/*
 * Copyright (c) 1995, 2004, 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.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.PushbackInputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;

This class defines the decoding half of character encoders.
A character decoder is an algorithim for transforming 8 bit
binary data that has been encoded into text by a character
encoder, back into original binary form.
The character encoders, in general, have been structured
around a central theme that binary data can be encoded into
text that has the form:
     [Buffer Prefix]
     [Line Prefix][encoded data atoms][Line Suffix]
     [Buffer Suffix]

Of course in the simplest encoding schemes, the buffer has no
distinct prefix of suffix, however all have some fixed relationship
between the text in an 'atom' and the binary data itself.
In the CharacterEncoder and CharacterDecoder classes, one complete
chunk of data is referred to as a buffer. Encoded buffers
are all text, and decoded buffers (sometimes just referred to as
buffers) are binary octets.
To create a custom decoder, you must, at a minimum,  overide three
abstract methods in this class.

bytesPerAtom which tells the decoder how many bytes to
expect from decodeAtom
decodeAtom which decodes the bytes sent to it as text.
bytesPerLine which tells the encoder the maximum number of
bytes per line.

In general, the character decoders return error in the form of a
CEFormatException. The syntax of the detail string is
     DecoderClassName: Error message.

Several useful decoders have already been written and are
referenced in the See Also list below.
Author:
     Chuck McManis
See Also:
CEFormatException
CharacterEncoder
UCDecoder
UUDecoder
BASE64Decoder/**
 * This class defines the decoding half of character encoders.
 * A character decoder is an algorithim for transforming 8 bit
 * binary data that has been encoded into text by a character
 * encoder, back into original binary form.
 *
 * The character encoders, in general, have been structured
 * around a central theme that binary data can be encoded into
 * text that has the form:
 *
 * <pre>
 *      [Buffer Prefix]
 *      [Line Prefix][encoded data atoms][Line Suffix]
 *      [Buffer Suffix]
 * </pre>
 *
 * Of course in the simplest encoding schemes, the buffer has no
 * distinct prefix of suffix, however all have some fixed relationship
 * between the text in an 'atom' and the binary data itself.
 *
 * In the CharacterEncoder and CharacterDecoder classes, one complete
 * chunk of data is referred to as a <i>buffer</i>. Encoded buffers
 * are all text, and decoded buffers (sometimes just referred to as
 * buffers) are binary octets.
 *
 * To create a custom decoder, you must, at a minimum,  overide three
 * abstract methods in this class.
 * <DL>
 * <DD>bytesPerAtom which tells the decoder how many bytes to
 * expect from decodeAtom
 * <DD>decodeAtom which decodes the bytes sent to it as text.
 * <DD>bytesPerLine which tells the encoder the maximum number of
 * bytes per line.
 * </DL>
 *
 * In general, the character decoders return error in the form of a
 * CEFormatException. The syntax of the detail string is
 * <pre>
 *      DecoderClassName: Error message.
 * </pre>
 *
 * Several useful decoders have already been written and are
 * referenced in the See Also list below.
 *
 * @author      Chuck McManis
 * @see         CEFormatException
 * @see         CharacterEncoder
 * @see         UCDecoder
 * @see         UUDecoder
 * @see         BASE64Decoder
 */

public abstract class CharacterDecoder {

    
Return the number of bytes per atom of decoding /** Return the number of bytes per atom of decoding */
    abstract protected int bytesPerAtom();

    
Return the maximum number of bytes that can be encoded per line /** Return the maximum number of bytes that can be encoded per line */
    abstract protected int bytesPerLine();

    
decode the beginning of the buffer, by default this is a NOP. /** decode the beginning of the buffer, by default this is a NOP. */
    protected void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }

    
decode the buffer suffix, again by default it is a NOP. /** decode the buffer suffix, again by default it is a NOP. */
    protected void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }

    
This method should return, if it knows, the number of bytes
that will be decoded. Many formats such as uuencoding provide
this information. By default we return the maximum bytes that
could have been encoded on the line.
/**
     * This method should return, if it knows, the number of bytes
     * that will be decoded. Many formats such as uuencoding provide
     * this information. By default we return the maximum bytes that
     * could have been encoded on the line.
     */
    protected int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException {
        return (bytesPerLine());
    }

    
This method post processes the line, if there are error detection
or correction codes in a line, they are generally processed by
this method. The simplest version of this method looks for the
(newline) character.
/**
     * This method post processes the line, if there are error detection
     * or correction codes in a line, they are generally processed by
     * this method. The simplest version of this method looks for the
     * (newline) character.
     */
    protected void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }

    
This method does an actual decode. It takes the decoded bytes and
writes them to the OutputStream. The integer l tells the
method how many bytes are required. This is always <= bytesPerAtom().
/**
     * This method does an actual decode. It takes the decoded bytes and
     * writes them to the OutputStream. The integer <i>l</i> tells the
     * method how many bytes are required. This is always <= bytesPerAtom().
     */
    protected void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l) throws IOException {
        throw new CEStreamExhausted();
    }

    
This method works around the bizarre semantics of BufferedInputStream's
read method.
/**
     * This method works around the bizarre semantics of BufferedInputStream's
     * read method.
     */
    protected int readFully(InputStream in, byte buffer[], int offset, int len)
        throws java.io.IOException {
        for (int i = 0; i < len; i++) {
            int q = in.read();
            if (q == -1)
                return ((i == 0) ? -1 : i);
            buffer[i+offset] = (byte)q;
        }
        return len;
    }

    
Decode the text from the InputStream and write the decoded
octets to the OutputStream. This method runs until the stream
is exhausted.
Throws:
CEFormatException – An error has occured while decoding
CEStreamExhausted – The input stream is unexpectedly out of data/**
     * Decode the text from the InputStream and write the decoded
     * octets to the OutputStream. This method runs until the stream
     * is exhausted.
     * @exception CEFormatException An error has occured while decoding
     * @exception CEStreamExhausted The input stream is unexpectedly out of data
     */
    public void decodeBuffer(InputStream aStream, OutputStream bStream) throws IOException {
        int     i;
        int     totalBytes = 0;

        PushbackInputStream ps = new PushbackInputStream (aStream);
        decodeBufferPrefix(ps, bStream);
        while (true) {
            int length;

            try {
                length = decodeLinePrefix(ps, bStream);
                for (i = 0; (i+bytesPerAtom()) < length; i += bytesPerAtom()) {
                    decodeAtom(ps, bStream, bytesPerAtom());
                    totalBytes += bytesPerAtom();
                }
                if ((i + bytesPerAtom()) == length) {
                    decodeAtom(ps, bStream, bytesPerAtom());
                    totalBytes += bytesPerAtom();
                } else {
                    decodeAtom(ps, bStream, length - i);
                    totalBytes += (length - i);
                }
                decodeLineSuffix(ps, bStream);
            } catch (CEStreamExhausted e) {
                break;
            }
        }
        decodeBufferSuffix(ps, bStream);
    }

    
Alternate decode interface that takes a String containing the encoded
buffer and returns a byte array containing the data.
Throws:
CEFormatException – An error has occured while decoding/**
     * Alternate decode interface that takes a String containing the encoded
     * buffer and returns a byte array containing the data.
     * @exception CEFormatException An error has occured while decoding
     */
    public byte decodeBuffer(String inputString)[] throws IOException {
        byte    inputBuffer[] = new byte[inputString.length()];
        ByteArrayInputStream inStream;
        ByteArrayOutputStream outStream;

        inputString.getBytes(0, inputString.length(), inputBuffer, 0);
        inStream = new ByteArrayInputStream(inputBuffer);
        outStream = new ByteArrayOutputStream();
        decodeBuffer(inStream, outStream);
        return (outStream.toByteArray());
    }

    
Decode the contents of the inputstream into a buffer.
/**
     * Decode the contents of the inputstream into a buffer.
     */
    public byte decodeBuffer(InputStream in)[] throws IOException {
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        decodeBuffer(in, outStream);
        return (outStream.toByteArray());
    }

    
Decode the contents of the String into a ByteBuffer.
/**
     * Decode the contents of the String into a ByteBuffer.
     */
    public ByteBuffer decodeBufferToByteBuffer(String inputString)
        throws IOException {
        return ByteBuffer.wrap(decodeBuffer(inputString));
    }

    
Decode the contents of the inputStream into a ByteBuffer.
/**
     * Decode the contents of the inputStream into a ByteBuffer.
     */
    public ByteBuffer decodeBufferToByteBuffer(InputStream in)
        throws IOException {
        return ByteBuffer.wrap(decodeBuffer(in));
    }
}