using System.Runtime.InteropServices;

namespace Aeshnidae.GracefulStop;

/// <summary>
/// Makes `systemctl stop|restart ace` graceful.
///
/// Found 2026-09-27: the units stop ACE with SIGINT, and ACE registers no handler for it, so
/// .NET simply ends the process. ACE's ProcessExit handler then only warns "Unsafe server
/// shutdown detected! Data loss is possible!" and stops the database - unless the process
/// runs with DOTNET_RUNNING_IN_CONTAINER, which would also move ACE's config, content and
/// database-update paths to /ace/..., so that flag is not the fix. No player was logged out
/// and saved, no landblock saved, no mod shutdown hook ran; live's 15:58 restart that day
/// went down and came back inside one second.
///
/// This mod catches SIGINT and SIGTERM, cancels the default exit, and runs ACE's own
/// shutdown instead - ServerManager.DoShutdownNow, what an admin's "/shutdown now" does: every
/// player logged off (and saved), every landblock unloaded (and saved), the world stopped,
/// mods shut down, offline players saved, the database queue drained, then Environment.Exit.
/// A second signal while that runs is ignored; systemd's TimeoutStopSec is the backstop.
/// </summary>
public class Mod : IHarmonyMod
{
    public static readonly string Name = typeof(Mod).Assembly.GetName().Name!;

    private static PosixSignalRegistration? _sigint, _sigterm;
    private static int _started;
    private bool _disposed;

    public void Initialize()
    {
        try
        {
            _sigint = PosixSignalRegistration.Create(PosixSignal.SIGINT, OnSignal);
            _sigterm = PosixSignalRegistration.Create(PosixSignal.SIGTERM, OnSignal);
            ModManager.Log($"[{Name}] ready - SIGINT and SIGTERM now run ACE's graceful shutdown");
        }
        catch (Exception ex)
        {
            // Never throw out of Initialize; without the handler ACE behaves as it always has.
            ModManager.Log($"[{Name}] could not register the signal handlers ({ex.Message}); a stop is still an instant exit", ModManager.LogLevel.Error);
        }
    }

    private static void OnSignal(PosixSignalContext context)
    {
        // Keep the process alive: ACE's shutdown ends it with Environment.Exit when it is done.
        context.Cancel = true;

        if (Interlocked.Exchange(ref _started, 1) == 1)
        {
            ModManager.Log($"[{Name}] {context.Signal} again - the graceful shutdown is already running");
            return;
        }

        ModManager.Log($"[{Name}] {context.Signal} received - logging everyone out and saving before exit");

        // Off the signal thread: the shutdown waits for players, landblocks and the database.
        var thread = new Thread(() =>
        {
            try
            {
                ServerManager.DoShutdownNow();
            }
            catch (Exception ex)
            {
                ModManager.Log($"[{Name}] graceful shutdown failed: {ex} - exiting", ModManager.LogLevel.Error);
                Environment.Exit(1);
            }
        })
        {
            Name = "GracefulStop shutdown",
            IsBackground = false,
        };
        thread.Start();
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (_disposed)
            return;

        if (disposing)
        {
            // Mods are shut down part way through the graceful shutdown itself; dropping the
            // handlers then is harmless, the shutdown thread carries on regardless.
            _sigint?.Dispose();
            _sigterm?.Dispose();
            _sigint = _sigterm = null;
            ModManager.Log($"[{Name}] shut down");
        }

        _disposed = true;
    }
}