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using System.Threading;
using System.Threading.Tasks;
using NUnit.Framework;
using Opc.Ua.Configuration;
using Opc.Ua.Server.TestFramework;
using Opc.Ua.Tests;

namespace Opc.Ua.Server.Tests
{
    /// <summary>
    /// Tests the deterministic synchronous and asynchronous disposal contracts of
    /// <see cref="StandardServer"/>.
    /// </summary>
    [TestFixture]
    [Category("StandardServer")]
    [NonParallelizable]
    public class StandardServerDisposeAsyncTests
    {
        private sealed class TestableStandardServer : StandardServer
        {
            private int m_serverStoppingCount;

            public TestableStandardServer(ITelemetryContext telemetry)
                : base(telemetry)
            {
            }

            /// <summary>
            /// The number of times the orderly stop sequence entered
            /// <see cref="OnServerStoppingAsync"/>.
            /// </summary>
            public int ServerStoppingCount => Volatile.Read(ref m_serverStoppingCount);

            protected override ValueTask OnServerStoppingAsync(
                CancellationToken cancellationToken = default)
            {
                Interlocked.Increment(ref m_serverStoppingCount);
                return base.OnServerStoppingAsync(cancellationToken);
            }
        }

        [Test]
        public async Task DisposeAsyncDisposesBaseResources()
        {
            ServerFixture<TestableStandardServer> fixture = CreateFixture();
            TestableStandardServer? server = null;

            try
            {
                server = await fixture.StartAsync().ConfigureAwait(false);

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

                AssertReleased(server);
            }
            finally
            {
                await CleanupAsync(fixture, server!).ConfigureAwait(false);
            }
        }

        [Test]
        public async Task DisposeAsyncIsIdempotentAndDisposeAfterDisposeAsyncIsSafe()
        {
            TestableStandardServer server = CreateServer();

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

            Assert.DoesNotThrow(server.Dispose);
            AssertReleased(server);
        }

        [Test]
        public async Task ConcurrentDisposeAndDisposeAsyncBothCompleteAndReleaseOnce()
        {
            ServerFixture<TestableStandardServer> fixture = CreateFixture();
            TestableStandardServer? server = null;

            try
            {
                server = await fixture.StartAsync().ConfigureAwait(false);

                Task disposeTask = Task.Run(server.Dispose);
                Task disposeAsyncTask = server.DisposeAsync().AsTask();

                await Task.WhenAll(disposeTask, disposeAsyncTask).ConfigureAwait(false);

                AssertReleased(server);
            }
            finally
            {
                await CleanupAsync(fixture, server!).ConfigureAwait(false);
            }
        }

        [Test]
        public async Task DisposeAsyncThenDisposeIsSafeAndReleasesOnce()
        {
            ServerFixture<TestableStandardServer> fixture = CreateFixture();
            TestableStandardServer? server = null;

            try
            {
                server = await fixture.StartAsync().ConfigureAwait(false);

                await server.DisposeAsync().ConfigureAwait(false);
                Assert.DoesNotThrow(server.Dispose);

                AssertReleased(server);
            }
            finally
            {
                await CleanupAsync(fixture, server!).ConfigureAwait(false);
            }
        }

        [Test]
        public async Task DisposeAsyncOnNeverStartedServerReleasesCleanly()
        {
            TestableStandardServer server = CreateServer();

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

            AssertReleased(server);
        }

        [Test]
        public async Task DisposeBlocksUntilShutdownCompletionAndReleasesOnce()
        {
            ServerFixture<TestableStandardServer> fixture = CreateFixture();
            TestableStandardServer? server = null;

            try
            {
                server = await fixture.StartAsync().ConfigureAwait(false);

                await Task.Run(server.Dispose).ConfigureAwait(false);

                AssertReleased(server);
            }
            finally
            {
                await CleanupAsync(fixture, server!).ConfigureAwait(false);
            }
        }

        [Test]
        public async Task ConcurrentAndRepeatStopAsyncRunTeardownOnce()
        {
            ServerFixture<TestableStandardServer> fixture = CreateFixture();
            TestableStandardServer? server = null;

            try
            {
                server = await fixture.StartAsync().ConfigureAwait(false);

                // Concurrent callers must join the single shared stop task.
                Task stopA = server.StopAsync().AsTask();
                Task stopB = server.StopAsync().AsTask();
                await Task.WhenAll(stopA, stopB).ConfigureAwait(false);

                // A later caller joins the same completed stop task and does not re-run teardown.
                await server.StopAsync().ConfigureAwait(false);

                Assert.That(server.ServerStoppingCount, Is.EqualTo(1));
            }
            finally
            {
                await CleanupAsync(fixture, server!).ConfigureAwait(false);
            }
        }

        private static ServerFixture<TestableStandardServer> CreateFixture()
        {
            return new ServerFixture<TestableStandardServer>(
                telemetry => new TestableStandardServer(telemetry))
            {
                SecurityNone = true
            };
        }

        private static TestableStandardServer CreateServer()
        {
            return new TestableStandardServer(NUnitTelemetryContext.Create());
        }

        private static void AssertReleased(TestableStandardServer server)
        {
            Assert.That(server.BaseResourcesDisposedForTest, Is.True);
        }

        private static async Task CleanupAsync(
            ServerFixture<TestableStandardServer> fixture,
            TestableStandardServer server)
        {
            if (server is not null && !server.BaseResourcesDisposedForTest)
            {
                await server.DisposeAsync().ConfigureAwait(false);
            }

            IApplicationInstance application = fixture.Application;
            if (application is not null)
            {
                await application.DisposeAsync().ConfigureAwait(false);
            }
        }
    }
}