// -----------------------------------------------------------------------------
// LatencyComparisonLogic.cs
// Sprint: SPRINT_5100_0008_0001_competitor_parity
// Task: PARITY-5100-006 - Implement latency comparison
// Description: Logic for comparing scan latency between scanners
// -----------------------------------------------------------------------------

namespace StellaOps.Parity.Tests;

/// <summary>
/// Compares latency metrics between scanner runs.
/// </summary>
public sealed class LatencyComparisonLogic
{
    /// <summary>
    /// Compares latency from multiple scan runs.
    /// </summary>
    public LatencyComparisonResult Compare(
        IEnumerable<ScannerOutput> baselineRuns,
        IEnumerable<ScannerOutput> candidateRuns)
    {
        var baselineList = baselineRuns.Where(r => r.Success).ToList();
        var candidateList = candidateRuns.Where(r => r.Success).ToList();

        if (baselineList.Count == 0 || candidateList.Count == 0)
        {
            return new LatencyComparisonResult
            {
                BaselineTool = baselineList.FirstOrDefault()?.ToolName ?? "unknown",
                CandidateTool = candidateList.FirstOrDefault()?.ToolName ?? "unknown",
                Error = "Insufficient successful runs for comparison"
            };
        }

        var baselineMs = baselineList.Select(r => r.DurationMs).OrderBy(d => d).ToList();
        var candidateMs = candidateList.Select(r => r.DurationMs).OrderBy(d => d).ToList();

        return new LatencyComparisonResult
        {
            BaselineTool = baselineList[0].ToolName,
            CandidateTool = candidateList[0].ToolName,
            Success = true,

            // Baseline stats
            BaselineP50 = CalculatePercentile(baselineMs, 50),
            BaselineP95 = CalculatePercentile(baselineMs, 95),
            BaselineP99 = CalculatePercentile(baselineMs, 99),
            BaselineMin = baselineMs.Min(),
            BaselineMax = baselineMs.Max(),
            BaselineMean = baselineMs.Average(),
            BaselineStdDev = CalculateStdDev(baselineMs),
            BaselineSampleCount = baselineMs.Count,

            // Candidate stats
            CandidateP50 = CalculatePercentile(candidateMs, 50),
            CandidateP95 = CalculatePercentile(candidateMs, 95),
            CandidateP99 = CalculatePercentile(candidateMs, 99),
            CandidateMin = candidateMs.Min(),
            CandidateMax = candidateMs.Max(),
            CandidateMean = candidateMs.Average(),
            CandidateStdDev = CalculateStdDev(candidateMs),
            CandidateSampleCount = candidateMs.Count,

            // Comparison metrics
            P50Ratio = CalculatePercentile(candidateMs, 50) / Math.Max(1, CalculatePercentile(baselineMs, 50)),
            P95Ratio = CalculatePercentile(candidateMs, 95) / Math.Max(1, CalculatePercentile(baselineMs, 95)),
            MeanRatio = candidateMs.Average() / Math.Max(1, baselineMs.Average())
        };
    }

    /// <summary>
    /// Calculates time-to-first-signal (TTFS) if available in scan output.
    /// </summary>
    public TimeToFirstSignalResult CalculateTtfs(ScannerOutput output)
    {
        return new TimeToFirstSignalResult
        {
            ToolName = output.ToolName,
            TotalDurationMs = output.DurationMs,
            // TTFS would require streaming output parsing, which most tools don't support
            // For now, we approximate as total duration
            TtfsMs = output.DurationMs,
            TtfsAvailable = false
        };
    }

    private static double CalculatePercentile(List<long> sortedValues, int percentile)
    {
        if (sortedValues.Count == 0)
            return 0;

        var index = (percentile / 100.0) * (sortedValues.Count - 1);
        var lower = (int)Math.Floor(index);
        var upper = (int)Math.Ceiling(index);

        if (lower == upper)
            return sortedValues[lower];

        var fraction = index - lower;
        return sortedValues[lower] * (1 - fraction) + sortedValues[upper] * fraction;
    }

    private static double CalculateStdDev(List<long> values)
    {
        if (values.Count < 2)
            return 0;

        var mean = values.Average();
        var sumSquares = values.Sum(v => Math.Pow(v - mean, 2));
        return Math.Sqrt(sumSquares / (values.Count - 1));
    }
}

/// <summary>
/// Result of latency comparison between two scanners.
/// </summary>
public sealed class LatencyComparisonResult
{
    public required string BaselineTool { get; init; }
    public required string CandidateTool { get; init; }
    public bool Success { get; set; }
    public string? Error { get; set; }

    // Baseline latency stats (milliseconds)
    public double BaselineP50 { get; set; }
    public double BaselineP95 { get; set; }
    public double BaselineP99 { get; set; }
    public long BaselineMin { get; set; }
    public long BaselineMax { get; set; }
    public double BaselineMean { get; set; }
    public double BaselineStdDev { get; set; }
    public int BaselineSampleCount { get; set; }

    // Candidate latency stats (milliseconds)
    public double CandidateP50 { get; set; }
    public double CandidateP95 { get; set; }
    public double CandidateP99 { get; set; }
    public long CandidateMin { get; set; }
    public long CandidateMax { get; set; }
    public double CandidateMean { get; set; }
    public double CandidateStdDev { get; set; }
    public int CandidateSampleCount { get; set; }

    // Comparison ratios (candidate / baseline, <1 means candidate is faster)
    public double P50Ratio { get; set; }
    public double P95Ratio { get; set; }
    public double MeanRatio { get; set; }

    /// <summary>
    /// Returns true if candidate is faster at P95 (ratio &lt; 1).
    /// </summary>
    public bool CandidateIsFaster => P95Ratio < 1.0;

    /// <summary>
    /// Returns the percentage improvement (positive = candidate faster).
    /// </summary>
    public double ImprovementPercent => (1 - P95Ratio) * 100;
}

/// <summary>
/// Time-to-first-signal measurement result.
/// </summary>
public sealed class TimeToFirstSignalResult
{
    public required string ToolName { get; init; }
    public long TotalDurationMs { get; set; }
    public long TtfsMs { get; set; }
    public bool TtfsAvailable { get; set; }
}