import java.awt.*;
import java.applet.*;
import java.awt.image.*;

public class Potbar extends Applet implements Runnable {
  Thread runstring;
  public Scrollbar leftRight;
  private MyCanvas canv;
  private MyPanel thePanel;
  BorderLayout MyLay;
  int Flag;
  public boolean stopped=false;

  public Potbar() //to initialize Flag
  {
     setFlag(0);
  }

  public void setFlag(int fl)
  {
     Flag=fl;    //Flag 0 do not begin string motion, 1 yes
   }
  public void init()
  {
    setLayout(MyLay=new BorderLayout());
    thePanel=new MyPanel(this,canv);
    leftRight=new Scrollbar(Scrollbar.HORIZONTAL,80,0,40,110);
    canv=new MyCanvas(this);
    canv.init();
    thePanel.init();
    add("Center",canv);
    add("North",leftRight);
    add("South", thePanel);
  }
  public void start()
  {
    if(! stopped)
    {
    if(Flag==1){
       canv.jj=1;
       canv.flag=1;
       runstring=new Thread(this);
       runstring.start();
     }
    }
  }
  public void stop()
  {
     if(runstring != null){
        runstring.suspend();
        runstring=null;
     }
  }

  public void brk()
  {   //stops motion temporarily
      runstring.stop();
      stopped=false;
      setFlag(0);
      canv.jj=1;
  }

  public void run()
  {
    while(true){
     
      try{
        Thread.currentThread().sleep(380);}
      catch
          (InterruptedException e){ }
            canv.repaint();
    }
  }

  public void paint(Graphics g){
     canv.repaint();    //called many times
  }

  public boolean handleEvent(Event ev){
  //events sent by Mypanel and scrollbar interpreted here
  if(ev.target instanceof Scrollbar){
    if(ev.target==leftRight)canv.setWidth(leftRight.getValue());
    canv.repaint();
    return true;
  }
  if((ev.id==ev.MOUSE_DRAG)){
       canv.Xmos=ev.x;
       canv.Ymos=ev.y;
       canv.erase=true;
       showStatus("Cursor" + ev.x + " " + ev.y);
       canv.repaint();
       return true;
  }
    if(ev.id==ev.MOUSE_ENTER){
    //to show black square at beginning
    //when mouse enters the applet
     canv.repaint();
     return true;
   }
    return false;
 }
} //class

class MyCanvas extends Canvas implements ImageObserver{
   //all the painting occurs here
   Potbar runstring;
    double myp,mxp,byp,bxp;
   double mxx,bxx,myy,byy,yypos,xxpos,pi,dx,dt;
   private Image offScreenImage;
   Graphics offScreenGraphics;
   int ypos,xpos,max,cor;
   int Xmos,Ymos,Xdef,Ydef; //mouse positions
   boolean erase=false;
   int first,incr,jj=1;
   double  psr[][], psi[][], v[], p2[];
   int flag=0; //do not draw equation

   public void init()
   {
     psr=new double[501][2];
     psi=new double[501][2];
     p2=new double[501];
     v=new double[501];
     jj=1;
     mxp=500/263.0;
     bxp=-mxp*17.0;
     myp=-600.0/155.0;
     byp=600*205.0/310.0;
     pi=3.14159265358979323846;
     max=500;
     dx=0.02;
     dt=0.9*dx*dx;
     Xdef=180;
     Ydef=45;
     incr=10;
     cor=-8;
 }

   public MyCanvas(Potbar runstring) //to initialize class and variables
   {
     this.runstring=runstring;
     setWidth(50);  //initial position of the horizontal
   }
  public void update(Graphics g)
  { //To avoid screen flicker use double buffer technique
    offScreenImage=createImage(size().width,size().height);
    offScreenGraphics=offScreenImage.getGraphics();
    offScreenGraphics.setColor(getBackground());
    offScreenGraphics.fillRect(0,0,size().width,size().height);
    offScreenGraphics.setColor(g.getColor());
    paint(offScreenGraphics);
    g.drawImage(offScreenImage,0,0,this);
  }
   public void setWidth(int hx)
   {
     xpos=hx;
   }
   void coormundo(double xiz,double ysu,double xde,double yinf)
  { //to convert world to screen coordinates. Gives mxx bxx for
    //x_screen=mxx*x_world +byy same for y.
    double maxx,maxy,xxfin,xxcom,yyin,yysu;
    maxx=350;
    maxy=250;
    xxcom=0.05*maxx;
    xxfin=0.8*maxx;
    yyin=0.98*maxy;
    yysu=0.2*maxy;
    mxx=(xxfin-xxcom)/(xde-xiz);
    bxx=0.5*(xxcom+xxfin-mxx*(xiz+xde));
    myy=(yyin-yysu)/(yinf-ysu);
    byy=0.5*(yysu+yyin-myy*(yinf+ysu));
  }
  public void rectangulo(Graphics g)
  {  //draws instruction rectangle
     g.drawRect(120,25,110,155);
     g.drawString("Drag mouse",142,60);
     g.drawString("in this area",142,80);
     g.drawString("to select potential",132,120);
  }

  public void inirec(Graphics g)
  {  //initial rectangle
     g.drawOval(Xdef-5,Ydef-10,10,10);
     g.drawLine(144,(int)(byy-50),144,Ydef+cor);
     g.drawLine(144,Ydef+cor,Xdef,Ydef+cor);
     g.drawLine(Xdef,Ydef+cor,Xdef,(int)(byy-50));
  }

  public void inipot(Graphics g)
  {  //initial potential shown
     g.setColor(Color.black);
     rectangulo(g);
     g.setColor(Color.blue);
     if(erase==false){
       inirec(g);
     }
     else {
       g.setColor(getBackground());
       inirec(g);
     }
     g.setColor(Color.blue);
  }
  public void potbar(Graphics g)
  { //selects potential as mouse drags
     if((Xmos<231)&&(Xmos>119)&&(Ymos>24)&&(Ymos<191)){
       g.drawLine(144,97,144,Ymos+cor);
       g.drawLine(144,Ymos+cor,Xmos,Ymos+cor);
       g.drawLine(Xmos,Ymos+cor,Xmos,97);
     }
  }
 public void selectmom(Graphics g)
 {  //select wave packet momentum with scrollbar
   int i;
   g.drawString("To Select Wave Packet Momentum ",100,10);
   g.setColor(Color.red);
   g.drawRect(5,10,340,190);
   for(i=0;i<6;i++){
     g.drawLine(20+i*55,10,20+55*i,20);
     g.drawString(Integer.toString(12+4*i),20+i*55,25 );
   }
   for(i=0;i<7;i++){
     g.drawLine(339,97-12*i,345,97-12*i);
   }
   for(i=0;i<4;i++){
     g.drawString(Integer.toString(100*i),315,104-24*i);
   }
   for(i=1;i<7;i++){
     g.drawLine(339,97+14*i,345,97+14*i);
   }
   for(i=1;i<4;i++){
     g.drawString(Integer.toString(-100*i),310,104+28*i);
   }
 }

 public void Equation1(Graphics g)
 { //to draw initial potential wavefunction
   //at beginning and after each stop
   int peo,peye,pex,peyo,peyv0,peyv1;
   double x,fact2;
   double k0,vh;
   double expon,poten;
   int minx,minix,maxix;
   int i,n,arrow;
   xxpos=(double)xpos;
   x=0.0;
   minix=0;// initialize
   selectmom(g);
   g.setColor(Color.blue);
   if(jj==1){
     // initial conditions
     coormundo(0.0,1.5,max+1,-1.5);
     inipot(g);
     xxpos=(double)xpos;
     k0=pi*xxpos/10.0;
     arrow=(int)(2.0*xxpos/5.0)+100;
     g.setColor(Color.yellow);
     g.drawLine(70,85,arrow,85);//arrow
     g.drawLine(arrow-5,80,arrow,85); //upper tip
     g.drawLine(arrow-5,90,arrow,85); //lower tip
     g.setColor(Color.blue);
     potbar(g);
     if(Ymos==0)Ymos=45;
     if(Xmos==0)Xmos=180;
     minx=(int)(Xmos*mxp+bxp);
     poten=(double)(myp*Ymos+byp);
     if(minx<240){
       minix=minx;
       maxix=240;
     }
     else{
       maxix=minx;
       minix=240;
     }
     vh=poten;
     g.drawLine(17,97,280,97); //middle line
     for(i=0;i<max+1;i++){
       if((i>minix)&&(i<maxix))v[i]=vh;
       else v[i]=0.0;
     }
     for(i=0;i<(int)(max/2)-70;i++){
       //real part of the initial wave function at t=0
       fact2=2.0*(x-2.7);
       expon=Math.exp(-fact2*fact2);
       psr[i][0] = (Math.cos(k0*x))*expon;
       //imaginary part of the initial wave function at t=0
       psi[i][0] = (Math.sin(k0*x))*expon;
       x=x+dx;
     }
   }//if jj
   // solution for new times
   for( n=first-1;n<jj+1;n++){
     //real part of wavefunction and probability
     for( i=1;i<(int)max/2-70;i++){
       psr[i][1]=psr[i][0] - dt*(psi[i+1][0] + psi[i-1][0]
                -2.0*psi[i][0])/(2.0*dx*dx)+dt*v[i]*psi[i][0];
       p2[i]=psr[i][0]*psr[i][1]+psi[i][0]*psi[i][0];
     }
       if(jj==1)byy=byy-25;
     // the probability plotted at times=incr
     if(n==jj){
       for(i=1;i<(int)max/2-70;i++){
         if(i>0){
            peo=(int)(mxx*(i-1)+bxx);
            peyo=(int)(myy*p2[i-1]+byy);
            peyv0=(int)(myy*v[i-1]/250.0+byy);
            pex=(int)(mxx*i+bxx);
            peye=(int)(myy*p2[i]+byy);
            g.drawLine(peo,peyo,pex,peye);
            peyv1=(int)(myy*v[i]/250.0+byy);
       
            if(n !=1)  g.drawLine(peo,peyv0,pex,peyv1);
          }
       }
     }
   }
 }
  public void Equation(Graphics g)
 {
   int peo,peye,pex,peyo,peyv0,peyv1;
   double x,fact2;
   double k0,vh;
   double expon,poten;
   int i,n,arrow;
   xxpos=(double)xpos;
   x=0.0;
   selectmom(g);
   g.setColor(Color.blue);
   if(jj==1){
     // initial conditions
     coormundo(0.0,1.5,max+1,-1.5);
     xxpos=(double)xpos;
     k0=pi*xxpos/10.0;
     g.setColor(Color.blue);
     for(i=0;i<max+1;i++){
       //real part of the initial wave function at t=0
       fact2=2.0*(x-2.7);
       expon=Math.exp(-fact2*fact2);
       psr[i][0] = (Math.cos(k0*x))*expon;
       //imaginary part of the initial wave function at t=0
       psi[i][0] = (Math.sin(k0*x))*expon;
       x=x+dx;
     }
   }//if jj
   // solution for new times
   for( n=first-1;n<jj+1;n++){
     //real part of wavefunction and probability
     for( i=1;i<max;i++){
       psr[i][1]=psr[i][0] - dt*(psi[i+1][0] + psi[i-1][0]
                -2.0*psi[i][0])/(2.0*dx*dx)+dt*v[i]*psi[i][0];
       p2[i]=psr[i][0]*psr[i][1]+psi[i][0]*psi[i][0];
     }
     //imaginary part of the wave function
     for(i=1;i<max;i++){
       psi[i][1] = psi[i][0]+dt*(psr[i+1][1] + psr[i-1][1]
                     -2.0*psr[i][1])/(2.0*dx*dx)-dt*v[i]*psr[i][1];
     }
     if(jj==1)byy=byy-25;
     // the probability plotted at times=incr
     if(n==jj){
       for(i=1;i<max+1;i++){
         if(i>0){
            peo=(int)(mxx*(i-1)+bxx);
            peyo=(int)(myy*p2[i-1]+byy);
            peyv0=(int)(myy*v[i-1]/250.0+byy);
            pex=(int)(mxx*i+bxx);
            peye=(int)(myy*p2[i]+byy);
            g.drawLine(peo,peyo,pex,peye);
            peyv1=(int)(myy*v[i]/250.0+byy);
            if(v[i] !=v[i-1])peo=pex;
            if(n !=1)g.drawLine(peo,peyv0,pex,peyv1);
          }
       }
     }
         // new iterations are now the old ones
     for(i=1;i<max+1;i++){
       psi[i][0]=psi[i][1];
       psr[i][0]=psr[i][1];
     }
   }
 }


  public void paint(Graphics g){
     first=jj;
     if(jj==1){
       Equation1(g);
     }
     if((runstring.Flag==1)&&(flag==1)){
       if(first==incr+1)first=1;
       if(first>=incr+1)first=jj-incr;
       Equation(g);
       jj=jj+incr;
     }
   }
 }

 class MyPanel extends Panel{
  //controls Stop, start and scrollbars
  //transmits to Eqstring the events
  Potbar runstring;
  GridBagLayout GBLay;
  GridBagConstraints c;
  MyCanvas canv;

  public void init(){
    GBLay=new GridBagLayout();
    c=new GridBagConstraints();
    setLayout(GBLay);
    c.gridx=1;
    c.gridy=1;
    c.gridheight=1;
    c.fill=GridBagConstraints.BOTH;
   /* Button sta=new Button("Cont");
    GBLay.setConstraints(sta,c);
    add(sta);*/
    //  c.gridx=2;
    Button stp=new Button("Stop");
    GBLay.setConstraints(stp,c);
    add(stp);
    c.gridx=2;
    Button rest=new Button("Start");
    GBLay.setConstraints(rest,c);
    add(rest);
  }
  public MyPanel(Potbar runstring, MyCanvas canv)
  {
    this.canv=canv;
    this.runstring=runstring;
  }

 public boolean action(Event ev, Object arg)
 {
   if (ev.target  instanceof Button) {
     String label=(String)ev.arg;
     if (label.equals("Stop")){
       runstring.brk();
     }
     if(label.equals("Start")){
       runstring.setFlag(1);
       runstring.stopped=false;
       runstring.start();
     }
     return true;
   }
   //else
    if(ev.target instanceof Scrollbar){
      runstring.postEvent(ev);//sent to Eqstring handlEvent
      return true;
    }
    if((ev.id==ev.MOUSE_DRAG)){
      runstring.postEvent(ev);
    }
    return false;
  }
}