using Microsoft.Extensions.Logging.Abstractions;
using Opc.Ua;
using Opc.Ua.Server;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using HistorianRead = ZB.MOM.WW.OtOpcUa.Core.Abstractions.HistoryReadResult;
using SdkHistoryReadResult = Opc.Ua.HistoryReadResult;

namespace ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests;

/// <summary>
///     Gitea #694 item 2 (live gate F4): a walked-back events read on the Gateway proves "nothing older" with one forward read
///     down to the Unix epoch (#691) — ~3.8 s live on <c>Runtime.dbo.Events</c>, and an unfiltered deep read hit the gateway's
///     30 s SQL timeout. The opt-in <c>ServerHistorian:EventReadHorizon</c> (<see cref="OtOpcUaNodeManager.EventReadHorizon"/>)
///     bounds every events read at <c>now − horizon</c>, in both directions; off (the default) nothing changes. The backend is
///     shaped like the Gateway's SQL event read: forward only, <c>[start, end]</c> inclusive, refuses <c>start &gt; end</c>
///     (counted), records every requested window.
/// </summary>
public sealed class NodeManagerHistoryReadEventsHorizonTests : IDisposable
{
    private static CancellationToken Ct => TestContext.Current.CancellationToken;
    private static readonly DateTime Now = new(2026, 10, 13, 12, 0, 0, DateTimeKind.Utc);
    private static readonly TimeSpan Horizon = TimeSpan.FromDays(30);
    private static readonly DateTime Floor = Now - Horizon;
    private readonly string _pkiRoot = Path.Combine(Path.GetTempPath(), $"otopcua-eventhorizon-{Guid.NewGuid():N}");

    /// <summary>Five recent events (the last five minutes) — a source with little history, as in the live gate.</summary>
    private static List<HistoricalEvent> Recent() =>
        Enumerable.Range(0, 5).Select(i => Ev($"r{i}", Now.AddMinutes(-5 + i))).ToList();

    [Fact]
    public async Task Without_a_horizon_a_walked_reverse_read_proves_the_rest_empty_down_to_the_epoch()
    {
        // The positive control: today's exact behaviour, and the cost the horizon removes.
        var (host, nm, node, gw) = await SetupAsync(Recent());
        try
        {
            var r = ReadEvents(nm, node, max: 10, start: DateTime.MinValue, end: Now);
            r.Error.StatusCode.Code.ShouldBe(StatusCodes.Good);
            r.Ids.ShouldBe(["r4", "r3", "r2", "r1", "r0"]);
            gw.Requests.Min(q => q.Start).ShouldBe(DateTime.UnixEpoch);
            gw.BadRequests.ShouldBe(0);
        }
        finally { await host.DisposeAsync(); }
    }

    [Fact]
    public async Task With_a_horizon_the_walk_never_reads_before_it_and_answers_the_same()
    {
        var (host, nm, node, gw) = await SetupAsync(Recent());
        try
        {
            nm.EventReadHorizon = Horizon;
            var r = ReadEvents(nm, node, max: 10, start: DateTime.MinValue, end: Now);
            r.Error.StatusCode.Code.ShouldBe(StatusCodes.Good);
            r.Ids.ShouldBe(["r4", "r3", "r2", "r1", "r0"]);
            r.Cp.ShouldBeNull();
            // Requests are rounded outward to the millisecond, so the earliest one may start up to 1 ms before the floor.
            gw.Requests.Min(q => q.Start).ShouldBeGreaterThanOrEqualTo(Floor.AddMilliseconds(-1));
            gw.BadRequests.ShouldBe(0);
        }
        finally { await host.DisposeAsync(); }
    }

    [Fact]
    public async Task Events_older_than_the_horizon_are_not_returned_in_either_direction()
    {
        var events = new List<HistoricalEvent> { Ev("old", Floor.AddDays(-10)), Ev("edge", Floor), Ev("new", Now.AddDays(-1)) };
        var (host, nm, node, gw) = await SetupAsync(events);
        try
        {
            nm.EventReadHorizon = Horizon;

            var reverse = ReadEvents(nm, node, max: 10, start: Now, end: DateTime.UnixEpoch);
            reverse.Ids.ShouldBe(["new", "edge"]); // the floor instant itself is inside

            var forward = ReadEvents(nm, node, max: 10, start: DateTime.UnixEpoch, end: Now);
            forward.Ids.ShouldBe(["edge", "new"]);

            gw.Requests.ShouldAllBe(q => q.Start >= Floor.AddMilliseconds(-1));

            nm.EventReadHorizon = TimeSpan.Zero; // off again: exact to the window
            ReadEvents(nm, node, max: 10, start: DateTime.UnixEpoch, end: Now).Ids.ShouldBe(["old", "edge", "new"]);
        }
        finally { await host.DisposeAsync(); }
    }

    [Fact]
    public async Task A_window_wholly_older_than_the_horizon_is_GoodNoData_and_never_sent()
    {
        var (host, nm, node, gw) = await SetupAsync([Ev("old", Floor.AddDays(-10))]);
        try
        {
            nm.EventReadHorizon = Horizon;
            var forward = ReadEvents(nm, node, max: 10, start: Floor.AddDays(-20), end: Floor.AddDays(-1));
            forward.Error.StatusCode.Code.ShouldBe(StatusCodes.Good);
            forward.Status.Code.ShouldBe(StatusCodes.GoodNoData);
            forward.Ids.ShouldBeEmpty();

            var reverse = ReadEvents(nm, node, max: 10, start: Floor.AddDays(-1), end: Floor.AddDays(-20));
            reverse.Status.Code.ShouldBe(StatusCodes.GoodNoData);

            gw.Requests.ShouldBeEmpty();
        }
        finally { await host.DisposeAsync(); }
    }

    [Fact]
    public async Task A_page_through_under_a_horizon_keeps_its_floor_across_continuation_points()
    {
        var events = Enumerable.Range(0, 25).Select(i => Ev($"e{i:00}", Now.AddMinutes(-i))).ToList();
        events.Add(Ev("old", Floor.AddDays(-1)));
        var (host, nm, node, gw) = await SetupAsync(events);
        try
        {
            nm.EventReadHorizon = Horizon;
            var all = new List<string>();
            byte[]? cp = null;
            var pages = 0;
            do
            {
                var r = ReadEvents(nm, node, max: 10, start: DateTime.MinValue, end: Now, inboundCp: cp);
                r.Error.StatusCode.Code.ShouldBe(StatusCodes.Good);
                all.AddRange(r.Ids);
                cp = r.Cp;
                (++pages).ShouldBeLessThan(10);
            }
            while (cp is not null);

            all.ShouldBe(Enumerable.Range(0, 25).Select(i => $"e{i:00}"));
            gw.Requests.ShouldAllBe(q => q.Start >= Floor.AddMilliseconds(-1));
        }
        finally { await host.DisposeAsync(); }
    }

    // ---- helpers ---------------------------------------------------------------------------------------------------------

    private static HistoricalEvent Ev(string id, DateTime at) => new(id, "src", at, at, "m", 500);

    private async Task<(OpcUaApplicationHost Host, OtOpcUaNodeManager Nm, NodeId Node, GatewayShapedEventSource Gw)> SetupAsync(
        List<HistoricalEvent> events)
    {
        var started = await OpcUaHostStart.StartAsync(
            port => new OpcUaApplicationHost(
                new OpcUaApplicationHostOptions
                {
                    ApplicationName = "OtOpcUa.EventHorizonTest",
                    ApplicationUri = $"urn:OtOpcUa.EventHorizonTest:{Guid.NewGuid():N}",
                    OpcUaPort = port,
                    PublicHostname = "localhost",
                    PkiStoreRoot = _pkiRoot,
                },
                NullLogger<OpcUaApplicationHost>.Instance),
            () => new OtOpcUaSdkServer(), Ct);
        var nm = started.Server.NodeManager!;
        nm.HistoryContinuationStore = new InMemoryHistoryContinuationStore();
        nm.Clock = new FixedClock(Now);
        var gw = new GatewayShapedEventSource(events);
        nm.HistorianDataSource = gw;
        nm.EnsureFolder("eq-evt", parentNodeId: null, displayName: "Equipment", realm: AddressSpaceRealm.Uns);
        nm.MaterialiseAlarmCondition("alarm-1", "eq-evt", "HighTemp", "OffNormalAlarm", severity: 700, realm: AddressSpaceRealm.Uns);
        return (started.Host, nm, nm.TryGetFolder("eq-evt")!.NodeId, gw);
    }

    private static (List<string> Ids, ServiceResult Error, StatusCode Status, byte[]? Cp) ReadEvents(
        OtOpcUaNodeManager nm, NodeId node, uint max, DateTime start, DateTime end, byte[]? inboundCp = null)
    {
        var context = new OperationContext(new RequestHeader(), secureChannelContext: null, RequestType.HistoryRead, identity: null);
        var filter = new EventFilter();
        filter.SelectClauses.Add(new SimpleAttributeOperand(ObjectTypeIds.BaseEventType, new QualifiedName("EventId"))
        {
            AttributeId = Attributes.Value,
        });
        var details = new ReadEventDetails { StartTime = start, EndTime = end, NumValuesPerNode = max, Filter = filter };
        var nodesToRead = new List<HistoryReadValueId> { new() { NodeId = node, ContinuationPoint = inboundCp } };
        var results = new List<SdkHistoryReadResult> { null! };
        var errors = new List<ServiceResult> { null! };
        nm.HistoryRead(context, details, TimestampsToReturn.Both, false, nodesToRead, results, errors);

        var ids = new List<string>();
        if (results[0]?.HistoryData is { } ho && !ExtensionObject.IsNull(ho))
            foreach (var e in ((HistoryEvent)ExtensionObject.ToEncodeable(ho)).Events)
                ids.Add(System.Text.Encoding.UTF8.GetString((byte[])e.EventFields[0].Value));
        return (ids, errors[0], results[0]?.StatusCode ?? StatusCodes.Good, results[0]?.ContinuationPoint);
    }

    /// <summary>The Gateway's SQL event read: forward only, <c>[start, end]</c> inclusive, time-ordered, capped + flag.</summary>
    private sealed class GatewayShapedEventSource(List<HistoricalEvent> events) : IHistorianDataSource
    {
        public List<(DateTime Start, DateTime End, int Max)> Requests { get; } = [];
        public int BadRequests { get; private set; }
        public bool SupportsReverseEvents => false;

        public Task<HistoricalEventsResult> ReadEventsAsync(string? n, DateTime s, DateTime e, int m, CancellationToken ct)
        {
            Requests.Add((s, e, m));
            if (s > e) BadRequests++; // the gateway's ValidateRange
            var window = events.Where(x => x.EventTimeUtc >= s && x.EventTimeUtc <= e).OrderBy(x => x.EventTimeUtc).ToList();
            var cap = m <= 0 ? int.MaxValue : m;
            return Task.FromResult(new HistoricalEventsResult(window.Take(cap).ToList(), window.Count > cap ? new byte[] { 1 } : null));
        }

        public Task<HistoricalEventsResult> ReadEventsAsync(string? n, DateTime s, DateTime e, int m, bool reverse, CancellationToken ct) =>
            reverse ? throw new NotSupportedException("forward only") : ReadEventsAsync(n, s, e, m, ct);

        public Task<HistorianRead> ReadRawAsync(string r, DateTime s, DateTime e, uint m, CancellationToken ct) =>
            NullHistorianDataSource.Instance.ReadRawAsync(r, s, e, m, ct);
        public Task<HistorianRead> ReadProcessedAsync(string r, DateTime s, DateTime e, TimeSpan i, HistoryAggregateType a, CancellationToken ct) =>
            NullHistorianDataSource.Instance.ReadProcessedAsync(r, s, e, i, a, ct);
        public Task<HistorianRead> ReadAtTimeAsync(string r, IReadOnlyList<DateTime> t, CancellationToken ct) =>
            NullHistorianDataSource.Instance.ReadAtTimeAsync(r, t, ct);
        public HistorianHealthSnapshot GetHealthSnapshot() => NullHistorianDataSource.Instance.GetHealthSnapshot();
        public void Dispose() { }
    }

    private sealed class FixedClock(DateTime now) : TimeProvider
    {
        public override DateTimeOffset GetUtcNow() => new(now);
    }

    public void Dispose()
    {
        if (Directory.Exists(_pkiRoot))
        {
            try { Directory.Delete(_pkiRoot, recursive: true); }
            catch { /* best-effort */ }
        }
    }
}