using Akka.Actor;
using Akka.TestKit.Xunit2;
using NSubstitute;
using NSubstitute.Core;
using ScadaLink.Commons.Interfaces.Protocol;
using ScadaLink.Commons.Messages.DataConnection;
using ScadaLink.Commons.Types.Enums;
using ScadaLink.DataConnectionLayer.Actors;
using ScadaLink.HealthMonitoring;

namespace ScadaLink.DataConnectionLayer.Tests;

/// <summary>
/// WP-6: Tests for DataConnectionActor Become/Stash state machine.
/// WP-9: Auto-reconnect and bad quality tests.
/// WP-10: Transparent re-subscribe tests.
/// WP-11: Write-back support tests.
/// WP-12: Tag path resolution with retry tests.
/// WP-13: Health reporting tests.
/// WP-14: Subscription lifecycle tests.
/// Task-4: Failover state machine tests.
/// </summary>
public class DataConnectionActorTests : TestKit
{
    private readonly IDataConnection _mockAdapter;
    private readonly DataConnectionOptions _options;
    private readonly ISiteHealthCollector _mockHealthCollector;
    private readonly IDataConnectionFactory _mockFactory;

    public DataConnectionActorTests()
        : base(@"akka.loglevel = DEBUG")
    {
        _mockAdapter = Substitute.For<IDataConnection>();
        _mockHealthCollector = Substitute.For<ISiteHealthCollector>();
        _mockFactory = Substitute.For<IDataConnectionFactory>();
        _options = new DataConnectionOptions
        {
            ReconnectInterval = TimeSpan.FromMilliseconds(100),
            TagResolutionRetryInterval = TimeSpan.FromMilliseconds(200),
            WriteTimeout = TimeSpan.FromSeconds(5)
        };
    }

    private IActorRef CreateConnectionActor(string name = "test-conn")
    {
        return Sys.ActorOf(Props.Create(() =>
            new DataConnectionActor(name, _mockAdapter, _options, _mockHealthCollector,
                _mockFactory, "OpcUa")), name);
    }

    /// <summary>
    /// Creates a DataConnectionActor with primary/backup failover configuration.
    /// </summary>
    private IActorRef CreateFailoverActor(
        IDataConnection adapter,
        string name,
        IDictionary<string, string> primaryConfig,
        IDictionary<string, string>? backupConfig,
        int failoverRetryCount)
    {
        return Sys.ActorOf(Props.Create(() =>
            new DataConnectionActor(
                name, adapter, _options, _mockHealthCollector, _mockFactory, "OpcUa",
                primaryConfig, backupConfig, failoverRetryCount)), name);
    }

    /// <summary>
    /// Raises the Disconnected event on a NSubstitute mock IDataConnection.
    /// </summary>
    private static void RaiseDisconnected(IDataConnection adapter)
    {
        adapter.Disconnected += Raise.Event<Action>();
    }

    [Fact]
    public void WP6_StartsInConnectingState_AttemptsConnect()
    {
        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        var actor = CreateConnectionActor();

        // Give it time to attempt connection
        AwaitCondition(() =>
            _mockAdapter.ReceivedCalls().Any(c => c.GetMethodInfo().Name == "ConnectAsync"),
            TimeSpan.FromSeconds(2));
    }

    [Fact]
    public void WP6_ConnectingState_StashesSubscribeRequests()
    {
        // Make connect hang so we stay in Connecting
        var tcs = new TaskCompletionSource();
        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(tcs.Task);

        var actor = CreateConnectionActor("stash-test");

        // Send subscribe while connecting — should be stashed
        actor.Tell(new SubscribeTagsRequest(
            "corr1", "inst1", "stash-test", ["tag1"], DateTimeOffset.UtcNow));

        // No response yet (stashed)
        ExpectNoMsg(TimeSpan.FromMilliseconds(200));

        // Complete connection — should unstash and process
        _mockAdapter.SubscribeAsync(Arg.Any<string>(), Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>())
            .Returns("sub-001");

        tcs.SetResult();

        // Now we should get the response
        ExpectMsg<SubscribeTagsResponse>(TimeSpan.FromSeconds(2));
    }

    [Fact]
    public async Task WP11_ConnectedState_Write_ReturnsResult()
    {
        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);
        _mockAdapter.WriteAsync("tag1", 42, Arg.Any<CancellationToken>())
            .Returns(new WriteResult(true, null));

        var actor = CreateConnectionActor("write-test");

        // Wait for connected state
        AwaitCondition(() =>
            _mockAdapter.ReceivedCalls().Any(c => c.GetMethodInfo().Name == "ConnectAsync"),
            TimeSpan.FromSeconds(2));

        // Small delay for state transition
        await Task.Delay(200);

        actor.Tell(new WriteTagRequest("corr1", "write-test", "tag1", 42, DateTimeOffset.UtcNow));

        var response = ExpectMsg<WriteTagResponse>(TimeSpan.FromSeconds(3));
        Assert.True(response.Success);
    }

    [Fact]
    public async Task WP11_Write_Failure_ReturnedSynchronously()
    {
        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);
        _mockAdapter.WriteAsync("tag1", 42, Arg.Any<CancellationToken>())
            .Returns(new WriteResult(false, "Device offline"));

        var actor = CreateConnectionActor("write-fail-test");

        await Task.Delay(300);

        actor.Tell(new WriteTagRequest("corr1", "write-fail-test", "tag1", 42, DateTimeOffset.UtcNow));

        var response = ExpectMsg<WriteTagResponse>(TimeSpan.FromSeconds(3));
        Assert.False(response.Success);
        Assert.Equal("Device offline", response.ErrorMessage);
    }

    [Fact]
    public async Task WP13_HealthReport_ReturnsConnectionStatus()
    {
        _mockAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);
        _mockAdapter.Status.Returns(ConnectionHealth.Connected);

        var actor = CreateConnectionActor("health-test");

        await Task.Delay(300);

        actor.Tell(new DataConnectionActor.GetHealthReport());

        var report = ExpectMsg<DataConnectionHealthReport>(TimeSpan.FromSeconds(2));
        Assert.Equal("health-test", report.ConnectionName);
        Assert.Equal(ConnectionHealth.Connected, report.Status);
    }

    // ── Task-4: Failover state machine tests ──

    [Fact]
    public async Task Task4_FailoverAfterNRetries_SwitchesToBackup()
    {
        // Arrange: primary + backup, failoverRetryCount = 2
        var primaryConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://primary:4840" };
        var backupConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://backup:4840" };
        var primaryAdapter = Substitute.For<IDataConnection>();
        var backupAdapter = Substitute.For<IDataConnection>();

        // Initial connect succeeds on primary
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        // Factory returns backup adapter when called with backup config
        _mockFactory.Create("OpcUa", Arg.Is<IDictionary<string, string>>(d => d["Endpoint"] == "opc.tcp://backup:4840"))
            .Returns(backupAdapter);

        // Backup adapter connect succeeds (so failover can complete)
        backupAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        var actor = CreateFailoverActor(primaryAdapter, "failover-test", primaryConfig, backupConfig, failoverRetryCount: 2);

        // Wait for initial connection on primary
        AwaitCondition(() =>
            primaryAdapter.ReceivedCalls().Any(c => c.GetMethodInfo().Name == "ConnectAsync"),
            TimeSpan.FromSeconds(2));
        await Task.Delay(200); // State transition to Connected

        // Now make primary reconnect fail
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.FromException(new Exception("Connection refused")));

        // Trigger disconnect
        RaiseDisconnected(primaryAdapter);

        // Wait for failover: after 2 failures, factory should be called with backup config
        AwaitCondition(() =>
            _mockFactory.ReceivedCalls().Any(c =>
                c.GetMethodInfo().Name == "Create" &&
                c.GetArguments()[1] is IDictionary<string, string> d &&
                d["Endpoint"] == "opc.tcp://backup:4840"),
            TimeSpan.FromSeconds(5));
    }

    [Fact]
    public async Task Task4_SingleEndpoint_RetriesIndefinitely_NoFailover()
    {
        // Arrange: primary only, no backup
        var primaryConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://primary:4840" };
        var primaryAdapter = Substitute.For<IDataConnection>();
        var connectCount = 0;

        // First connect succeeds, all subsequent fail
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(callInfo =>
            {
                var count = Interlocked.Increment(ref connectCount);
                if (count == 1) return Task.CompletedTask;
                return Task.FromException(new Exception("Connection refused"));
            });

        var actor = CreateFailoverActor(primaryAdapter, "no-backup-test", primaryConfig, backupConfig: null, failoverRetryCount: 3);

        // Wait for initial connection
        AwaitCondition(() => connectCount >= 1, TimeSpan.FromSeconds(2));
        await Task.Delay(200);

        // Trigger disconnect — starts reconnect attempts
        RaiseDisconnected(primaryAdapter);

        // Wait for many reconnect failures (well over the failoverRetryCount threshold)
        AwaitCondition(() => connectCount >= 8, TimeSpan.FromSeconds(10));

        // Factory should never be called — no backup to fail over to
        _mockFactory.DidNotReceive().Create(Arg.Any<string>(), Arg.Any<IDictionary<string, string>>());
    }

    [Fact]
    public async Task Task4_RoundRobin_BackToPrimary_AfterBackupFails()
    {
        // Arrange: primary + backup, failoverRetryCount = 1
        var primaryConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://primary:4840" };
        var backupConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://backup:4840" };
        var primaryAdapter = Substitute.For<IDataConnection>();
        var backupAdapter = Substitute.For<IDataConnection>();
        var secondPrimaryAdapter = Substitute.For<IDataConnection>();

        // Initial connect on primary succeeds
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        // After disconnect, primary reconnect fails (triggers failover to backup)
        var primaryConnectCount = 0;
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(callInfo =>
            {
                var count = Interlocked.Increment(ref primaryConnectCount);
                if (count == 1) return Task.CompletedTask; // Initial connect
                return Task.FromException(new Exception("Primary down")); // Reconnect fails
            });

        // Factory: backup config → backupAdapter, primary config → secondPrimaryAdapter
        _mockFactory.Create("OpcUa", Arg.Is<IDictionary<string, string>>(d => d["Endpoint"] == "opc.tcp://backup:4840"))
            .Returns(backupAdapter);
        _mockFactory.Create("OpcUa", Arg.Is<IDictionary<string, string>>(d => d["Endpoint"] == "opc.tcp://primary:4840"))
            .Returns(secondPrimaryAdapter);

        // Backup connect succeeds first time, then fails on reconnect
        var backupConnectCount = 0;
        backupAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(callInfo =>
            {
                var count = Interlocked.Increment(ref backupConnectCount);
                if (count == 1) return Task.CompletedTask; // First backup connect succeeds
                return Task.FromException(new Exception("Backup down")); // Backup reconnect fails
            });

        // Second primary adapter connects fine
        secondPrimaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        var actor = CreateFailoverActor(primaryAdapter, "roundrobin-test", primaryConfig, backupConfig, failoverRetryCount: 1);

        // Wait for initial primary connect
        AwaitCondition(() => primaryConnectCount >= 1, TimeSpan.FromSeconds(2));
        await Task.Delay(200);

        // Disconnect primary → 1 failure → failover to backup
        RaiseDisconnected(primaryAdapter);

        // Wait for backup adapter creation
        AwaitCondition(() =>
            _mockFactory.ReceivedCalls().Any(c =>
                c.GetMethodInfo().Name == "Create" &&
                c.GetArguments()[1] is IDictionary<string, string> d &&
                d["Endpoint"] == "opc.tcp://backup:4840"),
            TimeSpan.FromSeconds(5));

        // Wait for backup to connect successfully
        AwaitCondition(() => backupConnectCount >= 1, TimeSpan.FromSeconds(2));
        await Task.Delay(200);

        // Now disconnect backup → 1 failure → failover back to primary
        RaiseDisconnected(backupAdapter);

        // Wait for primary adapter re-creation
        AwaitCondition(() =>
            _mockFactory.ReceivedCalls().Any(c =>
                c.GetMethodInfo().Name == "Create" &&
                c.GetArguments()[1] is IDictionary<string, string> d &&
                d["Endpoint"] == "opc.tcp://primary:4840"),
            TimeSpan.FromSeconds(5));
    }

    [Fact]
    public async Task Task4_SuccessfulReconnect_ResetsFailureCounter()
    {
        // Arrange: primary + backup, failoverRetryCount = 3
        var primaryConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://primary:4840" };
        var backupConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://backup:4840" };
        var primaryAdapter = Substitute.For<IDataConnection>();
        var connectCount = 0;

        // First connect succeeds, then 2 failures, then success, then 2 more failures, then success
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(callInfo =>
            {
                var count = Interlocked.Increment(ref connectCount);
                // count 1: initial connect → success
                // count 2,3: reconnect failures
                // count 4: reconnect success
                // count 5,6: reconnect failures again
                // count 7: reconnect success again
                return count switch
                {
                    1 => Task.CompletedTask,
                    2 or 3 => Task.FromException(new Exception("Fail")),
                    4 => Task.CompletedTask,
                    5 or 6 => Task.FromException(new Exception("Fail")),
                    _ => Task.CompletedTask
                };
            });

        var actor = CreateFailoverActor(primaryAdapter, "reset-counter-test", primaryConfig, backupConfig, failoverRetryCount: 3);

        // Wait for initial connect
        AwaitCondition(() => connectCount >= 1, TimeSpan.FromSeconds(2));
        await Task.Delay(200);

        // Disconnect: triggers 1 unstable disconnect + 2 failures then success (count 2,3,4)
        RaiseDisconnected(primaryAdapter);

        // Wait for successful reconnect (count 4)
        AwaitCondition(() => connectCount >= 4, TimeSpan.FromSeconds(5));
        await Task.Delay(200);

        // Disconnect again: triggers 2 more failures then success (count 5,6,7)
        RaiseDisconnected(primaryAdapter);

        // Wait for second successful reconnect (count 7)
        AwaitCondition(() => connectCount >= 7, TimeSpan.FromSeconds(5));
        await Task.Delay(200);

        // Factory should never be called — connection failures counter resets on each
        // successful reconnect, and unstable disconnect counter is separate
        _mockFactory.DidNotReceive().Create(Arg.Any<string>(), Arg.Any<IDictionary<string, string>>());
    }

    [Fact]
    public async Task Task4_ReSubscribeAll_CalledAfterFailoverReconnect()
    {
        // Arrange: primary + backup, failoverRetryCount = 1
        var primaryConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://primary:4840" };
        var backupConfig = new Dictionary<string, string> { ["Endpoint"] = "opc.tcp://backup:4840" };
        var primaryAdapter = Substitute.For<IDataConnection>();
        var backupAdapter = Substitute.For<IDataConnection>();

        // Primary initial connect succeeds
        var primaryConnectCount = 0;
        primaryAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(callInfo =>
            {
                var count = Interlocked.Increment(ref primaryConnectCount);
                if (count == 1) return Task.CompletedTask;
                return Task.FromException(new Exception("Primary down"));
            });

        // Primary subscribe succeeds
        primaryAdapter.SubscribeAsync(Arg.Any<string>(), Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>())
            .Returns("sub-primary-001");

        // Primary read succeeds (for initial read after subscribe)
        primaryAdapter.ReadAsync(Arg.Any<string>(), Arg.Any<CancellationToken>())
            .Returns(new ReadResult(true, new TagValue(42.0, QualityCode.Good, DateTimeOffset.UtcNow), null));

        // Factory returns backup adapter
        _mockFactory.Create("OpcUa", Arg.Is<IDictionary<string, string>>(d => d["Endpoint"] == "opc.tcp://backup:4840"))
            .Returns(backupAdapter);

        // Backup connect succeeds
        backupAdapter.ConnectAsync(Arg.Any<IDictionary<string, string>>(), Arg.Any<CancellationToken>())
            .Returns(Task.CompletedTask);

        // Backup subscribe succeeds (for re-subscribe after failover)
        backupAdapter.SubscribeAsync(Arg.Any<string>(), Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>())
            .Returns("sub-backup-001");

        var actor = CreateFailoverActor(primaryAdapter, "resub-test", primaryConfig, backupConfig, failoverRetryCount: 1);

        // Wait for initial connect
        AwaitCondition(() => primaryConnectCount >= 1, TimeSpan.FromSeconds(2));
        await Task.Delay(200);

        // Subscribe to tags while connected on primary
        actor.Tell(new SubscribeTagsRequest("corr1", "inst1", "resub-test", ["sensor/temp"], DateTimeOffset.UtcNow));
        ExpectMsg<SubscribeTagsResponse>(TimeSpan.FromSeconds(3));

        // Verify primary adapter received subscribe call
        await primaryAdapter.Received().SubscribeAsync(
            "sensor/temp", Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>());

        // Disconnect primary → 1 failure → failover to backup
        RaiseDisconnected(primaryAdapter);

        // Wait for backup adapter creation and connect
        AwaitCondition(() =>
            _mockFactory.ReceivedCalls().Any(c =>
                c.GetMethodInfo().Name == "Create" &&
                c.GetArguments()[1] is IDictionary<string, string> d &&
                d["Endpoint"] == "opc.tcp://backup:4840"),
            TimeSpan.FromSeconds(5));

        // Wait for ReSubscribeAll to fire on backup adapter
        AwaitCondition(() =>
            backupAdapter.ReceivedCalls().Any(c => c.GetMethodInfo().Name == "SubscribeAsync"),
            TimeSpan.FromSeconds(5));

        // Verify backup adapter received SubscribeAsync for the same tag
        await backupAdapter.Received().SubscribeAsync(
            "sensor/temp", Arg.Any<SubscriptionCallback>(), Arg.Any<CancellationToken>());
    }
}