using StellaOps.Bench.ScannerAnalyzers.Baseline;

namespace StellaOps.Bench.ScannerAnalyzers.Reporting;

internal sealed class BenchmarkScenarioReport
{
    private const double RegressionLimitDefault = 1.2d;

    public BenchmarkScenarioReport(ScenarioResult result, BaselineEntry? baseline, double? regressionLimit = null)
    {
        Result = result ?? throw new ArgumentNullException(nameof(result));
        Baseline = baseline;
        RegressionLimit = regressionLimit is { } limit && limit > 0 ? limit : RegressionLimitDefault;
        MaxRegressionRatio = CalculateRatio(result.MaxMs, baseline?.MaxMs);
        MeanRegressionRatio = CalculateRatio(result.MeanMs, baseline?.MeanMs);
    }

    public ScenarioResult Result { get; }

    public BaselineEntry? Baseline { get; }

    public double RegressionLimit { get; }

    public double? MaxRegressionRatio { get; }

    public double? MeanRegressionRatio { get; }

    public bool RegressionBreached => MaxRegressionRatio.HasValue && MaxRegressionRatio.Value >= RegressionLimit;

    public string? BuildRegressionFailureMessage()
    {
        if (!RegressionBreached || MaxRegressionRatio is null)
        {
            return null;
        }

        var percentage = (MaxRegressionRatio.Value - 1d) * 100d;
        return $"{Result.Id} exceeded regression budget: max {Result.MaxMs:F2} ms vs baseline {Baseline!.MaxMs:F2} ms (+{percentage:F1}%)";
    }

    private static double? CalculateRatio(double current, double? baseline)
    {
        if (!baseline.HasValue)
        {
            return null;
        }

        if (baseline.Value <= 0d)
        {
            return null;
        }

        return current / baseline.Value;
    }
}