using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using MessagePack;
using Serilog.Core;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests.Ipc
{
    /// <summary>
    ///     Pins the sidecar's poison-event classifier and the per-event status mapping in
    ///     <see cref="HistorianFrameHandler"/>. A structurally-malformed alarm event is marked
    ///     Permanent (status 2) and excluded from the writer batch so the store-and-forward sink
    ///     dead-letters it immediately rather than looping to the retry cap; well-formed events
    ///     map to Ack (0) / Retry (1) from the writer's per-event bool result.
    /// </summary>
    [Trait("Category", "Unit")]
    public sealed class HistorianEventClassifierTests
    {
        /// <summary>Verifies a blank source name is classified structurally malformed.</summary>
        [Fact]
        public void IsStructurallyMalformed_BlankSourceName_IsTrue()
        {
            var e = WellFormed();
            e.SourceName = "   ";

            HistorianFrameHandler.IsStructurallyMalformed(e).ShouldBeTrue();
        }

        /// <summary>Verifies a blank alarm type is classified structurally malformed.</summary>
        [Fact]
        public void IsStructurallyMalformed_BlankAlarmType_IsTrue()
        {
            var e = WellFormed();
            e.AlarmType = "";

            HistorianFrameHandler.IsStructurallyMalformed(e).ShouldBeTrue();
        }

        /// <summary>Verifies a non-positive event timestamp is classified structurally malformed.</summary>
        /// <param name="ticks">The event timestamp in ticks to test.</param>
        [Theory]
        [InlineData(0L)]
        [InlineData(-1L)]
        public void IsStructurallyMalformed_NonPositiveTimestamp_IsTrue(long ticks)
        {
            var e = WellFormed();
            e.EventTimeUtcTicks = ticks;

            HistorianFrameHandler.IsStructurallyMalformed(e).ShouldBeTrue();
        }

        /// <summary>Verifies a well-formed event is not classified structurally malformed.</summary>
        [Fact]
        public void IsStructurallyMalformed_WellFormedEvent_IsFalse()
        {
            HistorianFrameHandler.IsStructurallyMalformed(WellFormed()).ShouldBeFalse();
        }

        /// <summary>
        ///     A mixed batch — one poison event then one well-formed event the writer acks — must
        ///     yield PerEventStatus = [2, 0]: the poison event is Permanent and excluded from the
        ///     writer batch, and only the well-formed event reaches the writer.
        /// </summary>
        [Fact]
        public async Task Handler_MixedBatch_MarksPoisonPermanent_AndOnlyWritesWellFormed()
        {
            var poison = WellFormed();
            poison.EventId = "poison";
            poison.SourceName = ""; // structurally malformed

            var good = WellFormed();
            good.EventId = "good";

            var fakeWriter = new RecordingAlarmEventWriter(_ => true);
            var handler = new HistorianFrameHandler(new StubHistorian(), Logger.None, fakeWriter);

            var req = new WriteAlarmEventsRequest { Events = new[] { poison, good }, CorrelationId = "c1" };
            var reply = await RoundTripAsync(handler, req);

            reply.Success.ShouldBeTrue();
            reply.PerEventStatus.ShouldBe(new byte[] { 2, 0 });
            reply.PerEventOk.ShouldBe(new[] { false, true });

            // The writer only ever saw the well-formed event.
            fakeWriter.Received.Count.ShouldBe(1);
            fakeWriter.Received[0].EventId.ShouldBe("good");
        }

        /// <summary>
        ///     A well-formed event the writer reports as not-persisted maps to Retry (status 1),
        ///     not Permanent — only structurally-malformed events are Permanent.
        /// </summary>
        [Fact]
        public async Task Handler_WriterReportsNotPersisted_MapsToRetry()
        {
            var good = WellFormed();
            good.EventId = "good";

            var fakeWriter = new RecordingAlarmEventWriter(_ => false);
            var handler = new HistorianFrameHandler(new StubHistorian(), Logger.None, fakeWriter);

            var req = new WriteAlarmEventsRequest { Events = new[] { good }, CorrelationId = "c2" };
            var reply = await RoundTripAsync(handler, req);

            reply.Success.ShouldBeTrue();
            reply.PerEventStatus.ShouldBe(new byte[] { 1 });
            reply.PerEventOk.ShouldBe(new[] { false });
        }

        /// <summary>
        ///     An all-poison batch must short-circuit the writer entirely (no WriteAsync call)
        ///     and mark every slot Permanent.
        /// </summary>
        [Fact]
        public async Task Handler_AllPoison_SkipsWriter_AllPermanent()
        {
            var p1 = WellFormed();
            p1.SourceName = "";
            var p2 = WellFormed();
            p2.AlarmType = "";

            var fakeWriter = new RecordingAlarmEventWriter(_ => true);
            var handler = new HistorianFrameHandler(new StubHistorian(), Logger.None, fakeWriter);

            var req = new WriteAlarmEventsRequest { Events = new[] { p1, p2 }, CorrelationId = "c3" };
            var reply = await RoundTripAsync(handler, req);

            reply.Success.ShouldBeTrue();
            reply.PerEventStatus.ShouldBe(new byte[] { 2, 2 });
            fakeWriter.Received.Count.ShouldBe(0);
        }

        private static AlarmHistorianEventDto WellFormed() => new()
        {
            EventId = "ev",
            SourceName = "Tank.HiHi",
            ConditionId = "HiHi",
            AlarmType = "LimitAlarm:Activated",
            Message = "msg",
            Severity = 700,
            EventTimeUtcTicks = new DateTime(2026, 6, 18, 12, 0, 0, DateTimeKind.Utc).Ticks,
            AckComment = null,
        };

        /// <summary>
        ///     Drives a WriteAlarmEvents request through the real frame handler over an in-memory
        ///     duplex stream pair and deserializes the reply the handler writes back.
        /// </summary>
        private static async Task<WriteAlarmEventsReply> RoundTripAsync(
            HistorianFrameHandler handler, WriteAlarmEventsRequest req)
        {
            var capture = new MemoryStream();
            using var writer = new FrameWriter(capture, leaveOpen: true);

            var body = MessagePackSerializer.Serialize(req);
            await handler.HandleAsync(MessageKind.WriteAlarmEventsRequest, body, writer, CancellationToken.None);

            capture.Position = 0;
            using var reader = new FrameReader(capture, leaveOpen: true);
            var frame = await reader.ReadFrameAsync(CancellationToken.None);
            frame.ShouldNotBeNull();
            frame!.Value.Kind.ShouldBe(MessageKind.WriteAlarmEventsReply);
            return MessagePackSerializer.Deserialize<WriteAlarmEventsReply>(frame.Value.Body);
        }

        /// <summary>An <see cref="IAlarmEventWriter"/> that records the batch it received and returns a fixed verdict.</summary>
        private sealed class RecordingAlarmEventWriter : IAlarmEventWriter
        {
            private readonly Func<AlarmHistorianEventDto, bool> _verdict;

            /// <summary>Initializes a new instance with the given per-event verdict.</summary>
            /// <param name="verdict">Maps each received event to its persisted/not-persisted result.</param>
            public RecordingAlarmEventWriter(Func<AlarmHistorianEventDto, bool> verdict) => _verdict = verdict;

            /// <summary>The events the writer was handed, in order.</summary>
            public List<AlarmHistorianEventDto> Received { get; } = new();

            /// <inheritdoc/>
            public Task<bool[]> WriteAsync(AlarmHistorianEventDto[] events, CancellationToken cancellationToken)
            {
                Received.AddRange(events);
                return Task.FromResult(events.Select(_verdict).ToArray());
            }
        }

        /// <summary>
        ///     A read data source the WriteAlarmEvents path never touches — present only to
        ///     satisfy the <see cref="HistorianFrameHandler"/> ctor's non-null requirement.
        /// </summary>
        private sealed class StubHistorian : IHistorianDataSource
        {
            /// <inheritdoc/>
            public Task<List<HistorianSample>> ReadRawAsync(
                string tagName, DateTime startTime, DateTime endTime, int maxValues, CancellationToken ct = default)
                => throw new NotSupportedException();

            /// <inheritdoc/>
            public Task<List<HistorianAggregateSample>> ReadAggregateAsync(
                string tagName, DateTime startTime, DateTime endTime, double intervalMs, string aggregateColumn, CancellationToken ct = default)
                => throw new NotSupportedException();

            /// <inheritdoc/>
            public Task<List<HistorianSample>> ReadAtTimeAsync(
                string tagName, DateTime[] timestamps, CancellationToken ct = default)
                => throw new NotSupportedException();

            /// <inheritdoc/>
            public Task<List<global::ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend.HistorianEventDto>> ReadEventsAsync(
                string? sourceName, DateTime startTime, DateTime endTime, int maxEvents, CancellationToken ct = default)
                => throw new NotSupportedException();

            /// <inheritdoc/>
            public HistorianHealthSnapshot GetHealthSnapshot() => throw new NotSupportedException();

            /// <inheritdoc/>
            public void Dispose() { }
        }
    }
}