// tank.java
// tank with inflow and outflow
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

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

public class tank extends Applet
{

 	Label prompt1, prompt2, prompt3;
 	TextField input1, input2, input3;
 	Choice chooseEvent;
 	Button drawButton;
 	GridBagLayout gbLayout;
 	GridBagConstraints gbConstraints;
 	double q, k0, k, t1, qi, dq, j0, j;
 	int a, t, ti;

 public void init()
 {
	prompt1 = new Label("Start value for Q : ");
	input1 = new TextField("10", 5);

	prompt2 = new Label("K Outflow coefficient : ");
	input2 = new TextField("5", 5);

	prompt3 = new Label("  t_1 : ");
	input3 = new TextField("96", 4);

	chooseEvent = new Choice();
	chooseEvent.addItem("No change of inflow/outflow");
	chooseEvent.addItem("Stop inflow at t_1");
	chooseEvent.addItem("Stop outflow at t_1");
	chooseEvent.addItem("Double inflow at t_1");
	chooseEvent.addItem("Double outflow at t_1");

	drawButton = new Button("Draw");

	add(prompt1);
	add(input1);
	add(drawButton);
	add(prompt2);
	add(input2);
	add(prompt3);
	add(input3);
	add(chooseEvent);
 }

 public boolean action(Event e, Object o)
 {
 	q = (float)Integer.parseInt(input1.getText());
 	k0 = 0.01f*(float)Integer.parseInt(input2.getText());
 	t1 = Integer.parseInt(input3.getText());

	if (e.target instanceof Choice)
		 a = chooseEvent.getSelectedIndex();

 	repaint();
 	return true;
 }

 public void paint(Graphics g)
 {
 	g.drawRect(0,90,320,250);
	t=0;
	j0=4;
	j=j0;
	k=k0;

 	while (t<320) {
		ti=t+1;
		if (ti >= t1) {
			switch(a) {
				case 0: break;
				case 1: j=0; break;
				case 2: k=0; break;
				case 3: j=j0*2; break;
				case 4: k=k0*2; break;
				default:  break;
				}
		}
		dq=j-k*q;
		qi=q+dq;
		g.setColor(Color.blue);
		g.drawLine((int)t, (int)(340-q), (int)ti, (int)(340-qi));
		t=ti; q=qi;
	}
  }
}
// Manuel Basler & E. Ortega, October 25th 2000/