using System.Globalization;
using System.Text;

namespace StellaOps.Bench.LinkNotMerge.Vex.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 linknotmerge_vex_bench_total_ms Link-Not-Merge VEX benchmark total duration (milliseconds).");
        builder.AppendLine("# TYPE linknotmerge_vex_bench_total_ms gauge");
        builder.AppendLine("# HELP linknotmerge_vex_bench_throughput_per_sec Link-Not-Merge VEX benchmark observation throughput (observations per second).");
        builder.AppendLine("# TYPE linknotmerge_vex_bench_throughput_per_sec gauge");
        builder.AppendLine("# HELP linknotmerge_vex_bench_event_throughput_per_sec Link-Not-Merge VEX benchmark event throughput (events per second).");
        builder.AppendLine("# TYPE linknotmerge_vex_bench_event_throughput_per_sec gauge");
        builder.AppendLine("# HELP linknotmerge_vex_bench_allocated_mb Link-Not-Merge VEX benchmark max allocations (megabytes).");
        builder.AppendLine("# TYPE linknotmerge_vex_bench_allocated_mb gauge");

        foreach (var report in reports)
        {
            var scenario = Escape(report.Result.Id);
            AppendMetric(builder, "linknotmerge_vex_bench_mean_total_ms", scenario, report.Result.TotalStatistics.MeanMs);
            AppendMetric(builder, "linknotmerge_vex_bench_p95_total_ms", scenario, report.Result.TotalStatistics.P95Ms);
            AppendMetric(builder, "linknotmerge_vex_bench_max_total_ms", scenario, report.Result.TotalStatistics.MaxMs);
            AppendMetric(builder, "linknotmerge_vex_bench_threshold_ms", scenario, report.Result.ThresholdMs);

            AppendMetric(builder, "linknotmerge_vex_bench_mean_observation_throughput_per_sec", scenario, report.Result.ObservationThroughputStatistics.MeanPerSecond);
            AppendMetric(builder, "linknotmerge_vex_bench_min_observation_throughput_per_sec", scenario, report.Result.ObservationThroughputStatistics.MinPerSecond);
            AppendMetric(builder, "linknotmerge_vex_bench_observation_throughput_floor_per_sec", scenario, report.Result.MinObservationThroughputPerSecond);

            AppendMetric(builder, "linknotmerge_vex_bench_mean_event_throughput_per_sec", scenario, report.Result.EventThroughputStatistics.MeanPerSecond);
            AppendMetric(builder, "linknotmerge_vex_bench_min_event_throughput_per_sec", scenario, report.Result.EventThroughputStatistics.MinPerSecond);
            AppendMetric(builder, "linknotmerge_vex_bench_event_throughput_floor_per_sec", scenario, report.Result.MinEventThroughputPerSecond);

            AppendMetric(builder, "linknotmerge_vex_bench_max_allocated_mb", scenario, report.Result.AllocationStatistics.MaxAllocatedMb);
            AppendMetric(builder, "linknotmerge_vex_bench_max_allocated_threshold_mb", scenario, report.Result.MaxAllocatedThresholdMb);

            if (report.Baseline is { } baseline)
            {
                AppendMetric(builder, "linknotmerge_vex_bench_baseline_max_total_ms", scenario, baseline.MaxTotalMs);
                AppendMetric(builder, "linknotmerge_vex_bench_baseline_min_observation_throughput_per_sec", scenario, baseline.MinObservationThroughputPerSecond);
                AppendMetric(builder, "linknotmerge_vex_bench_baseline_min_event_throughput_per_sec", scenario, baseline.MinEventThroughputPerSecond);
            }

            if (report.DurationRegressionRatio is { } durationRatio)
            {
                AppendMetric(builder, "linknotmerge_vex_bench_duration_regression_ratio", scenario, durationRatio);
            }

            if (report.ObservationThroughputRegressionRatio is { } obsRatio)
            {
                AppendMetric(builder, "linknotmerge_vex_bench_observation_regression_ratio", scenario, obsRatio);
            }

            if (report.EventThroughputRegressionRatio is { } evtRatio)
            {
                AppendMetric(builder, "linknotmerge_vex_bench_event_regression_ratio", scenario, evtRatio);
            }

            AppendMetric(builder, "linknotmerge_vex_bench_regression_limit", scenario, report.RegressionLimit);
            AppendMetric(builder, "linknotmerge_vex_bench_regression_breached", scenario, report.RegressionBreached ? 1 : 0);
        }

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

    private static void AppendMetric(StringBuilder builder, string metric, string scenario, double? value)
    {
        if (!value.HasValue)
        {
            return;
        }

        builder.Append(metric);
        builder.Append("{scenario=\"");
        builder.Append(scenario);
        builder.Append("\"} ");
        builder.AppendLine(value.Value.ToString("G17", CultureInfo.InvariantCulture));
    }

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