/*
 * Copyright (c) 2000, 2017 Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2021 Contributors to the Eclipse Foundation
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

/*
 * @(#)CharacterDecoder.java	1.4 06/29/07
 */

package com.sun.messaging.jmq.util;

import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;

/**
 * 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>
 *
 * Several useful decoders have already been written and are referenced in the See Also list below.
 *
 * @see CharacterEncoder
 * @see UCDecoder
 * @see UUDecoder
 * @see BASE64Decoder
 */

public abstract class CharacterDecoder {

    /** 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 */
    abstract protected int bytesPerLine();

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

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

    /**
     * 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(InputStream aStream, OutputStream bStream, int l) throws IOException {
        throw new CEStreamExhausted();
    }

    /**
     * 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.
     *
     * @exception CEStreamExhausted The input stream is unexpectedly out of data
     */
    public void decodeBuffer(InputStream aStream, OutputStream bStream) throws IOException {
        int i;

        decodeBufferPrefix(aStream, bStream);
        while (true) {
            int length;

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

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

        byte inputBuffer[] = inputString.getBytes();
        inStream = new ByteArrayInputStream(inputBuffer);
        outStream = new ByteArrayOutputStream();
        decodeBuffer(inStream, outStream);
        return (outStream.toByteArray());
    }

    /**
     * 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());
    }
}
