/*

 * Copyright (c) 1995, 1997, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.misc;

import java.io.OutputStream;

import java.io.InputStream;

import java.io.PrintStream;

import java.io.IOException;

/**

 * This class implements a robust character encoder. The encoder is designed

 * to convert binary data into printable characters. The characters are

 * assumed to exist but they are not assumed to be ASCII, the complete set

 * is 0-9, A-Z, a-z, "(", and ")".

 *

 * The basic encoding unit is a 3 character atom. It encodes two bytes

 * of data. Bytes are encoded into a 64 character set, the characters

 * were chosen specifically because they appear in all codesets.

 * We don't care what their numerical equivalent is because

 * we use a character array to map them. This is like UUencoding

 * with the dependency on ASCII removed.

 *

 * The three chars that make up an atom are encoded as follows:

 * <pre>

 *      00xxxyyy 00axxxxx 00byyyyy

 *      00 = leading zeros, all values are 0 - 63

 *      xxxyyy - Top 3 bits of X, Top 3 bits of Y

 *      axxxxx - a = X parity bit, xxxxx lower 5 bits of X

 *      byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y

 * </pre>

 *

 * The atoms are arranged into lines suitable for inclusion into an

 * email message or text file. The number of bytes that are encoded

 * per line is 48 which keeps the total line length  under 80 chars)

 *

 * Each line has the form(

 * <pre>

 *  *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)

 *  Where each (xxx) represents a three character atom.

 *  (LLSS) - 8 bit length (high byte), and sequence number

 *           modulo 256;

 *  (DDDD) - Data byte atoms, if length is odd, last data

 *           atom has (DD00) (high byte data, low byte 0)

 *  (CRC)  - 16 bit CRC for the line, includes length,

 *           sequence, and all data bytes. If there is a

 *           zero pad byte (odd length) it is _NOT_

 *           included in the CRC.

 * </pre>

 *

 * @author      Chuck McManis

 * @see         CharacterEncoder

 * @see         UCDecoder

 */

public class UCEncoder extends CharacterEncoder {

    /** this clase encodes two bytes per atom */

    protected int bytesPerAtom() {

        return (2);

    }

    /** this class encodes 48 bytes per line */

    protected int bytesPerLine() {

        return (48);

    }

    /* this is the UCE mapping of 0-63 to characters .. */

    private final static byte map_array[] = {

        //     0         1         2         3         4         5         6         7

        (byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0

        (byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1

        (byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2

        (byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3

        (byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4

        (byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5

        (byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6

        (byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')'  // 7

    };

    private int sequence;

    private byte tmp[] = new byte[2];

    private CRC16 crc = new CRC16();

    /**

     * encodeAtom - take two bytes and encode them into the correct

     * three characters. If only one byte is to be encoded, the other

     * must be zero. The padding byte is not included in the CRC computation.

     */

    protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len) throws IOException

    {

        int     i;

        int     p1, p2; // parity bits

        byte    a, b;

        a = data[offset];

        if (len == 2) {

            b = data[offset+1];

        } else {

            b = 0;

        }

        crc.update(a);

        if (len == 2) {

            crc.update(b);

        }

        outStream.write(map_array[((a >>> 2) & 0x38) + ((b >>> 5) & 0x7)]);

        p1 = 0; p2 = 0;

        for (i = 1; i < 256; i = i * 2) {

            if ((a & i) != 0) {

                p1++;

            }

            if ((b & i) != 0) {

                p2++;

            }

        }

        p1 = (p1 & 1) * 32;

        p2 = (p2 & 1) * 32;

        outStream.write(map_array[(a & 31) + p1]);

        outStream.write(map_array[(b & 31) + p2]);

        return;

    }

    /**

     * Each UCE encoded line starts with a prefix of '*[XXX]', where

     * the sequence number and the length are encoded in the first

     * atom.

     */

    protected void encodeLinePrefix(OutputStream outStream, int length) throws IOException {

        outStream.write('*');

        crc.value = 0;

        tmp[0] = (byte) length;

        tmp[1] = (byte) sequence;

        sequence = (sequence + 1) & 0xff;

        encodeAtom(outStream, tmp, 0, 2);

    }

    /**

     * each UCE encoded line ends with YYY and encoded version of the

     * 16 bit checksum. The most significant byte of the check sum

     * is always encoded FIRST.

     */

    protected void encodeLineSuffix(OutputStream outStream) throws IOException {

        tmp[0] = (byte) ((crc.value >>> 8) & 0xff);

        tmp[1] = (byte) (crc.value & 0xff);

        encodeAtom(outStream, tmp, 0, 2);

        super.pStream.println();

    }

    /**

     * The buffer prefix code is used to initialize the sequence number

     * to zero.

     */

    protected void encodeBufferPrefix(OutputStream a) throws IOException {

        sequence = 0;

        super.encodeBufferPrefix(a);

    }

}