using System.Diagnostics;
using System.Runtime.InteropServices;

namespace AcDream.Launcher.Core.Launching;

/// <summary>
/// Thin seam over <see cref="System.Diagnostics.Process"/> so
/// <see cref="LauncherProcessSupervisor"/>'s lifecycle and Stop
/// (CloseMainWindow, falling back to Kill after a timeout) state machine
/// can be unit-tested against an in-memory fake without spawning a real
/// OS process or depending on real window-message timing — both
/// "injectable for tests" per Campaign LA spec §3.
/// </summary>
public interface ILauncherChildProcess : IDisposable
{
    bool HasExited { get; }

    int ExitCode { get; }

    /// <summary>The child's redirected stdin. The supervisor writes the
    /// account password here (followed by a newline) and then closes it —
    /// never anywhere else.</summary>
    TextWriter StandardInput { get; }

    /// <summary>Fires exactly once, when the child process terminates
    /// (mirrors <see cref="Process.Exited"/> with
    /// <c>EnableRaisingEvents</c> on).</summary>
    event EventHandler? Exited;

    void Start();

    /// <summary>
    /// Attempts a graceful stop signal appropriate to the platform,
    /// tried BEFORE <see cref="CloseMainWindow"/> (Campaign LA plan §LA3
    /// review finding F3): a no-window console host (e.g.
    /// <c>AcDream.Headless</c>) never has a main window for
    /// <see cref="CloseMainWindow"/> to close, so without this step
    /// <see cref="LauncherProcessSupervisor.Stop"/> always degraded
    /// straight to a timeout + hard <see cref="Kill"/> — and a hard kill
    /// leaves the ACE account session stuck for several minutes (a
    /// documented project landmine; see CLAUDE.md
    /// "Logout-before-reconnect"). On Linux this sends SIGINT (K4 proved
    /// the headless host's SIGINT handler produces an ACE-confirmed
    /// graceful logout). On Windows, console-capable children are started
    /// as distinct process-group leaders and receive a targeted
    /// CTRL_BREAK_EVENT. Returns true only when the signal was actually
    /// delivered; never throws.
    /// </summary>
    bool TryRequestGracefulStop();

    /// <summary>Mirrors <see cref="Process.CloseMainWindow"/> — requests
    /// a graceful close via WM_CLOSE. Returns false for a console/no-
    /// window process (never throws), matching the real API.</summary>
    bool CloseMainWindow();

    /// <summary>Mirrors <see cref="Process.Kill(bool)"/> with
    /// <c>entireProcessTree: true</c>.</summary>
    void Kill();

    bool WaitForExit(TimeSpan timeout);
}

/// <summary>Creates <see cref="ILauncherChildProcess"/> instances from a
/// <see cref="LauncherProcessSpec"/>.</summary>
public interface ILauncherChildProcessFactory
{
    ILauncherChildProcess Create(LauncherProcessSpec spec);
}

/// <summary>Real-process implementation used in production.</summary>
public sealed class SystemChildProcessFactory : ILauncherChildProcessFactory
{
    public ILauncherChildProcess Create(LauncherProcessSpec spec) =>
        OperatingSystem.IsWindows() && spec.SupportsConsoleGracefulStop
            ? new WindowsSystemChildProcess(spec)
            : new SystemChildProcess(spec);
}

internal sealed partial class SystemChildProcess : ILauncherChildProcess
{
    // SIGINT's numeric value (POSIX-stable across Linux distributions).
    // K4/Slice K already proved the headless host's SIGINT handler
    // produces an ACE-confirmed graceful logout.
    private const int Sigint = 2;

    [LibraryImport("libc", SetLastError = true)]
    private static partial int kill(int pid, int sig);

    private readonly Process _process;
    private readonly bool _supportsConsoleGracefulStop;
    private readonly BoundedProcessOutputCapture? _stderrCapture;
    private bool _raisingEnabled;
    private bool _errorReadingEnabled;

    internal SystemChildProcess(LauncherProcessSpec spec)
    {
        ArgumentNullException.ThrowIfNull(spec);
        _supportsConsoleGracefulStop = spec.SupportsConsoleGracefulStop;

        var startInfo = new ProcessStartInfo
        {
            FileName = spec.ExecutablePath,
            RedirectStandardInput = true,
            UseShellExecute = false,
        };

        // fix #406 sibling gap: capture stderr (crash stack traces land
        // there) into a bounded per-session file instead of discarding it.
        // Purely additive — RedirectStandardOutput/CreateNoWindow are left
        // untouched, and a spec with no StderrLogPath behaves exactly as
        // before.
        if (!string.IsNullOrWhiteSpace(spec.StderrLogPath))
        {
            startInfo.RedirectStandardError = true;
            _stderrCapture = new BoundedProcessOutputCapture(spec.StderrLogPath);
        }

        foreach (string argument in spec.Arguments)
        {
            startInfo.ArgumentList.Add(argument);
        }

        if (!string.IsNullOrEmpty(spec.WorkingDirectory))
        {
            startInfo.WorkingDirectory = spec.WorkingDirectory;
        }

        _process = new Process { StartInfo = startInfo };
    }

    public bool HasExited => _process.HasExited;

    public int ExitCode => _process.ExitCode;

    public TextWriter StandardInput => _process.StandardInput;

    public event EventHandler? Exited;

    public void Start()
    {
        _process.EnableRaisingEvents = true;
        _process.Exited += OnExited;
        _raisingEnabled = true;
        if (_stderrCapture is not null)
        {
            _process.ErrorDataReceived += OnErrorDataReceived;
            _errorReadingEnabled = true;
        }

        _process.Start();
        if (_errorReadingEnabled)
        {
            _process.BeginErrorReadLine();
        }
    }

    public bool TryRequestGracefulStop()
    {
        if (!OperatingSystem.IsLinux() || !_supportsConsoleGracefulStop)
        {
            // Windows console-capable children use
            // WindowsSystemChildProcess. Graphical/non-console children
            // deliberately retain the Process/WM_CLOSE path.
            return false;
        }

        try
        {
            return kill(_process.Id, Sigint) == 0;
        }
        catch
        {
            // Matches CloseMainWindow's "never throws" contract — the
            // process may not have started yet, may have already exited
            // (ESRCH), or the platform may lack libc under an unusual
            // Linux runtime; any of these degrade to "signal not sent"
            // rather than an exception out of Stop().
            return false;
        }
    }

    public bool CloseMainWindow() => _process.CloseMainWindow();

    public void Kill() => _process.Kill(entireProcessTree: true);

    public bool WaitForExit(TimeSpan timeout) => _process.WaitForExit(timeout);

    public void Dispose()
    {
        if (_raisingEnabled)
        {
            _process.Exited -= OnExited;
        }

        if (_errorReadingEnabled)
        {
            _process.ErrorDataReceived -= OnErrorDataReceived;
        }

        _process.Dispose();
        _stderrCapture?.Dispose();
    }

    private void OnExited(object? sender, EventArgs e) =>
        Exited?.Invoke(this, EventArgs.Empty);

    private void OnErrorDataReceived(object? sender, DataReceivedEventArgs e) =>
        _stderrCapture?.AppendLine(e.Data);
}