/* Copyright (C) 1998, 1999  Cygnus Solutions

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */
 
package java.io;

/**
 * @author Per Bothner <bothner@cygnus.com>
 * @date April 22, 1998.  
 */
/* Written using "Java Class Libraries", 2nd edition, plus online
 * API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct.
 */

public class BufferedReader extends Reader
{
  Reader in;
  char[] buffer;
  /* Index of current read position.  Must be >= 0 and <= limit. */
  /* There is a special case where pos may be equal to limit+1; this
   * is used as an indicator that a readLine was done with a '\r' was
   * the very last char in the buffer.  Since we don't want to read-ahead
   * and potentially block, we set pos this way to indicate the situation
   * and deal with it later.  Doing it this way rather than having a
   * separate boolean field to indicate the condition has the advantage
   * that it is self-clearing on things like mark/reset.
   */
  int pos;
  /* Limit of valid data in buffer.  Must be >= pos and <= buffer.length. */
  /* This can be < pos in the one special case described above. */
  int limit;

  /* The value -1 means there is no mark, or the mark has been invalidated.
     Otherwise, markPos is the index in the buffer of the marked position.
     Must be >= 0 and <= pos.
     Note we do not explicitly store the read-limit.
     The implicit read-limit is (buffer.length - markPos), which is
     guaranteed to be >= the read-limit requested in the call to mark. */
  int markPos = -1;

  public BufferedReader(Reader in)
  {
    this(in, 8192);
  }

  public BufferedReader(Reader in, int size)
  {
    super(in.lock);
    this.in = in;
    buffer = new char[size];
  }

  public void close() throws IOException
  {
    synchronized (lock)
      {
	if (in != null)
	  in.close();
	in = null;
	buffer = null;
      }
  }

  public boolean markSupported()
  {
    return true;
  }

  public void mark(int readLimit) throws IOException
  {
    synchronized (lock)
      {
	// In this method we need to be aware of the special case where
	// pos + 1 == limit.  This indicates that a '\r' was the last char
	// in the buffer during a readLine.  We'll want to maintain that
	// condition after we shift things around and if a larger buffer is
	// needed to track readLimit, we'll have to make it one element
	// larger to ensure we don't invalidate the mark too early, if the
	// char following the '\r' is NOT a '\n'.  This is ok because, per
	// the spec, we are not required to invalidate when passing readLimit.
	//
	// Note that if 'pos > limit', then doing 'limit -= pos' will cause
	// limit to be negative.  This is the only way limit will be < 0.

	if (pos + readLimit > limit)
	  {
	    char[] old_buffer = buffer;
	    int extraBuffSpace = 0;
	    if (pos > limit)
	      extraBuffSpace = 1;
	    if (readLimit + extraBuffSpace > limit)
	      buffer = new char[readLimit + extraBuffSpace];
	    limit -= pos;
	    if (limit >= 0)
	      {
	        System.arraycopy(old_buffer, pos, buffer, 0, limit);
	        pos = 0;
	      }
	  }

	if (limit < 0)
	  {
	    // Maintain the relationship of 'pos > limit'.
	    pos = 1;
	    limit = markPos = 0;
	  }
	else
	  markPos = pos;
	// Now pos + readLimit <= buffer.length. thus if we need to read
	// beyond buffer.length, then we are allowed to invalidate markPos.
      }
  }

  public void reset() throws IOException
  {
    synchronized (lock)
      {
	if (markPos < 0)
	  throw new IOException("mark never set or invalidated");

	// Need to handle the extremely unlikely case where a readLine was
	// done with a '\r' as the last char in the buffer; which was then
	// immediately followed by a mark and a reset with NO intervening
	// read of any sort.  In that case, setting pos to markPos would
	// lose that info and a subsequent read would thus not skip a '\n'
	// (if one exists).  The value of limit in this rare case is zero.
	// We can assume that if limit is zero for other reasons, then
	// pos is already set to zero and doesn't need to be readjusted.
	if (limit > 0)
	  pos = markPos;
      }
  }

  public boolean ready() throws IOException
  {
    synchronized (lock)
      {
	return pos < limit || in.ready();
      }
  }

  public int read(char[] buf, int offset, int count) throws IOException
  {
    synchronized (lock)
      {
	// Once again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we'll
	// need to skip a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit'.
	boolean retAtEndOfBuffer = false;

	int avail = limit - pos;
	if (count > avail)
	  {
	    if (avail > 0)
	      count = avail;
	    else // pos >= limit
	      {
		if (limit == buffer.length)
		  markPos = -1; // read too far - invalidate the mark.
		if (pos > limit)
		  {
		    // Set a boolean and make pos == limit to simplify things.
		    retAtEndOfBuffer = true;
		    --pos;
		  }
		if (markPos < 0)
		  {
		    // Optimization:  can read directly into buf.
		    if (count >= buffer.length && !retAtEndOfBuffer)
		      return in.read(buf, offset, count);
		    pos = limit = 0;
		  }
		avail = in.read(buffer, limit, buffer.length - limit);
		if (retAtEndOfBuffer && avail > 0 && buffer[limit] == '\n')
		  {
		    --avail;
		    limit++;
		  }
		if (avail < count)
		  {
		    if (avail <= 0)
		      return avail;
		    count = avail;
		  }
		limit += avail;
	      }
	  }
	System.arraycopy(buffer, pos, buf, offset, count);
	pos += count;
	return count;
      }
  }

  /* Read more data into the buffer.  Update pos and limit appropriately.
     Assumes pos==limit initially.  May invalidate the mark if read too much.
     Return number of chars read (never 0), or -1 on eof. */
  private int fill() throws IOException
  {
    // Handle the special case of a readLine that has a '\r' at the end of
    // the buffer.  In this case, we'll need to skip a '\n' if it is the
    // next char to be read.  This special case is indicated by 'pos > limit'.
    boolean retAtEndOfBuffer = false;
    if (pos > limit)
      {
        retAtEndOfBuffer = true;
	--pos;
      }

    if (markPos >= 0 && limit == buffer.length)
      markPos = -1;
    if (markPos < 0)
      pos = limit = 0;
    int count = in.read(buffer, limit, buffer.length - limit);
    if (count > 0)
      limit += count;

    if (retAtEndOfBuffer && buffer[pos] == '\n')
      {
	--count;
	pos++;
      }

    return count;
  }

  public int read() throws IOException
  {
    synchronized (lock)
      {
	if (pos >= limit && fill () <= 0)
	  return -1;
	return buffer[pos++];
      }
  }

  /* Return the end of the line starting at this.pos and ending at limit.
   * The index returns is *before* any line terminators, or limit
   * if no line terminators were found.
   */
  private int lineEnd(int limit)
  {
    int i = pos;
    for (; i < limit; i++)
      {
	char ch = buffer[i];
	if (ch == '\n' || ch == '\r')
	  break;
      }
    return i;
  }

  public String readLine() throws IOException
  {
    // Handle the special case where a previous readLine (with no intervening
    // reads/skips) had a '\r' at the end of the buffer.
    // In this case, we'll need to skip a '\n' if it's the next char to be read.
    // This special case is indicated by 'pos > limit'.
    if (pos > limit)
      {
	int ch = read();
	if (ch < 0)
	  return null;
	if (ch != '\n')
	  --pos;
      }
    int i = lineEnd(limit);
    if (i < limit)
      {
	String str = new String(buffer, pos, i - pos);
	pos = i + 1;
	// If the last char in the buffer is a '\r', we must remember
	// to check if the next char to be read after the buffer is refilled
	// is a '\n'.  If so, skip it.  To indicate this condition, we set pos
	// to be limit + 1, which normally is never possible.
	if (buffer[i] == '\r')
	  if (pos == limit || buffer[pos] == '\n')
	    pos++;
	return str;
      }
    StringBuffer sbuf = new StringBuffer(200);
    sbuf.append(buffer, pos, i - pos);
    pos = i;
    // We only want to return null when no characters were read before
    // EOF.  So we must keep track of this separately.  Otherwise we
    // would treat an empty `sbuf' as an EOF condition, which is wrong
    // when there is just a newline.
    boolean eof = false;
    for (;;)
      {
	int ch = read();
	if (ch < 0)
	  {
	    eof = true;
	    break;
	  }
	if (ch == '\n' || ch == '\r')
	  {
	    // Check here if a '\r' was the last char in the buffer; if so,
	    // mark it as in the comment above to indicate future reads
	    // should skip a newline that is the next char read after
	    // refilling the buffer.
	    if (ch == '\r')
	      if (pos == limit || buffer[pos] == '\n')
	        pos++;
	    break;
	  }
	i = lineEnd(limit);
	sbuf.append(buffer, pos - 1, i - (pos - 1));
	pos = i;
      }
    return (sbuf.length() == 0 && eof) ? null : sbuf.toString();
  }

  public long skip(long count) throws IOException
  {
    if (count <= 0)
      return 0;
    synchronized (lock)
      {
	// Yet again, we need to handle the special case of a readLine
	// that has a '\r' at the end of the buffer.  In this case, we need
	// to ignore a '\n' if it is the next char to be read.
	// This special case is indicated by 'pos > limit' (i.e. avail < 0).
	// To simplify things, if we're dealing with the special case for
	// readLine, just read the next char (since the fill method will
	// skip the '\n' for us).  By doing this, we'll have to back up pos.
	// That's easier than trying to keep track of whether we've skipped
	// one element or not.
	int ch;
	if (pos > limit)
	  if ((ch = read()) < 0)
	    return 0;
	  else
	    --pos; 

	int avail = limit - pos;

	if (count < avail)
	  {
	    pos += count;
	    return count;
	  }

	pos = limit;
	long todo = count - avail;
	if (todo > buffer.length)
	  {
	    markPos = -1;
	    todo -= in.skip(todo);
	  }
	else
	  {
	    while (todo > 0)
	      {
		avail = fill();
		if (avail <= 0)
		  break;
		if (avail > todo)
		  avail = (int) todo;
		pos += avail;
		todo -= avail;
	      }
	  }
	return count - todo;
      }
  }
}