using Akka.Actor;
using Akka.Cluster.Tools.PublishSubscribe;
using Akka.Hosting;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.OpcUaServer;
using ZB.MOM.WW.OtOpcUa.OpcUaServer.Security;
using ZB.MOM.WW.OtOpcUa.Runtime;
using ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
using ZB.MOM.WW.OtOpcUa.Runtime.ScriptedAlarms;

namespace ZB.MOM.WW.OtOpcUa.Host.OpcUa;

/// <summary>
///     Owns the OPC UA SDK lifecycle on driver-role hosts. Reads
///     <see cref="OpcUaApplicationHostOptions"/> from the <c>OpcUa</c> config section, boots
///     an <see cref="OtOpcUaSdkServer"/> through <see cref="OpcUaApplicationHost"/>, then
///     swaps a real <see cref="SdkAddressSpaceSink"/> into the
///     <see cref="DeferredAddressSpaceSink"/> singleton so <c>OpcUaPublishActor</c>'s writes
///     start landing in the real address space.
///
///     Tests boot the OPC UA server directly via <see cref="OpcUaApplicationHost"/>; this
///     hosted service is the production wiring.
/// </summary>
public sealed class OtOpcUaServerHostedService : IHostedService, IAsyncDisposable
{
    private readonly OpcUaApplicationHostOptions _options;
    private readonly DeferredAddressSpaceSink _deferredSink;
    private readonly DeferredServiceLevelPublisher _deferredServiceLevel;
    private readonly IOpcUaUserAuthenticator _userAuthenticator;
    private readonly IHistorianDataSource _historianDataSource;
    private readonly Func<ActorSystem> _actorSystemAccessor;
    private readonly ActorRegistry _actorRegistry;
    private readonly ILoggerFactory _loggerFactory;
    private readonly ILogger<OtOpcUaServerHostedService> _logger;

    private OpcUaApplicationHost? _appHost;
    private OtOpcUaSdkServer? _server;

    /// <summary>
    /// Initializes a new instance of the OtOpcUaServerHostedService class.
    /// </summary>
    /// <param name="options">The validated OPC UA host options (bound from the <c>OpcUa</c> section and validated at startup via <c>ValidateOnStart</c>).</param>
    /// <param name="deferredSink">The deferred address space sink that receives the real sink once the server is ready.</param>
    /// <param name="deferredServiceLevel">The deferred service level publisher that receives the real publisher once the server is ready.</param>
    /// <param name="userAuthenticator">The OPC UA user authenticator.</param>
    /// <param name="historianDataSource">The server-side HistoryRead backend resolved from DI — the
    /// <c>NullHistorianDataSource</c> default seeded by <c>AddOtOpcUaRuntime</c> (which runs on this driver
    /// node, the same source the address-space sink + node-write gateway come from), or the configured
    /// Wonderware read client when <c>AddServerHistorian</c> enabled it. Wired onto the node manager in
    /// <see cref="StartAsync"/>.</param>
    /// <param name="actorSystemAccessor">Lazy accessor for the running <see cref="ActorSystem"/>, used to
    /// resolve the DistributedPubSub mediator the inbound alarm-command router publishes through. Resolved
    /// lazily (mirroring <c>DpsScriptLogPublisher</c>) so construction never races Akka startup.</param>
    /// <param name="actorRegistry">The Akka.Hosting actor registry, used to resolve the local
    /// <c>DriverHostActor</c> ref (<c>DriverHostActorKey</c>) the inbound node-write router Asks. Resolved
    /// in <see cref="StartAsync"/> after the runtime actors have been registered.</param>
    /// <param name="loggerFactory">The logger factory for creating loggers.</param>
    public OtOpcUaServerHostedService(
        IOptions<OpcUaApplicationHostOptions> options,
        DeferredAddressSpaceSink deferredSink,
        DeferredServiceLevelPublisher deferredServiceLevel,
        IOpcUaUserAuthenticator userAuthenticator,
        IHistorianDataSource historianDataSource,
        Func<ActorSystem> actorSystemAccessor,
        ActorRegistry actorRegistry,
        ILoggerFactory loggerFactory)
    {
        _options = options.Value;
        _deferredSink = deferredSink;
        _deferredServiceLevel = deferredServiceLevel;
        _userAuthenticator = userAuthenticator;
        _historianDataSource = historianDataSource;
        _actorSystemAccessor = actorSystemAccessor;
        _actorRegistry = actorRegistry;
        _loggerFactory = loggerFactory;
        _logger = loggerFactory.CreateLogger<OtOpcUaServerHostedService>();
    }

    /// <summary>
    /// Starts the OPC UA server asynchronously.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    public async Task StartAsync(CancellationToken cancellationToken)
    {
        _server = new OtOpcUaSdkServer();
        _appHost = new OpcUaApplicationHost(
            _options,
            _loggerFactory.CreateLogger<OpcUaApplicationHost>(),
            _userAuthenticator);

        try
        {
            await _appHost.StartAsync(_server, cancellationToken).ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex,
                "OtOpcUaServerHostedService: SDK start failed; OpcUaPublishActor writes will continue to no-op");
            // Don't rethrow — the rest of the host (admin UI, driver actors, etc.) can still boot.
            // Operators see the failure via the logs + can correct config without a process bounce
            // of the whole binary.
            return;
        }

        if (_server.NodeManager is null)
        {
            _logger.LogWarning(
                "OtOpcUaServerHostedService: SDK reported started but NodeManager is null; sink stays Null");
            return;
        }

        _deferredSink.SetSink(new SdkAddressSpaceSink(_server.NodeManager));

        // Wire the reverse-path inbound-alarm-command router: a client Acknowledge/Confirm/Shelve that
        // passes the node manager's AlarmAck gate publishes the mapped AlarmCommand onto the cluster
        // `alarm-commands` topic (same DistributedPubSub mediator the `alerts`/`script-logs` topics use).
        // The Tell is fire-and-forget so the handler — which runs under the SDK's Lock — never blocks.
        // The mediator is resolved per-publish via the lazy ActorSystem accessor so a transient cluster
        // condition is tolerated and construction never raced Akka startup.
        _server.SetAlarmCommandRouter(cmd =>
        {
            try
            {
                var mediator = DistributedPubSub.Get(_actorSystemAccessor()).Mediator;
                mediator.Tell(new Publish(ScriptedAlarmHostActor.AlarmCommandsTopic, cmd));
            }
            catch (Exception ex)
            {
                // The router runs under the SDK Lock on a server thread; a cluster hiccup must not
                // escape into the SDK's Call path. Log + drop — the client still gets Good for the
                // node-state change; the missed command surfaces as a non-applied engine transition.
                _logger.LogWarning(ex,
                    "OtOpcUaServerHostedService: failed to route inbound alarm command {Operation} for {AlarmId}",
                    cmd.Operation, cmd.AlarmId);
            }
        });

        // Wire the reverse-path inbound operator-write gateway: a client write to a writable equipment-tag
        // node that passes the node manager's WriteOperate gate routes the write to the owning driver child
        // (RouteNodeWrite → NodeWriteResult) via the local DriverHostActor. The node manager calls the
        // gateway's WriteAsync FIRE-AND-FORGET: the SDK's CustomNodeManager2.Write holds the node-manager
        // Lock while invoking OnWriteValue, so a blocking Ask here would freeze ALL address-space operations
        // (reads, subscription notifications, the publish path) for up to the Ask timeout. The gateway kicks
        // off the Ask and resolves a NodeWriteOutcome; the node manager applies the client value optimistically
        // and self-corrects (reverts to the pre-write value) when the device write comes back FAILED — but only
        // while the node still holds the optimistic value, so a fresh driver poll is not clobbered. The
        // DriverHostActor ref is resolved LAZILY per write (inside the gateway) — this hosted service's
        // StartAsync runs before the Akka DriverHostActor registers, so a one-shot resolve here would always
        // miss and leave every write unavailable. By write time (long after startup) the registry has it; a
        // node that genuinely has no driver-host (admin-only, no writable driver nodes materialised) logs +
        // resolves the write to "writes unavailable".
        _server.SetNodeWriteGateway(new ActorNodeWriteGateway(
            resolveDriverHost: () => _actorRegistry.TryGet<DriverHostActorKey>(out var driverHost) ? driverHost : null,
            logger: _loggerFactory.CreateLogger<ActorNodeWriteGateway>()));

        // Wire the server-side read backend resolved from DI — the NullHistorianDataSource default (when
        // the ServerHistorian section is disabled) or the configured Wonderware read client (when enabled).
        // The node manager's HistoryRead overrides block-bridge to whatever source is set here.
        _server.SetHistorianDataSource(_historianDataSource);

        // ServiceLevel publisher needs IServerInternal — only available after Start.
        if (_server.CurrentInstance is { } serverInternal)
        {
            _deferredServiceLevel.SetInner(new SdkServiceLevelPublisher(
                serverInternal,
                _loggerFactory.CreateLogger<SdkServiceLevelPublisher>()));
        }

        _logger.LogInformation("OtOpcUaServerHostedService: SDK started, address-space + ServiceLevel sinks bound");
    }

    /// <summary>
    /// Stops the OPC UA server asynchronously.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    public Task StopAsync(CancellationToken cancellationToken)
    {
        // Revert to Null adapters so any in-flight writes from a poison-pilled actor don't hit a
        // half-disposed NodeManager.
        _deferredSink.SetSink(null);
        _deferredServiceLevel.SetInner(null);
        // Restore the Null write gateway so a late client write doesn't Ask a stopping DriverHostActor.
        _server?.SetNodeWriteGateway(null);
        // Restore the Null historian so a late HistoryRead doesn't hit a disposed read client.
        _server?.SetHistorianDataSource(null);
        return Task.CompletedTask;
    }

    /// <summary>
    /// Disposes the hosted service and its resources asynchronously.
    /// </summary>
    public async ValueTask DisposeAsync()
    {
        if (_appHost is not null) await _appHost.DisposeAsync();
    }
}