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/*******************************************************************************
 * Copyright 2016 Sistcoop, Inc. and/or its affiliates
 * and other contributors as indicated by the @author tags.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *******************************************************************************/

package org.openfact.models.utils;


/* (PD) 2006 The Bitzi Corporation
 * Please see http://bitzi.com/publicdomain for more info.
 *
 * $Id: Base32.java,v 1.2 2006/07/14 04:58:39 gojomo Exp $
 */

/**
 * Base32 - encodes and decodes RFC3548 Base32 (see http://www.faqs.org/rfcs/rfc3548.html )
 */
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.
     */
    public static 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.
     */
    public static 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;
    }

}