maraphon-app/tests/Marathon.Domain.Tests/AnomalyDetection/SteamMoveDetectorTests.cs

using FluentAssertions;
using Marathon.Domain.AnomalyDetection;
using Marathon.Domain.Entities;
using Marathon.Domain.Enums;
using Marathon.Domain.ValueObjects;

namespace Marathon.Domain.Tests.AnomalyDetection;

public sealed class SteamMoveDetectorTests
{
    private static readonly TimeSpan MoscowOffset = TimeSpan.FromHours(3);
    private static readonly DateTimeOffset BaseTime = new(2026, 5, 10, 18, 0, 0, MoscowOffset);
    private static readonly EventId Event = new("26000001");

    // window 120s, drift threshold 0.20, min 3 snapshots, continuity break at 60s.
    private static SteamMoveDetector CreateSut() => new(120, 0.20m, 3, 60);

    private static OddsSnapshot Live(int seconds, decimal r1, decimal r2) =>
        new(Event, BaseTime.AddSeconds(seconds), OddsSource.Live,
            new List<Bet>
            {
                new(MatchScope.Instance, BetType.Win, Side.Side1, null, new OddsRate(r1)),
                new(MatchScope.Instance, BetType.Win, Side.Side2, null, new OddsRate(r2)),
            });

    [Fact]
    public void Should_FlagSteamMove_When_OneSideShortensContinuously()
    {
        // Side2 shortens (3.0 → 1.6) over 90s in continuous 30s steps: its normalised
        // implied probability rises ~0.33 → ~0.61, a ~0.28 drift > 0.20 threshold.
        var snapshots = new[]
        {
            Live(0,  1.5m, 3.0m),
            Live(30, 1.7m, 2.3m),
            Live(60, 2.1m, 1.9m),
            Live(90, 2.5m, 1.6m),
        };

        var result = CreateSut().Detect(Event, snapshots);

        result.Should().NotBeEmpty();
        result.Should().OnlyContain(a => a.Kind == AnomalyKind.SteamMove);
        result.Max(a => a.Score).Should().BeGreaterThanOrEqualTo(0.20m);
    }

    [Fact]
    public void Should_NotFlag_When_DriftBelowThreshold()
    {
        // Gentle drift: Side2 0.333 → ~0.38, well under the 0.20 threshold.
        var snapshots = new[]
        {
            Live(0,  1.5m, 3.0m),
            Live(30, 1.55m, 2.85m),
            Live(60, 1.6m, 2.7m),
        };

        CreateSut().Detect(Event, snapshots).Should().BeEmpty();
    }

    [Fact]
    public void Should_NotFlag_When_DriftSpansSuspensionGap()
    {
        // The big move happens across a 90s gap (> 60s continuity break) — that is the
        // SuspensionFlip detector's territory, so steam must not double-flag it.
        var snapshots = new[]
        {
            Live(0,   1.3m, 4.0m),
            Live(30,  1.3m, 4.0m),
            Live(120, 4.0m, 1.3m), // 90s gap
            Live(150, 4.0m, 1.3m),
        };

        CreateSut().Detect(Event, snapshots).Should().BeEmpty();
    }

    [Fact]
    public void Should_ReturnEmpty_When_FewerThanMinSnapshots()
    {
        var snapshots = new[] { Live(0, 1.5m, 3.0m), Live(30, 2.5m, 1.6m) };

        CreateSut().Detect(Event, snapshots).Should().BeEmpty();
    }

    [Fact]
    public void Should_IgnorePreMatchSnapshots()
    {
        var snapshots = new[]
        {
            new OddsSnapshot(Event, BaseTime, OddsSource.PreMatch,
                new List<Bet> { new(MatchScope.Instance, BetType.Win, Side.Side1, null, new OddsRate(1.5m)),
                                new(MatchScope.Instance, BetType.Win, Side.Side2, null, new OddsRate(3.0m)) }),
            new OddsSnapshot(Event, BaseTime.AddSeconds(30), OddsSource.PreMatch,
                new List<Bet> { new(MatchScope.Instance, BetType.Win, Side.Side1, null, new OddsRate(2.5m)),
                                new(MatchScope.Instance, BetType.Win, Side.Side2, null, new OddsRate(1.6m)) }),
            new OddsSnapshot(Event, BaseTime.AddSeconds(60), OddsSource.PreMatch,
                new List<Bet> { new(MatchScope.Instance, BetType.Win, Side.Side1, null, new OddsRate(2.6m)),
                                new(MatchScope.Instance, BetType.Win, Side.Side2, null, new OddsRate(1.55m)) }),
        };

        CreateSut().Detect(Event, snapshots).Should().BeEmpty();
    }

    [Fact]
    public void Should_EmitParseableEvidence_For_DetectedSteamMove()
    {
        var snapshots = new[]
        {
            Live(0,  1.5m, 3.0m),
            Live(30, 1.9m, 2.0m),
            Live(60, 2.5m, 1.6m),
        };

        var anomaly = CreateSut().Detect(Event, snapshots).First();

        AnomalyEvidenceParser.TryParse(anomaly.EvidenceJson, out var data).Should().BeTrue();
        data.PreSuspension.Should().NotBeNull();
        data.PostSuspension.Should().NotBeNull();
        // Post favourite is the steamed (shortened) side — drives the outcome evaluator.
        data.PostSuspension.Favourite.Should().Be(Side.Side2);
    }

    [Theory]
    [InlineData(0)]
    [InlineData(-30)]
    public void Should_Throw_When_ConstructedWithInvalidWindow(int windowSeconds)
    {
        var act = () => new SteamMoveDetector(windowSeconds, 0.20m, 3, 60);
        act.Should().Throw<ArgumentOutOfRangeException>();
    }
}