// © Copyright 1997, 1999, Joseph Bergin. All rights reserved.

import java.util.Hashtable;
import java.util.Enumeration;

import cs1.Die;

public class Simulator
{	public static void main(String argv[])
	{	Simulator scpu = new Simulator();
	}
	
	public Simulator()
	{	init();
	}
	
	public void init()
	{	_pc = 0;
	}
	
	public void step(int n)//Run for n steps or until all processes halt
	{	int quittime = _instructionCount + n;
		Die roller = new Die(8);
		System.out.println("Executing");
		while(! _processes.isEmpty() && _instructionCount < quittime)
		{	_current = (CPUProcess)_processes.dequeue();
			_processCount--;
			_pc = _current.getRestart();
			_quantum = roller.roll();
			int releaseTime = _instructionCount + _quantum;
			boolean terminated = false;
			while(_instructionCount < releaseTime && ! terminated)
			{	_instructionCount++;
				// fetch
				CPUProcess.Instruction IB = _current.fetch(_pc); 
				// increment
				_pc++;
				// decode
				// do
				terminated = IB.execute();
			}
			if( _current.isHalted()) 
			{	_haltedProcesses.enqueue(_current);
			}
			else
			{	_current.setRestart(_pc);
				_processes.enqueue(_current);
				_processCount++;
			}
		}
	}
	
	public void insertProcess(CPUProcess P)  //Enqueue it and give it a memory. 
	// Only insert a process after completely defining its program.  Otherwise
	// not all of its declarations will be seen. 
	{	P.setMemory(_memory);
		_processes.enqueue(P);
		_processCount++;
		P.setRunnable(); 
		P.setSimulator(this);
	}
	
	public void setPC(int newPC) // Called from the jump instructions.
	{	_pc = newPC;
	}
	
	public void reset() //Reset all processes and make executable
	{	Enumeration e = _processes.elements();
		CPUProcess P;
		while(e.hasMoreElements())
		{	P = (CPUProcess)e.nextElement();
			P.reset();
			P.setRunnable();
		}
		while(! _haltedProcesses.isEmpty())
		{	P = (CPUProcess)_haltedProcesses.dequeue();
			P.reset();
			_processes.enqueue(P);
			_processCount++;
		}
		_pc = 0;
		// Reset memory also? 
	}
		
	public String toString()
	{	String result = "Memory: ";	
		result += _memory.toString();
		return result;
	}
	
	private Queue  _processes = new Queue(); // Active processes.
	private int _processCount = 0; // Number of processes in active queue
	private int _instructionCount = 0;
	private Queue  _haltedProcesses = new Queue();
	private CPUProcess  _current = null; // volatile. Could be a local in step. Here for reporting. 
	private int _quantum = 0; // volatile. Quantum of currently executing process
	private int _pc = 0; // volatile 
	private Hashtable _memory = new Hashtable();
}