using Akka.Actor;
using Akka.Cluster;
using Akka.Event;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Artifacts;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.DebugView;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Deployment;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Health;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.InboundApi;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Integration;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Lifecycle;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Management;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Notification;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.RemoteQuery;

namespace ZB.MOM.WW.ScadaBridge.Communication.Actors;

/// <summary>
/// Site-side actor that receives messages from central over the site-hosted
/// <c>SiteCommandService</c> gRPC plane and routes them to the appropriate local actors.
/// Also sends heartbeats and health reports to central over its
/// <see cref="ICentralTransport"/> (<see cref="Grpc.GrpcCentralTransport"/> in production).
///
/// Routes all 8 message patterns to local handlers.
/// </summary>
public class SiteCommunicationActor : ReceiveActor, IWithTimers
{
    private readonly ILoggingAdapter _log = Context.GetLogger();
    private readonly string _siteId;
    private readonly CommunicationOptions _options;

    /// <summary>
    /// Predicate that returns <c>true</c> when this node is
    /// the active member of the local site cluster (used to stamp
    /// <see cref="HeartbeatMessage.IsActive"/>). Production builds default to
    /// the Akka <see cref="Cluster"/> leader check; tests inject a stub so they
    /// do not need a real cluster.
    /// </summary>
    private readonly Func<bool> _isActiveCheck;

    /// <summary>
    /// Reference to the local Deployment Manager singleton proxy.
    /// </summary>
    private readonly IActorRef _deploymentManagerProxy;

    /// <summary>
    /// The single routing truth for the 28 migrated central→site commands, shared with
    /// the gRPC <c>SiteCommandGrpcService</c> so the two transports cannot drift. In
    /// production it is created by the Host and passed in (so the gRPC server holds the
    /// same instance); when unset (tests) the actor builds its own from the failover seam.
    /// </summary>
    private readonly SiteCommandDispatcher _dispatcher;

    /// <summary>
    /// The site→central transport. Finalized in <see cref="PreStart"/> to the injected instance, or a
    /// fail-loud <see cref="NoOpCentralTransport"/> when none is supplied — so the seven site→central
    /// sends delegate here rather than owning the wire plumbing inline. Production injects the gRPC
    /// <see cref="Grpc.GrpcCentralTransport"/>.
    /// </summary>
    private ICentralTransport _transport;

    /// <summary>The transport supplied by the Host (null falls back to <see cref="NoOpCentralTransport"/>).</summary>
    private readonly ICentralTransport? _injectedTransport;

    /// <summary>Akka timer scheduler injected by the framework via <see cref="IWithTimers"/>.</summary>
    public ITimerScheduler Timers { get; set; } = null!;

    /// <summary>Initializes the actor, wires all message pattern handlers, and schedules the periodic heartbeat.</summary>
    /// <param name="siteId">The site identifier included in outbound messages.</param>
    /// <param name="options">Communication options including heartbeat interval and transport settings.</param>
    /// <param name="deploymentManagerProxy">Local reference to the Deployment Manager singleton proxy.</param>
    /// <param name="isActiveCheck">
    /// Optional override returning <c>true</c> when this node
    /// is the active member of the site cluster. <c>null</c> uses the shared oldest-Up
    /// evaluator (production wiring passes the Host's singleton-host delegate); tests
    /// pass a stub so they do not need to load Akka.Cluster into the <c>TestKit</c>
    /// ActorSystem.
    /// </param>
    /// <param name="transport">
    /// The site→central transport. Production always passes the Host-built gRPC
    /// <see cref="Grpc.GrpcCentralTransport"/>. <c>null</c> (used by TestKit suites that only
    /// exercise command dispatch) falls back to a fail-loud <see cref="NoOpCentralTransport"/>.
    /// </param>
    /// <param name="dispatcher">
    /// The shared <see cref="SiteCommandDispatcher"/> (production: created by the Host and also
    /// handed to the gRPC command service, so both transports route through one instance).
    /// <c>null</c> makes the actor build its own from <paramref name="failOverRole"/> — the shape
    /// the existing tests use.
    /// </param>
    public SiteCommunicationActor(
        string siteId,
        CommunicationOptions options,
        IActorRef deploymentManagerProxy,
        Func<bool>? isActiveCheck = null,
        Func<string, string?>? failOverRole = null,
        ICentralTransport? transport = null,
        SiteCommandDispatcher? dispatcher = null)
    {
        _siteId = siteId;
        _options = options;
        _deploymentManagerProxy = deploymentManagerProxy;
        _isActiveCheck = isActiveCheck ?? DefaultIsActiveCheck;
        _injectedTransport = transport;
        // Finalized in PreStart (where _log is usable for the default transport); assigned here
        // too so the field is definitely-assigned for the constructor's Receive closures.
        _transport = transport!;

        // When no shared dispatcher is supplied, build one over the same failover seam the
        // actor used before extraction: an injected Func (tests) that both resolves and leaves,
        // or the shared ClusterFailoverCoordinator. The actor only ever commits the leave
        // immediately (dryRun:false), so an injected coupled Func fits unchanged.
        var system = Context.System;
        Func<string, bool, string?> resolveFailover = failOverRole is not null
            ? (role, _) => failOverRole(role)
            : (role, dryRun) =>
                ClusterState.ClusterFailoverCoordinator.FailOverOldest(system, role, dryRun)?.ToString();
        _dispatcher = dispatcher ?? new SiteCommandDispatcher(siteId, deploymentManagerProxy, resolveFailover);

        Receive<RegisterLocalHandler>(HandleRegisterLocalHandler);

        // ── The 27 migrated central→site commands (28th is failover, below) all route
        // through the shared SiteCommandDispatcher — the single routing truth also used by
        // the gRPC SiteCommandGrpcService. The actor's job per command is unchanged: Forward
        // to the resolved target (preserving the central Ask sender so replies route straight
        // back to the waiting Ask), or Tell the caller the dispatcher's synthetic reply when a
        // null-guarded handler is unregistered. See SiteCommandDispatcher for the target of
        // each command and why the parked handler stays node-local.
        Receive<RefreshDeploymentCommand>(cmd => DispatchCommand(cmd));
        Receive<DisableInstanceCommand>(cmd => DispatchCommand(cmd));
        Receive<EnableInstanceCommand>(cmd => DispatchCommand(cmd));
        Receive<DeleteInstanceCommand>(cmd => DispatchCommand(cmd));
        Receive<DeploymentStateQueryRequest>(cmd => DispatchCommand(cmd));
        Receive<DeployArtifactsCommand>(cmd => DispatchCommand(cmd));
        Receive<SubscribeDebugViewRequest>(cmd => DispatchCommand(cmd));
        Receive<UnsubscribeDebugViewRequest>(cmd => DispatchCommand(cmd));
        Receive<DebugSnapshotRequest>(cmd => DispatchCommand(cmd));
        Receive<RouteToCallRequest>(cmd => DispatchCommand(cmd));
        Receive<RouteToGetAttributesRequest>(cmd => DispatchCommand(cmd));
        Receive<RouteToSetAttributesRequest>(cmd => DispatchCommand(cmd));
        Receive<RouteToWaitForAttributeRequest>(cmd => DispatchCommand(cmd));
        Receive<BrowseNodeCommand>(cmd => DispatchCommand(cmd));
        Receive<ReadTagValuesCommand>(cmd => DispatchCommand(cmd));
        Receive<SearchAddressSpaceCommand>(cmd => DispatchCommand(cmd));
        Receive<Commons.Messages.DataConnection.WriteTagRequest>(cmd => DispatchCommand(cmd));
        Receive<VerifyEndpointCommand>(cmd => DispatchCommand(cmd));
        Receive<TrustServerCertCommand>(cmd => DispatchCommand(cmd));
        Receive<ListServerCertsCommand>(cmd => DispatchCommand(cmd));
        Receive<RemoveServerCertCommand>(cmd => DispatchCommand(cmd));
        Receive<EventLogQueryRequest>(cmd => DispatchCommand(cmd));
        Receive<ParkedMessageQueryRequest>(cmd => DispatchCommand(cmd));
        Receive<ParkedMessageRetryRequest>(cmd => DispatchCommand(cmd));
        Receive<ParkedMessageDiscardRequest>(cmd => DispatchCommand(cmd));
        Receive<RetryParkedOperation>(cmd => DispatchCommand(cmd));
        Receive<DiscardParkedOperation>(cmd => DispatchCommand(cmd));

        // Central→site manual failover relay. Central and the site are separate clusters,
        // so central can only ask — this node performs the graceful Leave locally, scoped to
        // the SITE-SPECIFIC role, because that is what site singletons (the Deployment
        // Manager) are placed on. Either node may receive this (the actor is per-node, not a
        // singleton, and contact rotation picks whichever answers); the target is resolved
        // from cluster state, not from who received the message. The gRPC transport defers the
        // leave to keep ack-before-Leave — see PrepareFailover. (Under the removed ClusterClient
        // path the ack Tell merely enqueued, so the dispatcher resolved-and-left in one step.)
        Receive<TriggerSiteFailover>(msg => Sender.Tell(_dispatcher.HandleFailover(msg)));

        // The seven site→central sends delegate to the injected transport (GrpcCentralTransport in
        // production). Each handler captures the current Sender as the reply target so central's
        // reply routes straight back to the waiting Ask, not through this actor — preserving the
        // sender-forwarding the original ClusterClient path relied on. The per-message
        // "no transport / not-accepted" fallbacks live inside the transport now.

        // Notification Outbox: forward a buffered notification (S&F forwarder's Ask → ack back).
        Receive<NotificationSubmit>(msg => _transport.SubmitNotification(msg, Sender));

        // Notification Outbox: forward a Notify.Status query (Notify helper's Ask → response back).
        Receive<NotificationStatusQuery>(msg => _transport.QueryNotificationStatus(msg, Sender));

        // Audit Log: forward a batch of site-local audit events (telemetry drain's Ask → reply back).
        Receive<IngestAuditEventsCommand>(msg => _transport.IngestAuditEvents(msg, Sender));

        // Audit Log: forward a batch of combined cached-call telemetry (telemetry drain's Ask → reply back).
        Receive<IngestCachedTelemetryCommand>(msg => _transport.IngestCachedTelemetry(msg, Sender));

        // Site startup reconciliation: forward the node's local-inventory request (reconcile Ask → response back).
        Receive<ReconcileSiteRequest>(msg => _transport.ReconcileSite(msg, Sender));

        // Internal: send heartbeat tick.
        Receive<SendHeartbeat>(_ => SendHeartbeatToCentral());

        // Internal: forward the periodic health report (health transport's Ask → ack back), so a
        // lost report is observable end-to-end and the sender can restore its per-interval counters.
        Receive<SiteHealthReport>(msg => _transport.ReportSiteHealth(msg, Sender));
    }

    /// <inheritdoc />
    protected override SupervisorStrategy SupervisorStrategy()
    {
        return new OneForOneStrategy(
            maxNrOfRetries: -1,
            withinTimeRange: Timeout.InfiniteTimeSpan,
            decider: Decider.From(ex =>
            {
                _log.Warning(ex, "Child actor of SiteCommunicationActor faulted, resuming (state preserved)");
                return Directive.Resume;
            }));
    }

    /// <inheritdoc />
    protected override void PreStart()
    {
        // Finalize the transport now that the actor context (and _log) exist. When the Host injects
        // none, fall back to a fail-loud NoOpCentralTransport (given this actor's logging adapter so
        // "no transport configured" warnings surface). PreStart always runs before any message, so
        // the Receive closures above see a non-null _transport.
        _transport = _injectedTransport ?? new NoOpCentralTransport(_log);

        _log.Info("SiteCommunicationActor started for site {0}", _siteId);

        // Schedule periodic heartbeat to central. Uses the application heartbeat
        // cadence — distinct from the Akka.Remote transport failure-detector
        // interval — so the two can be tuned independently.
        Timers.StartPeriodicTimer(
            "heartbeat",
            new SendHeartbeat(),
            TimeSpan.FromSeconds(1), // initial delay
            _options.ApplicationHeartbeatInterval);
    }

    /// <summary>
    /// Executes a resolved command route within the actor: Forward to the target (preserving the
    /// central Ask sender so the reply routes straight back to the waiting Ask), or — when a
    /// null-guarded handler is unregistered — Tell the caller the dispatcher's synthetic reply.
    /// The fire-and-forget disposition (UnsubscribeDebugView) is a plain Forward here: the site
    /// never acked it under the original ClusterClient path either, so the synthetic ack is a
    /// gRPC-only concern.
    /// </summary>
    /// <param name="command">The migrated central→site command to route.</param>
    private void DispatchCommand(object command)
    {
        var route = _dispatcher.ResolveRoute(command);
        switch (route.Disposition)
        {
            case SiteCommandDispatcher.RouteDisposition.ImmediateReply:
                Sender.Tell(route.Reply!);
                break;
            default:
                // Forward and TellFireAndForget both Forward on the actor path.
                route.Target!.Forward(command);
                break;
        }
    }

    private void HandleRegisterLocalHandler(RegisterLocalHandler msg)
    {
        // The migrated handlers live on the shared dispatcher so the gRPC command service sees the
        // same registrations. Integration is the one command kept on the actor (see the receive).
        switch (msg.HandlerType)
        {
            case LocalHandlerType.EventLog:
                _dispatcher.RegisterEventLogHandler(msg.Handler);
                break;
            case LocalHandlerType.ParkedMessages:
                _dispatcher.RegisterParkedMessageHandler(msg.Handler);
                break;
            case LocalHandlerType.Artifacts:
                _dispatcher.RegisterArtifactHandler(msg.Handler);
                break;
        }

        _log.Info("Registered local handler for {0}", msg.HandlerType);
    }

    private void SendHeartbeatToCentral()
    {
        var hostname = Environment.MachineName;

        // Stamp HeartbeatMessage.IsActive with this node's
        // true active/standby role rather than hard-coding `true`. The field is
        // part of the wire contract (additive-only-evolution) so a future
        // central health dashboard can distinguish "active node down, standby
        // up" from "site fully offline" without a new message type.
        bool isActive;
        try
        {
            isActive = _isActiveCheck();
        }
        catch (Exception ex)
        {
            // Defensive: never let a cluster-state read failure abort the
            // heartbeat itself (heartbeats are health signal — their absence is
            // already meaningful). Fall back to the safest non-claiming value:
            // standby. Logged at Debug because this path normally only fires
            // during ActorSystem warm-up.
            _log.Debug(ex,
                "Active-node check threw while sending heartbeat for site {0}; reporting IsActive=false",
                _siteId);
            isActive = false;
        }

        var heartbeat = new HeartbeatMessage(
            _siteId,
            hostname,
            IsActive: isActive,
            DateTimeOffset.UtcNow);

        // Fire-and-forget on both transports: a failure here must never fault the heartbeat timer
        // path. Both real transports swallow their own errors; this catch is a belt-and-braces
        // guarantee that no transport (including a future one) can turn a heartbeat into a fault.
        try
        {
            _transport.SendHeartbeat(heartbeat, Self);
        }
        catch (Exception ex)
        {
            _log.Debug(ex, "Heartbeat send for site {0} failed; swallowed (heartbeats are fire-and-forget)", _siteId);
        }
    }

    /// <summary>
    /// Default active-node check used when no override is supplied: oldest-Up member
    /// semantics via the shared <see cref="ClusterState.ActiveNodeEvaluator"/> — the
    /// same predicate as the S&F delivery gate and the replication resync authority
    /// (review 02 round 2, N1). Unscoped by role: a site cluster's members all carry
    /// the site role, so role scoping is a no-op here; production wiring passes the
    /// Host's role-scoped IClusterNodeProvider delegate anyway. Any other state
    /// (still joining, leaving) reports standby — safe-by-default.
    /// </summary>
    private bool DefaultIsActiveCheck() =>
        ClusterState.ActiveNodeEvaluator.SelfIsOldestUp(Cluster.Get(Context.System));

    // ── Internal messages ──

    internal record SendHeartbeat;
}

/// <summary>
/// Command to register a local actor as a handler for a specific message pattern.
/// </summary>
public record RegisterLocalHandler(LocalHandlerType HandlerType, IActorRef Handler);

public enum LocalHandlerType
{
    EventLog,
    ParkedMessages,
    Artifacts
}
