/* 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 Warren Levy <warrenl@cygnus.com>
 * @date October 15, 1998.  
 */
/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
 * "The Java Language Specification", ISBN 0-201-63451-1
 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct.
 */
 
public class PushbackInputStream extends FilterInputStream
{
  /* Internal buffer array for data. */
  protected byte[] buf;

  /* The current position in the buffer. */
  protected int pos;

  public PushbackInputStream(InputStream in)
  {
    this(in, 1);
  }

  public PushbackInputStream(InputStream in, int size)
  {
    super(in);
    if (size < 0)
      throw new IllegalArgumentException();
    buf = new byte[size];
    pos = buf.length;
  }

  public int available() throws IOException
  {
    return pos + super.available();
  }

  public void close() throws IOException
  {
    buf = null;
    super.close();
  }

  public boolean markSupported()
  {
    return false;
  }

  public int read() throws IOException
  {
    if (pos < buf.length)
      return ((int) buf[pos++]) & 0xFF;

    return super.read();
  }

  public int read(byte[] b, int off, int len) throws IOException
  {
    if (off < 0 || len < 0 || off + len > b.length)
      throw new ArrayIndexOutOfBoundsException();

    int numBytes = Math.min(buf.length - pos, len);
    for (int i = 0; i < numBytes; i++)
      b[off++] = buf[pos++];

    // `off' was just incremented to include `numBytes', so we can
    // just pass ithere.
    return numBytes + super.read(b, off, len - numBytes);
  }

  public void unread(int b) throws IOException
  {
    if (pos <= 0)
      throw new IOException();

    buf[--pos] = (byte) b;
  }

  public void unread(byte[] b) throws IOException
  {
    unread(b, 0, b.length);
  }

  public void unread(byte[] b, int off, int len) throws IOException
  {
    if (pos < len)
      throw new IOException();

    // Note the order that these bytes are being added is the opposite
    // of what would be done if they were added to the buffer one at a time.
    // See the Java Class Libraries book p. 1390.
    System.arraycopy(b, off, buf, pos - len, len);

    // Don't put this into the arraycopy above, an exception might be thrown
    // and in that case we don't want to modify pos.
    pos -= len;
  }

  // JDK1.2
  public long skip(long n) throws IOException
  {
    final long origN = n;

    if (n > 0L)
      {
	int numread = (int) Math.min((long) (buf.length - pos), n);
	pos += numread;
	n -= numread;
	n -= super.skip(n);
      }

    return origN - n;
  }
}