using System;
using System.Collections.Generic;
using System.Web;
using System.Text;

namespace 報到系統
{
  public class EncDec
  {
    /// <summary>
    /// WLIB 新版密碼的加密函數
    /// </summary>
    /// <param name="S">欲加密之密碼字串，最大長度 8 位，僅可包含A-Z、a-z、0-9</param>
    /// <returns>加密後之密碼字串</returns>
    public static string KeyEnc(string S)
    {
      int k1 = 0;
      int k2 = 0;
      int i, j;
      Random rnd = new Random(DateTime.UtcNow.AddHours(8).Millisecond);
      byte[] inBuf = new byte[8];
      byte[] outBuf = new byte[10];
      string tmp;

      while (true)
      {
        k1 = rnd.Next(31);
        k2 = rnd.Next(31);
        outBuf[0] = (byte)(k1 + 44);
        outBuf[9] = (byte)(k2 + 66);

        if (S.Length < 8)
          inBuf = Encoding.ASCII.GetBytes(S.PadRight(8));
        else
          inBuf = Encoding.ASCII.GetBytes(S);

        for (i = 1; i <= 8; i++)
        {
          j = (k1 % 31) + i;
          j = ((k2 + j) % 31) + 1;

          outBuf[i] = (byte)(inBuf[i - 1] ^ j);
        }
        tmp = Encoding.ASCII.GetString(outBuf);
        if (tmp.IndexOf('\'') < 0 && tmp.IndexOf('"') < 0)
          break;
      }
      return tmp;
    }

    /// <summary>
    /// WLIB 新版密碼的解密函數
    /// </summary>
    /// <param name="S">欲解密之密碼字串，固定 10 位</param>
    /// <returns>解密後之密碼字串。若參數 S 長度不是 10 位，則傳回".." + S + ".."</returns>
    public static string KeyDec(string S)
    {
      int i, j;
      int Key1, Key2;
      byte[] inBuf;
      byte[] outBuf = new byte[8];

      if (S.Length != 10)
        return ".." + S + "..";

      //解密
      inBuf = Encoding.ASCII.GetBytes(S);
      Key1 = inBuf[0] - 44;
      Key2 = inBuf[9] - 66;

      for (i = 1; i <= 8; i++)
      {
        j = Key1 % 31 + i;
        j = (Key2 + j) % 31 + 1;
        outBuf[i - 1] = (byte)(inBuf[i] ^ j);
      }
      return Encoding.ASCII.GetString(outBuf).Trim();
    }
  }
}