// oscillat.java
// Prey-Predator Oscillation
// (a) constant force source
// (b) renewable source
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

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

public class oscillat extends Applet {

  	float ej, c, k1, k4, k5, k8, h1, c1, t0, e0, dt, t, ta, dh, dc;
	float k, k0, k6, k9, p, p0, p1, dp, h;
	int a=0;
	Label prompt1, prompt2;
	TextField input1, input2;
	CheckboxGroup source;
	Checkbox sourceUnlimited, sourceRenewable;
	Image oscillat, preypred;
	Panel panel;
	Button drawbutton;

  public void init() {

	prompt1 = new Label("E,J Energy source:");
	input1 = new TextField("10000",6);

	prompt2 = new Label("K6 Depreciation factor of H:");
	input2 = new TextField("5",6);

	source = new CheckboxGroup();
	sourceUnlimited = new Checkbox("Unlimited Source",source,true);
	sourceRenewable = new Checkbox("Renewable Source",source,false);

	drawbutton = new Button("Draw");

	panel = new Panel();
	panel.setLayout( new GridLayout(2,4,20,0));

	panel.add(prompt1);
	panel.add(input1);
	panel.add(sourceUnlimited);
	panel.add(drawbutton);
	panel.add(prompt2);
	panel.add(input2);
	panel.add(sourceRenewable);

	add(panel);

	oscillat = getImage(getDocumentBase(),"Gif/oscillat.gif");
	preypred = getImage(getDocumentBase(),"Gif/preypred.gif");

	}

  public boolean action (Event e,Object o) {

	ej = (float)Integer.parseInt(input1.getText());
  	k6 = 0.01f*(float)Integer.parseInt(input2.getText());

	if (e.target instanceof Checkbox) {
		if (sourceUnlimited.getState() == true) {
			a=0;
			input2.setEditable(false);
			input2.setBackground(Color.black);
			}
		else {
			a=1;
			input2.setEditable(true);
			input2.setBackground(Color.white);
			}
		}
	repaint();
	return true;
	}

  public void paint ( Graphics g ) {
	c=(float)5; k1=(float)0.002; k4=(float)0.1;
	k5=(float)0.02; k8=(float)0.3;p=(float)0; h=(float)10;
	t0=(float)3.2; e0=(float)0.08; dt=(float)0.1; t=(float)0; ta=(float)0;
	k=(float)0.01; k0=(float)0.01; k9=(float)0.005; p0=(float)0.08;

	g.drawRect(0,60,320,180);


	/*---- Start Program Oscillat----*/	if (a==0) {

	g.drawImage(oscillat, 321, 55, 380, 180, this);
	ej=0.1f*ej;

	while (t*t0<320) {
		dh=k1*ej*h-k4*c*h;
	   	dc=k5*c*h-k8*c;
		c1=c+dc*dt;
	  	if (c1<5) c1=5;
	  	h1=h+dh*dt;
	  	if (h1<8) h1=8;
		g.setColor(Color.blue);
		g.drawLine((int)(t0*ta),(int)(240-c),(int)(t0*t),(int)(240-c1));
		g.setColor(Color.red);
		g.drawLine((int)(t0*ta),(int)(240-h),(int)(t0*t),(int)(240-h1));
	  	ta=t;
		h=h1;
		c=c1;
		t+=dt;
		}
	/*----End Program Oscillat----*/	}

	/*---- Start Program Preypred----*/	else {

	g.drawImage(preypred, 321, 55, 450, 180, this);

	while (t*t0<320) {
		dp=k0*ej-k9*p-k*p*h;
		dh=k1*p*h-k4*c*h-k6*h;
	   	dc=k5*c*h-k8*c;
		c1=c+dc*dt;
	  	if (c1<1) c1=1;
	  	h1=h+dh*dt;
	  	if (h1<1) h1=1;
		p1=p+dp*dt;
		if(p1<0.001) p1=0.001f;
		g.setColor(Color.blue);
		g.drawLine((int)(t0*ta),(int)(240-c),(int)(t0*t),(int)(240-c1));
		g.setColor(Color.red);
		g.drawLine((int)(t0*ta),(int)(240-h),(int)(t0*t),(int)(240-h1));
		g.setColor(Color.green);
		g.drawLine((int)(t0*ta),(int)(240-p*p0),(int)(t0*t),(int)(240-p1*p0));
	  	ta=t;
		h=h1;
		c=c1;
		p=p1;
		t+=dt;
		}

	/*---End Program Preypred---*/		}
  }
}
// Stefan Kontur, August 28th 2000*/
// Manuel Basler, October 24th 2000*/
// Enrique Ortega. August 31st, 2001