import java.util.*;
import java.io.*;
import javax.swing.Timer;
import java.awt.event.*;

public class MyWorld {
   private PrintStream out;  
   private ArrayList<PhysicsElement> elements;  // array to hold everything in my world.
   private Timer passingTime;   // NEW
   private double t;        // simulation time
   private double delta_t;        // in seconds
   private double refreshPeriod;  // in seconds

   public MyWorld(){
      this(System.out);  
   }
   public MyWorld(PrintStream output){
      out = output;
      t = 0;
      refreshPeriod = 0.05;      // [s]
      delta_t = 0.005;          //  [s]
      elements = new ArrayList<PhysicsElement>();
      view = null;
      passingTime = //
   }

   public void addElement(PhysicsElement e) {
      elements.add(e);
      view.repaint();
   }
   public void setView(MyWorldView view) {
      this.view = view;
   }
   public void start() {
      if(passingTime.isRunning()) return;
      passingTime.start();      
   }
   public void actionPerformed (ActionEvent event) {  // like simulate method of Assignment 1, 
      double nextStop=t+refreshPeriod;                // the arguments are attributes here.
      for (; t<nextStop; t+=delta_t){
         for (PhysicsElement e: elements)
            if (e instanceof Simulateable) {
               Simulateable s = (Simulateable) e;
               s.computeNextState(delta_t); // compute each element next state based on current global state
            }
         for (PhysicsElement e: elements)  // for each element update its state. 
            if (e instanceof Simulateable) {
               Simulateable s = (Simulateable) e;
               s.updateState();            // update its state
            }
      }
      view.repaint();
   }
   
}