using Opc.Ua;
using Opc.Ua.Client;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using CoreHistoryReadResult = ZB.MOM.WW.OtOpcUa.Core.Abstractions.HistoryReadResult;
using static ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests.ServerEventRig;

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

/// <summary>
///     Gitea #669 over a real SDK client session: an event HistoryRead capped below the available events pages
///     through the PRODUCTION session-bound continuation store (<c>SessionHistoryContinuationStore</c>) — the
///     path the session-less unit tests cannot reach — and the union of pages is every event exactly once.
/// </summary>
public sealed class EventHistoryPagingOverTheWireTests
{
    private static readonly DateTime Epoch = new(2026, 10, 1, 0, 0, 0, DateTimeKind.Utc);

    [Fact]
    public async Task A_capped_event_read_pages_through_the_session_store_exactly_once()
    {
        var ct = TestContext.Current.CancellationToken;
        var rig = await StartAsync("EvtPagingWire", encrypted: false, ct);
        try
        {
            // Source installed BEFORE the alarm materialises so the folder is promoted with the HistoryRead bit.
            var events = Enumerable.Range(0, 25)
                .Select(i => new HistoricalEvent($"e{i:00}", "src", Epoch.AddSeconds(i / 2), Epoch, "m", 500))
                .ToList(); // pairs share a timestamp, so page boundaries cut through ties
            rig.Nm.HistorianDataSource = new SqlLikeEventSource(events);
            rig.MaterialiseNative();
            rig.Enforce(false, [Key()]);

            using var session = await rig.ConnectAsync(anonymous: true, ct);
            var node = new NodeId(RawDeviceFolder, (ushort)session.NamespaceUris.GetIndex(V3NodeIds.RawNamespaceUri));

            var collected = new List<string>();
            byte[]? cp = null;
            var pages = 0;
            do
            {
                var (ids, next) = await ReadPageAsync(session, node, cp, ct);
                collected.AddRange(ids);
                cp = next;
                (++pages).ShouldBeLessThan(30, "paging must terminate");
            }
            while (cp is not null);

            pages.ShouldBeGreaterThan(2, "25 events at a cap of 10 must page over the wire");
            collected.ShouldBe(events.Select(e => e.EventId));
        }
        finally { await rig.DisposeAsync(); }
    }

    [Fact]
    public async Task A_capped_REVERSE_event_read_pages_newest_first_through_the_session_store_exactly_once()
    {
        // Gitea #675: StartTime later than EndTime. Before the fix the cap kept the EARLIEST 10, ascending, with no
        // continuation point.
        var ct = TestContext.Current.CancellationToken;
        var rig = await StartAsync("EvtPagingWireRev", encrypted: false, ct);
        try
        {
            var events = Enumerable.Range(0, 25)
                .Select(i => new HistoricalEvent($"e{i:00}", "src", Epoch.AddSeconds(i / 2), Epoch, "m", 500))
                .ToList(); // pairs share a timestamp, so page boundaries cut through ties
            rig.Nm.HistorianDataSource = new SqlLikeEventSource(events);
            rig.MaterialiseNative();
            rig.Enforce(false, [Key()]);

            using var session = await rig.ConnectAsync(anonymous: true, ct);
            var node = new NodeId(RawDeviceFolder, (ushort)session.NamespaceUris.GetIndex(V3NodeIds.RawNamespaceUri));

            var collected = new List<string>();
            var sizes = new List<int>();
            byte[]? cp = null;
            do
            {
                var (ids, next) = await ReadPageAsync(session, node, cp, ct, reverse: true);
                collected.AddRange(ids);
                sizes.Add(ids.Count);
                cp = next;
                sizes.Count.ShouldBeLessThan(30, "paging must terminate");
            }
            while (cp is not null);

            sizes.ShouldBe([10, 10, 5]);
            // Newest-first: time descending, ties by EventId descending.
            collected.ShouldBe(events.OrderByDescending(e => e.EventTimeUtc)
                .ThenByDescending(e => e.EventId, StringComparer.Ordinal).Select(e => e.EventId));
        }
        finally { await rig.DisposeAsync(); }
    }

    private static async Task<(List<string> Ids, byte[]? Cp)> ReadPageAsync(
        ISession session, NodeId node, byte[]? cp, CancellationToken ct, bool reverse = false)
    {
        var filter = new EventFilter();
        filter.SelectClauses.Add(new SimpleAttributeOperand(ObjectTypeIds.BaseEventType, new QualifiedName("EventId"))
        {
            AttributeId = Attributes.Value,
        });
        var details = new ReadEventDetails
        {
            StartTime = reverse ? Epoch.AddDays(1) : Epoch.AddDays(-1),
            EndTime = reverse ? Epoch.AddDays(-1) : Epoch.AddDays(1),
            NumValuesPerNode = 10,
            Filter = filter,
        };
        var response = await session.HistoryReadAsync(
            null, new ExtensionObject(details), TimestampsToReturn.Both, false,
            new HistoryReadValueIdCollection { new HistoryReadValueId { NodeId = node, ContinuationPoint = cp } }, ct);
        var result = response.Results.ShouldHaveSingleItem();
        StatusCode.IsBad(result.StatusCode).ShouldBeFalse($"HistoryRead failed: {result.StatusCode}");
        var he = (HistoryEvent)ExtensionObject.ToEncodeable(result.HistoryData);
        var ids = he.Events.Select(e => System.Text.Encoding.UTF8.GetString((byte[])e.EventFields[0].Value)).ToList();
        return (ids, result.ContinuationPoint is { Length: > 0 } c ? c : null);
    }

    /// <summary>(time, id) order, [start, end), cap + truncation flag — the SQL backends' contract.</summary>
    private sealed class SqlLikeEventSource(List<HistoricalEvent> events) : IHistorianDataSource
    {
        private readonly List<HistoricalEvent> _all =
            events.OrderBy(e => e.EventTimeUtc).ThenBy(e => e.EventId, StringComparer.Ordinal).ToList();

        public async Task<HistoricalEventsResult> ReadEventsAsync(
            string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken ct)
        {
            await Task.Delay(1, ct).ConfigureAwait(false); // complete on a pool thread, like a real backend
            var window = _all.Where(e => e.EventTimeUtc >= startUtc && e.EventTimeUtc < endUtc).ToList();
            var cap = maxEvents <= 0 ? 1000 : maxEvents;
            return new HistoricalEventsResult(window.Take(cap).ToList(), window.Count > cap ? new byte[] { 1 } : null);
        }

        public bool SupportsReverseEvents => true;

        /// <summary>The #675 overload: reverse is <c>(lo, hi]</c> by (time, id) descending.</summary>
        public async Task<HistoricalEventsResult> ReadEventsAsync(
            string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, bool reverse, CancellationToken ct)
        {
            if (!reverse) return await ReadEventsAsync(sourceName, startUtc, endUtc, maxEvents, ct).ConfigureAwait(false);
            await Task.Delay(1, ct).ConfigureAwait(false);
            var (lo, hi) = startUtc <= endUtc ? (startUtc, endUtc) : (endUtc, startUtc);
            var window = _all.Where(e => e.EventTimeUtc > lo && e.EventTimeUtc <= hi).Reverse().ToList();
            var cap = maxEvents <= 0 ? 1000 : maxEvents;
            return new HistoricalEventsResult(window.Take(cap).ToList(), window.Count > cap ? new byte[] { 1 } : null);
        }

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