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using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Moq;
using NUnit.Framework;
using Opc.Ua.Server.TestFramework;
using Opc.Ua.Tests;
using Quickstarts.ReferenceServer;

namespace Opc.Ua.Server.Tests
{
    /// <summary>
    /// Tests the OPC 10000-12 §7.10.13 <c>ResetToServerDefaults</c> deferred
    /// shutdown sequencing: the Method returns its response before the reset
    /// runs, the server advertises the pending shutdown, the injected provider
    /// is invoked after the grace period, and a racing server shutdown cancels
    /// the reset. Each test uses its own dedicated server so the advertised
    /// <c>ServerState</c> = Shutdown never disturbs another test.
    /// </summary>
    [TestFixture]
    [Category("ConfigurationNodeManager")]
    [NonParallelizable]
    [Parallelizable(ParallelScope.None)]
    public sealed class ServerConfigurationResetTests
    {
        [TestCase(0)]
        [TestCase(1)]
        [TestCase(2)]
        public async Task ResetReturnsResponseThenRestoresStatusAfterProviderFinishesAsync(int outcome)
        {
            var fixture = new ServerFixture<StandardServer>(t => new ReferenceServer(t));
            StandardServer server = await fixture.StartAsync().ConfigureAwait(false);
            try
            {
                IServerInternal serverInternal = server.CurrentInstance;
                var provider = new FakeResetProvider
                {
                    Failure = outcome switch
                    {
                        1 => new InvalidOperationException("Reset provider failed."),
                        2 => new OperationCanceledException("Reset provider cancelled its own operation."),
                        _ => null
                    }
                };
                using ConfigurationNodeManager manager = await CreateManagerAsync(
                    fixture, serverInternal,
                    new ServerConfigurationOptions
                    {
                        ResetProvider = provider,
                        ResetShutdownDelay = TimeSpan.Zero
                    }).ConfigureAwait(false);

                var node = manager.FindPredefinedNode<ServerConfigurationState>(ObjectIds.ServerConfiguration);
                MethodState reset = node!.ResetToServerDefaults!;

                ServiceResult result = await reset.OnCallMethod2Async!(
                    CreateAdminContextForSession(new NodeId(1, 1)),
                    reset,
                    node.NodeId,
                    ArrayOf<Variant>.Empty,
                    new List<Variant>(),
                    CancellationToken.None).ConfigureAwait(false);

                // §7.10.13: the response is returned first.
                Assert.That(ServiceResult.IsGood(result), Is.True);

                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                {
                    await provider.Entered.WaitAsync(timeout.Token).ConfigureAwait(false);
                }

                // The reset only runs after the response, and the server has
                // advertised the pending shutdown by the time it runs.
                Assert.That(serverInternal.CurrentState, Is.EqualTo(ServerState.Shutdown));
                Task pending = manager.DrainPendingResetAsync();
                result = await reset.OnCallMethod2Async!(
                    CreateAdminContextForSession(new NodeId(1, 1)),
                    reset,
                    node.NodeId,
                    [],
                    [],
                    CancellationToken.None).ConfigureAwait(false);
                Assert.That(ServiceResult.IsGood(result), Is.True);
                Assert.That(manager.DrainPendingResetAsync(), Is.SameAs(pending));
                provider.Release();

                using (var drainTimeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                {
                    if (outcome == 1)
                    {
                        Assert.ThrowsAsync<InvalidOperationException>(async () =>
                            await manager.DrainPendingResetAsync(drainTimeout.Token).ConfigureAwait(false));
                    }
                    else
                    {
                        await manager.DrainPendingResetAsync(drainTimeout.Token).ConfigureAwait(false);
                    }
                }
                Assert.That(provider.InvocationCount, Is.EqualTo(1));
                Assert.That(serverInternal.CurrentState, Is.EqualTo(ServerState.Running));
                serverInternal.UpdateServerStatus(status =>
                {
                    Assert.That(status.Value.SecondsTillShutdown, Is.Zero);
                    Assert.That(status.Value.ShutdownReason.IsNull, Is.True);
                    Assert.That(status.Variable, Is.Not.Null);
                    Assert.That(status.Variable!.State!.Value, Is.EqualTo(ServerState.Running));
                    Assert.That(status.Variable.SecondsTillShutdown!.Value, Is.Zero);
                    Assert.That(status.Variable.ShutdownReason!.Value.IsNull, Is.True);
                });
                if (outcome == 1)
                {
                    Assert.ThrowsAsync<InvalidOperationException>(async () =>
                        await manager.DrainPendingResetAsync().ConfigureAwait(false));
                }

                manager.Dispose();
            }
            finally
            {
                await fixture.StopAsync().ConfigureAwait(false);
            }
        }

        [TestCase(ServerState.Shutdown, false)]
        [TestCase(ServerState.Failed, false)]
        [TestCase(ServerState.Shutdown, true)]
        public async Task ResetDoesNotOverwriteSubsequentServerShutdownOrFailureAsync(
            ServerState state,
            bool disposeManager)
        {
            var fixture = new ServerFixture<StandardServer>(t => new ReferenceServer(t));
            StandardServer server = await fixture.StartAsync().ConfigureAwait(false);
            try
            {
                IServerInternal serverInternal = server.CurrentInstance;
                var provider = new FakeResetProvider();
                using ConfigurationNodeManager manager = await CreateManagerAsync(
                    fixture, serverInternal,
                    new ServerConfigurationOptions
                    {
                        ResetProvider = provider,
                        ResetShutdownDelay = TimeSpan.Zero
                    }).ConfigureAwait(false);
                ServerConfigurationState? node = manager.FindPredefinedNode<ServerConfigurationState>(
                    ObjectIds.ServerConfiguration);
                MethodState reset = node!.ResetToServerDefaults!;
                ServiceResult result = await reset.OnCallMethod2Async!(
                    CreateAdminContextForSession(new NodeId(3, 1)), reset, node.NodeId,
                    [], [], CancellationToken.None).ConfigureAwait(false);
                Assert.That(ServiceResult.IsGood(result), Is.True);
                await provider.Entered.WaitAsync(TimeSpan.FromSeconds(30)).ConfigureAwait(false);

                LocalizedText expectedReason = default;
                serverInternal.UpdateServerStatus(status =>
                {
                    expectedReason = state == ServerState.Shutdown && !disposeManager
                        ? new LocalizedText("Application is shutting down.")
                        : status.Value.ShutdownReason;
                    status.Value.State = state;
                    status.Value.ShutdownReason = expectedReason;
                    status.Value.SecondsTillShutdown = 10;
                    status.Variable!.State!.Value = state;
                    status.Variable.ShutdownReason!.Value = expectedReason;
                    status.Variable.SecondsTillShutdown!.Value = 10;
                });

                if (disposeManager)
                {
                    manager.Dispose();
                }
                provider.Release();
                await manager.DrainPendingResetAsync().WaitAsync(TimeSpan.FromSeconds(30)).ConfigureAwait(false);

                serverInternal.UpdateServerStatus(status =>
                {
                    Assert.That(status.Value.State, Is.EqualTo(state));
                    Assert.That(status.Value.ShutdownReason, Is.EqualTo(expectedReason));
                    Assert.That(status.Value.SecondsTillShutdown, Is.EqualTo(10));
                    Assert.That(status.Variable!.State!.Value, Is.EqualTo(state));
                    Assert.That(status.Variable.ShutdownReason!.Value, Is.EqualTo(expectedReason));
                    Assert.That(status.Variable.SecondsTillShutdown!.Value, Is.EqualTo(10));
                });
            }
            finally
            {
                await fixture.StopAsync().ConfigureAwait(false);
            }
        }

        [Test]
        public async Task ResetCancelledByServerShutdownDoesNotInvokeProviderAsync()
        {
            var fixture = new ServerFixture<StandardServer>(t => new ReferenceServer(t));
            StandardServer server = await fixture.StartAsync().ConfigureAwait(false);
            try
            {
                IServerInternal serverInternal = server.CurrentInstance;
                var provider = new FakeResetProvider();
                ConfigurationNodeManager manager = await CreateManagerAsync(
                    fixture, serverInternal,
                    new ServerConfigurationOptions
                    {
                        ResetProvider = provider,
                        // A long grace period so that, unless shutdown cancels
                        // it, the provider would only run much later.
                        ResetShutdownDelay = TimeSpan.FromSeconds(30)
                    }).ConfigureAwait(false);

                var node = manager.FindPredefinedNode<ServerConfigurationState>(ObjectIds.ServerConfiguration);
                MethodState reset = node!.ResetToServerDefaults!;

                ServiceResult result = await reset.OnCallMethod2Async!(
                    CreateAdminContextForSession(new NodeId(2, 1)),
                    reset,
                    node.NodeId,
                    ArrayOf<Variant>.Empty,
                    new List<Variant>(),
                    CancellationToken.None).ConfigureAwait(false);
                Assert.That(ServiceResult.IsGood(result), Is.True);

                // Disposing the manager signals the shutdown token; the deferred
                // reset must abandon its grace wait without invoking the provider.
                manager.Dispose();

                using (var drainTimeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                {
                    await manager.DrainPendingResetAsync(drainTimeout.Token).ConfigureAwait(false);
                }

                Assert.That(provider.InvocationCount, Is.Zero,
                    "a reset cancelled during its grace period must not run the provider");
            }
            finally
            {
                await fixture.StopAsync().ConfigureAwait(false);
            }
        }

        private static async Task<ConfigurationNodeManager> CreateManagerAsync(
            ServerFixture<StandardServer> fixture,
            IServerInternal serverInternal,
            ServerConfigurationOptions options)
        {
            var coordinator = new PushConfigurationTransactionCoordinator(serverInternal.Telemetry);
            var manager = new ConfigurationNodeManager(
                serverInternal,
                fixture.Config,
                serverInternal.Telemetry.CreateLogger<ConfigurationNodeManager>(),
                timeProvider: null,
                coordinator,
                pendingKeyStore: null,
                keyGenerator: null,
                trustListEffectHandler: null,
                serverConfigurationOptions: options);

            IDictionary<NodeId, IList<IReference>> externalReferences =
                new Dictionary<NodeId, IList<IReference>>();
            await manager.CreateAddressSpaceAsync(externalReferences, CancellationToken.None).ConfigureAwait(false);
            manager.CreateServerConfiguration(serverInternal.DefaultSystemContext, fixture.Config);
            return manager;
        }

        private static SessionSystemContext CreateAdminContextForSession(NodeId sessionId)
        {
            var identity = new Mock<IUserIdentity>();
            identity.Setup(i => i.TokenType).Returns(UserTokenType.UserName);
            identity.Setup(i => i.DisplayName).Returns(nameof(UserTokenType.UserName));
            identity.Setup(i => i.GrantedRoleIds).Returns(ArrayOf.Wrapped(ObjectIds.WellKnownRole_SecurityAdmin));

            var session = new Mock<ISession>();
            session.Setup(s => s.Id).Returns(sessionId);
            session.Setup(s => s.EffectiveIdentity).Returns(identity.Object);
            session.Setup(s => s.PreferredLocales).Returns([]);

            var endpoint = new EndpointDescription { SecurityMode = MessageSecurityMode.SignAndEncrypt };
            var channelContext = new SecureChannelContext("test", endpoint, RequestEncoding.Binary);
            var operationContext = new OperationContext(
                new RequestHeader(),
                channelContext,
                RequestType.Call,
                RequestLifetime.None,
                session.Object);
            return new SessionSystemContext(operationContext, s_telemetry)
            {
                NamespaceUris = new NamespaceTable(),
                ServerUris = new StringTable()
            };
        }

        private sealed class FakeResetProvider : IServerConfigurationResetProvider
        {
            public int InvocationCount { get; private set; }

            public Exception? Failure { get; init; }

            public Task Entered => m_entered.Task;

            public void Release()
            {
                m_release.TrySetResult(true);
            }

            public async ValueTask ResetToServerDefaultsAsync(CancellationToken cancellationToken = default)
            {
                InvocationCount++;
                m_entered.TrySetResult(true);
                await m_release.Task.WaitAsync(cancellationToken).ConfigureAwait(false);
                if (Failure != null)
                {
                    throw Failure;
                }
            }

            private readonly TaskCompletionSource<bool> m_release =
                new(TaskCreationOptions.RunContinuationsAsynchronously);

            private readonly TaskCompletionSource<bool> m_entered =
                new(TaskCreationOptions.RunContinuationsAsynchronously);
        }

        private static readonly ITelemetryContext s_telemetry = NUnitTelemetryContext.Create();
    }
}