using System.Globalization;
using Azaion.Missions.E2E.Fixtures;
using Azaion.Missions.E2E.Helpers;
using Xunit;

namespace Azaion.Missions.E2E.Tests.ResourceLimits;

/// <summary>
/// NFT-RES-LIM-01..03 — three observations on a SINGLE 5-minute sustained
/// load window. The window itself lives in
/// <see cref="SteadyStateLoadFixture"/> (class-scoped, runs once); each
/// test asserts one metric against its provisional gate.
/// </summary>
/// <remarks>
/// The fixture skips itself when docker primitives are unavailable; the
/// tests detect that via <see cref="SteadyStateLoadFixture.SkipReason"/>
/// and surface the same reason through <c>Skip.IfNot</c>. The fixture
/// also flips <see cref="SteadyStateLoadFixture.SutExitedDuringWindow"/>
/// if the SUT crashes mid-window — every test fails fast with a clear
/// message rather than reporting a misleading metric.
/// </remarks>
[Collection("ResLimSteadyState")]
[Trait("Category", "ResLim")]
public sealed class SteadyStateLoadTests : TestBase, IClassFixture<SteadyStateLoadFixture>
{
    private static readonly MetricCsvRecorder Csv = new("RESLIM_RESULTS_FILE");
    private const long ProvisionalRssCapMiB = 250;
    private const int ProvisionalConnectionCap = 100;
    private const int ProvisionalFdCap = 1024;

    private readonly SteadyStateLoadFixture _load;

    public SteadyStateLoadTests(SteadyStateLoadFixture load) => _load = load;

    [SkippableFact]
    [Trait("Traces", "H1|H6|O10")]
    [Trait("max_ms", "360000")]
    public void NFT_RES_LIM_01_steady_state_rss_within_provisional_gate_and_no_leak()
    {
        Skip.If(_load.SkipReason is not null, _load.SkipReason);
        Skip.IfNot(_load.LoadGeneratorMetTargetRps,
            "runner cannot sustain target load (NFR Reliability — not a SUT defect)");
        Assert.False(_load.SutExitedDuringWindow, "SUT exited during measurement window");

        // Arrange
        var samplesMiB = _load.RssBytesSamples.Select(b => b / (double)(1024 * 1024)).ToList();
        Assert.True(samplesMiB.Count >= 30,
            $"expected ≥ 30 RSS samples over 5-min window, got {samplesMiB.Count}");

        // Act
        var p95 = LatencyPercentiles.P95(samplesMiB);
        var finalMiB = samplesMiB[^1];

        var leakRatio = Math.Abs(finalMiB - p95) / Math.Max(p95, 1.0);
        var withinCap = p95 <= ProvisionalRssCapMiB;
        var noLeak = leakRatio <= 0.20;
        var pass = withinCap && noLeak;

        Csv.Record(
            category: "ResLim",
            scenario: "NFT-RES-LIM-01",
            result: pass ? "pass" : "fail",
            traces: $"H1|H6|O10; "
                  + $"P95_RSS_MiB={p95.ToString("F1", CultureInfo.InvariantCulture)}; "
                  + $"FINAL_RSS_MiB={finalMiB.ToString("F1", CultureInfo.InvariantCulture)}; "
                  + $"LEAK_RATIO={leakRatio.ToString("F2", CultureInfo.InvariantCulture)}");

        // Assert — provisional gate; lock at measured + 50% after first green run.
        Assert.True(withinCap,
            $"P95 RSS {p95:F1} MiB exceeds provisional {ProvisionalRssCapMiB} MiB gate");
        Assert.True(noLeak,
            $"final RSS {finalMiB:F1} MiB diverges {leakRatio:P0} from P95 {p95:F1} MiB (gate 20%)");
    }

    [SkippableFact]
    [Trait("Traces", "O10")]
    [Trait("max_ms", "360000")]
    public void NFT_RES_LIM_02_npgsql_connection_pool_within_100_no_unbounded_growth()
    {
        Skip.If(_load.SkipReason is not null, _load.SkipReason);
        Skip.IfNot(_load.LoadGeneratorMetTargetRps,
            "runner cannot sustain target load (NFR Reliability — not a SUT defect)");
        Assert.False(_load.SutExitedDuringWindow, "SUT exited during measurement window");

        var samples = _load.NpgsqlConnectionSamples;
        Assert.True(samples.Count >= 30,
            $"expected ≥ 30 connection samples over 5-min window, got {samples.Count}");

        // Act
        var max = samples.Max();
        var firstMinuteSampleCount = 60 / SteadyStateLoadFixture.SampleIntervalSeconds;
        var firstMinute = samples.Take(firstMinuteSampleCount).ToList();
        var firstMinuteMean = firstMinute.Average();
        var finalCount = samples[^1];

        var withinCap = max <= ProvisionalConnectionCap;
        var noUnboundedGrowth = finalCount <= 1.3 * Math.Max(firstMinuteMean, 1.0);
        var pass = withinCap && noUnboundedGrowth;

        Csv.Record(
            category: "ResLim",
            scenario: "NFT-RES-LIM-02",
            result: pass ? "pass" : "fail",
            traces: $"O10; MAX_NPGSQL_CONNS={max}; "
                  + $"FINAL_CONNS={finalCount}; "
                  + $"MINUTE1_MEAN={firstMinuteMean.ToString("F1", CultureInfo.InvariantCulture)}");

        // Assert
        Assert.True(withinCap,
            $"max Npgsql connections {max} exceeds provisional cap {ProvisionalConnectionCap}");
        Assert.True(noUnboundedGrowth,
            $"final connection count {finalCount} > 1.3 × first-minute mean {firstMinuteMean:F1}");
    }

    [SkippableFact]
    [Trait("Traces", "H6|O10")]
    [Trait("max_ms", "360000")]
    public void NFT_RES_LIM_03_file_descriptors_within_1024_no_leak()
    {
        Skip.If(_load.SkipReason is not null, _load.SkipReason);
        Skip.IfNot(_load.LoadGeneratorMetTargetRps,
            "runner cannot sustain target load (NFR Reliability — not a SUT defect)");
        Assert.False(_load.SutExitedDuringWindow, "SUT exited during measurement window");

        var samples = _load.FileDescriptorSamples;
        Assert.True(samples.Count >= 30,
            $"expected ≥ 30 FD samples over 5-min window, got {samples.Count}");

        // Act
        var max = samples.Max();
        var minuteOneSampleCount = 60 / SteadyStateLoadFixture.SampleIntervalSeconds;
        // The spec calls out "count at t=1min" — anchor on the sample whose
        // timestamp is closest to (start + 60s).
        var minuteOneIx = Math.Min(minuteOneSampleCount - 1, samples.Count - 1);
        var minuteOneCount = samples[minuteOneIx];
        var finalCount = samples[^1];

        var withinCap = max <= ProvisionalFdCap;
        var noLeak = finalCount <= 1.3 * Math.Max(minuteOneCount, 1);
        var pass = withinCap && noLeak;

        Csv.Record(
            category: "ResLim",
            scenario: "NFT-RES-LIM-03",
            result: pass ? "pass" : "fail",
            traces: $"H6|O10; MAX_FD={max}; "
                  + $"FINAL_FD={finalCount}; MINUTE1_FD={minuteOneCount}");

        // Assert
        Assert.True(withinCap,
            $"max FD count {max} exceeds provisional cap {ProvisionalFdCap}");
        Assert.True(noLeak,
            $"final FD count {finalCount} > 1.3 × minute-1 count {minuteOneCount}");
    }

}