/* -*- Mode: java; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.0 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.  See
 * the License for the specific language governing rights and limitations
 * under the License.
 *
 * The Original Code is the Grendel mail/news client.
 *
 * The Initial Developer of the Original Code is Netscape Communications
 * Corporation.  Portions created by Netscape are Copyright (C) 1997
 * Netscape Communications Corporation.  All Rights Reserved.
 *
 * Created: Jamie Zawinski <jwz@netscape.com>, 28 Aug 1997.
 *
 * Contributors: Edwin Woudt <edwin@woudt.nl>
 */

package grendel.mime.encoder;

import calypso.util.ByteBuf;

/** Implements a plaintext -> Base64 encoder.
 */
public final class MimeBase64Decoder extends MimeEncoder {

  private byte token[] = new byte[4];      // input buffer
  private byte bytes[] = new byte[3];      // output buffer
  private int token_length = 0;            // input buffer length

  static private final byte NUL = 127;     // must be out of range 0-64
  static private final byte EOF = 126;     // must be out of range 0-64

  static private final byte map[] = {
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   000-007
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   010-017
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   020-027
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   030-037
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   040-047   !"#$%&'
    NUL, NUL, NUL,  62, NUL, NUL, NUL,  63,      //   050-057  ()*+,-./
     52,  53,  54,  55,  56,  57,  58,  59,      //   060-067  01234567
     60,  61, NUL, NUL, NUL, EOF, NUL, NUL,      //   070-077  89:;<=>?

    NUL,   0,   1,   2,   3,   4,   5,   6,      //   100-107  @ABCDEFG
      7,   8,   9,  10,  11,  12,  13,  14,      //   110-117  HIJKLMNO
     15,  16,  17,  18,  19,  20,  21,  22,      //   120-127  PQRSTUVW
     23,  24,  25, NUL, NUL, NUL, NUL, NUL,      //   130-137  XYZ[\]^_
    NUL,  26,  27,  28,  29,  30,  31,  32,      //   140-147  `abcdefg
     33,  34,  35,  36,  37,  38,  39,  40,      //   150-157  hijklmno
     41,  42,  43,  44,  45,  46,  47,  48,      //   160-167  pqrstuvw
     49,  50,  51, NUL, NUL, NUL, NUL, NUL,      //   170-177  xyz{|}~

    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   200-207
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   210-217
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   220-227
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   230-237
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   240-247
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   250-257
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   260-267
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   270-277

    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   300-307
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   310-317
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   320-327
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   330-337
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   340-347
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   350-357
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   360-367
    NUL, NUL, NUL, NUL, NUL, NUL, NUL, NUL,      //   370-377
  };


  // Fast routine that assumes full 4-char tokens with no '=' in them.
  //
  private final void decode_token(ByteBuf out) {

    int num = ((map[token[0]] << 18) |
               (map[token[1]] << 12) |
               (map[token[2]] << 6) |
               (map[token[3]]));

    bytes[0] = (byte) (0xFF & (num >> 16));
    bytes[1] = (byte) (0xFF & (num >> 8));
    bytes[2] = (byte) (0xFF & num);

    out.append(bytes);
  }


  // Hairier routine that deals with the final token, which can have fewer
  // than four characters, and that might be padded with '='.
  //
  private final void decode_final_token(ByteBuf out) {

    byte b0 = map[token[0]];
    byte b1 = map[token[1]];
    byte b2 = map[token[2]];
    byte b3 = map[token[3]];

    int eq_count = 0;

    if (b0 == EOF) { b0 = 0; eq_count++; }
    if (b1 == EOF) { b1 = 0; eq_count++; }
    if (b2 == EOF) { b2 = 0; eq_count++; }
    if (b3 == EOF) { b3 = 0; eq_count++; }

    int num = ((b0 << 18) | (b1 << 12) | (b2 << 6) | (b3));

    // eq_count will be 0, 1, or 2.
    // No "=" padding means 4 bytes mapped to 3, the normal case,
    //        not handled in this routine.
    // "xxx=" means 3 bytes mapped to 2.
    // "xx==" means 2 bytes mapped to 1.
    // "x===" can't happen, because "x" would then be encoding
    //        only 6 bits, not 8, the minimum possible.

    out.append((byte) (num >> 16));             // byte 1, count = 0 or 1 or 2
    if (eq_count <= 1) {
      out.append((byte) ((num >> 8) & 0xFF));   // byte 2, count = 0 or 1
      if (eq_count == 0) {
        out.append((byte) (num & 0xFF));        // byte 3, count = 0
      }
    }
  }


  /** Given a sequence of input bytes using the Base64 encoding, produces a
      sequence of unencoded output bytes.  Note that some (small) amount of
      buffering may be necessary, if the input byte stream didn't fall on an
      appropriate boundary.  If there are bytes in `out' already, the new
      bytes are appended, so the caller should do `out.setLength(0)' first
      if that's desired.
   */
  public final void translate(ByteBuf in, ByteBuf out) {

    if (token == null) // already saw eof marker?
      return;

    byte inb[] = in.toBytes();
    int in_length = in.length();

    for (int i = 0; i < in_length; i++) {
      byte b = inb[i];
      byte t = map[b];

      if (t != NUL)
        token[token_length++] = b;

      if (t == EOF) {
        eof(out);
        return;

      } else if (token_length == 4) {
        decode_token(out);
        token_length = 0;
      }
    }
  }


  /** Tell the Base64 decoder that no more input data will be forthcoming.
      This may result in output, as a result of flushing the internal buffer.
      This object must not be used again after calling eof().  If there are
      bytes in `out' already, the new bytes are appended, so the caller should
      do `out.setLength(0)' first if that's desired.
   */
  public final void eof(ByteBuf out) {
    if (token != null && token_length != 0) {
      while (token_length < 4)
        token[token_length++] = (byte)'=';
      decode_final_token(out);
    }
    token_length = 0;
    token = null;
    bytes = null;
  }

}
