import java.io.*;
public class BinaryFile {

/**
 * Binary File constructor.  Open a file for reading, or create
 * a file for writing.  If we create a file, and a file already
 * exists with that name, the old file will be removed.
 * @param filename The name of the file to read from or write to
 * @param readOrWrite 'w' or 'W' for an output file (open for writing), 
 *        and 'r' or 'R' for an input file (open for reading)
 */
    public BinaryFile(String filename, char readOrWrite) {
	buffer = (byte) 0;
	int buf_length = 0;
	total_bits = 0;
	bitsleft = 0;
	bitsread = 0;
	total_bits = 0;
	buffer=0;
	bitsread = 0;
	try {
	    if (readOrWrite == 'w' || readOrWrite == 'W') {
		inputFile = false;
		file = new RandomAccessFile(filename, "rw");
		file.writeInt(0); /* header -- # of bits in the file */
	    } else if (readOrWrite == 'r' || readOrWrite == 'R') {  
		inputFile = true;
		file = new RandomAccessFile(filename, "r");
		total_bits = file.readInt();
	    }
	} catch(Exception e) {
	    System.out.println(e.getMessage());
	    System.exit(0);
	}
    }


/**
 * Checks to see if we are at the end of a file.  This method is only 
 * valid for input files, calling EndOfFile on an output fill will
 * cause the program to halt execution.
 * (This method should probably really throw an
 * exception instead of halting the program on an error, but I'm 
 * trying to make your code a little simplier)
 * @return True if we are at the end of an input file, and false otherwise
 */
    public boolean EndOfFile() 
    {
	Assert.notFalse(inputFile,"EndOfFile only relevant for input files");
	return bitsread == total_bits;
    }

/**
 * Read in the next 8 bits to the input file, and interpret them as 
 * a character.  This method is only valud for input files, and
 * will halt exection of called on an output file.
 * (This method should probably really throw an
 * exception instead of halting the program on an error, but I'm 
 * trying to make your code a little simplier)
 * @return The next character from an input file
 */
    public char readChar() 
    {
	int charbuf = 0;
	int revcharbuf = 0;
	int i;

	Assert.notFalse(inputFile,"Can only read from input files");
	for (i=0; i<8; i++) 
        {
	    charbuf = charbuf << 1;
	    if (readBit())
            {
		charbuf += 1;
	    }
	}
	for (i=0; i<8; i++) 
        {
	    revcharbuf = revcharbuf << 1;
	    revcharbuf += charbuf % 2;
	    charbuf = charbuf >> 1;
	}
	return (char) revcharbuf;
    }

/**
 * Write a character to an output file.  The 8 bits representing the character
 * are written one at a time to the file.  This method is only valid for
 * output files, and will halt execution if called on an input file.
 *(This method should probably really throw an
 * exception instead of halting the program on an error, but I'm 
 * trying to make your code a little simplier)
 * @param c The character to write to the output file.
 */
    public void writeChar(char c) 
    {
	Assert.notFalse(!inputFile,"Can only write to output files");

	int i;
	int charbuf = (int) c;
	for (i=0; i<8; i++) 
        {
	    writeBit(charbuf % 2 > 0);
	    charbuf = charbuf >> 1;
	}
    }

/**
 * Write a bit to an output file  This method is only valid for
 * output files, and will halt execution if called on an input file.
 * (This method should probably really throw an
 * exception instead of halting the program on an error, but I'm 
 * trying to make your code a little simplier)
 * @param bit The bit to write.  false writes a 0 and true writes a 1.
 */    
     public void writeBit(boolean bit) 
       {
	byte bit_;
	Assert.notFalse(!inputFile,"Can't write to an input file");
	total_bits++;

	if (bit)
	    bit_ = 1;
	else
	    bit_ = 0;
	buffer |= (bit_ << (7 - buf_length++));
	try 
        {
	    if (buf_length == 8) 
            {
		file.writeByte(buffer);
		buf_length = 0;
		buffer = 0;
	    }
	} 
        catch (Exception e) 
        {
	    System.out.println(e.getMessage());
	    System.exit(0);
	}
    }
    
/**
 * Read a bit froman input file.  This method is only valid for
 * input files, and will halt exeuction if called on an output file.
 * (This method should probably really throw an
 * exception instead of halting the program on an error, but I'm 
 * trying to make your code a little simplier)
 * @return The next bit in the input file -- false for 0 and true for 1.
 */    
    public boolean readBit() 
    {
	Assert.notFalse(inputFile,"Can't read from an output file");
	Assert.notFalse(bitsread < total_bits,"Read past end of file");
	try 
        {
	    if (bitsleft == 0) 
            {
		buffer = file.readByte();
		bitsleft = 8;
	    }
	} 
        catch (Exception e) 
        {
	    System.out.println(e.getMessage());
	    System.exit(0);
	}
	bitsread++;
	return (((buffer >> --bitsleft) & 0x01) > 0);
    }

/**
 * Close the file (works for input and output files).  Output files will
 * not be properly written to disk if this method is not called.
 */    
    public void close() {
	try 
        {
	    if (!inputFile)  
            {
		if (buf_length != 0) 
                {
		    while (buf_length < 8) 
                    {
			buffer |= (0 << (7 - buf_length++));
		    }
		    file.writeByte(buffer);
		}
		file.seek(0);
		file.writeInt(total_bits);
	    }
	    file.close();
	} 
        catch (Exception e) 
        {
	    System.out.println(e.getMessage());
	    System.exit(0);
	}
	
    }

    private boolean inputFile;
    private RandomAccessFile file;
    private byte buffer;
    private int buf_length;
    private int total_bits;
    private int bitsleft;
    private int bitsread;
}