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 via ClusterClient and routes
/// them to the appropriate local actors. Also sends heartbeats and health reports
/// to central via the registered ClusterClient.
///
/// 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;
    private readonly Func<string, string?> _failOverRole;

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

    /// <summary>
    /// The site→central transport. Finalized in <see cref="PreStart"/> to the injected instance,
    /// or a default <see cref="AkkaCentralTransport"/> (ClusterClient) when none is supplied — so
    /// the seven site→central sends delegate here rather than owning the wire plumbing inline.
    /// </summary>
    private ICentralTransport _transport;

    /// <summary>The transport supplied by the Host (null selects the default Akka transport).</summary>
    private readonly ICentralTransport? _injectedTransport;

    /// <summary>
    /// Local actor references for routing specific message patterns.
    /// Populated via registration messages.
    /// </summary>
    private IActorRef? _eventLogHandler;
    private IActorRef? _parkedMessageHandler;
    private IActorRef? _integrationHandler;
    private IActorRef? _artifactHandler;

    /// <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. <c>null</c> (the default, used by every existing test and by
    /// the Host's Akka path) selects an <see cref="AkkaCentralTransport"/> over ClusterClient; the
    /// Host injects a <see cref="Grpc.GrpcCentralTransport"/> when
    /// <c>ScadaBridge:Communication:CentralTransport</c> is <c>Grpc</c>.
    /// </param>
    public SiteCommunicationActor(
        string siteId,
        CommunicationOptions options,
        IActorRef deploymentManagerProxy,
        Func<bool>? isActiveCheck = null,
        Func<string, string?>? failOverRole = null,
        ICentralTransport? transport = null)
    {
        _siteId = siteId;
        _options = options;
        _deploymentManagerProxy = deploymentManagerProxy;
        _isActiveCheck = isActiveCheck ?? DefaultIsActiveCheck;
        _failOverRole = failOverRole ?? DefaultFailOverRole;
        _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!;

        // Registration. Feeding the ClusterClient into the transport is a no-op unless the
        // default/Akka transport is in use — the gRPC transport dials configured endpoints and
        // never receives this message (the Host does not create a ClusterClient for it).
        Receive<RegisterCentralClient>(msg =>
        {
            (_transport as AkkaCentralTransport)?.SetCentralClient(msg.Client);
        });
        Receive<RegisterLocalHandler>(HandleRegisterLocalHandler);

        // Pattern 1: Instance Deployment — forward to Deployment Manager
        Receive<RefreshDeploymentCommand>(msg =>
        {
            _log.Debug("Routing RefreshDeploymentCommand for {0} to DeploymentManager", msg.InstanceUniqueName);
            _deploymentManagerProxy.Forward(msg);
        });

        // Pattern 2: Lifecycle — forward to Deployment Manager
        Receive<DisableInstanceCommand>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<EnableInstanceCommand>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<DeleteInstanceCommand>(msg => _deploymentManagerProxy.Forward(msg));

        // Query-the-site-before-redeploy — forward to
        // the Deployment Manager, which owns the deployed-config store and
        // answers with the instance's currently-applied deployment identity.
        Receive<DeploymentStateQueryRequest>(msg => _deploymentManagerProxy.Forward(msg));

        // Pattern 3: Artifact Deployment — forward to artifact handler if registered
        Receive<DeployArtifactsCommand>(msg =>
        {
            if (_artifactHandler != null)
                _artifactHandler.Forward(msg);
            else
            {
                _log.Warning("No artifact handler registered, replying with failure");
                Sender.Tell(new ArtifactDeploymentResponse(
                    msg.DeploymentId, _siteId, false, "Artifact handler not available", DateTimeOffset.UtcNow));
            }
        });

        // Pattern 4: Integration Routing — forward to integration handler
        Receive<IntegrationCallRequest>(msg =>
        {
            if (_integrationHandler != null)
                _integrationHandler.Forward(msg);
            else
            {
                Sender.Tell(new IntegrationCallResponse(
                    msg.CorrelationId, _siteId, false, null, "Integration handler not available", DateTimeOffset.UtcNow));
            }
        });

        // Pattern 5: Debug View — forward to Deployment Manager (which routes to Instance Actor)
        Receive<SubscribeDebugViewRequest>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<UnsubscribeDebugViewRequest>(msg => _deploymentManagerProxy.Forward(msg));

        // Pattern 6a: Debug Snapshot (one-shot) — forward to Deployment Manager
        Receive<DebugSnapshotRequest>(msg => _deploymentManagerProxy.Forward(msg));

        // Inbound API Route.To() — forward to Deployment Manager for instance routing
        Receive<RouteToCallRequest>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<RouteToGetAttributesRequest>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<RouteToSetAttributesRequest>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<RouteToWaitForAttributeRequest>(msg => _deploymentManagerProxy.Forward(msg));

        // OPC UA Tag Browser (interactive design-time query) — forward to the
        // Deployment Manager singleton, which always lands on the active site
        // node. Routing to the site-local /user/dcl-manager directly is wrong
        // because the standby node has a dcl-manager too, but its
        // DataConnectionActor children (which own the live OPC UA sessions)
        // only exist on the singleton's node. The singleton then re-forwards
        // to its own /user/dcl-manager, which DOES have the connection.
        Receive<BrowseNodeCommand>(msg => _deploymentManagerProxy.Forward(msg));

        // Test Bindings (interactive design-time read) — same routing rationale
        // as BrowseNodeCommand above: the singleton always lands on the
        // active site node, which is the node that owns the DataConnectionActor
        // children holding the live OPC UA sessions.
        Receive<ReadTagValuesCommand>(msg => _deploymentManagerProxy.Forward(msg));

        // OPC UA tag-picker address-space search and secured-write execute
        // — same singleton routing rationale as BrowseNodeCommand above: the
        // DataConnectionActor children that own the live OPC UA sessions exist only
        // on the singleton's (active) node, so these must hop through the Deployment
        // Manager proxy too. Without these forwards the commands dead-letter and the
        // central Ask times out. Forward preserves the central Ask sender so the
        // result routes straight back to the waiting Ask.
        Receive<SearchAddressSpaceCommand>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<Commons.Messages.DataConnection.WriteTagRequest>(msg => _deploymentManagerProxy.Forward(msg));

        // OPC UA endpoint Verify — probes a (possibly unsaved) endpoint config
        // WITHOUT persisting it. The Deployment Manager singleton's dcl-manager runs
        // the probe directly (no existing connection required), so — like the
        // commands above — Verify routes through the singleton's active node.
        Receive<VerifyEndpointCommand>(msg => _deploymentManagerProxy.Forward(msg));

        // OPC UA server-certificate trust management — forward to the
        // Deployment Manager singleton, which owns the cross-node trust broadcast.
        // The trusted-peer PKI store is node-wide per site node, so a trust/remove
        // decision must reach BOTH nodes' CertStoreActor; the singleton broadcasts
        // to every site node (list answers from the singleton's own node). The
        // singleton always lands on the active node, the same routing rationale as
        // BrowseNodeCommand above. Forward preserves the central Ask sender so the
        // CertTrustResult routes straight back to the waiting Ask.
        Receive<TrustServerCertCommand>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<ListServerCertsCommand>(msg => _deploymentManagerProxy.Forward(msg));
        Receive<RemoveServerCertCommand>(msg => _deploymentManagerProxy.Forward(msg));

        // Pattern 7: Remote Queries
        Receive<EventLogQueryRequest>(msg =>
        {
            if (_eventLogHandler != null)
                _eventLogHandler.Forward(msg);
            else
            {
                Sender.Tell(new EventLogQueryResponse(
                    msg.CorrelationId, _siteId, [], null, false, false,
                    "Event log handler not available", DateTimeOffset.UtcNow));
            }
        });

        Receive<ParkedMessageQueryRequest>(msg =>
        {
            if (_parkedMessageHandler != null)
                _parkedMessageHandler.Forward(msg);
            else
            {
                Sender.Tell(new ParkedMessageQueryResponse(
                    msg.CorrelationId, _siteId, [], 0, msg.PageNumber, msg.PageSize, false,
                    "Parked message handler not available", DateTimeOffset.UtcNow));
            }
        });

        Receive<ParkedMessageRetryRequest>(msg =>
        {
            if (_parkedMessageHandler != null)
                _parkedMessageHandler.Forward(msg);
            else
            {
                Sender.Tell(new ParkedMessageRetryResponse(
                    msg.CorrelationId, false, "Parked message handler not available"));
            }
        });

        Receive<ParkedMessageDiscardRequest>(msg =>
        {
            if (_parkedMessageHandler != null)
                _parkedMessageHandler.Forward(msg);
            else
            {
                Sender.Tell(new ParkedMessageDiscardResponse(
                    msg.CorrelationId, false, "Parked message handler not available"));
            }
        });

        // Central→site Retry/Discard relay for parked cached
        // operations. SiteCallAuditActor relays these over the command/control
        // channel; the parked-message handler executes them against the local
        // S&F buffer and replies a ParkedOperationActionAck that routes back to
        // the relaying SiteCallAuditActor's Ask.
        Receive<RetryParkedOperation>(msg =>
        {
            if (_parkedMessageHandler != null)
                _parkedMessageHandler.Forward(msg);
            else
            {
                Sender.Tell(new ParkedOperationActionAck(
                    msg.CorrelationId, Applied: false, "Parked message handler not available"));
            }
        });

        Receive<DiscardParkedOperation>(msg =>
        {
            if (_parkedMessageHandler != null)
                _parkedMessageHandler.Forward(msg);
            else
            {
                Sender.Tell(new ParkedOperationActionAck(
                    msg.CorrelationId, Applied: false, "Parked message handler not available"));
            }
        });

        // 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.
        Receive<TriggerSiteFailover>(HandleTriggerSiteFailover);

        // The seven site→central sends now delegate to the injected transport (ClusterClient by
        // default, gRPC when configured). 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 — the exact sender-forwarding the 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. The default Akka
        // transport is given this actor's logging adapter so the "no ClusterClient registered"
        // warnings are preserved exactly. PreStart always runs before any message, so the Receive
        // closures above see a non-null _transport.
        _transport = _injectedTransport ?? new AkkaCentralTransport(_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);
    }

    private void HandleRegisterLocalHandler(RegisterLocalHandler msg)
    {
        switch (msg.HandlerType)
        {
            case LocalHandlerType.EventLog:
                _eventLogHandler = msg.Handler;
                break;
            case LocalHandlerType.ParkedMessages:
                _parkedMessageHandler = msg.Handler;
                break;
            case LocalHandlerType.Integration:
                _integrationHandler = msg.Handler;
                break;
            case LocalHandlerType.Artifacts:
                _artifactHandler = 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));

    /// <summary>
    /// Handles a central-initiated site failover. Refuses a command addressed to a different
    /// site (a misroute must never silently fail over a site the operator did not select) and
    /// refuses when the site pair has no peer to take over. The ack is sent BEFORE the Leave
    /// takes effect on the wire, so it still reaches central even when this node is the one
    /// leaving.
    /// </summary>
    private void HandleTriggerSiteFailover(TriggerSiteFailover msg)
    {
        if (!string.Equals(msg.SiteId, _siteId, StringComparison.Ordinal))
        {
            _log.Warning(
                "Refusing TriggerSiteFailover addressed to site {Requested}; this node serves {Actual}",
                msg.SiteId, _siteId);
            Sender.Tell(new SiteFailoverAck(
                msg.CorrelationId, Accepted: false, TargetAddress: null,
                ErrorMessage: $"Command addressed to site '{msg.SiteId}' but this node serves '{_siteId}'."));
            return;
        }

        var role = $"site-{_siteId}";
        try
        {
            var target = _failOverRole(role);
            if (target is null)
            {
                _log.Warning(
                    "Refusing TriggerSiteFailover for {SiteId}: fewer than 2 Up members in role {Role}, "
                    + "so there is no standby to take over", _siteId, role);
                Sender.Tell(new SiteFailoverAck(
                    msg.CorrelationId, Accepted: false, TargetAddress: null,
                    ErrorMessage: "No standby available — failing over a lone node would be an outage."));
                return;
            }

            _log.Warning(
                "Manual failover requested by central for site {SiteId}: {Target} is leaving the "
                + "site cluster gracefully; its singletons hand over to the standby.", _siteId, target);
            Sender.Tell(new SiteFailoverAck(msg.CorrelationId, Accepted: true, target, ErrorMessage: null));
        }
        catch (Exception ex)
        {
            // A fault here must be reported to the operator, not thrown into supervision —
            // restarting the communication actor would drop central's Ask into a timeout and
            // lose the reason.
            _log.Error(ex, "TriggerSiteFailover for {SiteId} faulted", _siteId);
            Sender.Tell(new SiteFailoverAck(
                msg.CorrelationId, Accepted: false, TargetAddress: null, ErrorMessage: ex.Message));
        }
    }

    /// <summary>
    /// Production failover action: gracefully Leave the oldest Up member carrying
    /// <paramref name="role"/>, via the shared <see cref="ClusterState.ClusterFailoverCoordinator"/>
    /// so the central and site paths cannot drift. Injected in tests for the same reason
    /// <see cref="DefaultIsActiveCheck"/> is — a real Leave needs Akka.Cluster in the
    /// ActorSystem, which the TestKit system does not load.
    /// </summary>
    /// <param name="role">Site-specific role scope.</param>
    /// <returns>Address of the leaving node, or null when there is no peer.</returns>
    private string? DefaultFailOverRole(string role) =>
        ClusterState.ClusterFailoverCoordinator.FailOverOldest(Context.System, role)?.ToString();

    // ── Internal messages ──

    internal record SendHeartbeat;
}

/// <summary>
/// Command to register a ClusterClient for communicating with the central cluster.
/// </summary>
public record RegisterCentralClient(IActorRef Client);

/// <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,
    Integration,
    Artifacts
}