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

public class AppletTest extends Applet{
    public AppletTest() {
        setLayout(new BorderLayout());
        add("Center",new TestCanvas("($$$$+$$$$$)/($$*$$$)"));        
        setVisible(true);
    }
}
class TestCanvas extends Canvas implements KeyListener{
    public static char DEFAULT_NUMBER = '$';
    
    private Dimension preferredSize = new Dimension(300,200);
    private String theString;
    private StringBuffer sb;   
    Vector tokens = new Vector();
    Vector numbers = new Vector();
    int[]  numberPos;
    int    numPos = 0;

    public TestCanvas() {
        this("$$$$$/$$$$$");
    }
    public TestCanvas(String str) {
        setExpression(str);
        addKeyListener(this);
    }
    public void setExpression(String str) {
        theString = new String(str);
        
        StringTokenizer st = new StringTokenizer(str, "/*+-()", true);
        int counter = 0;
        while (st.hasMoreTokens()) {
            String s = st.nextToken();
            if (s.startsWith("$")) {
                numbers.addElement(new Integer(counter));
                tokens.addElement(new StringBuffer(s));
            }
            else 
            tokens.addElement(s);
            counter++;
        }
        for (int n = 0; n < tokens.size(); n++) {
            System.out.println(n+"-"+((Object)tokens.elementAt(n)).toString());
        }        
        numberPos = new int[numbers.size()+1];     
        int total = 0; 
        for (int n = 0; n < numbers.size(); n++) {
            System.out.println(n+"-"+((Integer)numbers.elementAt(n)).intValue());
            numberPos[n] = total;
            total += ((Object)tokens.elementAt(((Integer)numbers.elementAt(n)).intValue())).toString().length();
        }  
        numberPos[numberPos.length-1] = total;
        numPos = 0;
        for (int n = 0; n < numberPos.length; n++) 
            System.out.println(n+"."+numberPos[n]);
        
        repaint();
    }
    public void paint(Graphics g) {
        super.paint(g);
        FontMetrics fm = g.getFontMetrics();
        int x = getWidth()- fm.stringWidth(theString)/2;
        int y = getHeight()/2+fm.getHeight()/2;

        sb = new StringBuffer();
        for (int n=0; n < tokens.size(); n++)
            sb = sb.append(tokens.elementAt(n));
                
        theString = sb.toString();
        g.drawString(theString, 10, 10);
    }
    public void keyPressed(KeyEvent e) {
        char i = e.getKeyChar();
        if (i == '\b') {
//            System.out.print("Back");
            if (numPos > 0 ) {
                numPos--;
    
                int word = -1;
                for (int n = 0; n < numberPos.length; n++) {
                    if (numPos < numberPos[n]) {
                        word = n-1;
                        break;
                    }
                }
                if (word >= 0 && word < numberPos.length) {
                    int relPos = numPos -numberPos[word];
                    StringBuffer buffer = (StringBuffer)tokens.elementAt(((Integer)numbers.elementAt(word)).intValue());
                    buffer.setCharAt(relPos, '$');
                    repaint();
                }
            }
        }
        else if ((i >= 'A' && i <= 'Z') || (i >= 'a' && i <= 'z') || (i >= '0' && i <= '9')) {
            System.out.println(i);
            int word = -1;
            for (int n = 0; n < numberPos.length; n++) {
                if (numPos < numberPos[n]) {
                    word = n-1;
                    break;
                }
            }
            System.out.println("NumPos:"+numPos+"\nWord:"+word);
            if (word >= 0 && word < numberPos.length) {
                int relPos = numPos -numberPos[word];
                StringBuffer buffer = (StringBuffer)tokens.elementAt(((Integer)numbers.elementAt(word)).intValue());
                buffer.setCharAt(relPos, (char)i);
                numPos++;
                repaint();
            }
        }    
    }
    public void keyTyped(KeyEvent e) {

    }
    public void keyReleased(KeyEvent e) {
    }
    
    
    public Dimension getPreferredSize() {
        return preferredSize;
    }
    public Dimension getMinimumSize() {
        return getPreferredSize();
    }
    public Dimension getMaximumSize() {
        return getPreferredSize();
    }
}