// Joseph Bergin
// Pace University
// May 1996, April 1999


//	CPU defines a stack oriented simulated cpu.  Variables have names that are a 
//	single char.  Variables must be declared before they can be used. 
//	All operations are done on the run time stack.  We may push an integer literal
// 	or the current value of a variable.  We may pop a value to a variable.
//	The arithmetic operations always pop the stack enough times to get the required
//	number of operands.  The values are used in the computation.  Note that the first 
//	value popped is the rightmost operand for the operation. Thus
//		aCpu.push(3);
//		aCpu.push(5);
//		aCpu.sub();
//	will leave -2 at the top of the stack and the 3 and 5 will have been previously 
//	popped, so will no longer be in the stack.  
//	The machine will halt on stack errors or on encountering an undeclared variable.
//  This simple language has no jumps, so only simple programs may be written. 

import java.util.Random;
import java.lang.Math;
import java.awt.*;
import java.applet.*;
import java.util.*;
import java.io.*;

class SimpleCPUModel extends Thread
{	public SimpleCPUModel(Prompter input, SimpleCPU control)
	{	sysin = input;
		controller = control;
	}

	public void declare(int c)	// declare a variable // initialized to zero
	{	Integer C = new Integer(c);
		if(!_storage.containsKey(C)) _storage.put(C, new Integer(0));
	}

	public void pushv(int c)		// push the current value of a variable
	{	Integer C = new Integer(c);
		Integer val = (Integer)_storage.get(C);
		if(val == null)
		 	System.out.println("No such variable: " + c);
		else
			_runStack.push(val);
	}

	public void pushi(int i)		// push a literal
	{	_runStack.push(new Integer(i));
	}

	public void pop(int c)		// pop a value to a declared variable
	{	Integer C = new Integer(c);
		Integer val = (Integer)_storage.get(C);
		if(val == null)
		 	System.out.println("No such variable: " + c);
		else
			_storage.put(C, _runStack.pop());
	}

	public void add()		// add two top values(popping) and push the result
	{	Integer second = (Integer)_runStack.pop();
		Integer first = (Integer)_runStack.pop();
		pushi(first.intValue() + second.intValue());
	}

	public void sub()		// top value is RIGHT operand
	{	Integer second = (Integer)_runStack.pop();
		Integer first = (Integer)_runStack.pop();
		pushi(first.intValue() - second.intValue());
	}

	public void negate()	// negate the top of the stack (in place)
	{	Integer first = (Integer)_runStack.pop();
		pushi( - first.intValue() );
	}

	public void output()	// copy top of run time stack to output
	{	System.out.println(((Integer)_runStack.peek()).intValue());
		controller.show(((Integer)_runStack.peek()).intValue());
	}

	public void input()		// push a value from the input
	{	int x = (int)sysin.getLong("An Int is required.");
		pushi(x);
	}

	public void toss()		// discard top of run time stack
	{	_runStack.pop();
	}

	public void dup()		// duplicate top of run time stack
	{	_runStack.push(_runStack.peek());
	}

	public void halt()		// Halts your program (with a message).
	{	
		System.out.println("Memory dump");
		for(Enumeration E = _storage.keys(); E.hasMoreElements();)
		{	Object k = E.nextElement();
			Object v = _storage.get(k);	
			System.out.println(k.toString() + " " + v.toString());
		}	
		System.out.println("CPU halted.");
	}
	
	// Two extensions to be made by students.
	
	public boolean pos()	// true if top of stack is positive
	{	return ((Integer)_runStack.peek()).intValue() > 0;
	}

	public boolean zero()	// true if top of stack is zero
	{	return((Integer)_runStack.peek()).intValue() == 0;
	}

	/* These enable two permitted forms
		if(pos()){ 
		...
		}  // conditional forward jump
		and
		do { 
		...
		} while (pos()); // conditional backward jum;
	
	*/
	
	private Hashtable _storage = new Hashtable(); // Address, Value pairs
	private Stack _runStack = new Stack(); // of Integer objects
	private Prompter sysin;
	private SimpleCPU controller;
	
	public void run()
	{		int 	a = 0,
					b = 1;	// Give names to our variables
		declare		(a);
		declare		(b);
		input		();
		output		();
		pop			(a);
		input		();
		output		();
		pop			(b);
		pushv		(a);
		dup			();
		pushv		(b);
		div			();
		pushv		(b);
		mult		();
		sub			();
		output		();
		input();
		halt		();
	}
}

public class SimpleCPU extends Applet
{	private Prompter sysin;
	private SimpleCPUModel model;
	private TextArea theOutput;
	
	public static void main(String argv[])
	{	Frame f = new Frame("CPU test");
		f.setLayout(new FlowLayout());
		SimpleCPU scpu = new SimpleCPU();
		scpu.init();
		f.add("Center", scpu);
		f.setSize(100,100);
		f.show();
	}
	
	public void show(int x)
	{	theOutput.append('\n' + Integer.toString(x) );
		repaint();
	}
	
	public void init()
	{	theOutput = new TextArea("The Output\n", 20, 20);
		theOutput.setEditable(false);
		add(theOutput);
		Component c = this;
		while(!(c instanceof Frame)) c = c.getParent();
		sysin = new Prompter((Frame)c);
		model = new SimpleCPUModel(sysin, this);
		model.start();
	}

}