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using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Time.Testing;
using NUnit.Framework;
using Opc.Ua.PubSub.DataSets;
using Opc.Ua.PubSub.Encoding;
using Opc.Ua.PubSub.Groups;
using Opc.Ua.PubSub.MetaData;
using UadpDataSetMessageV2 = Opc.Ua.PubSub.Encoding.Uadp.UadpDataSetMessage;

namespace Opc.Ua.PubSub.Tests.Groups
{
    /// <summary>
    /// Validates the event-mode publisher: <see cref="EventDataSetWriter"/>
    /// drains pending events from the
    /// <see cref="EventPublishedDataSet"/> sampler, projects them via
    /// <see cref="SimpleAttributeOperand"/>s and emits one
    /// <see cref="PubSubDataSetMessage"/> per event with
    /// <see cref="PubSubDataSetMessageType.Event"/>.
    /// </summary>
    [TestFixture]
    [TestSpec("5.3.3", Summary = "EventDataSetWriter event-message build")]
    [TestSpec("6.2.4")]
    public class EventDataSetWriterTests
    {
        [Test]
        [TestSpec("5.3.3")]
        public async Task BuildEventMessagesAsync_EmitsOneMessagePerEventAsync()
        {
            var clock = new FakeTimeProvider();
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant("A1"), new Variant(1.0)]);
            sampler.Enqueue([new Variant("A2"), new Variant(2.0)]);
            EventDataSetWriter writer = BuildWriter(sampler, clock);

            ArrayOf<PubSubDataSetMessage> messages =
                await writer.BuildEventMessagesAsync().ConfigureAwait(false);

            Assert.That(messages, Has.Count.EqualTo(2));
            Assert.That(messages[0].MessageType,
                Is.EqualTo(PubSubDataSetMessageType.Event));
            Assert.That(((DataSetField[]?)messages[0].Fields) ?? [], Has.Length.EqualTo(2));
            Assert.That(messages[0].Fields[0].Value, Is.EqualTo(new Variant("A1")));
            Assert.That(messages[1].Fields[1].Value, Is.EqualTo(new Variant(2.0)));
            Assert.That(messages[0].SequenceNumber, Is.LessThan(messages[1].SequenceNumber));
        }

        [Test]
        [TestSpec("5.3.3")]
        public async Task BuildEventMessagesAsync_NoEvents_ReturnsEmptyAsync()
        {
            var sampler = new StubSampler();
            EventDataSetWriter writer = BuildWriter(sampler, new FakeTimeProvider());
            ArrayOf<PubSubDataSetMessage> messages =
                await writer.BuildEventMessagesAsync().ConfigureAwait(false);
            Assert.That(messages, Is.Empty);
        }

        [Test]
        [TestSpec("6.2.4")]
        public async Task BuildEventMessagesAsync_HonoursFieldContentMaskAsync()
        {
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant(1.0), new Variant(2.0)]);
            EventDataSetWriter writer = BuildWriter(
                sampler,
                new FakeTimeProvider(),
                contentMask: (uint)DataSetFieldContentMask.StatusCode);

            ArrayOf<PubSubDataSetMessage> messages =
                await writer.BuildEventMessagesAsync().ConfigureAwait(false);

            Assert.That(messages, Has.Count.EqualTo(1));
            var dsm = (UadpDataSetMessageV2)messages[0];
            Assert.That(dsm.FieldContentMask & DataSetFieldContentMask.StatusCode,
                Is.EqualTo(DataSetFieldContentMask.StatusCode));
        }

        [Test]
        [TestSpec("6.2.4")]
        public async Task EventPublishedDataSet_AlignsFieldsToMetaDataAsync()
        {
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant("event"), new Variant(99)]);
            EventPublishedDataSet pds = BuildPublishedDataSet(sampler);
            ArrayOf<ArrayOf<DataSetField>> rows =
                await pds.SampleEventsAsync().ConfigureAwait(false);

            Assert.That(((ArrayOf<DataSetField>[]?)rows) ?? [], Has.Length.EqualTo(1));
            Assert.That(rows[0][0].Name, Is.EqualTo("Message"));
            Assert.That(rows[0][1].Name, Is.EqualTo("Severity"));
            Assert.That(rows[0][0].Value, Is.EqualTo(new Variant("event")));
            Assert.That(rows[0][1].Value, Is.EqualTo(new Variant(99)));
        }

        [Test]
        [TestSpec("6.2.4")]
        public async Task EventPublishedDataSet_SamplesOneOccurrencePerSnapshotAsync()
        {
            //
            // An event dataset has no current state to sample, so the general
            // IPublishedDataSet contract drains one occurrence per call and
            // declares it as an event. Without the declaration a writer group
            // would treat the occurrence as a state snapshot and derive delta
            // frames by comparing it against an unrelated earlier occurrence.
            //
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant("first"), new Variant(1)]);
            sampler.Enqueue([new Variant("second"), new Variant(2)]);
            EventPublishedDataSet pds = BuildPublishedDataSet(sampler);

            PublishedDataSetSnapshot first = await pds.SampleAsync().ConfigureAwait(false);
            PublishedDataSetSnapshot second = await pds.SampleAsync().ConfigureAwait(false);
            PublishedDataSetSnapshot exhausted = await pds.SampleAsync().ConfigureAwait(false);

            Assert.Multiple(() =>
            {
                Assert.That(first.MessageType, Is.EqualTo(PubSubDataSetMessageType.Event));
                Assert.That(first.Fields[0].Value, Is.EqualTo(new Variant("first")));
                Assert.That(second.MessageType, Is.EqualTo(PubSubDataSetMessageType.Event));
                Assert.That(second.Fields[0].Value, Is.EqualTo(new Variant("second")));
                Assert.That(exhausted.MessageType, Is.Null);
                Assert.That(exhausted.Fields.Count, Is.Zero);
            });
        }

        [Test]
        public async Task EventPublishedDataSetExposesClassIdAndFixedMetadataAsync()
        {
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant("event"), new Variant(1)]);
            EventPublishedDataSet dataSet = BuildPublishedDataSet(sampler);
            var classId = new Uuid(Guid.NewGuid());
            dataSet.MetaData.DataSetClassId = classId;
            bool metadataChanged = false;
            EventHandler<DataSetMetaDataChangedEventArgs> handler =
                (_, _) => metadataChanged = true;

            dataSet.MetaDataChanged += handler;
            PublishedDataSetSnapshot snapshot =
                await dataSet.SampleAsync().ConfigureAwait(false);
            dataSet.MetaDataChanged -= handler;

            Assert.Multiple(() =>
            {
                Assert.That(
                    ((IPublishedDataSet)dataSet).DataSetClassId,
                    Is.EqualTo(classId));
                Assert.That(snapshot.MessageType, Is.EqualTo(PubSubDataSetMessageType.Event));
                Assert.That(metadataChanged, Is.False);
            });
        }

        [Test]
        public async Task EventDataSetWriterExposesContractAndBuildsJsonMessageAsync()
        {
            var sampler = new StubSampler();
            sampler.Enqueue([new Variant("event"), new Variant(1)]);
            EventPublishedDataSet dataSet = BuildPublishedDataSet(sampler);
            var configuration = new DataSetWriterDataType
            {
                Name = "json-event-writer",
                DataSetWriterId = 8
            };
            var writer = new EventDataSetWriter(
                configuration,
                dataSet,
                new FakeTimeProvider(),
                Profiles.PubSubMqttJsonTransport);

            ArrayOf<PubSubDataSetMessage> messages =
                await writer.BuildEventMessagesAsync().ConfigureAwait(false);

            Assert.Multiple(() =>
            {
                Assert.That(
                    ((IDataSetWriter)writer).PublishedDataSet,
                    Is.SameAs(dataSet));
                Assert.That(writer.KeyFrameCount, Is.Zero);
                Assert.That(writer.State.ComponentName, Is.EqualTo(configuration.Name));
                Assert.That(messages, Has.Count.EqualTo(1));
                Assert.That(
                    messages[0],
                    Is.TypeOf<Opc.Ua.PubSub.Encoding.Json.JsonDataSetMessage>());
            });
        }

        private static EventDataSetWriter BuildWriter(
            IEventSampler sampler,
            TimeProvider clock,
            uint contentMask = 0)
        {
            EventPublishedDataSet pds = BuildPublishedDataSet(sampler);
            var writerCfg = new DataSetWriterDataType
            {
                Name = "evt-writer",
                DataSetWriterId = 7,
                DataSetFieldContentMask = contentMask
            };
            return new EventDataSetWriter(writerCfg, pds, clock);
        }

        private static EventPublishedDataSet BuildPublishedDataSet(IEventSampler sampler)
        {
            var pubEvents = new PublishedEventsDataType
            {
                EventNotifier = new NodeId("notifier", 1),
                SelectedFields =
                [
                    new SimpleAttributeOperand { TypeDefinitionId = new NodeId("Base", 1) },
                    new SimpleAttributeOperand { TypeDefinitionId = new NodeId("Base", 1) }
                ]
            };
            var pdsCfg = new PublishedDataSetDataType
            {
                Name = "events-pds",
                DataSetMetaData = new DataSetMetaDataType
                {
                    Fields =
                    [
                        new FieldMetaData { Name = "Message" },
                        new FieldMetaData { Name = "Severity" }
                    ]
                },
                DataSetSource = new ExtensionObject(pubEvents)
            };
            return new EventPublishedDataSet(pdsCfg, sampler);
        }

        private sealed class StubSampler : IEventSampler
        {
            private readonly List<IReadOnlyList<Variant>> m_pending = [];
            public string Name => "stub";

            public void Enqueue(IReadOnlyList<Variant> row)
            {
                m_pending.Add(row);
            }

            public ValueTask<IReadOnlyList<IReadOnlyList<Variant>>> SampleEventsAsync(
                ArrayOf<SimpleAttributeOperand> selectedFields,
                ContentFilter? filter,
                CancellationToken cancellationToken = default)
            {
                IReadOnlyList<IReadOnlyList<Variant>> copy = [.. m_pending];
                m_pending.Clear();
                return new ValueTask<IReadOnlyList<IReadOnlyList<Variant>>>(copy);
            }
        }
    }
}