public class Base32 extends Object {
    private static final String base32Chars = "abcdefghijklmnopqrstuvwxyz234567";
    private static final int[] base32Lookup = {0xFF, 0xFF, 0x1A, 0x1B, 0x1C,
            0x1D, 0x1E, 0x1F, // '0', '1', '2', '3', '4', '5', '6', '7'
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // '8', '9', ':',
            // ';', '<', '=',
            // '>', '?'
            0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '@', 'A', 'B',
            // 'C', 'D', 'E',
            // 'F', 'G'
            0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'H', 'I', 'J',
            // 'K', 'L', 'M',
            // 'N', 'O'
            0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'P', 'Q', 'R',
            // 'S', 'T', 'U',
            // 'V', 'W'
            0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 'X', 'Y', 'Z',
            // '[', '', ']',
            // '^', '_'
            0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '`', 'a', 'b',
            // 'c', 'd', 'e',
            // 'f', 'g'
            0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'h', 'i', 'j',
            // 'k', 'l', 'm',
            // 'n', 'o'
            0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'p', 'q', 'r',
            // 's', 't', 'u',
            // 'v', 'w'
            0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF // 'x', 'y', 'z',
            // '{', '|', '}',
            // '~', 'DEL'
    };

    static public String encode(int version, byte[] payload) {
        if (version < 0 || version > 255)
            throw new IllegalArgumentException("Version not in range.");

        // A stringified buffer is:
        // 1 byte version + data bytes + 4 bytes check code (a truncated hash)
        byte[] addressBytes = new byte[1 + payload.length + 4];
        addressBytes[0] = (byte) version;
        System.arraycopy(payload, 0, addressBytes, 1, payload.length);
        byte[] checksum = Sha256Hash.hashTwice(addressBytes, 0, payload.length + 1);
        System.arraycopy(checksum, 0, addressBytes, payload.length + 1, 4);
        return encode(addressBytes);
    }

    /**
     * Encodes byte array to base32 String.
     *
     * @param bytes Bytes to encode.
     * @return Encoded byte array <code>bytes</code> as a String.
     */
    static public String encode(final byte[] bytes) {
        int i = 0, index = 0, digit = 0;
        int currByte, nextByte;
        StringBuffer base32 = new StringBuffer((bytes.length + 7) * 8 / 5);
        while (i < bytes.length) {
            currByte = (bytes[i] >= 0) ? bytes[i] : (bytes[i] + 256); // unsign
            /* Is the current digit going to span a byte boundary? */
            if (index > 3) {
                if ((i + 1) < bytes.length) {
                    nextByte = (bytes[i + 1] >= 0) ? bytes[i + 1]
                            : (bytes[i + 1] + 256);
                } else {
                    nextByte = 0;
                }
                digit = currByte & (0xFF >> index);
                index = (index + 5) % 8;
                digit <<= index;
                digit |= nextByte >> (8 - index);
                i++;
            } else {
                digit = (currByte >> (8 - (index + 5))) & 0x1F;
                index = (index + 5) % 8;
                if (index == 0)
                    i++;
            }
            base32.append(base32Chars.charAt(digit));
        }
        return base32.toString();
    }

    /**
     * Decodes the given base32 String to a raw byte array.
     *
     * @param base32
     * @return Decoded <code>base32</code> String as a raw byte array.
     */
    static public byte[] decode(final String base32) {
        int i, index, lookup, offset, digit;
        byte[] bytes = new byte[base32.length() * 5 / 8];
        for (i = 0, index = 0, offset = 0; i < base32.length(); i++) {
            lookup = base32.charAt(i) - '0';
            /* Skip chars outside the lookup table */
            if (lookup < 0 || lookup >= base32Lookup.length) {
                continue;
            }
            digit = base32Lookup[lookup];
            /* If this digit is not in the table, ignore it */
            if (digit == 0xFF) {
                continue;
            }
            if (index <= 3) {
                index = (index + 5) % 8;
                if (index == 0) {
                    bytes[offset] |= digit;
                    offset++;
                    if (offset >= bytes.length)
                        break;
                } else {
                    bytes[offset] |= digit << (8 - index);
                }
            } else {
                index = (index + 5) % 8;
                bytes[offset] |= (digit >>> index);
                offset++;
                if (offset >= bytes.length) {
                    break;
                }
                bytes[offset] |= digit << (8 - index);
            }
        }
        return bytes;
    }

    private static String toHex(byte[] decoded) {
        StringBuffer sb = new StringBuffer();
        sb.append("{");
        for (int i = 0; i < decoded.length; i++) {
            int b = decoded[i];
            if (b < 0) {
                b += 256;
            }
            sb.append("0x" + (Integer.toHexString(b + 256)).substring(1) + ",");
        }
        sb.deleteCharAt(sb.length() - 1);
        sb.append("}");
        return sb.toString();
    }

}