using Akka.Actor;
using Akka.TestKit;
using Akka.TestKit.Xunit2;
using ScadaLink.Commons.Messages.DebugView;
using ScadaLink.Commons.Messages.Streaming;
using ScadaLink.Communication.Actors;
using ScadaLink.Communication.Grpc;

namespace ScadaLink.Communication.Tests.Grpc;

/// <summary>
/// Tests for DebugStreamBridgeActor with gRPC streaming integration.
/// </summary>
public class DebugStreamBridgeActorTests : TestKit
{
    private const string SiteId = "site-alpha";
    private const string InstanceName = "Site1.Pump01";
    private const string GrpcNodeA = "http://localhost:5100";
    private const string GrpcNodeB = "http://localhost:5200";

    public DebugStreamBridgeActorTests() : base(@"akka.loglevel = DEBUG")
    {
        // Use a very short reconnect delay for testing
        DebugStreamBridgeActor.ReconnectDelay = TimeSpan.FromMilliseconds(100);
        // Long stability window so streams are never considered "stable" mid-test
        // unless a test deliberately waits it out.
        DebugStreamBridgeActor.StabilityWindow = TimeSpan.FromSeconds(30);
    }

    private record TestContext(
        IActorRef BridgeActor,
        TestProbe CommProbe,
        MockSiteStreamGrpcClient MockGrpcClient,
        List<object> ReceivedEvents,
        bool[] TerminatedFlag);

    private TestContext CreateBridgeActor()
    {
        var commProbe = CreateTestProbe();
        var mockClient = new MockSiteStreamGrpcClient();
        var factory = new MockSiteStreamGrpcClientFactory(mockClient);
        var events = new List<object>();
        var terminated = new[] { false };

        Action<object> onEvent = evt => { lock (events) { events.Add(evt); } };
        Action onTerminated = () => terminated[0] = true;

        var props = Props.Create(typeof(DebugStreamBridgeActor),
            SiteId,
            InstanceName,
            "corr-1",
            commProbe.Ref,
            onEvent,
            onTerminated,
            factory,
            GrpcNodeA,
            GrpcNodeB);

        var actor = Sys.ActorOf(props);
        return new TestContext(actor, commProbe, mockClient, events, terminated);
    }

    [Fact]
    public void PreStart_Sends_SubscribeDebugViewRequest_Via_ClusterClient()
    {
        var ctx = CreateBridgeActor();

        var envelope = ctx.CommProbe.ExpectMsg<SiteEnvelope>();
        Assert.Equal(SiteId, envelope.SiteId);
        Assert.IsType<SubscribeDebugViewRequest>(envelope.Message);

        var req = (SubscribeDebugViewRequest)envelope.Message;
        Assert.Equal(InstanceName, req.InstanceUniqueName);
        Assert.Equal("corr-1", req.CorrelationId);
    }

    [Fact]
    public void On_Snapshot_Forwards_To_OnEvent_Callback()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        ctx.BridgeActor.Tell(snapshot);

        AwaitCondition(() => { lock (ctx.ReceivedEvents) { return ctx.ReceivedEvents.Count == 1; } },
            TimeSpan.FromSeconds(3));
        lock (ctx.ReceivedEvents) { Assert.IsType<DebugViewSnapshot>(ctx.ReceivedEvents[0]); }
    }

    [Fact]
    public void On_Snapshot_Opens_GrpcStream()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        ctx.BridgeActor.Tell(snapshot);

        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        var call = ctx.MockGrpcClient.SubscribeCalls[0];
        Assert.Equal("corr-1", call.CorrelationId);
        Assert.Equal(InstanceName, call.InstanceUniqueName);
    }

    [Fact]
    public void Events_From_GrpcCallback_Forwarded_To_OnEvent()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        // Simulate gRPC event arriving via the onEvent callback
        var attrChange = new AttributeValueChanged(InstanceName, "IO", "Temp", 42.5, "Good", DateTimeOffset.UtcNow);
        ctx.MockGrpcClient.SubscribeCalls[0].OnEvent(attrChange);

        // snapshot + attr change
        AwaitCondition(() => { lock (ctx.ReceivedEvents) { return ctx.ReceivedEvents.Count == 2; } },
            TimeSpan.FromSeconds(3));
        lock (ctx.ReceivedEvents) { Assert.IsType<AttributeValueChanged>(ctx.ReceivedEvents[1]); }
    }

    [Fact]
    public void On_GrpcError_Reconnects_To_Other_Node()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        // Simulate gRPC error
        ctx.MockGrpcClient.SubscribeCalls[0].OnError(new Exception("Stream broken"));

        // Should resubscribe
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 2, TimeSpan.FromSeconds(5));
        Assert.Equal("corr-1", ctx.MockGrpcClient.SubscribeCalls[1].CorrelationId);
    }

    [Fact]
    public void On_GrpcError_Unsubscribes_Old_Stream_Before_Reconnect()
    {
        // Communication-002 regression: a reconnect must unsubscribe the previous
        // stream so the old node does not keep a zombie relay actor / subscription.
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        // Simulate gRPC error → reconnect
        ctx.MockGrpcClient.SubscribeCalls[0].OnError(new Exception("Stream broken"));

        // Should resubscribe...
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 2, TimeSpan.FromSeconds(5));

        // ...and must have unsubscribed the prior correlation ID so the old node's
        // relay actor is released rather than left zombie.
        Assert.Contains("corr-1", ctx.MockGrpcClient.UnsubscribedCorrelationIds);
    }

    [Fact]
    public void After_MaxRetries_Terminates()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        Watch(ctx.BridgeActor);
        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        // 4 consecutive errors: initial + 3 retries, then terminate
        ctx.MockGrpcClient.SubscribeCalls[0].OnError(new Exception("Error 1"));
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 2, TimeSpan.FromSeconds(5));

        ctx.MockGrpcClient.SubscribeCalls[1].OnError(new Exception("Error 2"));
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 3, TimeSpan.FromSeconds(5));

        ctx.MockGrpcClient.SubscribeCalls[2].OnError(new Exception("Error 3"));
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 4, TimeSpan.FromSeconds(5));

        // Fourth error exceeds max retries
        ctx.MockGrpcClient.SubscribeCalls[3].OnError(new Exception("Error 4"));

        ExpectTerminated(ctx.BridgeActor, TimeSpan.FromSeconds(5));
        Assert.True(ctx.TerminatedFlag[0]);
    }

    [Fact]
    public void StopDebugStream_Cancels_Grpc_And_Sends_Unsubscribe()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>(); // subscribe

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        Watch(ctx.BridgeActor);
        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        ctx.BridgeActor.Tell(new StopDebugStream());

        // Should send ClusterClient unsubscribe
        var envelope = ctx.CommProbe.ExpectMsg<SiteEnvelope>();
        Assert.IsType<UnsubscribeDebugViewRequest>(envelope.Message);

        // Should unsubscribe gRPC
        AwaitCondition(() => ctx.MockGrpcClient.UnsubscribedCorrelationIds.Count > 0, TimeSpan.FromSeconds(3));
        Assert.Contains("corr-1", ctx.MockGrpcClient.UnsubscribedCorrelationIds);

        // Should stop self
        ExpectTerminated(ctx.BridgeActor);
    }

    [Fact]
    public void DebugStreamTerminated_Stops_Actor_Idempotently()
    {
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        Watch(ctx.BridgeActor);
        ctx.BridgeActor.Tell(new DebugStreamTerminated(SiteId, "corr-1"));

        ExpectTerminated(ctx.BridgeActor);
        Assert.True(ctx.TerminatedFlag[0]);
    }

    [Fact]
    public void FlappingStream_DeliveringEventsBetweenFailures_StillTerminatesAfterMaxRetries()
    {
        // Communication-008 regression: a stream that connects, delivers an event,
        // then fails — repeatedly — must still trip MaxRetries. The retry count is
        // NO LONGER reset by a received event (only by the stability window). The
        // previous behaviour reset _retryCount on every event, so a flapping site
        // reconnected forever and the debug session lived on indefinitely.
        var ctx = CreateBridgeActor();
        ctx.CommProbe.ExpectMsg<SiteEnvelope>();

        var snapshot = new DebugViewSnapshot(
            InstanceName,
            new List<AttributeValueChanged>(),
            new List<AlarmStateChanged>(),
            DateTimeOffset.UtcNow);

        Watch(ctx.BridgeActor);
        ctx.BridgeActor.Tell(snapshot);
        AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

        var attrChange = new AttributeValueChanged(InstanceName, "IO", "Temp", 42.5, "Good", DateTimeOffset.UtcNow);

        // Flap: deliver one event then fail, three times. Each event would, under
        // the old buggy logic, reset the retry budget and prevent termination.
        for (var i = 0; i < 3; i++)
        {
            var call = ctx.MockGrpcClient.SubscribeCalls[i];
            call.OnEvent(attrChange);
            call.OnError(new Exception($"Flap {i + 1}"));
            var expected = i + 2;
            AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == expected, TimeSpan.FromSeconds(5));
        }

        // Fourth error (after the 3 retries) must exceed MaxRetries and terminate.
        ctx.MockGrpcClient.SubscribeCalls[3].OnEvent(attrChange);
        ctx.MockGrpcClient.SubscribeCalls[3].OnError(new Exception("Flap 4"));

        ExpectTerminated(ctx.BridgeActor, TimeSpan.FromSeconds(5));
        Assert.True(ctx.TerminatedFlag[0]);
    }

    [Fact]
    public void RetryCount_RecoveredOnlyAfterStreamStaysStableForStabilityWindow()
    {
        // Communication-008: after a stream has been connected for the stability
        // window, the retry budget is recovered — a later transient fault then gets
        // a fresh set of retries rather than being counted against the old budget.
        DebugStreamBridgeActor.StabilityWindow = TimeSpan.FromMilliseconds(300);
        try
        {
            var ctx = CreateBridgeActor();
            ctx.CommProbe.ExpectMsg<SiteEnvelope>();

            var snapshot = new DebugViewSnapshot(
                InstanceName,
                new List<AttributeValueChanged>(),
                new List<AlarmStateChanged>(),
                DateTimeOffset.UtcNow);

            Watch(ctx.BridgeActor);
            ctx.BridgeActor.Tell(snapshot);
            AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == 1, TimeSpan.FromSeconds(3));

            // Two failures — but each new stream stays up long enough (the mock
            // stream only completes on cancel) for the stability window to elapse
            // and reset the retry budget before the next failure.
            for (var i = 0; i < 5; i++)
            {
                Thread.Sleep(450); // exceed the 300ms stability window
                ctx.MockGrpcClient.SubscribeCalls[i].OnError(new Exception($"Error {i + 1}"));
                var expected = i + 2;
                AwaitCondition(() => ctx.MockGrpcClient.SubscribeCalls.Count == expected, TimeSpan.FromSeconds(5));
            }

            // Five well-spaced failures did NOT terminate the actor because each
            // reconnect recovered its retry budget after the stability window.
            Assert.False(ctx.TerminatedFlag[0]);
        }
        finally
        {
            DebugStreamBridgeActor.StabilityWindow = TimeSpan.FromSeconds(30);
        }
    }
}

/// <summary>
/// Mock gRPC client that records SubscribeAsync and Unsubscribe calls.
/// </summary>
internal class MockSiteStreamGrpcClient : SiteStreamGrpcClient
{
    public List<MockSubscription> SubscribeCalls { get; } = new();
    public List<string> UnsubscribedCorrelationIds { get; } = new();

    private MockSiteStreamGrpcClient(bool _) : base() { }

    public MockSiteStreamGrpcClient() : base()
    {
    }

    public override Task SubscribeAsync(
        string correlationId,
        string instanceUniqueName,
        Action<object> onEvent,
        Action<Exception> onError,
        CancellationToken ct)
    {
        var subscription = new MockSubscription(correlationId, instanceUniqueName, onEvent, onError, ct);
        SubscribeCalls.Add(subscription);

        // Return a task that completes when cancelled (simulates long-running stream)
        var tcs = new TaskCompletionSource();
        ct.Register(() => tcs.TrySetResult());
        return tcs.Task;
    }

    public override void Unsubscribe(string correlationId)
    {
        UnsubscribedCorrelationIds.Add(correlationId);
    }
}

internal record MockSubscription(
    string CorrelationId,
    string InstanceUniqueName,
    Action<object> OnEvent,
    Action<Exception> OnError,
    CancellationToken CancellationToken);

/// <summary>
/// Factory that always returns the pre-configured mock client.
/// </summary>
internal class MockSiteStreamGrpcClientFactory : SiteStreamGrpcClientFactory
{
    private readonly MockSiteStreamGrpcClient _mockClient;
    public List<string> RequestedEndpoints { get; } = new();

    public MockSiteStreamGrpcClientFactory(MockSiteStreamGrpcClient mockClient)
        : base(Microsoft.Extensions.Logging.Abstractions.NullLoggerFactory.Instance)
    {
        _mockClient = mockClient;
    }

    public override SiteStreamGrpcClient GetOrCreate(string siteIdentifier, string grpcEndpoint)
    {
        RequestedEndpoints.Add(grpcEndpoint);
        return _mockClient;
    }
}