/*
    * Copyright 2005 Ralf Joachim
    *
    * 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.castor.core.util;
  
  import java.io.ByteArrayOutputStream;
  
  /**
   * Class decodes a Base64 encoded string back into the original byte representation that can be read
   * as byte array.
   *
   * @author <a href="mailto:ralf DOT joachim AT syscon DOT eu">Ralf Joachim</a>
   * @version $Revision: 6907 $ $Date: 2005-08-05 13:58:36 -0600 (Fri, 05 Aug 2005) $
   * @since 0.9.9
   */
  public final class Base64Decoder {
    /** Mask buffer to or with first sextet. */
    private static final int SEXTET_1_MASK = 0x03FFFF;
  
    /** Mask buffer to or with second sextet. */
    private static final int SEXTET_2_MASK = 0xFC0FFF;
  
    /** Mask buffer to or with third sextet. */
    private static final int SEXTET_3_MASK = 0xFFF03F;
  
    /** Mask buffer to or with forth sextet. */
    private static final int SEXTET_4_MASK = 0xFFFFC0;
  
    /** Number of bits to shift for one sextet. */
    private static final int SHIFT_1_SEXTET = 6;
  
    /** Number of bits to shift for two sextet. */
    private static final int SHIFT_2_SEXTET = 12;
  
    /** Number of bits to shift for three sextet. */
    private static final int SHIFT_3_SEXTET = 18;
  
    /** Second sextets in buffer. */
    private static final int SEXTET_2 = 2;
  
    /** Third sextets in buffer. */
    private static final int SEXTET_3 = 3;
  
    /** Forth sextets in buffer. */
    private static final int SEXTET_4 = 4;
  
    /** Mask an octet. */
    private static final int OCTET_MASK = 0xFF;
  
    /** Number of bits to shift for one octet. */
    private static final int SHIFT_1_OCTET = 8;
  
    /** Number of bits to shift for two octet. */
    private static final int SHIFT_2_OCTET = 16;
  
    /** White space character (out of range 0 - 63). */
    private static final byte SPC = 127;
  
    /** Padding character (out of range 0 - 63). */
    private static final byte PAD = 64;
  
    /** Array to translate base64 characters into sextet byte values. */
    private static final byte[] MAP = {SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 00-07
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 08-0F
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 10-17
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 18-1F
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 20-27
        SPC, SPC, SPC, 62, SPC, SPC, SPC, 63, // 28-2F ' + /'
        52, 53, 54, 55, 56, 57, 58, 59, // 30-37 '01234567'
        60, 61, SPC, SPC, SPC, PAD, SPC, SPC, // 38-3F '89 = '
        SPC, 0, 1, 2, 3, 4, 5, 6, // 40-47 ' ABCDEFG'
        7, 8, 9, 10, 11, 12, 13, 14, // 48-4F 'HIJKLMNO'
        15, 16, 17, 18, 19, 20, 21, 22, // 50-57 'PQRSTUVW'
        23, 24, 25, SPC, SPC, SPC, SPC, SPC, // 58-5F 'XYZ '
        SPC, 26, 27, 28, 29, 30, 31, 32, // 60-67 ' abcdefg'
        33, 34, 35, 36, 37, 38, 39, 40, // 68-6F 'hijklmno'
        41, 42, 43, 44, 45, 46, 47, 48, // 70-77 'pqrstuvw'
        49, 50, 51, SPC, SPC, SPC, SPC, SPC, // 78-7F 'xyz '
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 80-87
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 88-8F
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 90-97
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // 98-9F
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // A0-A7
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // A8-AF
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // B0-B7
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // B8-BF
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // C0-C7
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // C8-CF
        SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // D0-D7
       SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // D8-DF
       SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // E0-E7
       SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // E8-EF
       SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // F0-F7
       SPC, SPC, SPC, SPC, SPC, SPC, SPC, SPC, // F8-FF
   };
 
   /** 24-bit buffer to translate 4 sextets into 3 octets. */
   private int _buffer = 0;
 
   /** Number of octets in buffer. */
   private int _sextets = 0;
 
   /** Stream buffer for decoded octets waiting to be read. */
   private ByteArrayOutputStream _stream = new ByteArrayOutputStream();
 
   /**
    * Decode given string into a decoded byte array.
    * 
    * @param str Base64 String to be decoded.
    * @return All decoded octets as byte array.
    */
   public static byte[] decode(final String str) {
     Base64Decoder dec = new Base64Decoder();
     dec.translate(str);
     return dec.getByteArray();
   }
 
   /**
    * Construct a default Base64Decoder waiting on calls to its translate() method.
    */
   public Base64Decoder() {}
 
   /**
    * Translate every base64 character from given string into a sextet byte value by using above
    * translation array. The sextets are then shiftet into an buffer until the buffer contains 4
    * sextets which are then decoded into 3 octets. The translate and decode process is continued
    * until all characters of given string are evaluated. If there are remaing sextets in the buffer
    * they also will be converted into octets at the end. All the converted octets are added to the
    * list for later read.
    * 
    * @param string Base64 String to be decoded.
    */
   public void translate(final String string) {
     int len = string.length();
     int index = 0;
     int data = MAP[string.charAt(index)];
     while ((index < len) && (data != PAD)) {
       if (data != SPC) {
         if (_sextets == 0) {
           _buffer = (_buffer & SEXTET_1_MASK) | (data << SHIFT_3_SEXTET);
         } else if (_sextets == 1) {
           _buffer = (_buffer & SEXTET_2_MASK) | (data << SHIFT_2_SEXTET);
         } else if (_sextets == 2) {
           _buffer = (_buffer & SEXTET_3_MASK) | (data << SHIFT_1_SEXTET);
         } else {
           _buffer = (_buffer & SEXTET_4_MASK) | data;
         }
 
         if ((++_sextets) == SEXTET_4) {
           decode();
         }
       }
 
       if (++index < len) {
         data = MAP[string.charAt(index)];
       }
     }
 
     if (_sextets > 0) {
       decodeWithPadding();
     }
   }
 
   /**
    * Decode 3 octets from buffer and add them to list of octets to read.
    */
   private void decode() {
     _stream.write((byte) ((_buffer >> SHIFT_2_OCTET) & OCTET_MASK)); // octet 1
     _stream.write((byte) ((_buffer >> SHIFT_1_OCTET) & OCTET_MASK)); // octet 2
     _stream.write((byte) (_buffer & OCTET_MASK)); // octet 3
     _buffer = 0;
     _sextets = 0;
   }
 
   /**
    * Decode the remaining octets from buffer and add them to list of octets to read.
    */
   private void decodeWithPadding() {
     if (_sextets >= SEXTET_2) { // octet 1
       _stream.write((byte) ((_buffer >> SHIFT_2_OCTET) & OCTET_MASK));
     }
     if (_sextets >= SEXTET_3) { // octet 2
       _stream.write((byte) ((_buffer >> SHIFT_1_OCTET) & OCTET_MASK));
     }
     if (_sextets >= SEXTET_4) { // octet 3
       _stream.write((byte) (_buffer & OCTET_MASK));
     }
     _buffer = 0;
     _sextets = 0;
   }
 
   /**
    * Get all decoded octets as byte array.
    * 
    * @return All decoded octets as byte array.
    */
   public byte[] getByteArray() {
     return _stream.toByteArray();
   }
 }