//********************************************************************
// The purpose of this code is to demonstrate binary operations.
// This code will read and count the number of bytes in a file input by the user, 
//  then push that integer value onto the first four bytes of an output file, 
//  then read back in the first four bytes of that output file, and put them back 
//	into an integer value and print it out.  By understanding this code and 
//  running it, you can see how binary files are read from, written to,
//  and you can see how to shift bytes one at a time into an integer.
//  You will also learn how to count the number of bytes in a file.
// (Adapted from a Fall 2006, 1501 student assignment)
//********************************************************************
import java.io.*;

public class ByteCountDemo
{
	private String originalfile; //the file whose size will be counted

	//*******************************************************************
	// Name: ByteCountDemo(constructor)
	// Description:  Instantiates the ByteCountDemo object.
	//*******************************************************************
	ByteCountDemo(String fname)
	{
		originalfile = fname;
	}
		
	//*******************************************************************
	// Name: countBytesAndWrite
	// Description:  Counts the number of bytes in originalfile and 
	//	outputs that value to a binary file specified by the input parameter
	//  (assuming it is not too big)
	//*******************************************************************	
	public void countBytesAndWrite(String outfilename)
	{
	    FileInputStream infile = null;
        FileOutputStream outfile = null;
		
		try 
		{
			//Opens the stream
			infile = new FileInputStream(originalfile);
			int counter=0;
			//count the number of bytes in the file
			while (infile.read() != -1) //-1 is the end of file sentinel
				counter++;
			
			infile.close();
			
			outfile = new FileOutputStream(outfilename);
			
			//writes the counter value as the first 4 bytes of the output file
			//(if the size is greater than 2^32 bits (around 4 gigs) then the decoding wont work right)
			outfile.write(counter>>>24);
			outfile.write(counter>>16);
			outfile.write(counter>>8);
			outfile.write(counter);
			
			outfile.close();
		}		
		catch(FileNotFoundException e)
		{
			System.out.println("File Not Found: " + originalfile);
		}	
		catch (IOException e)
		{
			System.out.println("IOException " + e.getMessage());
		}
	}
			
	//*******************************************************************
	// Name: readFourBytes
	// Description:  Reads the first four bytes from the file passed in
	//  through the parameter, shifts them into one integer, and returns
	//  out the value of that integer.
	//*******************************************************************
	public int readFourBytes(String thefilename)
	{
      	FileInputStream infile = null;
      	int size=0;	//will hold the value of the first four bytes of the file		
		try 
		{
			//Opens the file, notice this program adds the .enc extension
			//to the input file.  Therefore the original file must be
			//the passed filename.
			infile = new FileInputStream(thefilename);			
			//reads the first 4 bytes and shifts them into one integer variable 
			size = infile.read();	
			size = ((size << 8) | infile.read());
			size = ((size << 8) | infile.read());
			size = ((size << 8) | infile.read());
			infile.close();			
			return size;
		}
		catch (IOException e)
		{
			System.err.println("IOException " + e.getMessage());
		}	
		return 0;
	}

		
	public static void main (String[] args)
	{
		System.out.println("Enter the name of the file whose size in bytes you would like me to count:");
		BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
		try
		{
			String filename = keyboard.readLine();
			ByteCountDemo bcd = new ByteCountDemo(filename);
			//we write four bytes (that represent the file size) to this output file
			bcd.countBytesAndWrite("binaryoutput.txt"); 
			int filesize = bcd.readFourBytes("binaryoutput.txt"); //then we read them right back in
			System.out.println("The file you input is " + filesize + " bytes.");
		}
		catch (Exception e)
		{
			System.out.println(e);
		}
	}
		
}