//Nbody Applet vers.1, Last updated 5/09/99
//M.Dubson, April/May 1999, ENVD 3252 Final Project
import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
import java.lang.Thread;

public class Nbody extends Applet 
       implements Runnable, MouseListener, MouseMotionListener, 
                  ActionListener, ItemListener
{

  int w, h; //screen width, height
  int x,y; //present coordinates of mouse
  int xPrevious, yPrevious; //most recent previous mouse coordinates.
  int nbrBodies; // number of bodies
  int bodyClicked;
  int movieLength; //number of time steps (dtFixed) in movie
  int movieTime; //time index in movie 
  double dt; //the (variable)time step used in calculating trajectories
  double dtFixed; //the (fixed) time step used when playing back movie
  int moviePause; //delay is msec between movie frames
  double dtTot; // time since last screen paint
  double sizA;  //size of accelerations - used to set dt
  
  
  
  Body bod[];
  boolean calculating; //true if trajectories are being calculated
  boolean setPosState;
  boolean setVelState;
  boolean playMovieState;
  boolean removeCMState;
  
  Thread theThread;
  Image offscreen;
  static Color colorArray[]= {Color.red, Color.orange, Color.green, Color.blue,  
                               Color.yellow};
  private Panel buttonPanel, massPanel;
  private Button buttons[]; 
  private Checkbox checkCM;
  private Label massLabel[];
  private TextField massField[];
  
  public void init()
  {
    addMouseMotionListener(this);
    addMouseListener(this);
    w = getSize().width; h = getSize().height;
    
    nbrBodies = 3;
    dt = 0.1; //initial time step
    dtFixed = 2; //time step between screen paints
    moviePause = 8;
    movieLength = 10000;
    dtTot = 0.0;
    bod = new Body[nbrBodies];
    for (int i = 0; i < nbrBodies; i++)
    {
      bod[i] = new Body(i);
    }
    setPosState = true;
    setVelState = false;
    playMovieState = false;
    calculating = false;
    removeCMState = true;
    
    //GUI controls
    buttonPanel = new Panel();
    buttons = new Button[8];
    checkCM = new Checkbox("C.M.frame");
    massPanel = new Panel();
    massField = new TextField[5];
    massLabel = new Label[5];
    

    
    buttonPanel.setLayout( new GridLayout(2, buttons.length+2));
    massPanel.setLayout ( new GridLayout(1,5));
    
    buttons[0] = new Button("Position");
    buttons[1] = new Button("Velocity");
    buttons[2] = new Button("Start");
    buttons[3] = new Button("Stop");
    buttons[4] = new Button("Reset");
    buttons[5] = new Button("Play Movie");
    buttons[6] = new Button("Slower");
    buttons[7] = new Button("Faster");


    for (int i = 0; i < nbrBodies; i++)
    {   
        String str1 = String.valueOf(bod[i].mass);
        massField[i] = new TextField(str1,5);
        massField[i].setBackground(colorArray[i]);
    } 

    for (int i = 0; i < buttons.length; i++)
    {
      buttonPanel.add(buttons[i]);
    } 

    buttonPanel.add(checkCM);
    
    massLabel[0]= new Label("Masses");
    massPanel.add(massLabel[0]);
    for (int i = 0; i < nbrBodies; i++)   
    {
       //massPanel.add(massLabel[i]);
       massPanel.add(massField[i]);
    }
    for (int i = 0; i < nbrBodies; i++)
    {
      massField[i].addActionListener(this);
    }

    for (int i = 0; i < buttons.length; i++)
    {  
      buttons[i].addActionListener(this);  
    }
    
    checkCM.addItemListener(this);
    
    setLayout(new BorderLayout());
    add(buttonPanel, BorderLayout.SOUTH);
    add(massPanel, BorderLayout.NORTH);
    //End of GUI controls
  
  }// end of init method
 
  public void actionPerformed( ActionEvent e )
  {
    if( e.getSource() == buttons[0] ){buttonPos_action(e);}
    if( e.getSource() == buttons[1] ){buttonVel_action(e);}
    if( e.getSource() == buttons[2] ){buttonStart(e);}
    if( e.getSource() == buttons[3] ){buttonStop(e);}
    if( e.getSource() == buttons[4] ){buttonReset(e);}
    if( e.getSource() == buttons[5] ){buttonPlayMovie(e);}
    if( e.getSource() == buttons[6] ){buttonSlower(e);}
    if( e.getSource() == buttons[7] ){buttonFaster(e);}
    
    for (int i = 0; i < nbrBodies; i++)
    { 
      if( e.getSource() == massField[i] ) 
      {
        bod[i].mass = Double.valueOf(massField[i].getText()).doubleValue();
        bod[i].radius = 1 + (int) (1.5*Math.pow(bod[i].mass, 0.333));
        Graphics g = getGraphics();
        this.paint(g);
        String str = String.valueOf(i+1);
        System.out.println("Mass"+ str + " is "+ bod[i].mass);
      }
    }
  }   
 
  public void itemStateChanged( ItemEvent ie)
  {
   if (checkCM.getState()) { removeCMState = true;}
   else { removeCMState = false;}
   System.out.println("removeCMState is " + removeCMState);
  }
  public final void paint(Graphics g)
  {
    g.setColor(Color.black);
    g.fillRect(0, 0, w, h);
    
     
    for (int i = 0; i < nbrBodies; i++)  //Color bars for mass Textfields
    {
      bod[i].paint(g);
      //System.out.println("Painting " + i + ".");
    }

  }//end of paint method  
  
  public final void paintPaths(Graphics g)
  {
    for (int i = 0; i < nbrBodies; i++)
    {
      bod[i].paintTrajectory(g);
      bod[i].xLastPaint = bod[i].xPos;
      bod[i].yLastPaint = bod[i].yPos;
      //System.out.println("Painting " + i + ".");
    }

  }//end of paintPaths method  
  
  //Double-buffered graphics code
/*  public void update (Graphics g)
  {
    if ( offscreen == null || offscreen.getWidth(this) != w 
          || offscreen.getHeight(this) != h )
    {
      offscreen = createImage ( w, h );
    }
    Graphics g2 = offscreen.getGraphics();
    paint (g2);
    g.drawImage ( offscreen, 0, 0, this);
  } */
  
  public final void step()
  {
    //System.out.println("Calculating is  " + calculating + ".");
    
    if (calculating) 
    {
       update_as();
       update_rs();     //4rd order Verlet
       update_vs();
       //update_rs2(); //6th order Verlet
    
        dtTot += dt;
        if ( dtTot > dtFixed)
        {
            Graphics g = getGraphics();
            paintPaths(g);
            dtTot = 0.0;
            //System.out.println("dt is " + dt + ".");
            for (int i = 0; i < nbrBodies; i++)
            {
              bod[i].xMovie[movieTime] = bod[i].xPos;
              bod[i].yMovie[movieTime] = bod[i].yPos;
              //bod[i].vXMovie[movieTime] = bod[i].vX;
              //bod[i].vYMovie[movieTime] = bod[i].vY;
            }
            movieTime ++;
            if (movieTime == 1000){System.out.println("movieTime is "+movieTime+".");}
        }
    }//end of if (calculating) loop
    
    if (playMovieState && movieTime < 10000)
    {
      Graphics g = getGraphics();
      g.setColor(Color.black);
      g.fillRect(0, 0, w, h);
      for (int b = 0; b < nbrBodies; b++)
      {
        int xTemp = (int) bod[b].xMovie[movieTime];
        int yTemp = (int) bod[b].yMovie[movieTime];
        bod[b].posPaintIn(g, xTemp, yTemp);
      } 
      movieTime ++;
    }//end of playMovie Loop
    //repaint();
  }//end of step method
  
  public void start()
  {
    if ( theThread == null ){ theThread = new Thread (this);}
    theThread.start();
  }
  
  public void run()
  {
    while(true)  
    { 
      //System.out.println("Hit run method...");
      
      step();
      
      if (playMovieState)
      {
          try {theThread.sleep(moviePause);}
          catch (Exception e){;}
      }
    }
  }
  
  public void stop()
  {
    if (theThread != null && theThread.isAlive())
      {theThread.stop();}
    theThread = null;
  }
  


  public void mousePressed (MouseEvent e)
  {
    x = e.getX();
    y = e.getY();
    xPrevious = x;
    yPrevious = y;
    bodyClicked = whoIsClicked(x,y);
    
    
  }//end of mousePressed method
  
  public void mouseReleased (MouseEvent e)
  {
   Graphics g = getGraphics();
   update_as();
   paint(g);
   if (setPosState && bodyClicked != 100)
   {
      bod[bodyClicked].setR(x,y);
      //bod[bodyClicked].xInit = bod[bodyClicked].xPos;
      //bod[bodyClicked].yInit = bod[bodyClicked].yPos;


      System.out.println("X is " + bod[bodyClicked].xPos 
          + ".  Y is "+ bod[bodyClicked].yPos + ". ");
      System.out.println("XLastPnt is " + bod[bodyClicked].xLastPaint
          + ".  YLastPnt is "+ bod[bodyClicked].yLastPaint + ". ");

      /*System.out.println("aX=" + bod[bodyClicked].aX 
           + "  aY=" + bod[bodyClicked].aY + ".");
      System.out.println("sizA is " + sizA + ".  dt is" + dt + "."); */
   }
   if (setVelState && bodyClicked != 100)
   {
      bod[bodyClicked].setV(x,y);
      bod[bodyClicked].vXInit = bod[bodyClicked].vX;
      bod[bodyClicked].vYInit = bod[bodyClicked].vY;
      
      System.out.println("vCMX is " + vCMX()+" . vCMY is " + vCMY() + ".");
      System.out.println("vXInit is " + bod[bodyClicked].vXInit + 
          ".  vYInit is "+ bod[bodyClicked].vYInit + ". ");
   }
      
      //System.out.println("vXInitCM is " + bod[bodyClicked].vXInitCM + 
      //    ".  vYInitCM is "+ bod[bodyClicked].vYInitCM + ". ");   
          
    /*  System.out.println("X is " + bod[bodyClicked].xPos 
          + ".  Y is "+ bod[bodyClicked].yPos + ". ");
      System.out.println("XLastPnt is " + bod[bodyClicked].xLastPaint
          + ".  YLastPnt is "+ bod[bodyClicked].yLastPaint + ". ");
    */
    }//end of mouseReleased method
  
  public void mouseDragged (MouseEvent e)
  {
    x = e.getX();
    y = e.getY();
    Graphics g = getGraphics();
    if (setPosState && bodyClicked != 100)
      {
        bod[bodyClicked].paintOut(g);
        bod[bodyClicked].posPaintIn(g, x, y);
        bod[bodyClicked].setR(x,y);
        //System.out.println("xPos=" + bod[bodyClicked].xPos 
            //+ "  yPos=" + bod[bodyClicked].yPos + ".");

      }
    if (setVelState && bodyClicked != 100)
      {
        bod[bodyClicked].paintOut(g);
        bod[bodyClicked].velPaintIn(g, x, y);
        bod[bodyClicked].setV(x,y);
        //System.out.println("vX=" + bod[bodyClicked].vX 
            //+ "  vY=" + bod[bodyClicked].vY + ".");
      }
      
  }
  
  public void mouseClicked( MouseEvent e){;}
  
  void buttonPos_action(ActionEvent e) {
    setPosState = true;
    setVelState = false;
    System.out.println("Setting positions.");
  }
  void buttonVel_action(ActionEvent e) {
    setPosState = false;
    setVelState = true;
    System.out.println("Setting velocities.");
  }
  
  void buttonStart(ActionEvent e) {
    
    if (removeCMState)
    {
      for (int i=0; i < nbrBodies; i++ )
      {
        bod[i].vXInitCM = bod[i].vX - vCMX();
        bod[i].vYInitCM = bod[i].vY - vCMY();
        bod[i].vX = bod[i].vXInitCM;
        bod[i].vY = bod[i].vYInitCM;
      }
    }
    //Paint out bodies to see trajectories clearly
    Graphics g = getGraphics();
    g.setColor(Color.black);
    g.fillRect(0, 0, w, h);
    
    System.out.println("Starting calculation.");
    double pXtot = 0.0;
    double pYtot = 0.0;
    for (int i = 0; i < nbrBodies; i++)
    {
      pXtot += bod[i].mass * bod[i].vX;
      pYtot += bod[i].mass * bod[i].vY;
    }
    System.out.println("pXtot = " + pXtot + ". pYtot = " + pYtot + ".");
    double p_tot = magnitude_Totp();
    System.out.println("P_tot is " + p_tot + ".");
    calculating = true;
  }//end of buttonStart method
  
  void buttonStop(ActionEvent e) {
    calculating = false;
    playMovieState = false;
    double p_tot = magnitude_Totp();
    System.out.println("movieTime is "+movieTime);
    //System.out.println("P_tot is " + p_tot + ".");
  }
  void buttonReset(ActionEvent e) {
    for (int i = 0; i < nbrBodies; i++)
        {
          bod[i].xPos = bod[i].xInit;
          bod[i].yPos = bod[i].yInit;
          bod[i].vX = bod[i].vXInit;
          bod[i].vY = bod[i].vYInit;
          bod[i].xLastPaint = bod[i].xInit;
          bod[i].yLastPaint = bod[i].yInit;
        }
    movieTime = 0;
    setPosState = true;
    setVelState = false;
    calculating = false;
    playMovieState = false;
    repaint();
    System.out.println("Stopping calculation.");
  }  
  
  void buttonPlayMovie(ActionEvent e) {
    calculating = false;
    playMovieState = true;
    moviePause = 16;
    movieTime = 0;
  }  
  void buttonSlower(ActionEvent e) {
    moviePause += 2;
    System.out.println("moviePause  = "+ moviePause+ ".");
  } 
  void buttonFaster(ActionEvent e) {  
    if (moviePause > 6){moviePause -= 2 ;}
    
    System.out.println("moviePause  = " + moviePause + ".");
  } 
  
  public int whoIsClicked(int xPress, int yPress)
  { 
    for ( int i = 0; i < nbrBodies; i++)
    {
      if (setPosState && bod[i].bodClicked(xPress, yPress))
        {
          System.out.println("Body "+i+" is clicked.");
          return i;
        }
      if (setVelState && bod[i].velClicked(xPress, yPress))
        {
          System.out.println("Velocity "+i+" is clicked.");
          return i;
        }           

    }
    System.out.println("No body is clicked.");
    return 100;
}//end of whoIsClicked()method
    
 //method update_as() computes present accelerations of all bodies
 //***************************************************************
  public final void update_as()
  {
    dt = 0.1;
    for(int i = 0; i < nbrBodies; i++)
    {
      bod[i].aXBeforeLast = bod[i].aXLast;
      bod[i].aYBeforeLast = bod[i].aYLast;
      bod[i].aXLast = bod[i].aX;
      bod[i].aYLast = bod[i].aY;      
      bod[i].aX = 0.0;
      bod[i].aY = 0.0;
      for(int j = 0; j < nbrBodies; j++)
      {
        if (j != i)
        {
          double rQ =Math.pow((Math.pow((bod[i].xPos - bod[j].xPos),2)+ 
            Math.pow((bod[i].yPos - bod[j].yPos),2))  , -1.5);
          bod[i].aX += bod[j].mass*(bod[j].xPos - bod[i].xPos)*rQ;  
          bod[i].aY += bod[j].mass*(bod[j].yPos - bod[i].yPos)*rQ;  
          double dtTemp = 0.0005*Math.pow(rQ*bod[j].mass,-0.5);
          if (dtTemp < dt) {dt = dtTemp;}
        }
      }//end of j-loop
    }//end of i-loop
    
  }// end of update_as method
  
  //Update positions of all bodies
  //****************************************************************
  public final void update_rs()
  {
    for(int i = 0; i < nbrBodies; i++)
    {
      bod[i].xLast = bod[i].xPos; 
      bod[i].yLast = bod[i].yPos;
      bod[i].xPos = bod[i].xPos + dt*bod[i].vX + dt*dt*0.5*bod[i].aX;
      bod[i].yPos = bod[i].yPos + dt*bod[i].vY + dt*dt*0.5*bod[i].aY;
    }
  }//end of update_rs
  
  //Update velocities of all bodies
  //*****************************************************************
  public final void update_vs()
  {
    for(int i = 0; i < nbrBodies; i++)
    {
        bod[i].vX = bod[i].vX + dt*0.5*(bod[i].aX + bod[i].aXLast);
        bod[i].vY = bod[i].vY + dt*0.5*(bod[i].aY + bod[i].aYLast);
    }
  }//end of update_vx
  
  //Compute x- and y-component of center-of-mass velocity.
  //******************************************************************
  public double vCMX()
  {
      double totMass = 0.0; 
      double totxMom = 0.0; 
      for (int i = 0; i < nbrBodies; i++)
      {
        totMass += bod[i].mass;
        totxMom += bod[i].mass * bod[i].vXInit;
      }
      return totxMom/totMass;
  }
  public double vCMY()
  {
      double totMass = 0.0; 
      double totyMom = 0.0; 
      for (int i = 0; i < nbrBodies; i++)
      {
        totMass += bod[i].mass;
        totyMom += bod[i].mass * bod[i].vYInit;
      }
      return totyMom/totMass;
  }
  public double totpX()
  { 
      double totxMom = 0.0; 
      for (int i = 0; i < nbrBodies; i++)
      {
        totxMom += bod[i].mass * bod[i].vX;
      }
      return totxMom;
  }
  public double totpY()
  { 
      double totyMom = 0.0; 
      for (int i = 0; i < nbrBodies; i++)
      {
        totyMom += bod[i].mass * bod[i].vY;
      }
      return totyMom;
  }
  public double magnitude_Totp()
  { 
      double totp = 0.0; 
      for (int i = 0; i < nbrBodies; i++)
      {
        totp += Math.pow((Math.pow(totpX(),2) + Math.pow(totpY(),2)),0.5);
      }
      return totp;
  }
  
  public void mouseMoved( MouseEvent e){;}
  public void mouseEntered( MouseEvent e){;}
  public void mouseExited( MouseEvent e){;}
  
}//end of class Nbody