/*  
 * Class representing circular buffer with 5 elements. 
 * Synchronized methods prevent simultaneous
 * reading and writing - monitor structure
 */

import javax.swing.*;

class HoldInteger{
	private static final int BUFFER_SIZE = 5; // size of buffer
	protected static final int EMPTY = 0;  // code for empty slot
	
	protected int[] sharedInt = {EMPTY,EMPTY,EMPTY,EMPTY,EMPTY};
	
	protected boolean writeable = true;		// start out able to write into buffer
	protected boolean readable = false;		// but nothing to read
	
	protected int readLoc = 0, writeLoc = 0;	// where to next read or write in buffer
	
	protected JTextArea output;						// Place to write buffer status
	
	// initialize buffer and save text area for writing
	public HoldInteger(JTextArea out)
	{
		output = out;
	}
	
	// Write value in buffer
	public synchronized void setSharedInt(int value)
	{
		while(!writeable){		// No room to write - wait until notified something there
			try{								// wait is in loop in case someone else sneaks in
				output.append("\nWaiting to produce "+value+"\n");
				wait();
			} catch (InterruptedException ie){
				System.out.println("Exception: "+ie.toString());
			}
		}
		
		sharedInt[writeLoc] = value;		// insert value into buffer
		readable = true;								// let others know will now be something to read
		
		output.append("\nProduced "+value+" into cell "+writeLoc);
		
		writeLoc = (writeLoc+1) % BUFFER_SIZE;		// move index of next slot to write to
		
		output.append("\nready to write to "+writeLoc+" and read from "+readLoc);
		
		printBuffer(output,sharedInt);	// print buffer contents

		if (writeLoc == readLoc)				// buffer is full now
		{
			writeable = false;
			output.append("\nBuffer full\n");
		}
		
		notifyAll();		// Notify everyone waiting that something has happened.
	}
	
	// return next available integer in buffer
	public synchronized int getSharedInt()
	{
		int value;					// Data item to be returned
		
		while (!readable)		// nothing to read - wait until notified something there
		{										// Put in loop in case some other process sneaks in
			try{
				output.append("\nWaiting to consume\n");
				wait();
			} catch (InterruptedException ie){
				System.out.println("Exception: "+ie.toString());
			}
		}

		writeable = true;						// since reading, now room to write something
		value = sharedInt[readLoc];	// Get value from buffer
		sharedInt[readLoc] = EMPTY;		// fill removed slot w/ -1 to make display clearer
		
		output.append("\nConsumed "+value+" from cell "+readLoc);
		
		readLoc = (readLoc+1) % BUFFER_SIZE;	// move readLoc to next slot of Buffer
		
		output.append("\nReady to write to "+writeLoc+" and read from "+readLoc);
		
		printBuffer(output,sharedInt);	// print current buffer contents

		if (writeLoc == readLoc)		// Just emptied buffer
		{
			readable = false;
			output.append("\nBuffer empty\n");
		}
		
		notifyAll();				// tell anyone waiting that something has happened
		return value;
	}
	
	// print contents of buffer so can see what is happening
	public void printBuffer(JTextArea out, int[] buf)
	{
		output.append("\nbuffer: ");
		
		for (int i = 0; i < buf.length; i++)	//print contents of all slots in buffer
			out.append(" " + buf[i]);
		out.append("\n");
	}
}