// GeometricPlot.java

// Written by Julian Devlin, 8/97, for the text book
// "Introduction to Probability," by Charles M. Grinstead & J. Laurie Snell

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

public class GeometricPlot
	extends java.applet.Applet
{
	Float[] xCoords;		// Variables for simulation
	Float[] yCoords;
	
	SpikeGraph sg;				// AWT elements
	
	Panel dispArea;
	Panel controls;		// Panel for user controls
	
	Label numl;			// Controls
	TextField num;
	Button go;
	
	GridBagLayout gbl;
	GridBagConstraints cc;
		
	// Initialize applet
	public void init()
	{	
		numl = new Label("p =");			// Create controls
		num = new TextField(".5", 4);
		go = new Button("Go");
		
		sg = new SpikeGraph(); // initialize a graphing space
		
		dispArea = new Panel();				// Set up window
		controls = new Panel();
		setLayout(new BorderLayout(5, 5));
		
		add("South", controls);
		add("Center", dispArea);
		
		dispArea.setLayout(new GridLayout(1, 1));
		dispArea.add(sg);
		
		gbl = new GridBagLayout();
		controls.setLayout(gbl);
		
		cc = new GridBagConstraints();
		
		cc.gridx = 0;
		cc.gridy = 0;
		gbl.setConstraints(numl, cc);
		controls.add(numl);
		
		cc.gridx = 1;
		gbl.setConstraints(num, cc);
		controls.add(num);
		
		cc.gridx = 0;
		cc.gridy = 1;
		cc.gridwidth = 2;
		gbl.setConstraints(go, cc);
		controls.add(go);
		
		validate();
	}
	
	// Handle events
	public boolean handleEvent(Event evt)
	{
		if (evt.target instanceof Button)
		{
			if (evt.target == go && evt.id == Event.ACTION_EVENT)	// When button is clicked
			{
        		simulate(Float.valueOf(num.getText()).floatValue());
        		return true;					// Generate correct number of tosses
			}
		}
		return super.handleEvent(evt);	// Handle other events as usual
	}
	
	// Calculate probabilities
    public void simulate(float prob)
    {	
    	float temp;
    	float q = 1f - prob;
    	xCoords = new Float[20 + 2];			// we add an extra point with y == 0 so that x labels
    	yCoords = new Float[20 + 2];			// will be shown for sure - a stupid fakeout
    	for (int i = 0; i <= 20; i++) {
    		xCoords[i] = new Float(i);
    		temp = (float) Math.pow((double) q, (double) i - 1) * prob;
    		yCoords[i] = new Float(temp);
	    }
	    xCoords[21] = new Float(19.5f);
	    yCoords[21] = new Float(0f);
		dispArea.remove(sg);
		sg = new SpikeGraph(xCoords, yCoords);	// Create new SpikeGraph
		dispArea.add(sg);							// Put up the graph
		validate();
	}
}