using System;
using System.IO;
using System.Linq;

namespace Patch_libnp
{
    internal class Program
    {
        private static void Main()
        {
            if (!File.Exists("libnp.dll"))
            {
                Console.WriteLine("libnp.dll not found, exiting...");
                return;
            }
            Console.WriteLine("Loading libnp.dll....");
            _file = File.ReadAllBytes("libnp.dll");
            Console.WriteLine("Finding patch point...");
            var index =
                FindPattern(
                    new byte[]
                        {
                            0x55, 0x8b, 0xec, 0x83, 0xec, 0x00, 0x53, 0x56, 0x57, 0x8b, 0x45, 0x00, 0xa3, 0x00, 0x00,
                            0x00, 0x00, 0x6a, 0x00, 0xff, 0x15, 0x00, 0x00, 0x00, 0x00, 0x83, 0xc4, 0x00, 0x5f, 0x5e,
                            0x5b, 0x8b, 0xe5
                        },
                    "xxxxx?xxxxx?x????x?xx????xx?xxxxx");
            if (index == -1)
            {
                Console.WriteLine("Patch point not found! Exiting...");
                return;
            }
            _file[index] = 0xc3;
            Console.WriteLine("Backing up libnp.dll as libnp.dll.bak");
            File.Move("libnp.dll", "libnp.dll.bak");
            Console.WriteLine("Writing patches...");
            File.WriteAllBytes("libnp.dll", _file);
            Console.WriteLine("File written.");
            Console.Read();
        }

        /// <summary>
        /// Byte array to be used by FindPattern
        /// </summary>
        private static byte[] _file;
        /// <summary>
        /// Finds a specific pattern in a byte array
        /// Example:
        /// FindPattern(
        ///            new byte[]
        ///                {
        ///                    0x55, 0x8b, 0xec, 0x83, 0xec, 0x00, 0x53, 0x56, 0x57, 0x8b, 0x45, 0x00, 0xa3, 0x00, 0x00,
        ///                    0x00, 0x00, 0x6a, 0x00, 0xff, 0x15, 0x00, 0x00, 0x00, 0x00, 0x83, 0xc4, 0x00, 0x5f, 0x5e,
        ///                    0x5b, 0x8b, 0xe5
        ///                },
        ///            "xxxxx?xxxxx?x????x?xx????xx?xxxxx");
        /// </summary>
        /// <param name="btPattern">Byte array containing pattern to search</param>
        /// <param name="strMask">x for exact match, ? for wildcard</param>
        /// <returns>Position of pattern in _file, -1 if pattern not found</returns>
        private static int FindPattern(byte[] btPattern, string strMask)
        {
            try
            {
                if (strMask.Length != btPattern.Length)
                    return -1;
                for (int x = 0; x < _file.Length; x++)
                {
                    if (MaskCheck(x, btPattern, strMask))
                    {
                        return x;
                    }
                }
                return -1;
            }
            catch (Exception ex)
            {
                return -1;
            }
        }

        private static bool MaskCheck(int nOffset, byte[] btPattern, string strMask)
        {
            return !btPattern.Where((t, x) => strMask[x] != '?' && ((strMask[x] == 'x') && (t != _file[nOffset + x]))).Any();
        }
    }
}