using System;
using System.Runtime.InteropServices;

namespace CSharpPlayground
{
    public static class GetProcArgv
    {
        private const int CTL_KERN = 1;
        private const int KERN_ARGMAX = 8;
        private const int KERN_PROCARGS2 = 49;

        public static void PrintCurrProcArgv()
        {
            unsafe
            {
                // Get current process pid
                int pid = getpid();

                // Get proc table size
                int[] mib = new [] { CTL_KERN, KERN_ARGMAX };
                int size = sizeof(int);
                int maxargs = 0;

                if (sysctl(mib, mib.Length, &maxargs, &size, IntPtr.Zero, 0) == -1)
                {
                    Console.Error.WriteLine("argmax");
                    return;
                }

                // Now read the proc table

                IntPtr procargs = Marshal.AllocHGlobal(maxargs);
                size = maxargs;

                mib = new [] { CTL_KERN, KERN_PROCARGS2, pid };

                if (sysctl(mib, mib.Length, procargs.ToPointer(), &size, IntPtr.Zero, 0) == -1)
                {
                    Console.Error.WriteLine("procargs");
                    return;
                }

                // Skip over argc
                IntPtr argv0Ptr = IntPtr.Add(procargs, sizeof(int));
                string argv0 = Marshal.PtrToStringAnsi(argv0Ptr);
                Console.WriteLine(argv0);
            }
        }

        [DllImport("libc")]
        private static extern int getpid();

        [DllImport("libc")]
        private static unsafe extern int sysctl(int[] mib, int length, void* oldp, int* oldlenp, IntPtr newp, int newlenp);
    }
}