using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Chop.Game.Encryption
{
    class RC4
    {
        private int _i = 0;
        private int _j = 0;
        private readonly int[] _table = new int[256];

        /// <summary>
        /// Init RC4
        /// </summary>
        /// <param name="a">Init RC4 using Byte</param>
        public void Init(byte[] a)
        {
            int k = a.Length;
            this._i = 0;
            while (this._i < 256)
            {
                this._table[this._i] = this._i;
                this._i++;
            }
            this._j = 0;
            this._i = 0;
            while (this._i < 256)
            {
                this._j = ((this._j + this._table[this._i]) + (a[this._i % k] & 0xff)) % 256;
                this.Swamp(this._i, this._j);
                this._i++;
            }
            this._i = 0;
            this._j = 0;
        }

        /// <summary>
        /// Encode and Decode
        /// </summary>
        /// <param name="b">Encode/Decode Byte</param>
        public void Parse(byte[] b)
        {
            for (int a = 0; a < b.Length; a++)
            {
                this._i = (this._i + 1) % 256;
                this._j = (this._j + this._table[this._i]) % 256;
                this.Swamp(this._i, this._j);
                b[a] = (byte)((b[a] & 0xff) ^ this._table[(this._table[this._i] + this._table[this._j]) % 256]);
            }
        }

        /// <summary>
        /// Swamp
        /// </summary>
        /// <param name="a1">Int 1</param>
        /// <param name="a2">Int 2</param>
        private void Swamp(int a1, int a2)
        {
            int k = this._table[a1];
            this._table[a1] = this._table[a2];
            this._table[a2] = k;
        }
    }
}