using System;
using System.Diagnostics;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Engines;

namespace ParadoxSaveParser.Benchmarks;

/// <summary>
///     jq runs as an external process on the JSON twin of the save.
///     Numbers therefore include process start and reading the file from the OS page cache,
///     which is exactly what you pay when you shell out to jq.
///     <see cref="JqNoop" /> measures that fixed overhead so it can be subtracted.
/// </summary>
[SimpleJob(RunStrategy.Monitoring, launchCount: 1, warmupCount: 1, iterationCount: 5)]
public class JqBenchmarks
{
    public static string JqPath { get; set; } = "jq";

    [GlobalSetup]
    public void Setup() => Run("--version", null);

    [Benchmark(Description = "jq  .countries | map_values(.technology)")]
    public int Jq() => Run("-c", BenchData.JqQuery);

    [Benchmark(Description = "jq  empty (parse only)")]
    public int JqParseOnly() => Run("-c", "empty");

    [Benchmark(Description = "jq  --stream (no DOM)")]
    public int JqStream() => Run("-c --stream", "empty");

    [Benchmark(Description = "jq  process startup only (tiny input)")]
    public int JqNoop()
    {
        var psi = new ProcessStartInfo(JqPath)
        {
            RedirectStandardOutput = true,
            RedirectStandardInput = true,
            UseShellExecute = false,
        };
        psi.ArgumentList.Add("-c");
        psi.ArgumentList.Add("empty");
        using var p = Process.Start(psi)!;
        p.StandardInput.Write("{}");
        p.StandardInput.Close();
        p.StandardOutput.ReadToEnd();
        p.WaitForExit();
        return p.ExitCode;
    }

    private static int Run(string flags, string? program)
    {
        var psi = new ProcessStartInfo(JqPath)
        {
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            UseShellExecute = false,
        };
        foreach (var f in flags.Split(' ', StringSplitOptions.RemoveEmptyEntries))
            psi.ArgumentList.Add(f);
        if (program != null)
        {
            psi.ArgumentList.Add(program);
            psi.ArgumentList.Add(BenchData.JsonPath);
        }

        using var p = Process.Start(psi)!;
        // output must be drained, otherwise jq blocks on a full pipe
        long bytes = 0;
        var buf = new char[1 << 16];
        int read;
        while ((read = p.StandardOutput.Read(buf, 0, buf.Length)) > 0)
            bytes += read;
        p.StandardError.ReadToEnd();
        p.WaitForExit();
        if (p.ExitCode != 0)
            throw new Exception($"jq exited with {p.ExitCode}");
        return (int)(bytes & int.MaxValue);
    }
}