/**
 * This class was not made by me.  It can be found at:
 * http://www.cs.wisc.edu/~smethegj/imageprocessor/
 */

import java.io.*;

public class BitInputStream extends ByteArrayInputStream {
  private int bitsRead;
  private int bitPosition;
  private int currentByte;
  private int myMark;
  private final static int NUM_BITS_IN_BYTE = 8;
  private final static int END_POSITION = -1;
  private boolean readingStarted;


  /**
   * Create a BitInputStream for a File on disk.
   */
  public BitInputStream( byte[] buf ) throws IOException {
	super( buf );

	myMark         = 0;
	bitsRead       = 0;
	bitPosition    = NUM_BITS_IN_BYTE-1;
	currentByte    = 0;
	readingStarted = false;
  }


  /**
   * Read a binary "1" or "0" from the File.
   */
  public int readBit() throws IOException {
	int theBit = -1;

	if( bitPosition == END_POSITION || !readingStarted ) {
	  currentByte    = super.read();
	  bitPosition    = NUM_BITS_IN_BYTE-1;
	  readingStarted = true;
	}

	theBit = (0x01 << bitPosition) & currentByte;
	bitPosition--;

	if( theBit > 0 ) {
	  theBit = 1;
	}

	return( theBit );
  }


  /**
   * Return the next byte in the File as lowest 8 bits of int.
   */
  public int read() {
	currentByte    = super.read();
	bitPosition    = END_POSITION;
	readingStarted = true;

	return( currentByte );
  }


  /**
   *
   */
  public void mark( int readAheadLimit ) {
	super.mark(readAheadLimit);
	myMark = bitPosition;
  }


  /**
   * Add needed functionality to super's reset() method. Reset to
   * the last valid position marked in the input stream.
   */
  public void reset() {
	super.pos   = super.mark-1;
	currentByte = super.read();
	bitPosition = myMark;
  }


  /**
   * Returns the number of bits still available to be read.
   */
  public int availableBits() throws IOException {
	return(  ((super.available() * 8) + (bitPosition + 1))  );
  }
}