.Message));
        }
    }

    private async Task UnsubscribeAsync()
    {
        if (_driver is not ISubscribable subscribable || _subscriptionHandle is null)
        {
            DetachSubscription();
            return;
        }
        try
        {
            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
            await subscribable.UnsubscribeAsync(_subscriptionHandle, cts.Token).ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            _log.Warning(ex, "DriverInstance {Id}: unsubscribe threw (continuing)", _driverInstanceId);
        }
        finally
        {
            DetachSubscription();
        }
    }

    /// <summary>Tear down the event handler + null the handle. Called from Unsubscribe path, on
    /// PostStop, and on Connected → Reconnecting transitions so a stale handler doesn't push
    /// data-change events to an actor that has lost its driver connection.</summary>
    private void DetachSubscription()
    {
        if (_driver is ISubscribable subscribable && _dataChangeHandler is not null)
        {
            subscribable.OnDataChange -= _dataChangeHandler;
        }
        _dataChangeHandler = null;
        _subscriptionHandle = null;
    }

    private void OnDataChangeForward(DataChangeForward msg)
    {
        var quality = QualityFromStatus(msg.Snapshot.StatusCode);
        var ts = msg.Snapshot.SourceTimestampUtc ?? msg.Snapshot.ServerTimestampUtc;
        Context.Parent.Tell(new AttributeValuePublished(msg.FullReference, msg.Snapshot.Value, quality, ts));
    }

    /// <summary>Translate an OPC UA status code to the 3-state <see cref="OpcUaQuality"/> projection
    /// the publish actor consumes. Severity bits (top 2): 00 = Good, 01 = Uncertain, 10/11 = Bad.</summary>
    private static OpcUaQuality QualityFromStatus(uint statusCode)
    {
        var severity = statusCode >> 30;
        return severity switch
        {
            0 => OpcUaQuality.Good,
            1 => OpcUaQuality.Uncertain,
            _ => OpcUaQuality.Bad,
        };
    }

    private static bool IsGoodStatus(uint statusCode) => (statusCode >> 30) == 0;

    /// <summary>
    ///     Records a transition into a Faulted / error state for the 5-minute sliding counter.
    ///     Thread-safe: called from actor message-handling (single-threaded) but guard is cheap.
    /// </summary>
    private void RecordFault()
    {
        lock (_faultLock)
        {
            _faultTimestamps.Enqueue(DateTime.UtcNow);
        }
    }

    /// <summary>Returns how many fault transitions occurred in the last 5 minutes.</summary>
    private int ErrorCount5Min()
    {
        var cutoff = DateTime.UtcNow.AddMinutes(-5);
        lock (_faultLock)
        {
            while (_faultTimestamps.Count > 0 && _faultTimestamps.Peek() < cutoff)
                _faultTimestamps.Dequeue();
            return _faultTimestamps.Count;
        }
    }

    /// <summary>
    ///     Polls <see cref="IDriver.GetHealth"/> and forwards the snapshot to the health publisher.
    ///     Called on every observable state change and by the periodic <see cref="HealthPollTick"/>
    ///     so the AdminUI snapshot store is warmed up for newly-joined SignalR clients.
    /// </summary>
    private void PublishHealthSnapshot()
    {
        try
        {
            var health = _driver.GetHealth();
            _healthPublisher.Publish(_clusterId, _driverInstanceId, health, ErrorCount5Min());
        }
        catch (Exception ex)
        {
            _log.Warning(ex, "DriverInstance {Id}: GetHealth threw during health publish; skipping", _driverInstanceId);
        }
    }

    /// <inheritdoc />
    protected override void PostStop()
    {
        DetachSubscription();
        try { _driver.ShutdownAsync(CancellationToken.None).GetAwaiter().GetResult(); }
        catch (Exception ex) { _log.Warning(ex, "DriverInstance {Id}: ShutdownAsync threw on PostStop", _driverInstanceId); }
        OtOpcUaTelemetry.DriverInstanceLifecycle.Add(1,
            new KeyValuePair<string, object?>("event", "stop"),
            new KeyValuePair<string, object?>("driver_type", _driver.DriverType));
    }
}