using Akka.TestKit.Xunit2;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using NSubstitute;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Instances;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using ZB.MOM.WW.ScadaBridge.Communication;
using ZB.MOM.WW.ScadaBridge.Communication.Grpc;

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

/// <summary>
/// Tests for <see cref="SiteAlarmLiveCacheService"/> (plan #10, Task 4) — the DI singleton
/// that reference-counts Alarm Summary viewers over one shared per-site aggregator. Covers
/// shared start (one aggregator for many viewers), last-out linger stop, and re-subscribe
/// cancelling a pending stop. Uses a real (in-memory) ActorSystem and a mock gRPC factory
/// whose site-wide stream never faults, so no reconnect noise.
/// </summary>
public class SiteAlarmLiveCacheServiceTests : TestKit
{
    private const int SiteId = 7;

    // A mock site-wide alarm stream client whose subscription hangs until cancelled.
    private sealed class HangingClient : SiteStreamGrpcClient
    {
        public HangingClient() : base() { }
        public override Task SubscribeSiteAsync(
            string correlationId, Action<Commons.Messages.Streaming.AlarmStateChanged> onAlarmEvent,
            Action<Exception> onError, CancellationToken ct)
        {
            var tcs = new TaskCompletionSource();
            ct.Register(() => tcs.TrySetResult());
            return tcs.Task;
        }
        public override void Unsubscribe(string correlationId) { }
    }

    private sealed class CountingFactory : SiteStreamGrpcClientFactory
    {
        private readonly HangingClient _client = new();
        public int GetOrCreateCount;

        public CountingFactory() : base(NullLoggerFactory.Instance) { }

        public override SiteStreamGrpcClient GetOrCreate(string siteIdentifier, string grpcEndpoint)
        {
            Interlocked.Increment(ref GetOrCreateCount);
            return _client;
        }

        public override SiteStreamGrpcClient? TryGet(string siteIdentifier, string grpcEndpoint) => _client;
    }

    private SiteAlarmLiveCacheService CreateService(TimeSpan linger, out CountingFactory factory,
        int maxSubscribersPerSite = 200)
    {
        // Site with gRPC addresses, and NO enabled instances → the seed fan-out returns
        // empty immediately (so IsLive flips true fast without any snapshot Asks).
        var site = new Site("Alpha", "site-alpha")
        {
            Id = SiteId,
            GrpcNodeAAddress = "http://localhost:5100",
            GrpcNodeBAddress = "http://localhost:5200"
        };

        var siteRepo = Substitute.For<ISiteRepository>();
        siteRepo.GetSiteByIdAsync(SiteId, Arg.Any<CancellationToken>()).Returns(site);

        var instanceRepo = Substitute.For<ITemplateEngineRepository>();
        instanceRepo.GetInstancesBySiteIdAsync(SiteId, Arg.Any<CancellationToken>())
            .Returns(new List<Instance>());

        var services = new ServiceCollection();
        services.AddScoped(_ => siteRepo);
        services.AddScoped(_ => instanceRepo);
        var provider = services.BuildServiceProvider();

        var options = Options.Create(new CommunicationOptions
        {
            LiveAlarmCacheLinger = linger,
            LiveAlarmCacheReconcileInterval = TimeSpan.FromMinutes(10),
            LiveAlarmCacheMaxSubscribersPerSite = maxSubscribersPerSite
        });

        var comm = new CommunicationService(Options.Create(new CommunicationOptions()),
            NullLogger<CommunicationService>.Instance);

        factory = new CountingFactory();
        var service = new SiteAlarmLiveCacheService(
            provider, comm, factory, options, NullLogger<SiteAlarmLiveCacheService>.Instance);
        service.SetActorSystem(Sys);
        return service;
    }

    [Fact]
    public void First_Subscriber_Starts_One_Aggregator_Shared_By_Multiple_Viewers()
    {
        var service = CreateService(TimeSpan.FromMilliseconds(200), out var factory);

        var changes1 = 0;
        var changes2 = 0;
        using var sub1 = service.Subscribe(SiteId, () => Interlocked.Increment(ref changes1));
        using var sub2 = service.Subscribe(SiteId, () => Interlocked.Increment(ref changes2));

        // The (empty) seed completes → aggregator publishes → live.
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));

        // Exactly ONE gRPC stream opened for the site regardless of viewer count.
        Assert.Equal(1, factory.GetOrCreateCount);
        // Empty seed → empty current snapshot.
        Assert.Empty(service.GetCurrentAlarms(SiteId));
        // Both viewers were notified of the initial publish.
        AwaitCondition(() => changes1 >= 1 && changes2 >= 1, TimeSpan.FromSeconds(3));
    }

    [Fact]
    public void Last_Viewer_Leaving_Stops_Aggregator_After_Linger()
    {
        var service = CreateService(TimeSpan.FromMilliseconds(200), out _);

        var sub1 = service.Subscribe(SiteId, () => { });
        var sub2 = service.Subscribe(SiteId, () => { });
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));

        sub1.Dispose();
        // One viewer remains — still live, not stopped.
        Thread.Sleep(300);
        Assert.True(service.IsLive(SiteId));

        sub2.Dispose();
        // Last viewer left → after the linger the aggregator is torn down and the entry cleared.
        AwaitCondition(() => !service.IsLive(SiteId), TimeSpan.FromSeconds(3));
        Assert.Empty(service.GetCurrentAlarms(SiteId));
    }

    [Fact]
    public void Resubscribe_Within_Linger_Cancels_The_Pending_Stop()
    {
        var service = CreateService(TimeSpan.FromMilliseconds(400), out var factory);

        var sub1 = service.Subscribe(SiteId, () => { });
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));

        sub1.Dispose();                 // schedules linger stop
        var sub2 = service.Subscribe(SiteId, () => { }); // returns within the linger window → cancels it

        // Wait comfortably past the original linger; the aggregator must still be alive.
        Thread.Sleep(700);
        Assert.True(service.IsLive(SiteId));
        // No second aggregator/stream was opened — the same one was kept warm.
        Assert.Equal(1, factory.GetOrCreateCount);

        sub2.Dispose();
    }

    [Fact]
    public void Dispose_Is_Idempotent()
    {
        var service = CreateService(TimeSpan.FromMilliseconds(200), out _);
        var sub = service.Subscribe(SiteId, () => { });
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));

        sub.Dispose();
        sub.Dispose(); // must not throw or double-decrement

        AwaitCondition(() => !service.IsLive(SiteId), TimeSpan.FromSeconds(3));
    }

    [Fact]
    public void Transient_Start_Failure_Self_Heals_On_Retry_For_A_Stable_Viewer_Cohort()
    {
        // A transient failure resolving the site at first-subscribe must NOT leave the
        // viewer cohort polling forever — a bounded retry re-attempts and self-heals.
        var site = new Site("Alpha", "site-alpha")
        {
            Id = SiteId,
            GrpcNodeAAddress = "http://localhost:5100",
            GrpcNodeBAddress = "http://localhost:5200"
        };

        var siteRepo = Substitute.For<ISiteRepository>();
        // First resolve returns null (transient blip); every resolve thereafter succeeds.
        siteRepo.GetSiteByIdAsync(SiteId, Arg.Any<CancellationToken>()).Returns((Site?)null, site);

        var instanceRepo = Substitute.For<ITemplateEngineRepository>();
        instanceRepo.GetInstancesBySiteIdAsync(SiteId, Arg.Any<CancellationToken>())
            .Returns(new List<Instance>());

        var services = new ServiceCollection();
        services.AddScoped(_ => siteRepo);
        services.AddScoped(_ => instanceRepo);
        var provider = services.BuildServiceProvider();

        var options = Options.Create(new CommunicationOptions
        {
            LiveAlarmCacheLinger = TimeSpan.FromSeconds(30),
            // Retry cadence reuses the reconcile interval — keep it short for the test.
            LiveAlarmCacheReconcileInterval = TimeSpan.FromMilliseconds(300)
        });
        var comm = new CommunicationService(Options.Create(new CommunicationOptions()),
            NullLogger<CommunicationService>.Instance);
        var factory = new CountingFactory();

        var service = new SiteAlarmLiveCacheService(
            provider, comm, factory, options, NullLogger<SiteAlarmLiveCacheService>.Instance);
        service.SetActorSystem(Sys);

        using var sub = service.Subscribe(SiteId, () => { });

        // First start failed (site not found); a stable single viewer stays subscribed.
        // The retry eventually resolves the site and the aggregator goes live — without
        // any further Subscribe call.
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));
    }

    [Fact]
    public void Viewer_Over_The_Per_Site_Cap_Is_Rejected_Safely_And_Not_Counted()
    {
        // Cap of 2: the first two viewers register; a third is rejected fail-safe with a
        // no-op handle (never throws into the render path, never grows the list). Proof it
        // was NOT counted: disposing only the two real viewers tears the aggregator down
        // after the linger — if the rejected viewer had been registered, one subscriber
        // would remain and the site would stay live forever.
        var service = CreateService(TimeSpan.FromMilliseconds(200), out _, maxSubscribersPerSite: 2);

        var sub1 = service.Subscribe(SiteId, () => { });
        var sub2 = service.Subscribe(SiteId, () => { });
        AwaitCondition(() => service.IsLive(SiteId), TimeSpan.FromSeconds(5));

        // Third viewer is over the cap.
        var overflow = service.Subscribe(SiteId, () => { });
        Assert.NotNull(overflow);
        // Disposing the rejected handle is a genuine no-op — safe, idempotent, touches nothing.
        overflow.Dispose();
        overflow.Dispose();

        // Still live with the two real viewers present.
        Assert.True(service.IsLive(SiteId));

        sub1.Dispose();
        sub2.Dispose();

        // Both real viewers gone → after the linger the aggregator stops. This only holds
        // if the overflow viewer was never added to the subscriber list.
        AwaitCondition(() => !service.IsLive(SiteId), TimeSpan.FromSeconds(3));
    }

    [Fact]
    public void Unknown_Site_Registers_Viewer_But_Never_Goes_Live()
    {
        var service = CreateService(TimeSpan.FromMilliseconds(200), out _);

        using var sub = service.Subscribe(999, () => { }); // no such site in the repo
        Thread.Sleep(300);
        Assert.False(service.IsLive(999));
        Assert.Empty(service.GetCurrentAlarms(999));
    }
}