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

namespace ClaudeDo.Worker.Runner;

// Process leak guard (Windows). The worker spawns `claude` (which spawns node + conhost).
// Cancellation kills the tree via Process.Kill(entireProcessTree: true), but a *hard* worker
// death — Task Manager End Task, crash, OS restart, installer update — runs no cleanup, so the
// whole claude→node→conhost tree is orphaned and lingers. Over many restarts these pile up.
//
// Fix: one Job Object with JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE, created once and held for the
// worker's lifetime. Every spawned claude process is assigned to it. The worker holds the only
// handle to the job; when the worker process terminates for ANY reason the OS closes that handle
// and tears down every process still in the job. This is the only mechanism that survives a hard
// kill — which entireProcessTree cannot.
internal static class ProcessJobObject
{
    private const int JobObjectExtendedLimitInformation = 9;
    private const uint JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE = 0x2000;

    private static readonly object _gate = new();
    private static IntPtr _job = IntPtr.Zero; // held for process lifetime, never closed
    private static bool _disabled;
    private static bool _warned;

    public static void Assign(Process process, ILogger logger)
    {
        if (!OperatingSystem.IsWindows() || _disabled) return;

        lock (_gate)
        {
            if (_disabled) return;

            if (_job == IntPtr.Zero)
            {
                _job = TryCreateJob(logger);
                if (_job == IntPtr.Zero)
                {
                    _disabled = true;
                    return;
                }
            }

            try
            {
                if (!AssignProcessToJobObject(_job, process.Handle))
                    WarnOnce(logger, "AssignProcessToJobObject failed", Marshal.GetLastWin32Error());
            }
            catch (Exception ex)
            {
                // process may have already exited, or handle is unavailable — best effort.
                WarnOnce(logger, $"could not assign process to job: {ex.Message}", 0);
            }
        }
    }

    [SupportedOSPlatform("windows")]
    private static IntPtr TryCreateJob(ILogger logger)
    {
        var job = CreateJobObject(IntPtr.Zero, null);
        if (job == IntPtr.Zero)
        {
            WarnOnce(logger, "CreateJobObject failed", Marshal.GetLastWin32Error());
            return IntPtr.Zero;
        }

        var info = new JOBOBJECT_EXTENDED_LIMIT_INFORMATION
        {
            BasicLimitInformation = new JOBOBJECT_BASIC_LIMIT_INFORMATION
            {
                LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE,
            },
        };

        var length = Marshal.SizeOf<JOBOBJECT_EXTENDED_LIMIT_INFORMATION>();
        var ptr = Marshal.AllocHGlobal(length);
        try
        {
            Marshal.StructureToPtr(info, ptr, false);
            if (!SetInformationJobObject(job, JobObjectExtendedLimitInformation, ptr, (uint)length))
            {
                WarnOnce(logger, "SetInformationJobObject failed", Marshal.GetLastWin32Error());
                CloseHandle(job);
                return IntPtr.Zero;
            }
        }
        finally
        {
            Marshal.FreeHGlobal(ptr);
        }

        logger.LogInformation("Process job object created — spawned claude processes will be killed if the worker dies.");
        return job;
    }

    private static void WarnOnce(ILogger logger, string message, int win32Error)
    {
        if (_warned) return;
        _warned = true;
        logger.LogWarning(
            "Process leak guard inactive: {Message} (win32={Win32Error}). Orphaned claude processes may survive a hard worker kill.",
            message, win32Error);
    }

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    private static extern IntPtr CreateJobObject(IntPtr lpJobAttributes, string? lpName);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool SetInformationJobObject(
        IntPtr hJob, int jobObjectInfoClass, IntPtr lpJobObjectInfo, uint cbJobObjectInfoLength);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool AssignProcessToJobObject(IntPtr hJob, IntPtr hProcess);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool CloseHandle(IntPtr hObject);

    [StructLayout(LayoutKind.Sequential)]
    private struct JOBOBJECT_BASIC_LIMIT_INFORMATION
    {
        public long PerProcessUserTimeLimit;
        public long PerJobUserTimeLimit;
        public uint LimitFlags;
        public UIntPtr MinimumWorkingSetSize;
        public UIntPtr MaximumWorkingSetSize;
        public uint ActiveProcessLimit;
        public UIntPtr Affinity;
        public uint PriorityClass;
        public uint SchedulingClass;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct IO_COUNTERS
    {
        public ulong ReadOperationCount;
        public ulong WriteOperationCount;
        public ulong OtherOperationCount;
        public ulong ReadTransferCount;
        public ulong WriteTransferCount;
        public ulong OtherTransferCount;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct JOBOBJECT_EXTENDED_LIMIT_INFORMATION
    {
        public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
        public IO_COUNTERS IoInfo;
        public UIntPtr ProcessMemoryLimit;
        public UIntPtr JobMemoryLimit;
        public UIntPtr PeakProcessMemoryUsed;
        public UIntPtr PeakJobMemoryUsed;
    }
}