using System.Runtime.CompilerServices;
using Google.Protobuf.WellKnownTypes;
using Microsoft.Extensions.Options;
using MxGateway.Contracts.Proto;
using MxGateway.Server.Configuration;
using MxGateway.Server.Metrics;
using MxGateway.Server.Sessions;
using MxGateway.Server.Workers;

namespace MxGateway.Tests.Gateway.Sessions;

/// <summary>
///     Pins the alarm auto-subscribe hook on session open. Runs in
///     its own file because the cases are orthogonal to
///     <see cref="SessionManagerTests"/> (alarms-disabled vs.
///     alarms-enabled lanes), and the fake worker client below verifies
///     the issued <c>SubscribeAlarms</c> command shape directly.
/// </summary>
public sealed class SessionManagerAlarmAutoSubscribeTests
{
    [Fact]
    public async Task OpenSessionAsync_DoesNotAutoSubscribe_WhenAlarmsDisabled()
    {
        AlarmAutoSubscribeWorkerClient worker = new();
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions { Enabled = false });

        await manager.OpenSessionAsync(CreateOpenRequest(), "client-1", CancellationToken.None);

        Assert.Equal(0, worker.SubscribeAlarmsInvokeCount);
    }

    [Fact]
    public async Task OpenSessionAsync_AutoSubscribes_WhenEnabledWithExpression()
    {
        AlarmAutoSubscribeWorkerClient worker = new();
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            SubscriptionExpression = @"\\HOST\Galaxy!Area1",
        });

        GatewaySession session = await manager.OpenSessionAsync(
            CreateOpenRequest(), "client-1", CancellationToken.None);

        Assert.Equal(SessionState.Ready, session.State);
        Assert.Equal(1, worker.SubscribeAlarmsInvokeCount);
        Assert.Equal(@"\\HOST\Galaxy!Area1",
            worker.LastSubscribeAlarmsCommand!.SubscriptionExpression);
    }

    [Fact]
    public async Task OpenSessionAsync_FallsBackToDefaultArea_WhenExpressionEmpty()
    {
        AlarmAutoSubscribeWorkerClient worker = new();
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            DefaultArea = "DEV",
        });

        await manager.OpenSessionAsync(CreateOpenRequest(), "client-1", CancellationToken.None);

        Assert.Equal(1, worker.SubscribeAlarmsInvokeCount);
        Assert.Contains(@"\Galaxy!DEV",
            worker.LastSubscribeAlarmsCommand!.SubscriptionExpression);
    }

    [Fact]
    public async Task OpenSessionAsync_Succeeds_WhenAutoSubscribeFailsWithRequireOff()
    {
        // Worker rejects the SubscribeAlarms command. With RequireSubscribeOnOpen=false
        // (the default), the session still opens — alarm-side commands later return
        // "not subscribed", but data subscriptions work.
        AlarmAutoSubscribeWorkerClient worker = new()
        {
            SubscribeAlarmsReplyFactory = _ => new MxCommandReply
            {
                Kind = MxCommandKind.SubscribeAlarms,
                ProtocolStatus = new ProtocolStatus
                {
                    Code = ProtocolStatusCode.MxaccessFailure,
                    Message = "wnwrap subscribe failed",
                },
                DiagnosticMessage = "alarm provider unavailable",
            },
        };
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            SubscriptionExpression = @"\\HOST\Galaxy!Area1",
            RequireSubscribeOnOpen = false,
        });

        GatewaySession session = await manager.OpenSessionAsync(
            CreateOpenRequest(), "client-1", CancellationToken.None);

        Assert.Equal(SessionState.Ready, session.State);
        Assert.Equal(1, worker.SubscribeAlarmsInvokeCount);
    }

    [Fact]
    public async Task OpenSessionAsync_Throws_WhenAutoSubscribeFailsWithRequireOn()
    {
        AlarmAutoSubscribeWorkerClient worker = new()
        {
            SubscribeAlarmsReplyFactory = _ => new MxCommandReply
            {
                Kind = MxCommandKind.SubscribeAlarms,
                ProtocolStatus = new ProtocolStatus
                {
                    Code = ProtocolStatusCode.MxaccessFailure,
                    Message = "wnwrap subscribe failed",
                },
            },
        };
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            SubscriptionExpression = @"\\HOST\Galaxy!Area1",
            RequireSubscribeOnOpen = true,
        });

        await Assert.ThrowsAsync<SessionManagerException>(
            async () => await manager.OpenSessionAsync(
                CreateOpenRequest(), "client-1", CancellationToken.None));
    }

    /// <summary>
    ///     Server-006 regression: when auto-subscribe throws after
    ///     <c>SessionOpened()</c> incremented the open-session gauge, the failed
    ///     open must not leave <c>mxgateway.sessions.open</c> over-counted.
    /// </summary>
    [Fact]
    public async Task OpenSessionAsync_DoesNotLeakOpenSessionGauge_WhenAutoSubscribeFailsWithRequireOn()
    {
        AlarmAutoSubscribeWorkerClient worker = new()
        {
            SubscribeAlarmsReplyFactory = _ => new MxCommandReply
            {
                Kind = MxCommandKind.SubscribeAlarms,
                ProtocolStatus = new ProtocolStatus
                {
                    Code = ProtocolStatusCode.MxaccessFailure,
                    Message = "wnwrap subscribe failed",
                },
            },
        };
        using GatewayMetrics metrics = new();
        SessionManager manager = NewManager(
            worker,
            alarms: new AlarmsOptions
            {
                Enabled = true,
                SubscriptionExpression = @"\\HOST\Galaxy!Area1",
                RequireSubscribeOnOpen = true,
            },
            metrics: metrics);

        await Assert.ThrowsAsync<SessionManagerException>(
            async () => await manager.OpenSessionAsync(
                CreateOpenRequest(), "client-1", CancellationToken.None));

        Assert.Equal(0, metrics.GetSnapshot().OpenSessions);
    }

    [Fact]
    public async Task OpenSessionAsync_Throws_WhenEnabledButNoExpressionAndRequireOn()
    {
        AlarmAutoSubscribeWorkerClient worker = new();
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            // No SubscriptionExpression and no DefaultArea.
            RequireSubscribeOnOpen = true,
        });

        await Assert.ThrowsAsync<SessionManagerException>(
            async () => await manager.OpenSessionAsync(
                CreateOpenRequest(), "client-1", CancellationToken.None));
        Assert.Equal(0, worker.SubscribeAlarmsInvokeCount);
    }

    [Fact]
    public async Task OpenSessionAsync_Succeeds_WhenEnabledButNoExpressionAndRequireOff()
    {
        AlarmAutoSubscribeWorkerClient worker = new();
        SessionManager manager = NewManager(worker, alarms: new AlarmsOptions
        {
            Enabled = true,
            // No SubscriptionExpression and no DefaultArea — default require=false.
        });

        GatewaySession session = await manager.OpenSessionAsync(
            CreateOpenRequest(), "client-1", CancellationToken.None);

        Assert.Equal(SessionState.Ready, session.State);
        Assert.Equal(0, worker.SubscribeAlarmsInvokeCount);
    }

    private static SessionManager NewManager(
        AlarmAutoSubscribeWorkerClient worker,
        AlarmsOptions alarms,
        GatewayMetrics? metrics = null)
    {
        FakeSessionWorkerClientFactory factory = new(worker);
        GatewayOptions options = new GatewayOptions
        {
            Sessions = new SessionOptions
            {
                DefaultCommandTimeoutSeconds = 30,
                MaxSessions = 64,
                DefaultLeaseSeconds = 1800,
            },
            Worker = new WorkerOptions
            {
                StartupTimeoutSeconds = 30,
                ShutdownTimeoutSeconds = 10,
            },
            Alarms = alarms,
        };
        return new SessionManager(
            new SessionRegistry(),
            factory,
            Options.Create(options),
            metrics ?? new GatewayMetrics());
    }

    private static SessionOpenRequest CreateOpenRequest()
    {
        return new SessionOpenRequest(
            RequestedBackend: null,
            ClientSessionName: "test-session",
            ClientCorrelationId: "client-correlation-1",
            CommandTimeout: Duration.FromTimeSpan(TimeSpan.FromSeconds(5)));
    }

    private sealed class FakeSessionWorkerClientFactory(IWorkerClient client) : ISessionWorkerClientFactory
    {
        public Task<IWorkerClient> CreateAsync(
            GatewaySession session,
            CancellationToken cancellationToken)
        {
            return Task.FromResult(client);
        }
    }

    private sealed class AlarmAutoSubscribeWorkerClient : IWorkerClient
    {
        public string SessionId { get; } = "session-1";
        public int? ProcessId { get; } = 1234;
        public WorkerClientState State { get; set; } = WorkerClientState.Ready;
        public DateTimeOffset LastHeartbeatAt { get; } = DateTimeOffset.UtcNow;

        public int SubscribeAlarmsInvokeCount { get; private set; }
        public SubscribeAlarmsCommand? LastSubscribeAlarmsCommand { get; private set; }
        public Func<WorkerCommand, MxCommandReply>? SubscribeAlarmsReplyFactory { get; init; }

        public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;

        public Task<WorkerCommandReply> InvokeAsync(
            WorkerCommand command, TimeSpan timeout, CancellationToken cancellationToken)
        {
            if (command.Command?.Kind == MxCommandKind.SubscribeAlarms)
            {
                SubscribeAlarmsInvokeCount++;
                LastSubscribeAlarmsCommand = command.Command.SubscribeAlarms;
                MxCommandReply reply = SubscribeAlarmsReplyFactory?.Invoke(command)
                    ?? new MxCommandReply
                    {
                        Kind = MxCommandKind.SubscribeAlarms,
                        ProtocolStatus = new ProtocolStatus
                        {
                            Code = ProtocolStatusCode.Ok,
                            Message = "OK",
                        },
                    };
                return Task.FromResult(new WorkerCommandReply { Reply = reply });
            }
            return Task.FromResult(new WorkerCommandReply
            {
                Reply = new MxCommandReply
                {
                    Kind = command.Command?.Kind ?? MxCommandKind.Unspecified,
                    ProtocolStatus = new ProtocolStatus
                    {
                        Code = ProtocolStatusCode.Ok,
                        Message = "OK",
                    },
                },
            });
        }

        public async IAsyncEnumerable<WorkerEvent> ReadEventsAsync(
            [EnumeratorCancellation] CancellationToken cancellationToken)
        {
            await Task.CompletedTask;
            yield break;
        }

        public Task ShutdownAsync(TimeSpan timeout, CancellationToken cancellationToken)
            => Task.CompletedTask;
        public void Kill(string reason) { }
        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
    }
}