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using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Options;
using Moq;
using NUnit.Framework;
using Opc.Ua.PubSub.Adapter.DependencyInjection;
using Opc.Ua.PubSub.Adapter.Diagnostics;
using Opc.Ua.PubSub.Adapter.Publisher;
using Opc.Ua.PubSub.Adapter.Session;
using Opc.Ua.PubSub.Application;
using Opc.Ua.PubSub.Configuration;
using Opc.Ua.PubSub.DataSets;

namespace Opc.Ua.PubSub.Adapter.Tests
{
    /// <summary>
    /// Unit tests for the dependency-injection runtime types:
    /// <see cref="ServerSessionFactory"/>,
    /// <see cref="ServerAdapterRuntime"/> and
    /// <see cref="ServerAdapterHostedService"/>.
    /// </summary>
    [TestFixture]
    public sealed class ServerAdapterRuntimeTests
    {
        private static SubscriptionCoordinator CreateCoordinator(
            List<FakeDataChangeSubscription> created)
        {
            PublishedDataSetDataType pds = AdapterTestHelpers.PublishedDataSet(
                "PDS", AdapterTestHelpers.Variable.Value(new NodeId(11u)));
            PubSubConfigurationDataType config = AdapterTestHelpers.Configuration(
                500, [pds]);

            Mock<IServerSession> session = AdapterTestHelpers.ConnectedSession();
            session
                .Setup(s => s.CreateDataChangeSubscriptionAsync(
                    It.IsAny<double>(), It.IsAny<CancellationToken>()))
                .Returns((double interval, CancellationToken ct) =>
                {
                    var sub = new FakeDataChangeSubscription();
                    created.Add(sub);
                    return new ValueTask<IDataChangeSubscription>(sub);
                });
            session
                .Setup(s => s.ReadAsync(
                    It.IsAny<ArrayOf<ReadValueId>>(), It.IsAny<CancellationToken>()))
                .Returns((ArrayOf<ReadValueId> reads, CancellationToken ct) =>
                {
                    var values = new DataValue[reads.Count];
                    for (int i = 0; i < reads.Count; i++)
                    {
                        values[i] = new DataValue(new Variant(i));
                    }
                    return new ValueTask<ArrayOf<DataValue>>(values.ToArrayOf());
                });

            return new SubscriptionCoordinator(
                config,
                session.Object,
                SubscriptionAffinity.WriterGroup,
                AdapterTestHelpers.Telemetry());
        }

        private static ServerAdapterReloadCoordinator CreateReloadCoordinator(
            ServerAdapterRuntime runtime)
        {
            return new ServerAdapterReloadCoordinator(
                new FakeConfigurationStore(new PubSubConfigurationDataType()),
                new OptionsMonitorStub<ServerPublisherOptions>(new ServerPublisherOptions()),
                new OptionsMonitorStub<ServerSubscriberOptions>(new ServerSubscriberOptions()),
                new OptionsMonitorStub<ServerActionResponderOptions>(
                    new ServerActionResponderOptions()),
                new MutableDataSetSourceProvider(),
                new MutableDataSetSinkProvider(),
                runtime,
                AdapterTestHelpers.Telemetry(),
                new AdapterMetrics());
        }

        [Test]
        public void FactoryCreateNullOptionsThrows()
        {
            var factory = new ServerSessionFactory();

            Assert.That(
                () => factory.Create(null!, AdapterTestHelpers.Telemetry()),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("options"));
        }

        [Test]
        public void FactoryCreateNullTelemetryThrows()
        {
            var factory = new ServerSessionFactory();

            Assert.That(
                () => factory.Create(
                    new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                    null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("telemetry"));
        }

        [Test]
        public async Task FactoryCreateReturnsExternalServerSessionAsync()
        {
            var factory = new ServerSessionFactory();

            IServerSession session = factory.Create(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                AdapterTestHelpers.Telemetry());

            Assert.That(session, Is.InstanceOf<ServerSession>());
            Assert.That(session.IsConnected, Is.False);
            await session.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public void RuntimeAddSessionNullThrows()
        {
            var runtime = new ServerAdapterRuntime();

            Assert.That(
                () => runtime.AddSession(null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("session"));
        }

        [Test]
        public void RuntimeAddCoordinatorNullThrows()
        {
            var runtime = new ServerAdapterRuntime();

            Assert.That(
                () => runtime.AddCoordinator(null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("coordinator"));
        }

        [Test]
        public async Task RuntimeStartStartsRegisteredCoordinatorsAsync()
        {
            var created = new List<FakeDataChangeSubscription>();
            SubscriptionCoordinator coordinator = CreateCoordinator(created);
            var runtime = new ServerAdapterRuntime();
            runtime.AddCoordinator(coordinator);

            await runtime.StartAsync().ConfigureAwait(false);

            Assert.That(created, Has.Count.EqualTo(1));

            await runtime.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public async Task RuntimeStartIsIdempotentAsync()
        {
            var created = new List<FakeDataChangeSubscription>();
            SubscriptionCoordinator coordinator = CreateCoordinator(created);
            var runtime = new ServerAdapterRuntime();
            runtime.AddCoordinator(coordinator);

            await runtime.StartAsync().ConfigureAwait(false);
            await runtime.StartAsync().ConfigureAwait(false);

            Assert.That(created, Has.Count.EqualTo(1));

            await runtime.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public async Task RuntimeDisposeDisposesSessionsAsync()
        {
            var session = new Mock<IServerSession>();
            session.Setup(s => s.DisposeAsync()).Returns(default(ValueTask));
            var runtime = new ServerAdapterRuntime();
            runtime.AddSession(session.Object);

            await runtime.DisposeAsync().ConfigureAwait(false);

            session.Verify(s => s.DisposeAsync(), Times.Once);
        }

        [Test]
        public async Task RuntimeAcquireSessionReusesEqualConnectionOptionsAsync()
        {
            var session = new Mock<IServerSession>();
            session.Setup(s => s.DisposeAsync()).Returns(default(ValueTask));
            var factory = new Mock<IServerSessionFactory>();
            factory
                .Setup(f => f.Create(
                    It.IsAny<ServerConnectionOptions>(), It.IsAny<ITelemetryContext>()))
                .Returns(session.Object);
            var runtime = new ServerAdapterRuntime(factory.Object);

            await using ServerAdapterRuntime.ServerSessionLease first = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                AdapterTestHelpers.Telemetry());
            await using ServerAdapterRuntime.ServerSessionLease second = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                AdapterTestHelpers.Telemetry());

            Assert.That(second.Session, Is.SameAs(first.Session));
            factory.Verify(f => f.Create(
                It.IsAny<ServerConnectionOptions>(), It.IsAny<ITelemetryContext>()), Times.Once);

            await runtime.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public async Task RuntimeAcquireSessionCreatesDistinctSessionsForDifferentEndpointsAsync()
        {
            var sessions = new Queue<IServerSession>(
                [new Mock<IServerSession>().Object, new Mock<IServerSession>().Object]);
            var factory = new Mock<IServerSessionFactory>();
            factory
                .Setup(f => f.Create(
                    It.IsAny<ServerConnectionOptions>(), It.IsAny<ITelemetryContext>()))
                .Returns(() => sessions.Dequeue());
            var runtime = new ServerAdapterRuntime(factory.Object);

            await using ServerAdapterRuntime.ServerSessionLease first = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://one:4840" },
                AdapterTestHelpers.Telemetry());
            await using ServerAdapterRuntime.ServerSessionLease second = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://two:4840" },
                AdapterTestHelpers.Telemetry());

            Assert.That(second.Session, Is.Not.SameAs(first.Session));
            factory.Verify(f => f.Create(
                It.IsAny<ServerConnectionOptions>(), It.IsAny<ITelemetryContext>()), Times.Exactly(2));

            await runtime.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public async Task RuntimeReleaseLastSessionLeaseDisposesSessionAsync()
        {
            var session = new Mock<IServerSession>();
            session.Setup(s => s.DisposeAsync()).Returns(default(ValueTask));
            var factory = new Mock<IServerSessionFactory>();
            factory
                .Setup(f => f.Create(
                    It.IsAny<ServerConnectionOptions>(), It.IsAny<ITelemetryContext>()))
                .Returns(session.Object);
            var runtime = new ServerAdapterRuntime(factory.Object);

            ServerAdapterRuntime.ServerSessionLease first = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                AdapterTestHelpers.Telemetry());
            ServerAdapterRuntime.ServerSessionLease second = runtime.AcquireSession(
                new ServerConnectionOptions { EndpointUrl = "opc.tcp://host:4840" },
                AdapterTestHelpers.Telemetry());

            await first.DisposeAsync().ConfigureAwait(false);
            session.Verify(s => s.DisposeAsync(), Times.Never);
            await second.DisposeAsync().ConfigureAwait(false);

            session.Verify(s => s.DisposeAsync(), Times.Once);
            await runtime.DisposeAsync().ConfigureAwait(false);
        }

        [Test]
        public async Task RuntimeAddSessionAfterDisposeThrowsAsync()
        {
            var runtime = new ServerAdapterRuntime();
            await runtime.DisposeAsync().ConfigureAwait(false);

            var session = new Mock<IServerSession>();
            Assert.That(
                () => runtime.AddSession(session.Object),
                Throws.TypeOf<ObjectDisposedException>());
        }

        [Test]
        public async Task RuntimeDisposeIsIdempotentAsync()
        {
            var session = new Mock<IServerSession>();
            session.Setup(s => s.DisposeAsync()).Returns(default(ValueTask));
            var runtime = new ServerAdapterRuntime();
            runtime.AddSession(session.Object);

            await runtime.DisposeAsync().ConfigureAwait(false);
            await runtime.DisposeAsync().ConfigureAwait(false);

            session.Verify(s => s.DisposeAsync(), Times.Once);
        }

        [Test]
        public void HostedServiceNullApplicationThrows()
        {
            var runtime = new ServerAdapterRuntime();

            Assert.That(
                () => new ServerAdapterHostedService(
                    null!, runtime, null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("application"));
        }

        [Test]
        public void HostedServiceNullRuntimeThrows()
        {
            IPubSubApplication application = new Mock<IPubSubApplication>().Object;

            Assert.That(
                () => new ServerAdapterHostedService(
                    application, null!, null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("runtime"));
        }

        [Test]
        public void HostedServiceNullReloadCoordinatorThrows()
        {
            IPubSubApplication application = new Mock<IPubSubApplication>().Object;
            var runtime = new ServerAdapterRuntime();

            Assert.That(
                () => new ServerAdapterHostedService(application, runtime, null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("reloadCoordinator"));
        }

        [Test]
        public async Task HostedServiceStartStartsCoordinatorsAndStopDisposesAsync()
        {
            var created = new List<FakeDataChangeSubscription>();
            SubscriptionCoordinator coordinator = CreateCoordinator(created);
            var session = new Mock<IServerSession>();
            session.Setup(s => s.DisposeAsync()).Returns(default(ValueTask));
            var runtime = new ServerAdapterRuntime();
            runtime.AddCoordinator(coordinator);
            runtime.AddSession(session.Object);
            var hosted = new ServerAdapterHostedService(
                new Mock<IPubSubApplication>().Object,
                runtime,
                CreateReloadCoordinator(runtime));

            await hosted.StartAsync(CancellationToken.None).ConfigureAwait(false);
            Assert.That(created, Has.Count.EqualTo(1));

            await hosted.StopAsync(CancellationToken.None).ConfigureAwait(false);
            session.Verify(s => s.DisposeAsync(), Times.Once);
        }

        private sealed class OptionsMonitorStub<T> : IOptionsMonitor<T>
        {
            public OptionsMonitorStub(T value)
            {
                CurrentValue = value;
            }

            public T CurrentValue { get; }

            public T Get(string? name)
            {
                return CurrentValue;
            }

            public IDisposable? OnChange(Action<T, string?> listener)
            {
                return null;
            }
        }

        private sealed class FakeConfigurationStore : IPubSubConfigurationStore
        {
            public FakeConfigurationStore(PubSubConfigurationDataType configuration)
            {
                m_configuration = configuration;
            }

            public event EventHandler<PubSubConfigurationChangedEventArgs>? Changed;

            public ValueTask<PubSubConfigurationDataType> LoadAsync(
                CancellationToken cancellationToken = default)
            {
                return new ValueTask<PubSubConfigurationDataType>(m_configuration);
            }

            public ValueTask SaveAsync(
                PubSubConfigurationDataType configuration,
                CancellationToken cancellationToken = default)
            {
                PubSubConfigurationDataType previous = m_configuration;
                m_configuration = configuration;
                Changed?.Invoke(this, new PubSubConfigurationChangedEventArgs(previous, configuration));
                return default;
            }

            public ValueTask<ConfigurationVersionDataType?> GetConfigurationVersionAsync(
                CancellationToken cancellationToken = default)
            {
                return new ValueTask<ConfigurationVersionDataType?>((ConfigurationVersionDataType?)null);
            }

            public ValueTask SetConfigurationVersionAsync(
                ConfigurationVersionDataType configurationVersion,
                CancellationToken cancellationToken = default)
            {
                return default;
            }

            public ValueTask<ConfigurationVersionDataType?> GetPublishedDataSetConfigurationVersionAsync(
                string publishedDataSetName,
                CancellationToken cancellationToken = default)
            {
                return new ValueTask<ConfigurationVersionDataType?>((ConfigurationVersionDataType?)null);
            }

            public ValueTask SetPublishedDataSetConfigurationVersionAsync(
                string publishedDataSetName,
                ConfigurationVersionDataType configurationVersion,
                CancellationToken cancellationToken = default)
            {
                return default;
            }

            private PubSubConfigurationDataType m_configuration;
        }
    }
}