using Google.Protobuf.WellKnownTypes;
using Microsoft.Extensions.Logging.Abstractions;
using Shouldly;
using Xunit;
using ZB.MOM.WW.HistorianGateway.Contracts.Grpc;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.OpcUaServer;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests;

/// <summary>
///     Gitea #691.4 review: events read uncapped (and walked back newest-first) through the REAL
///     <see cref="GatewayHistorianDataSource"/> over a gateway-shaped fake — inclusive <c>[start, end]</c>, ordered by event time.
/// </summary>
public sealed class GatewayReverseEventsTests
{
    private static CancellationToken Ct => TestContext.Current.CancellationToken;

    private static readonly DateTime T0 = new(2026, 10, 12, 18, 0, 0, DateTimeKind.Utc);

    private static FakeHistorianGatewayClient Store(int count)
    {
        var stored = Enumerable.Range(0, count)
            .Select(i => new HistorianEvent { Id = $"e{i:0000}", Type = "Alarm", EventTime = Timestamp.FromDateTime(T0.AddSeconds(i)) })
            .ToList();
        return new FakeHistorianGatewayClient
        {
            EventsSource = (start, end) => stored.Where(e => e.EventTime.ToDateTime() >= start && e.EventTime.ToDateTime() <= end),
        };
    }

    /// <summary>
    ///     <c>NumValuesPerNode = 0</c> reaches the source as <c>int.MaxValue</c>; the result list used to be pre-sized to it
    ///     ("Array dimensions exceeded") — every uncapped Gateway events read failed and counted as a backend failure.
    /// </summary>
    [Fact]
    public async Task An_uncapped_forward_events_read_is_served()
    {
        var fake = Store(30);
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);

        var r = await ds.ReadEventsAsync(null, T0, T0.AddMinutes(1), int.MaxValue, Ct);

        r.Events.Count.ShouldBe(30);
        r.ContinuationPoint.ShouldBeNull();
        ds.GetHealthSnapshot().TotalFailures.ShouldBe(0);
    }

    [Fact]
    public async Task An_uncapped_reverse_events_read_is_one_forward_read_newest_first()
    {
        var fake = Store(30);
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);

        var page = await ReverseEventsReader.ReadAsync(ds, null, hi: T0.AddSeconds(25), lo: T0.AddSeconds(5), want: 0,
            maxTieCluster: 65536, nowUtc: T0.AddHours(1), hint: default, Ct);

        page.Events.Select(e => e.EventId).ShouldBe(Enumerable.Range(6, 20).Reverse().Select(i => $"e{i:0000}"));
        fake.ReadEventsCallCount.ShouldBe(1);
        ds.GetHealthSnapshot().TotalFailures.ShouldBe(0);
    }

    [Fact]
    public async Task A_capped_reverse_events_read_walked_back_over_the_gateway_returns_the_latest_newest_first()
    {
        var fake = Store(300);
        var ds = new GatewayHistorianDataSource(fake, NullLogger<GatewayHistorianDataSource>.Instance);

        var page = await ReverseEventsReader.ReadAsync(ds, null, hi: T0.AddSeconds(200), lo: T0.AddSeconds(50), want: 10,
            maxTieCluster: 65536, nowUtc: T0.AddHours(1), hint: default, Ct);

        page.Events.Select(e => e.EventId).ShouldBe(Enumerable.Range(191, 10).Reverse().Select(i => $"e{i:0000}"));
        fake.LastReadEventsStartUtc.ShouldBeLessThanOrEqualTo(fake.LastReadEventsEndUtc);
        ds.GetHealthSnapshot().TotalFailures.ShouldBe(0);
    }
}