/*
 * Copyright (c) 1995, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * 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
 */

package com.sun.ts.lib.util;

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:
 *
 * <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 */
  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(PushbackInputStream aStream,
      OutputStream bStream) throws IOException {
  }

  /** 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.
   */
  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.
   */
  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 <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.
   */
  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 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.
   * 
   * @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.
   */
  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.
   */
  public ByteBuffer decodeBufferToByteBuffer(String inputString)
      throws IOException {
    return ByteBuffer.wrap(decodeBuffer(inputString));
  }

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