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using System;
using System.Threading;
using System.Threading.Tasks;
using NUnit.Framework;
using Opc.Ua.PubSub.Adapter.Publisher;

namespace Opc.Ua.PubSub.Adapter.Tests
{
    /// <summary>
    /// Unit tests for <see cref="SubscriptionReadStrategy"/>: the latest-value
    /// cache, attribute normalization, subscription-driven updates and lifetime.
    /// </summary>
    [TestFixture]
    public sealed class SubscriptionReadStrategyTests
    {
        [Test]
        public void ConstructorNullTelemetryThrows()
        {
            Assert.That(
                () => new SubscriptionReadStrategy(null!),
                Throws.ArgumentNullException.With.Property("ParamName").EqualTo("telemetry"));
        }

        [Test]
        public async Task ReadUnprimedKeyReturnsUncertainInitialValue()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = new NodeId(1u), AttributeId = Attributes.Value }
            ];

            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(values.Count, Is.EqualTo(1));
            Assert.That(values[0].StatusCode, Is.EqualTo(StatusCodes.UncertainInitialValue));
        }

        [Test]
        public async Task SeedThenReadReturnsCachedValue()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var nodeId = new NodeId(5u);
            strategy.Seed(nodeId, Attributes.Value, new DataValue(new Variant(42)));

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Value }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(values[0].StatusCode, Is.EqualTo(StatusCodes.Good));
            Assert.That(values[0].WrappedValue, Is.EqualTo(new Variant(42)));
        }

        [Test]
        public async Task ReadNormalizesZeroAttributeToValue()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var nodeId = new NodeId(7u);
            strategy.Seed(nodeId, Attributes.Value, new DataValue(new Variant(11)));

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = 0 }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(values[0].WrappedValue, Is.EqualTo(new Variant(11)));
        }

        [Test]
        public async Task CacheKeyDistinguishesAttributes()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var nodeId = new NodeId(9u);
            strategy.Seed(nodeId, Attributes.Value, new DataValue(new Variant(1)));

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Description }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(
                values[0].StatusCode,
                Is.EqualTo(StatusCodes.UncertainInitialValue));
        }

        [Test]
        public async Task RegisterMonitoredItemSeedsUncertainPlaceholder()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var nodeId = new NodeId(13u);
            strategy.RegisterMonitoredItem(100, nodeId, Attributes.Value);

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Value }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(
                values[0].StatusCode,
                Is.EqualTo(StatusCodes.UncertainInitialValue));
        }

        [Test]
        public async Task DataChangedUpdatesCacheByClientHandle()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var subscription = new FakeDataChangeSubscription();
            strategy.Attach(subscription);

            var nodeId = new NodeId(21u);
            strategy.RegisterMonitoredItem(55, nodeId, Attributes.Value);
            subscription.Raise(55, nodeId, new DataValue(new Variant(99)));

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Value }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(values[0].WrappedValue, Is.EqualTo(new Variant(99)));
        }

        [Test]
        public async Task DataChangedFallsBackToNodeIdWhenHandleUnknown()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            var subscription = new FakeDataChangeSubscription();
            strategy.Attach(subscription);

            var nodeId = new NodeId(23u);
            subscription.Raise(999, nodeId, new DataValue(new Variant(7)));

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = nodeId, AttributeId = Attributes.Value }
            ];
            ArrayOf<DataValue> values = await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false);

            Assert.That(values[0].WrappedValue, Is.EqualTo(new Variant(7)));
        }

        [Test]
        public void ReadAfterDisposeThrows()
        {
            var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            strategy.Dispose();

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = new NodeId(1u), AttributeId = Attributes.Value }
            ];

            Assert.That(
                async () => await strategy.ReadAsync(reads.ToArrayOf()).ConfigureAwait(false),
                Throws.TypeOf<ObjectDisposedException>());
        }

        [Test]
        public void ReadCanceledThrows()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            using var cts = new CancellationTokenSource();
            cts.Cancel();

            ReadValueId[] reads =
            [
                new ReadValueId { NodeId = new NodeId(1u), AttributeId = Attributes.Value }
            ];

            Assert.That(
                async () => await strategy.ReadAsync(reads.ToArrayOf(), cts.Token).ConfigureAwait(false),
                Throws.InstanceOf<OperationCanceledException>());
        }

        [Test]
        public async Task ReadEmptyInputReturnsEmpty()
        {
            using var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());

            ArrayOf<DataValue> values = await strategy.ReadAsync([]).ConfigureAwait(false);

            Assert.That(values.Count, Is.Zero);
        }

        [Test]
        public void DisposeIsIdempotent()
        {
            var strategy = new SubscriptionReadStrategy(AdapterTestHelpers.Telemetry());
            strategy.Dispose();

            Assert.That(strategy.Dispose, Throws.Nothing);
        }
    }
}