/*

 * Copyright 1995-2000 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package sun.misc;

import java.io.OutputStream;

import java.io.ByteArrayOutputStream;

import java.io.PushbackInputStream;

import java.io.PrintStream;

import java.io.IOException;

/**

 * This class implements a robust character decoder. The decoder will

 * converted encoded text into binary data.

 *

 * 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>

 *

 * If an error is encountered during decoding this class throws a

 * CEFormatException. The specific detail messages are:

 *

 * <pre>

 *    "UCDecoder: High byte parity error."

 *    "UCDecoder: Low byte parity error."

 *    "UCDecoder: Out of sequence line."

 *    "UCDecoder: CRC check failed."

 * </pre>

 *

 * @author      Chuck McManis

 * @see         CharacterEncoder

 * @see         UCEncoder

 */

public class UCDecoder extends CharacterDecoder {

    /** This class 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();

    /**

     * Decode one atom - reads the characters from the input stream, decodes

     * them, and checks for valid parity.

     */

    protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int l) throws IOException {

        int i, p1, p2, np1, np2;

        byte a = -1, b = -1, c = -1;

        byte high_byte, low_byte;

        byte tmp[] = new byte[3];

        i = inStream.read(tmp);

        if (i != 3) {

                throw new CEStreamExhausted();

        }

        for (i = 0; (i < 64) && ((a == -1) || (b == -1) || (c == -1)); i++) {

            if (tmp[0] == map_array[i]) {

                a = (byte) i;

            }

            if (tmp[1] == map_array[i]) {

                b = (byte) i;

            }

            if (tmp[2] == map_array[i]) {

                c = (byte) i;

            }

        }

        high_byte = (byte) (((a & 0x38) << 2) + (b & 0x1f));

        low_byte = (byte) (((a & 0x7) << 5) + (c & 0x1f));

        p1 = 0;

        p2 = 0;

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

            if ((high_byte & i) != 0)

                p1++;

            if ((low_byte & i) != 0)

                p2++;

        }

        np1 = (b & 32) / 32;

        np2 = (c & 32) / 32;

        if ((p1 & 1) != np1) {

            throw new CEFormatException("UCDecoder: High byte parity error.");

        }

        if ((p2 & 1) != np2) {

            throw new CEFormatException("UCDecoder: Low byte parity error.");

        }

        outStream.write(high_byte);

        crc.update(high_byte);

        if (l == 2) {

            outStream.write(low_byte);

            crc.update(low_byte);

        }

    }

    private ByteArrayOutputStream lineAndSeq = new ByteArrayOutputStream(2);

    /**

     * decodeBufferPrefix initializes the sequence number to zero.

     */

    protected void decodeBufferPrefix(PushbackInputStream inStream, OutputStream outStream) {

        sequence = 0;

    }

    /**

     * decodeLinePrefix reads the sequence number and the number of

     * encoded bytes from the line. If the sequence number is not the

     * previous sequence number + 1 then an exception is thrown.

     * UCE lines are line terminator immune, they all start with *

     * so the other thing this method does is scan for the next line

     * by looking for the * character.

     *

     * @exception CEFormatException out of sequence lines detected.

     */

    protected int decodeLinePrefix(PushbackInputStream inStream, OutputStream outStream)  throws IOException {

        int     i;

        int     nLen, nSeq;

        byte    xtmp[];

        int     c;

        crc.value = 0;

        while (true) {

            c = inStream.read(tmp, 0, 1);

            if (c == -1) {

                throw new CEStreamExhausted();

            }

            if (tmp[0] == '*') {

                break;

            }

        }

        lineAndSeq.reset();

        decodeAtom(inStream, lineAndSeq, 2);

        xtmp = lineAndSeq.toByteArray();

        nLen = xtmp[0] & 0xff;

        nSeq = xtmp[1] & 0xff;

        if (nSeq != sequence) {

            throw new CEFormatException("UCDecoder: Out of sequence line.");

        }

        sequence = (sequence + 1) & 0xff;

        return (nLen);

    }

    /**

     * this method reads the CRC that is at the end of every line and

     * verifies that it matches the computed CRC.

     *

     * @exception CEFormatException if CRC check fails.

     */

    protected void decodeLineSuffix(PushbackInputStream inStream, OutputStream outStream) throws IOException {

        int i;

        int lineCRC = crc.value;

        int readCRC;

        byte tmp[];

        lineAndSeq.reset();

        decodeAtom(inStream, lineAndSeq, 2);

        tmp = lineAndSeq.toByteArray();

        readCRC = ((tmp[0] << 8) & 0xFF00) + (tmp[1] & 0xff);

        if (readCRC != lineCRC) {

            throw new CEFormatException("UCDecoder: CRC check failed.");

        }

    }

}