using System.Diagnostics;
using System.Globalization;
using System.Net.Http.Headers;
using Azaion.Missions.E2E.Helpers;
using Npgsql;
using Xunit;

namespace Azaion.Missions.E2E.Fixtures;

/// <summary>
/// Shared 5-minute steady-state load fixture for NFT-RES-LIM-01 / -02 / -03.
/// Runs the load generator once, samples RSS / connection count / FD count
/// every 5s, and exposes the time series + sentinel "did the SUT exit" flag.
/// </summary>
/// <remarks>
/// <para>The fixture is class-scoped (xUnit <see cref="IClassFixture{TFixture}"/>)
/// and shared across all three NFT-RES-LIM-01/02/03 tests so the 5-minute
/// window runs once per CI invocation.</para>
/// <para>Disabled when <c>COMPOSE_RESTART_ENABLED != 1</c> or docker CLI
/// is missing. Disabled state is observable via <see cref="Enabled"/>; tests
/// must call <see cref="Xunit.Skip.IfNot(bool, string)"/> at the top of the
/// method body — initialising the fixture without docker would throw inside
/// <see cref="InitializeAsync"/> and surface as a hard failure instead of
/// the explicit skip the spec requires.</para>
/// </remarks>
public sealed class SteadyStateLoadFixture : IAsyncLifetime
{
    public const int SampleIntervalSeconds = 5;
    public const int LoadDurationSeconds = 300;
    public const int TargetRps = 50;
    public const string ContainerName = "missions-sut";

    public bool Enabled =>
        Environment.GetEnvironmentVariable("COMPOSE_RESTART_ENABLED") == "1";

    public bool LoadGeneratorMetTargetRps { get; private set; }
    public bool SutExitedDuringWindow { get; private set; }
    public string? SkipReason { get; private set; }

    public List<long> RssBytesSamples { get; } = new();
    public List<int> NpgsqlConnectionSamples { get; } = new();
    public List<int> FileDescriptorSamples { get; } = new();
    public List<DateTime> SampleTimestamps { get; } = new();

    public async Task InitializeAsync()
    {
        if (!Enabled)
        {
            SkipReason = "COMPOSE_RESTART_ENABLED!=1 — docker CLI primitives unavailable";
            return;
        }
        if (!CommandAvailable("docker"))
        {
            SkipReason = "docker CLI not on PATH in this consumer image";
            return;
        }

        using var http = new HttpClient { BaseAddress = new Uri(TestEnvironment.MissionsBaseUrl) };
        var token = await new TokenMinter(TestEnvironment.JwksMockBaseUrl + "/sign").MintDefaultAsync();
        http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token.Jwt);

        var cancel = new CancellationTokenSource();
        var endpoints = new[] { "/vehicles", "/missions", "/missions?page=1&pageSize=20" };
        long requestsSent = 0;

        var loadTask = Task.Run(async () =>
        {
            var ix = 0;
            while (!cancel.IsCancellationRequested)
            {
                try
                {
                    var url = endpoints[ix++ % endpoints.Length];
                    using var resp = await http.GetAsync(url, cancel.Token);
                    Interlocked.Increment(ref requestsSent);
                }
                catch (HttpRequestException) { /* surfaces via SutExitedDuringWindow below */ }
                catch (OperationCanceledException) { return; }
            }
        }, cancel.Token);

        var samplingDeadline = DateTime.UtcNow.AddSeconds(LoadDurationSeconds);
        while (DateTime.UtcNow < samplingDeadline)
        {
            await Task.Delay(TimeSpan.FromSeconds(SampleIntervalSeconds), cancel.Token);
            if (!ContainerIsRunning(ContainerName))
            {
                SutExitedDuringWindow = true;
                break;
            }
            SampleTimestamps.Add(DateTime.UtcNow);
            RssBytesSamples.Add(ReadRssBytes(ContainerName));
            NpgsqlConnectionSamples.Add(ReadNpgsqlConnectionCount());
            FileDescriptorSamples.Add(ReadFileDescriptorCount(ContainerName));
        }

        cancel.Cancel();
        try { await loadTask; } catch (OperationCanceledException) { }

        // Sustained 50 RPS over 300s = 15000 requests; allow 10% slack for
        // CI variance / connection-refused retries.
        LoadGeneratorMetTargetRps =
            requestsSent >= (long)(TargetRps * LoadDurationSeconds * 0.9);
    }

    public Task DisposeAsync() => Task.CompletedTask;

    private static long ReadRssBytes(string containerName)
    {
        // `docker stats --no-stream --format '{{.MemUsage}}'` prints e.g.
        // "187.4MiB / 7.7GiB". We need the LHS in bytes.
        var raw = Run("docker",
            $"stats --no-stream --format '{{{{.MemUsage}}}}' {containerName}");
        var lhs = raw.Split('/')[0].Trim().Trim('\'');
        return ParseHumanBytes(lhs);
    }

    private static int ReadNpgsqlConnectionCount()
    {
        using var conn = new NpgsqlConnection(TestEnvironment.DbSideChannel);
        conn.Open();
        using var cmd = conn.CreateCommand();
        cmd.CommandText = """
            SELECT count(*)::INTEGER FROM pg_stat_activity
            WHERE application_name LIKE 'Npgsql%'
               OR (usename = 'postgres' AND backend_type = 'client backend');
            """;
        return Convert.ToInt32(cmd.ExecuteScalar());
    }

    private static int ReadFileDescriptorCount(string containerName)
    {
        // `pgrep` is not guaranteed in the runtime image; we walk /proc
        // directly. `/proc/1/comm` is the entrypoint process name; for the
        // ASP.NET Core SDK image this is `dotnet`.
        var stdout = Run("docker",
            $"exec {containerName} sh -c 'ls /proc/1/fd | wc -l'");
        return int.Parse(stdout.Trim(), CultureInfo.InvariantCulture);
    }

    private static long ParseHumanBytes(string text)
    {
        // "187.4MiB" / "1.2GiB" / "234KiB" / "987B"
        var unitIx = text.IndexOfAny(new[] { 'K', 'M', 'G', 'T', 'B' });
        if (unitIx < 0) return long.Parse(text, CultureInfo.InvariantCulture);
        var num = double.Parse(text.Substring(0, unitIx), CultureInfo.InvariantCulture);
        var unit = text.Substring(unitIx);
        return unit switch
        {
            "B"   => (long)num,
            "KiB" or "KB" or "K" => (long)(num * 1024),
            "MiB" or "MB" or "M" => (long)(num * 1024 * 1024),
            "GiB" or "GB" or "G" => (long)(num * 1024 * 1024 * 1024),
            "TiB" or "TB" or "T" => (long)(num * 1024L * 1024 * 1024 * 1024),
            _ => throw new FormatException($"unknown human-bytes unit in '{text}'")
        };
    }

    private static bool ContainerIsRunning(string containerName)
    {
        try
        {
            var stdout = Run("docker",
                $"inspect --format '{{{{.State.Running}}}}' {containerName}");
            return stdout.Trim().Trim('\'').Equals("true", StringComparison.Ordinal);
        }
        catch (InvalidOperationException) { return false; }
    }

    private static bool CommandAvailable(string command)
    {
        try
        {
            var psi = new ProcessStartInfo(command, "--version")
            {
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                UseShellExecute = false
            };
            using var p = Process.Start(psi);
            if (p is null) return false;
            p.WaitForExit();
            return p.ExitCode == 0;
        }
        catch (System.ComponentModel.Win32Exception) { return false; }
    }

    private static string Run(string file, string args)
    {
        var psi = new ProcessStartInfo(file, args)
        {
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            UseShellExecute = false
        };
        using var p = Process.Start(psi)
            ?? throw new InvalidOperationException($"failed to launch `{file} {args}`");
        var stdout = p.StandardOutput.ReadToEnd();
        var stderr = p.StandardError.ReadToEnd();
        p.WaitForExit();
        if (p.ExitCode != 0)
            throw new InvalidOperationException(
                $"`{file} {args}` exited {p.ExitCode}: {stderr}");
        return stdout;
    }
}