using System;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;

namespace ConsoleApp
{
    class Program
    {
        class FunctionLoader
        {
            [DllImport("Kernel32.dll")]
            private static extern IntPtr LoadLibrary(string path);

            [DllImport("Kernel32.dll")]
            private static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

            public static T LoadFunction<T>(string dllPath, string functionName)
            {
                var hModule = LoadLibrary(dllPath);
                var functionAddress = GetProcAddress(hModule, functionName);
                return (T) (object) Marshal.GetDelegateForFunctionPointer(functionAddress, typeof(T));
            }
        }

        private delegate void XRefDelegate(IntPtr pyobject);
        private delegate IntPtr PyLong_FromLong(IntPtr pyobject);
        private delegate IntPtr PyErr_Occurred();

        static void Main(string[] args)
        {
            //MessageBox = (MessageBoxDelegate)
            var pydll = FindPythonDll(36);
            FunctionLoader.LoadFunction<Action>(pydll, "Py_Initialize")();
            var incr = FunctionLoader.LoadFunction<XRefDelegate>(pydll, "Py_IncRef");
            var dcr = FunctionLoader.LoadFunction<XRefDelegate>(pydll, "Py_DecRef");

            var created_int_object = FunctionLoader.LoadFunction<PyLong_FromLong>(pydll, "PyLong_FromLong")((IntPtr) 1098080);

            var checkerFunc = FunctionLoader.LoadFunction<PyErr_Occurred>(pydll, "PyErr_Occurred");
            void checkError() {
                if (checkerFunc() != IntPtr.Zero)
                    throw new Exception();
            }

            var a = Refcount(created_int_object);
            checkError();
            incr(created_int_object);
            var b = Refcount(created_int_object);
            Debug.Assert(a+1==b);
            dcr(created_int_object);
            b = Refcount(created_int_object);
            Debug.Assert(a==b);
        }

        internal static unsafe long Refcount(IntPtr op)
        {
            var p = (void*)op;
            if ((void*)0 == p)
            {
                return 0;
            }
            return !Environment.Is64BitProcess ? (*(int*)p) : (*(long*)p);
        }


        static string FindPythonDll(int version) {
            return Environment.GetEnvironmentVariable("PATH")
                .Split(';')
                .Where(p => Regex.IsMatch(p, @"[Pp]ython\d\d[/\\]?$"))
                .SelectMany(p => Directory.GetFiles(p, "python*.dll").Where(pa => Regex.IsMatch(pa, $@"[Pp]ython{version}\.dll")))
                .Single();
        }


    }
}