lmxopcua/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/RawPageLimitTests.cs

using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

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

/// <summary>
///     Gitea #694: <see cref="RawPageLimit"/> — the page plan (P = min(want, L − k − 1), request = P + k + 1 ≤ L) and the one
///     re-plan after a refusal. The end-to-end behaviour over the real Gateway data source is pinned in
///     <c>GatewayCeilingPagingTests</c>.
/// </summary>
public sealed class RawPageLimitTests
{
    [Theory]
    // want, k, L ⇒ page, request, noRoom
    [InlineData(5000u, 0, 0, 5000u, 5001u, false)]   // no limit: #692 unchanged (page + ties + lookahead)
    [InlineData(5000u, 3, 0, 5000u, 5004u, false)]
    [InlineData(0u, 3, 0, 0u, 0u, false)]            // no limit, uncapped: one uncapped read
    [InlineData(5000u, 0, 984, 983u, 984u, false)]   // over the limit: the request fills the limit exactly
    [InlineData(5000u, 10, 984, 973u, 984u, false)]  // boundary ties take room from the page
    [InlineData(10u, 10, 984, 10u, 21u, false)]      // under the limit: unchanged
    [InlineData(0u, 0, 984, 983u, 984u, false)]      // uncapped: a limit-sized page
    [InlineData(0u, 982, 984, 1u, 984u, false)]
    [InlineData(5000u, 983, 984, 0u, 0u, true)]      // the ties alone fill a read: never a 0 (uncapped) request
    [InlineData(5000u, 5000, 984, 0u, 0u, true)]     // never an underflow
    [InlineData(5000u, 0, 1, 0u, 0u, true)]
    public void Plan_fits_page_ties_and_lookahead_into_the_limit(uint want, int k, int limit, uint page, uint request, bool noRoom)
    {
        var plan = RawPageLimit.Plan(want, k, limit);
        plan.PageCap.ShouldBe(page);
        plan.RequestCap.ShouldBe(request);
        plan.NoRoom.ShouldBe(noRoom);
        if (limit > 0 && !noRoom) plan.RequestCap.ShouldBeLessThanOrEqualTo((uint)limit);
    }

    [Fact]
    public async Task A_read_that_teaches_the_limit_is_re_planned_once_at_it()
    {
        var source = new LimitSource();
        var asked = new List<uint>();
        var (page, plan) = await RawPageLimit.ReadAsync(source, 5000u, 0, p =>
        {
            asked.Add(p.RequestCap);
            if (p.RequestCap > 984) { source.Limit = 984; throw new HistoryReadLimitExceededException(1000, "ceiling"); }
            return Task.FromResult("ok");
        });
        page.ShouldBe("ok");
        plan.PageCap.ShouldBe(983u);
        asked.ShouldBe([5001u, 984u]);
    }

    [Fact]
    public async Task A_crowded_refusal_shrinks_the_page_by_the_pre_window_rows()
    {
        var source = new LimitSource { Limit = 984 };
        var asked = new List<uint>();
        var (_, plan) = await RawPageLimit.ReadAsync(source, 0u, 2, p =>
        {
            asked.Add(p.RequestCap);
            if (asked.Count == 1) throw new HistoryReadLimitExceededException(1000, "crowded") { PreWindowRows = 21 };
            return Task.FromResult("ok");
        });
        asked.ShouldBe([984u, 963u]);
        plan.PageCap.ShouldBe(960u);
    }

    [Fact]
    public async Task A_refusal_at_an_unchanged_limit_without_crowding_is_the_answer()
    {
        var source = new LimitSource { Limit = 984 };
        var calls = 0;
        await Should.ThrowAsync<HistoryReadLimitExceededException>(() => RawPageLimit.ReadAsync<string>(source, 5000u, 0, _ =>
        {
            calls++;
            throw new HistoryReadLimitExceededException(1000, "tie cluster");
        }));
        calls.ShouldBe(1);
    }

    [Fact]
    public async Task A_second_refusal_is_not_retried_again()
    {
        var source = new LimitSource();
        var calls = 0;
        await Should.ThrowAsync<HistoryReadLimitExceededException>(() => RawPageLimit.ReadAsync<string>(source, 0u, 0, _ =>
        {
            calls++;
            source.Limit = 984 - calls; // even if the limit keeps moving
            throw new HistoryReadLimitExceededException(1000, "refused") { PreWindowRows = 5 };
        }));
        calls.ShouldBe(2);
    }

    [Fact]
    public async Task No_room_is_returned_without_a_read()
    {
        var source = new LimitSource { Limit = 10 };
        var calls = 0;
        var (page, plan) = await RawPageLimit.ReadAsync(source, 5u, 9, _ => { calls++; return Task.FromResult("x"); });
        plan.NoRoom.ShouldBeTrue();
        page.ShouldBeNull();
        calls.ShouldBe(0);
    }

    [Fact]
    public async Task Other_failures_are_not_retried()
    {
        var source = new LimitSource();
        var calls = 0;
        await Should.ThrowAsync<InvalidOperationException>(() => RawPageLimit.ReadAsync<string>(source, 5000u, 0, _ =>
        {
            calls++;
            source.Limit = 984;
            throw new InvalidOperationException("backend fault");
        }));
        calls.ShouldBe(1);
    }

    /// <summary>Only <see cref="IHistorianDataSource.MaxRawValuesPerRead"/> matters here.</summary>
    private sealed class LimitSource : IHistorianDataSource
    {
        public int Limit;

        public int MaxRawValuesPerRead => Limit;

        public Task<HistoryReadResult> ReadRawAsync(string fullReference, DateTime startUtc, DateTime endUtc, uint maxValuesPerNode,
            CancellationToken cancellationToken) => throw new NotSupportedException();

        public Task<HistoryReadResult> ReadProcessedAsync(string fullReference, DateTime startUtc, DateTime endUtc, TimeSpan interval,
            HistoryAggregateType aggregate, CancellationToken cancellationToken) => throw new NotSupportedException();

        public Task<HistoryReadResult> ReadAtTimeAsync(string fullReference, IReadOnlyList<DateTime> timestampsUtc,
            CancellationToken cancellationToken) => throw new NotSupportedException();

        public Task<HistoricalEventsResult> ReadEventsAsync(string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents,
            CancellationToken cancellationToken) => throw new NotSupportedException();

        public HistorianHealthSnapshot GetHealthSnapshot() => NullHistorianDataSource.Instance.GetHealthSnapshot();

        public void Dispose() { }
    }
}