using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Ansi2Utf8
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1)
            {
                Console.WriteLine("None file path !!!");
                return;
            }
            string fileName = args[0];
            try
            {
                FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
                if (fs == null)
                {
                    Console.WriteLine(fileName + " is null !!!");
                    return;
                }
                byte[] flieByte = new byte[fs.Length];
                fs.Read(flieByte, 0, flieByte.Length);
                fs.Close();
                if (IsUtf8(flieByte))
                {
                    Console.WriteLine(fileName + " is utf8 coding");
                    return;
                }
                Encoding ansi = Encoding.GetEncoding("GB2312");
                Encoding utf = Encoding.UTF8;
                flieByte = Encoding.Convert(ansi, utf, flieByte);
                StreamWriter docWriter;
                var utf8WithoutBom = new UTF8Encoding(false);
                docWriter = new StreamWriter(fileName, false, utf8WithoutBom);
                docWriter.Write(utf.GetString(flieByte));
                docWriter.Close();
            }
            catch
            {
                Console.WriteLine(fileName + " convert error !!!!!!!!!!!!!!");
            }
        }
        static bool IsUtf8(byte[] bs)
        {
            int len = bs.Length;
            if (len >= 3 && bs[0] == 0xEF && bs[1] == 0xBB && bs[2] == 0xBF)
            {
                return true; //Encoding.UTF8;
            }
            int[] cs = { 7, 5, 4, 3, 2, 1, 0, 6, 14, 30, 62, 126 };
            for (int i = 0; i < len; i++)
            {
                int bits = -1;
                for (int j = 0; j < 6; j++)
                {
                    if (bs[i] >> cs[j] == cs[j + 6])
                    {
                        bits = j;
                        break;
                    }
                }
                if (bits == -1)
                {
                    return false; //Encoding.Default;
                }
                while (bits-- > 0)
                {
                    i++;
                    if (i == len || bs[i] >> 6 != 2)
                    {
                        return false; //Encoding.Default;
                    }
                }
            }
            return true; //Encoding.UTF8;
        }
    }
}