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

namespace Opc.Ua.Server.Tests.Redundancy
{
    /// <summary>
    /// Unit tests for <see cref="ServiceLevelStartupTask"/> guard paths and the happy-path update of the live
    /// <c>Server.ServiceLevel</c> node from an <see cref="IServiceLevelProvider"/>.
    /// </summary>
    [TestFixture]
    [Category("Distributed")]
    [Parallelizable(ParallelScope.All)]
    public class ServiceLevelStartupTaskTests
    {
        [Test]
        public void ConstructorThrowsOnNullProvider()
        {
            Assert.That(() => new ServiceLevelStartupTask(null!), Throws.ArgumentNullException);
        }

        [Test]
        public void OnServerStartedThrowsOnNullServer()
        {
            var task = new ServiceLevelStartupTask(new ConstantServiceLevelProvider());

            Assert.That(async () => await task.OnServerStartedAsync(null!).ConfigureAwait(false), Throws.ArgumentNullException);
        }

        [Test]
        public async Task OnServerStartedNoOpsWhenServerObjectMissingAsync()
        {
            var task = new ServiceLevelStartupTask(new ConstantServiceLevelProvider());
            var server = new Mock<IServerInternal>();
            server.Setup(s => s.ServerObject).Returns((ServerObjectState)null!);

            await task.OnServerStartedAsync(server.Object).ConfigureAwait(false);

            server.VerifyGet(s => s.ServerObject, Times.Once);
        }

        [Test]
        public async Task OnServerStartedAppliesInitialAndChangedServiceLevelAsync()
        {
            using DiagnosticsServerHarness harness = await DiagnosticsServerHarness.CreateAsync().ConfigureAwait(false);
            var provider = new MutableServiceLevelProvider(150);
            var task = new ServiceLevelStartupTask(provider);

            await task.OnServerStartedAsync(harness.Server.Object).ConfigureAwait(false);

            Assert.That(harness.ServerObject.ServiceLevel, Is.Not.Null);
            Assert.That(harness.ServerObject.ServiceLevel!.Value, Is.EqualTo((byte)150), "the initial level is applied");

            provider.Raise(42);

            Assert.That(
                harness.ServerObject.ServiceLevel!.Value,
                Is.EqualTo((byte)42),
                "a provider change is mirrored onto the live node");
        }

        private sealed class MutableServiceLevelProvider : IServiceLevelProvider
        {
            public MutableServiceLevelProvider(byte serviceLevel)
            {
                m_serviceLevel = serviceLevel;
            }

            public event System.Action<byte>? ServiceLevelChanged;

            public byte GetServiceLevel()
            {
                return m_serviceLevel;
            }

            public void Raise(byte serviceLevel)
            {
                m_serviceLevel = serviceLevel;
                ServiceLevelChanged?.Invoke(serviceLevel);
            }

            private byte m_serviceLevel;
        }
    }
}