using System.Globalization;
using System.Text;

namespace StellaOps.Bench.ScannerAnalyzers.Reporting;

internal static class PrometheusWriter
{
    public static void Write(string path, IReadOnlyList<BenchmarkScenarioReport> reports)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(path);
        ArgumentNullException.ThrowIfNull(reports);

        var resolved = Path.GetFullPath(path);
        var directory = Path.GetDirectoryName(resolved);
        if (!string.IsNullOrEmpty(directory))
        {
            Directory.CreateDirectory(directory);
        }

        var builder = new StringBuilder();
        builder.AppendLine("# HELP scanner_analyzer_bench_duration_ms Analyzer benchmark duration metrics in milliseconds.");
        builder.AppendLine("# TYPE scanner_analyzer_bench_duration_ms gauge");

        foreach (var report in reports)
        {
            var scenarioLabel = Escape(report.Result.Id);
            AppendMetric(builder, "scanner_analyzer_bench_mean_ms", scenarioLabel, report.Result.MeanMs);
            AppendMetric(builder, "scanner_analyzer_bench_p95_ms", scenarioLabel, report.Result.P95Ms);
            AppendMetric(builder, "scanner_analyzer_bench_max_ms", scenarioLabel, report.Result.MaxMs);
            AppendMetric(builder, "scanner_analyzer_bench_threshold_ms", scenarioLabel, report.Result.ThresholdMs);

            if (report.Baseline is { } baseline)
            {
                AppendMetric(builder, "scanner_analyzer_bench_baseline_max_ms", scenarioLabel, baseline.MaxMs);
                AppendMetric(builder, "scanner_analyzer_bench_baseline_mean_ms", scenarioLabel, baseline.MeanMs);
            }

            if (report.MaxRegressionRatio is { } ratio)
            {
                AppendMetric(builder, "scanner_analyzer_bench_regression_ratio", scenarioLabel, ratio);
                AppendMetric(builder, "scanner_analyzer_bench_regression_limit", scenarioLabel, report.RegressionLimit);
                AppendMetric(builder, "scanner_analyzer_bench_regression_breached", scenarioLabel, report.RegressionBreached ? 1 : 0);
            }
        }

        File.WriteAllText(resolved, builder.ToString(), Encoding.UTF8);
    }

    private static void AppendMetric(StringBuilder builder, string metric, string scenarioLabel, double value)
    {
        builder.Append(metric);
        builder.Append("{scenario=\"");
        builder.Append(scenarioLabel);
        builder.Append("\"} ");
        builder.AppendLine(value.ToString("G17", CultureInfo.InvariantCulture));
    }

    private static string Escape(string value) => value.Replace("\\", "\\\\", StringComparison.Ordinal).Replace("\"", "\\\"", StringComparison.Ordinal);
}