/* gnu.classpath.tools.NotifyingInputStreamReader
   Copyright (C) 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */

package gnu.classpath.tools;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;

import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;

import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 *  Similar to {@link java.io.InputStreamReader}, but can give
 *  notification when malformed input is encountered.
 *
 *  <p> Users of this class can register interest in the event of
 *  malformed input by calling {@link
 *  #addMalformedInputListener}. Each time a run of malformed input
 *  data is encountered, all listener objects are notified. For
 *  instance, this allows the calling code to inform the user about
 *  problems in the input stream. </p>
 *
 *  <p> <strong>Background:</strong> The default
 *  <code>InputStreamReader</code> implementation will ignore
 *  malformed input, silently replacing it with the default
 *  replacement string (usually the question mark). Alternatively, you
 *  can configure a <code>CharsetDecoder</code> for the default
 *  <char>InputStreamReader</code> implementation, instructing it to
 *  ignore malformed input without replacing it; to replace it with a
 *  different string; or to throw an exception when malformed input is
 *  encountered. However, you cannot configure an
 *  <code>InputStreamReader</code> to gracefully handle malformed data
 *  but notify the client code about such
 *  problems. <code>NotifyingInputStreamReader</code> fills this
 *  gap. </p>
 *
 *  @author Julian Scheid
 */
public class NotifyingInputStreamReader 
   extends Reader
{
   /**
    *  The default size (in bytes) for byteBuf, i.e. the size of data
    *  chunks read from the underlying input stream.
    */
   private static final int DEFAULT_INPUT_BUFFER_SIZE = 64;

   /**
    *  The default size (in chars) for charBuf. This should be large
    *  enough to hold a decoded chunk of input data for the Charset
    *  with the minimum number of bytes per character. Since the
    *  minimum number of bytes per character for usual Charsets is
    *  one, this number should be identical to
    *  DEFAULT_INPUT_BUFFER_SIZE.
    */
   private static final int DEFAULT_OUTPUT_BUFFER_SIZE = 64;

   /**
    *  The underlying InputStream.
    */
   private InputStream in;

   /**
    *  The CharsetDecoder used to decode the underlying stream.
    */
   private CharsetDecoder decoder;

   /**
    *  Holds bytes already read from the underlying stream, but not
    *  yet decoded.
    */
   private ByteBuffer byteBuffer;

   /**
    *  Holds characters already decoded, but not yet fetched via
    *  read().
    */
   private CharBuffer charBuffer;
   
   /**
    *  This is the primitive byte array wrapped in byteBuffer for
    *  passing to to InputStream.read().
    */
   private byte[] readBuffer;

   /**
    *  Keeps track of the current line number (1-based).
    */
   private int lineNumber = 1;

   /**
    *  Keeps track of the current column number (0-based).
    */
   private int columnNumber = 0;

   /**
    *  Becomes true as soon as EOF has been reached in the underlying
    *  InputStream. At this point, byteBuffer contains the last chunk
    *  of data from the underlying InputStream.
    */
   private boolean allInputConsumed = false;

   /**
    *  Becomes true as soon as the decoder has been supplied with the
    *  last chunk of data from the InputStream after EOF has been
    *  reached. At this point, the last chunk of data has been drained
    *  from the byteBuffer.
    */
   private boolean decodingFinished = false;

   /**
    *  Becomes true as soon as the decoder has been flushed. At this
    *  point, the last chunk of character data has been written to the
    *  charBuffer.
    */
   private boolean flushed = false;

   /**
    *  Stores all registered MalformedInputListeners.
    */
   private Set listeners = new LinkedHashSet();

   /**
    *  Initializes a new instance for reading from the given
    *  InputStream using the default encoding. The default encoding is
    *  currently determined by looking at the system property
    *  <code>file.encoding</code>. If this property isn't set,
    *  <code>ISO-8859-1</code> is used as a fallback.
    *
    *  <p>This method should use {@link Charset.defaultCharset()}
    *  instead, but this isn't implemented in Classpath at the
    *  moment.</p>
    *
    *  @param in the <code>InputStream</code> to read from.
    */
   public NotifyingInputStreamReader(InputStream in)
   {
      this(in, System.getProperty("file.encoding", "ISO-8859-1"));
   }

   /**
    *  Initializes a new instance for reading from the given
    *  InputStream using the specified charset.
    *
    *  @param in the <code>InputStream</code> to read from.
    *  @param charsetName the canonical name or an alias of a
    *  <code>Charset</code>.
    *
    *  @throws IllegalCharsetNameException if there is no
    *  <code>Charset</code> with the given canonical name or alias.
    *
    *  @throws UnsupportedCharsetException if there is no support for
    *  the specified <code>Charset</code> in the runtime environment.
    */
   public NotifyingInputStreamReader(InputStream in, String charsetName)
      throws IllegalCharsetNameException, UnsupportedCharsetException
   {
      this(in, Charset.forName(charsetName));
   }

   /**
    *  Initializes a new instance for reading from the given
    *  InputStream using the specified charset.
    *
    *  @param in the <code>InputStream</code> to read from.
    *  @param charset the <code>Charset</code> to use for decoding
    *  characters.
    */
   public NotifyingInputStreamReader(InputStream in, Charset charset)
   {
      this(in, charset.newDecoder());
   }

   /**
    *  Initializes a new instance for reading from the given
    *  InputStream using the specified charset decoder.
    *
    *  <strong>Note:</strong> the
    *  <code>NotifyingInputStreamReader</code> will not exhibit the
    *  advertised behaviour if you changed the action to take on
    *  malformed input in the specified
    *  <code>CharsetDecoder</code>. In other words, you should not
    *  call {@link CharsetDecoder.onMalformedInput(CodingErrorAction)}
    *  on the specified decoder before or while this reader is being
    *  used unless you know what you're doing.
    *
    *  @param in the <code>InputStream</code> to read from.
    *  @param charset the <code>CharsetDecoder</code> to use for
    *  decoding characters.
    */
   public NotifyingInputStreamReader(InputStream in, CharsetDecoder decoder)
   {
      this.in = in;
      this.decoder = decoder;
      this.charBuffer = CharBuffer.wrap(new char[DEFAULT_INPUT_BUFFER_SIZE]);
      this.charBuffer.position(charBuffer.limit());
      this.readBuffer = new byte[DEFAULT_OUTPUT_BUFFER_SIZE];
      this.byteBuffer = ByteBuffer.wrap(readBuffer);
      this.byteBuffer.position(byteBuffer.limit());
   }

   public void close()
      throws IOException
   {
      in.close();
   }

   /**
    *  Fill charBuffer with new character data. This method returns if
    *  either the charBuffer has been filled completely with decoded
    *  character data, or if EOF is reached in the underlying
    *  InputStream. When this method returns, charBuffer is flipped
    *  and ready to be read from.
    */
   private void fillCharBuf()
      throws IOException
   {
      charBuffer.clear();
   outer:
      while (!flushed) {
         CoderResult coderResult;
         int charBufferPositionBefore = charBuffer.position();
         if (!decodingFinished) {
            coderResult = decoder.decode(byteBuffer, charBuffer, allInputConsumed);
            if (allInputConsumed) {
               decodingFinished = true;
            }
         }
         else {
            coderResult = decoder.flush(charBuffer);
            flushed = coderResult.isUnderflow();
         }

         int charBufferPositionAfter = charBuffer.position();
         for (int i=charBufferPositionBefore; i<charBufferPositionAfter; ++i) {
            if (10 == charBuffer.get(i)) {
               ++ lineNumber;
               columnNumber = 0;
            }
            else {
               ++ columnNumber;
            }
         }
         if (coderResult.isOverflow()) {
            break;
         }
         else if (coderResult.isUnderflow()) {
            if (!allInputConsumed) {
               int nRemainingBytes = 0;
               if (byteBuffer.position() > 0) {
                  nRemainingBytes = Math.max(0, byteBuffer.limit() - byteBuffer.position());
               }
               if (nRemainingBytes > 0) {
                  byteBuffer.get(readBuffer, 0, nRemainingBytes);
               }
               byteBuffer.rewind();
               int nread = in.read(readBuffer, nRemainingBytes, 
                                   readBuffer.length - nRemainingBytes);
               if (nread < 0) {
                  allInputConsumed = true;
               }
               byteBuffer.limit(nRemainingBytes + Math.max(0, nread));
            }
            else {
               break;
            }
         }
         else if (coderResult.isMalformed()) {
            fireMalformedInputEncountered(coderResult.length());
            String replacement = decoder.replacement();
            for (int i=0; i<coderResult.length(); ++i) {
               if (charBuffer.remaining() > replacement.length()) {
                  charBuffer.put(replacement);
                  byteBuffer.position(byteBuffer.position() + 1);
                  columnNumber ++;
               }
               else {
                  break outer;
               }
            }
         }
         else if (coderResult.isUnmappable()) {
            // This should not happen, since unmappable input bytes
            // trigger a "malformed" event instead.
            coderResult.throwException();
         }
         else {
            // This should only happen if run in a future environment
            // where additional events apart from underflow, overflow,
            // malformed and unmappable can be generated.
            coderResult.throwException();
         }
      }
      charBuffer.flip();
   }

   /**
    *  Fire a MalformedInputEvent, notifying all registered listeners.
    */
   private void fireMalformedInputEncountered(int length)
   {
      MalformedInputEvent event
         = new MalformedInputEvent(this, lineNumber, columnNumber, length);
      Iterator it = listeners.iterator();
      while (it.hasNext()) {
         MalformedInputListener listener
            = (MalformedInputListener)it.next();
         listener.malformedInputEncountered(event);
      }
   }
   
   public int read(char[] cbuf, int offset, int length)
      throws IOException
   {
      if (flushed) {
         return -1;
      }
      else {
         int nread = 0;
         while (nread < length && !flushed) {
            while (charBuffer.hasRemaining() && nread < length) {
               int copyLen = Math.min(length - nread, 
                                      charBuffer.remaining());
               charBuffer.get(cbuf, offset + nread, copyLen);
               nread += copyLen;
            }
            if (nread < length) {
               fillCharBuf();
            }
         }
         return nread;
      }
   }

   public int read()
      throws IOException
   {
      while (!flushed) {
         if (charBuffer.hasRemaining()) {
            return charBuffer.get();
         }
         else {
            fillCharBuf();
         }
      }
      return -1;
   }

   /**
    *  Returns whether this reader is ready. The reader is ready if
    *  there is data in the internal buffer, or if additional data can
    *  be read from the underlying InputStream.
    */
   public boolean ready()
   {
      return charBuffer.hasRemaining() || !flushed;
   }

   /**
    *  Register a <code>MalformedInputListener</code> which should be
    *  notified when malformed input is encountered.
    */
   public void addMalformedInputListener(MalformedInputListener listener)
   {
      this.listeners.add(listener);
   }

   /**
    *  Unregister a previously registered
    *  <code>MalformedInputListener</code> if it should no longer be
    *  notified when malformed input is encountered.
    */
   public void removeMalformedInputListener(MalformedInputListener listener)
   {
      this.listeners.remove(listener);
   }

}