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/*
 * Copyright 2017 Baidu, Inc.
 *
 * 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 com.baidu.aip.util;

public class Base64Util {
    private static final char[] ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
            .toCharArray();

    private static final char last2byte = (char) Integer
            .parseInt("00000011", 2);
    private static final char last4byte = (char) Integer
            .parseInt("00001111", 2);
    private static final char last6byte = (char) Integer
            .parseInt("00111111", 2);
    private static final char lead6byte = (char) Integer
            .parseInt("11111100", 2);
    private static final char lead4byte = (char) Integer
            .parseInt("11110000", 2);
    private static final char lead2byte = (char) Integer
            .parseInt("11000000", 2);
    private static final char[] encodeTable = new char[] { 'A', 'B', 'C', 'D',
            'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',
            'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
            'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',
            'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3',
            '4', '5', '6', '7', '8', '9', '+', '/' };

    private static int[]  toInt   = new int[128];

    static {
        for (int i = 0; i < ALPHABET.length; i++) {
            toInt[ALPHABET[i]] = i;
        }
    }

    /**
     * Base64 encoding.
     *
     * @param from
     *            The src data.
     * @return cryto_str
     */
    public static String encode(byte[] from) {
        StringBuilder to = new StringBuilder((int) (from.length * 1.34) + 3);
        int num = 0;
        char currentByte = 0;
        for (int i = 0; i < from.length; i++) {
            num = num % 8;
            while (num < 8) {
                switch (num) {
                    case 0:
                        currentByte = (char) (from[i] & lead6byte);
                        currentByte = (char) (currentByte >>> 2);
                        break;
                    case 2:
                        currentByte = (char) (from[i] & last6byte);
                        break;
                    case 4:
                        currentByte = (char) (from[i] & last4byte);
                        currentByte = (char) (currentByte << 2);
                        if ((i + 1) < from.length) {
                            currentByte |= (from[i + 1] & lead2byte) >>> 6;
                        }
                        break;
                    case 6:
                        currentByte = (char) (from[i] & last2byte);
                        currentByte = (char) (currentByte << 4);
                        if ((i + 1) < from.length) {
                            currentByte |= (from[i + 1] & lead4byte) >>> 4;
                        }
                        break;
                    default:
                        break;
                }
                to.append(encodeTable[currentByte]);
                num += 6;
            }
        }
        if (to.length() % 4 != 0) {
            for (int i = 4 - to.length() % 4; i > 0; i--) {
                to.append("=");
            }
        }
        return to.toString();
    }

    /**
     * Translates the specified Base64 string into a byte array.
     *
     * @param s the Base64 string (not null)
     * @return the byte array (not null)
     */
    public static byte[] decode(String s) {
        int delta = s.endsWith( "==" ) ? 2 : s.endsWith( "=" ) ? 1 : 0;
        byte[] buffer = new byte[s.length() * 3 / 4 - delta];
        int mask = 0xFF;
        int index = 0;
        for (int i = 0; i < s.length(); i += 4) {
            int c0 = toInt[s.charAt( i )];
            int c1 = toInt[s.charAt( i + 1)];
            buffer[index++] = (byte)(((c0 << 2) | (c1 >> 4)) & mask);
            if (index >= buffer.length) {
                return buffer;
            }
            int c2 = toInt[s.charAt( i + 2)];
            buffer[index++] = (byte)(((c1 << 4) | (c2 >> 2)) & mask);
            if (index >= buffer.length) {
                return buffer;
            }
            int c3 = toInt[s.charAt( i + 3 )];
            buffer[index++] = (byte)(((c2 << 6) | c3) & mask);
        }
        return buffer;
    }
}