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

/** BigPixelApplet is the superclass for applets that draw big fat pixels
    on screen.  It doesn't do anything interesting by itself */
public class BigPixelApplet extends Applet implements Runnable {
  
    BigPixelCanvas canvas; //drawing area
    Button step; //The button that user clicks on to get algorithm to do next step
    Checkbox stepMode; //So user can turn off single step execution
    TextArea state; //For displaying internal state of a particular algorithm

    /* Next four methods are for convenience - we just use method forwarding
       to the BigPixelCanvas object */

    /* map from virtual pixels to real ones */
    int toScreenX(int x) {
	return canvas.toScreenX(x);
    }

    /* map from virtual pixels to real ones */
    int toScreenY(int y) {
	return canvas.toScreenY(y);
    }

    /* map from real pixels to virtual ones */
    int fromScreenX(int x) {
	return canvas.fromScreenX(x);
    }

    /* map from real pixels to virtual ones */
    int fromScreenY(int y) {
	return canvas.fromScreenY(y);
    }

    void fillSpan(int startx, int endx, int y) {
	canvas.fillSpan(startx,endx,y);
    }

    void drawPixel(int x, int y) {
	canvas.drawPixel(x,y);
    }

    /** Thread that executes given algorithm */
    Thread runner;

    /** Start thread that executes given algorithm */
    public void begin() {
	runner = new Thread(this);
	runner.start(); //Do drawing is separate thread so it can step
    }

    /** Subclasses should overide this method to call the particular algorithm
	being animated.
    */
    public void run() {
	/* Do nothing - subclasses should override */
    }

    /** Make algorithm continue execution after step() has been called */
    synchronized void wakeUp() {
	notify();
    }

    /** Stop execution until "Step" button is pressed */
    /* if this returns true, running thread should stop itself 
       since another one has started */
    synchronized boolean step() {
	state.append("\n---------\n");
	state.append(showState());
	state.setCaretPosition(999999);
	if (stepMode.getState()) {
	    try {
		wait();
	    } catch (InterruptedException e) {
		/*nothing */
	    }
	}
	//System.out.println(Thread.currentThread() != runner);

	return  Thread.currentThread() != runner;
    }

    /** show state of important data structures used by this algorithm */
    String showState() {
	return ""; //default is nothing
    }

    /** init() is called by browser to initialize the applet */
    public void init() {
	setBackground(Color.white);
	setFont(new Font("Default",Font.PLAIN,16));
	setLayout(new BorderLayout());
	canvas = new BigPixelCanvas();
	add(canvas,"Center");

	Panel p = new Panel();

	/* When this button is clicked on the wakeUp method is called */
	step = new Button("Step");
	p.add(step);
	step.addActionListener( new ActionListener() {
		public void actionPerformed(ActionEvent e){
		    wakeUp();
		}
	    });

	/* No need to do anything when user changes state of the checkbox */
	stepMode = new Checkbox("Step Mode",true);
	p.add(stepMode);

	Button clear = new Button("Clear");
	p.add(clear);
	clear.addActionListener( new ActionListener() {
		public void actionPerformed(ActionEvent e){
		    canvas.clear();
		    state.setText("");
		}
	    });
	add(p,"South");
	state = new TextArea(20,30);
	add(state,"East");
    }
}