using System;
using System.Text;

namespace Yi.Framework.Core.Helper
{
    public sealed class Base32Helper
    {

        // the valid chars for the encoding
        private static string ValidChars = "QAZ2WSX3" + "EDC4RFV5" + "TGB6YHN7" + "UJM8K9LP";

        /// <summary>
        /// Converts an array of bytes to a Base32-k string.
        /// </summary>
        public static string ToString(byte[] bytes)
        {
            StringBuilder sb = new StringBuilder();         // holds the base32 chars
            byte index;
            int hi = 5;
            int currentByte = 0;

            while (currentByte < bytes.Length)
            {
                // do we need to use the next byte?
                if (hi > 8)
                {
                    // get the last piece from the current byte, shift it to the right
                    // and increment the byte counter
                    index = (byte)(bytes[currentByte++] >> hi - 5);
                    if (currentByte != bytes.Length)
                    {
                        // if we are not at the end, get the first piece from
                        // the next byte, clear it and shift it to the left
                        index = (byte)((byte)(bytes[currentByte] << 16 - hi) >> 3 | index);
                    }

                    hi -= 3;
                }
                else if (hi == 8)
                {
                    index = (byte)(bytes[currentByte++] >> 3);
                    hi -= 3;
                }
                else
                {

                    // simply get the stuff from the current byte
                    index = (byte)((byte)(bytes[currentByte] << 8 - hi) >> 3);
                    hi += 5;
                }

                sb.Append(ValidChars[index]);
            }

            return sb.ToString();
        }


        /// <summary>
        /// Converts a Base32-k string into an array of bytes.
        /// </summary>
        /// <exception cref="ArgumentException">
        /// Input string <paramref name="s">s</paramref> contains invalid Base32-k characters.
        /// </exception>
        public static byte[] FromBase32String(string str)
        {
            int numBytes = str.Length * 5 / 8;
            byte[] bytes = new byte[numBytes];

            // all UPPERCASE chars
            str = str.ToUpper();

            int bit_buffer;
            int currentCharIndex;
            int bits_in_buffer;

            if (str.Length < 3)
            {
                bytes[0] = (byte)(ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5);
                return bytes;
            }

            bit_buffer = ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5;
            bits_in_buffer = 10;
            currentCharIndex = 2;
            for (int i = 0; i < bytes.Length; i++)
            {
                bytes[i] = (byte)bit_buffer;
                bit_buffer >>= 8;
                bits_in_buffer -= 8;
                while (bits_in_buffer < 8 && currentCharIndex < str.Length)
                {
                    bit_buffer |= ValidChars.IndexOf(str[currentCharIndex++]) << bits_in_buffer;
                    bits_in_buffer += 5;
                }
            }

            return bytes;
        }
    }
}
