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// CA2007: tests run without a SynchronizationContext; ConfigureAwait(false)
// adds noise without a behavioural benefit. Disabled file-level for the suite.
#pragma warning disable CA2007

using System;
using System.Threading;
using System.Threading.Tasks;
using Moq;
using NUnit.Framework;
using Opc.Ua.Redundancy.Server;

namespace Opc.Ua.Server.Tests.Redundancy
{
    /// <summary>
    /// Unit tests for the <see cref="ServerLoadDirector"/> fail-safe and skip paths using mocked collaborators:
    /// a policy or directory that throws, a null target, an unchanged publish signature, and a publisher that
    /// throws — all of which must degrade to serving the local Server without surfacing an exception.
    /// </summary>
    [TestFixture]
    [Category("Distributed")]
    [Parallelizable(ParallelScope.All)]
    public sealed class ServerLoadDirectorErrorPathTests
    {
        private const string BalancingUrl = "opc.tcp://balance:4840";
        private const string NormalUrl = "opc.tcp://a:4840";
        private const string LocalServerUri = "urn:A";
        private const string PeerServerUri = "urn:B";

        [Test]
        public void ConfigureThrowsOnEmptyLocalServerUri()
        {
            var director = new ServerLoadDirector(
                new ConstantServiceLevelProvider(255), new ConstantLoadWeightProvider(0), new LoadDirectionOptions());

            Assert.That(
                () => director.Configure(
                    Mock.Of<IServerDirectionPolicy>(),
                    Mock.Of<IPeerEndpointDirectory>(),
                    Mock.Of<IPeerEndpointPublisher>(),
                    string.Empty),
                Throws.ArgumentException);
        }

        [Test]
        public async Task PolicyFailureServesLocalAsync()
        {
            var policy = new Mock<IServerDirectionPolicy>();
            policy
                .Setup(p => p.SelectTargetServerUriAsync(
                    It.IsAny<string>(), It.IsAny<byte>(), It.IsAny<byte>(), It.IsAny<CancellationToken>()))
                .Throws(new InvalidOperationException("policy boom"));

            ServerLoadDirector director = Configure(policy.Object, Mock.Of<IPeerEndpointDirectory>());

            (bool redirect, _) = await director.TryGetDirectedEndpointsAsync(BalancingUrl, LocalEndpoints()).ConfigureAwait(false);

            Assert.That(redirect, Is.False, "a failing policy fails safe to the local Server");
        }

        [Test]
        public async Task NullTargetServesLocalAsync()
        {
            var policy = new Mock<IServerDirectionPolicy>();
            policy
                .Setup(p => p.SelectTargetServerUriAsync(
                    It.IsAny<string>(), It.IsAny<byte>(), It.IsAny<byte>(), It.IsAny<CancellationToken>()))
                .Returns(new ValueTask<string?>((string?)null));

            ServerLoadDirector director = Configure(policy.Object, Mock.Of<IPeerEndpointDirectory>());

            (bool redirect, _) = await director.TryGetDirectedEndpointsAsync(BalancingUrl, LocalEndpoints()).ConfigureAwait(false);

            Assert.That(redirect, Is.False, "a null target means the local Server serves the request");
        }

        [Test]
        public async Task DirectoryFailureServesLocalAsync()
        {
            var policy = new Mock<IServerDirectionPolicy>();
            policy
                .Setup(p => p.SelectTargetServerUriAsync(
                    It.IsAny<string>(), It.IsAny<byte>(), It.IsAny<byte>(), It.IsAny<CancellationToken>()))
                .Returns(new ValueTask<string?>(PeerServerUri));
            var directory = new Mock<IPeerEndpointDirectory>();
            directory
                .Setup(d => d.GetEndpointsAsync(It.IsAny<string>(), It.IsAny<CancellationToken>()))
                .Throws(new InvalidOperationException("directory boom"));

            ServerLoadDirector director = Configure(policy.Object, directory.Object);

            (bool redirect, _) = await director.TryGetDirectedEndpointsAsync(BalancingUrl, LocalEndpoints()).ConfigureAwait(false);

            Assert.That(redirect, Is.False, "a failing endpoint directory fails safe to the local Server");
        }

        [Test]
        public async Task NormalRequestWithoutLocalEndpointsSkipsPublishAsync()
        {
            var publisher = new Mock<IPeerEndpointPublisher>();
            ServerLoadDirector director = Configure(Mock.Of<IServerDirectionPolicy>(), publisher: publisher.Object);

            // A null endpoint URL is never the balancing URL, and no local endpoints means nothing to publish.
            (bool redirect, _) = await director.TryGetDirectedEndpointsAsync(null, default).ConfigureAwait(false);

            Assert.That(redirect, Is.False);
            publisher.Verify(
                p => p.PublishAsync(It.IsAny<ArrayOf<EndpointDescription>>(), It.IsAny<CancellationToken>()),
                Times.Never);
        }

        [Test]
        public async Task RepeatedNormalRequestPublishesLocalEndpointsOnceAsync()
        {
            var publisher = new Mock<IPeerEndpointPublisher>();
            ServerLoadDirector director = Configure(Mock.Of<IServerDirectionPolicy>(), publisher: publisher.Object);

            await director.TryGetDirectedEndpointsAsync(NormalUrl, LocalEndpoints()).ConfigureAwait(false);
            await director.TryGetDirectedEndpointsAsync(NormalUrl, LocalEndpoints()).ConfigureAwait(false);

            publisher.Verify(
                p => p.PublishAsync(It.IsAny<ArrayOf<EndpointDescription>>(), It.IsAny<CancellationToken>()),
                Times.Once,
                "an unchanged endpoint signature must not be republished");
        }

        [Test]
        public async Task PublishFailureIsSwallowedAsync()
        {
            var publisher = new Mock<IPeerEndpointPublisher>();
            publisher
                .Setup(p => p.PublishAsync(It.IsAny<ArrayOf<EndpointDescription>>(), It.IsAny<CancellationToken>()))
                .Throws(new InvalidOperationException("publish boom"));
            ServerLoadDirector director = Configure(Mock.Of<IServerDirectionPolicy>(), publisher: publisher.Object);

            (bool redirect, _) = await director.TryGetDirectedEndpointsAsync(NormalUrl, LocalEndpoints()).ConfigureAwait(false);

            Assert.That(redirect, Is.False, "a failing endpoint publish must not break local discovery");
        }

        private static ServerLoadDirector Configure(
            IServerDirectionPolicy policy,
            IPeerEndpointDirectory? directory = null,
            IPeerEndpointPublisher? publisher = null)
        {
            var director = new ServerLoadDirector(
                new ConstantServiceLevelProvider(255),
                new ConstantLoadWeightProvider(200),
                new LoadDirectionOptions { BalancingEndpointUrl = BalancingUrl });
            director.Configure(
                policy,
                directory ?? Mock.Of<IPeerEndpointDirectory>(),
                publisher ?? Mock.Of<IPeerEndpointPublisher>(),
                LocalServerUri);
            return director;
        }

        private static ArrayOf<EndpointDescription> LocalEndpoints()
        {
            return
            [
                new EndpointDescription
                {
                    EndpointUrl = "opc.tcp://" + LocalServerUri + ":4840",
                    SecurityMode = MessageSecurityMode.None,
                    SecurityPolicyUri = SecurityPolicies.None,
                    Server = new ApplicationDescription
                    {
                        ApplicationUri = LocalServerUri,
                        ApplicationType = ApplicationType.Server
                    }
                }
            ];
        }
    }
}