using System;
using System.Text;
using System.Text.RegularExpressions;

namespace CipherTest
{
    // Thanks to Nathan Moinvaziri on stackoverflow for the original byte <-> hex code transformers! https://stackoverflow.com/a/5919521
    static class Helpers
    {
        static readonly Regex ValidRegex = new Regex(@"^[\x20-\xFF]+$", RegexOptions.Compiled);
        static readonly Regex HexRegex = new Regex("^[0-9A-Fa-f]+$", RegexOptions.Compiled);

        static readonly string HexAlphabet = "0123456789ABCDEF";
        static readonly int[] HexValue = new int[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F };

        public static ulong RL(this ulong x, int n) => (x << n) | (x >> (64 - n));

        public static bool IsValidString(string str) => ValidRegex.IsMatch(str);

        public static bool IsHexString(string str) => HexRegex.IsMatch(str);

        public static string BytesToHex(byte[] bytes)
        {
            StringBuilder result = new StringBuilder(bytes.Length * 2);

            foreach (byte b in bytes)
            {
                result.Append(HexAlphabet[(int)(b >> 4)]);
                result.Append(HexAlphabet[(int)(b & 0xF)]);
            }

            return result.ToString();
        }

        public static byte[] HexToBytes(string hex)
        {
            if ((hex.Length & 1) == 1 || !IsHexString(hex))
            {
                return null;
            }

            byte[] bytes = new byte[hex.Length / 2];

            for (int x = 0, i = 0; i < hex.Length; i += 2, x += 1)
            {
                bytes[x] = (byte) (HexValue[Char.ToUpper(hex[i + 0]) - '0'] << 4 | HexValue[Char.ToUpper(hex[i + 1]) - '0']);
            }

            return bytes;
        }
    }
}