#region license

// Copyright (C) 2020 ClassicUO Development Community on Github
// 
// This project is an alternative client for the game Ultima Online.
// The goal of this is to develop a lightweight client considering
// new technologies.
// 
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
// 
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
// 
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.

#endregion

using System;
using System.Text;

namespace ClassicAssist.Data
{
    internal static class Crypter
    {
        public static string Encrypt( string source )
        {
            byte[] buff = Encoding.ASCII.GetBytes( source );
            int kidx = 0;
            string key = CalculateKey();

            if ( key == string.Empty )
            {
                return string.Empty;
            }

            StringBuilder sb = new StringBuilder( source.Length * 2 + 2 );
            sb.Append( "1+" );

            for ( int i = 0; i < buff.Length; i++ )
            {
                sb.AppendFormat( "{0:X2}", (byte) ( buff[i] ^ (byte) key[kidx++] ) );

                if ( kidx >= key.Length )
                {
                    kidx = 0;
                }
            }

            return sb.ToString();
        }

        public static string Decrypt( string source )
        {
            byte[] buff;

            if ( source.Length > 2 && source[0] == '1' && source[1] == '+' )
            {
                buff = new byte[( source.Length - 2 ) >> 1];
                string key = CalculateKey();

                if ( key == string.Empty )
                {
                    return string.Empty;
                }

                int kidx = 0;

                for ( int i = 2; i < source.Length; i += 2 )
                {
                    byte c;

                    try
                    {
                        c = Convert.ToByte( source.Substring( i, 2 ), 16 );
                    }
                    catch
                    {
                        continue;
                    }

                    buff[( i - 2 ) >> 1] = (byte) ( c ^ (byte) key[kidx++] );

                    if ( kidx >= key.Length )
                    {
                        kidx = 0;
                    }
                }
            }
            else
            {
                byte key = (byte) ( source.Length >> 1 );
                buff = new byte[key];

                for ( int i = 0; i < source.Length; i += 2 )
                {
                    byte c;

                    try
                    {
                        c = Convert.ToByte( source.Substring( i, 2 ), 16 );
                    }
                    catch
                    {
                        continue;
                    }

                    buff[i >> 1] = (byte) ( c ^ key++ );
                }
            }

            return Encoding.ASCII.GetString( buff );
        }

        private static string CalculateKey()
        {
            return Environment.MachineName;
        }
    }
}