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package com.olapdb.obase.utils;

/**
 * Base32 - encodes and decodes RFC3548 Base32
 * (see http://www.faqs.org/rfcs/rfc3548.html )
 *
 * @author Robert Kaye
 * @author Gordon Mohr
 */
public class Base32 {
    private static final String base32Chars =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
    private static final int[] base32Lookup =
    { 0xFF,0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,
      0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
      0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,
      0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
      0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,
      0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF,
      0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,
      0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
      0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,
      0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF
    };

    /**
     * Encodes byte array to Base32 String.
     *
     * @param bytes Bytes to encode.
     * @return Encoded byte array bytes 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);

            /* 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 base32 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;
    }

    static public void main(String[] args) {
        if (args.length == 0) {
            System.out.println("Supply a Base32-encoded argument.");
            return;
        }
        System.out.println(" Original: " + args[0]);
        byte[] decoded = Base32.decode(args[0]);
        System.out.print("      Hex: ");
        for (int i = 0; i < decoded.length; i++) {
            int b = decoded[i];
            if (b < 0) {
                b += 256;
            }
            System.out.print(
               (Integer.toHexString(b + 256)).substring(1));
        }
        System.out.println();
        System.out.println("Reencoded: " + Base32.encode(decoded));
    }
}