package week1;

/*  
This applet draws a red-and-black checkerboard.
It is assumed that the size of the applet is 160
by 160 pixels.  When the user clicks a square, that
square is selected, unless it is already selected.
When the user clicks the selected square, it is
unselected.  If there is a selected square, it is
hilited with a cyan border.
*/


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

public class ClickableCheckerboard extends Applet 
                                   implements MouseListener{
                                   

int selectedRow; // Row and column of selected square.  If no
int selectedCol; //      square is selected, selectedRow is -1.


public void init() {
     // Initialize the applet.  Set selectedRow to -1 to indicate
     // that no square is selected.  And listen for mouse events.
  selectedRow = -1;  
  selectedCol = -1;
  addMouseListener(this);
}


public void update(Graphics g) {
     // Since the paint method paints the whole applet, there is
     // no need to fill it with the background color first.  To 
     // avoid flickering, redefine update so it just calls paint.
  paint(g);
}


public void paint(Graphics g) {
     // Draw the checkerboard and hilite the selected square, if any.
   
  int row;   // Row number, from 0 to 7
  int col;   // Column number, from 0 to 7
  int x,y;   // Top-left corner of square

  for ( row = 0;  row < 8;  row++ ) {
   
     for ( col = 0;  col < 8;  col++) {
         x = col * 20;
         y = row * 20;
         if ( (row % 2) == (col % 2) )
            g.setColor(Color.red);
         else
            g.setColor(Color.black);
         g.fillRect(x, y, 20, 20);
     } 
   
  } // end for row
  
  if (selectedRow <= 8) {
        // Since there is a selected square, draw a cyan
        // border around it.
     g.setColor(Color.cyan);
     y = selectedRow * 20;
     x = selectedCol * 20;
     g.drawRect(x, y, 19, 19);
     g.drawRect(x+1, y+1, 17, 17);
  }
  if (selectedCol <= 8) {
      // Since there is a selected square, draw a cyan
      // border around it.
   g.setColor(Color.cyan);
   y = selectedRow * 20;
   x = selectedCol * 20;
   g.drawRect(x, y, 19, 19);
   g.drawRect(x+1, y+1, 17, 17);
}

}  // end paint()


public void mousePressed(MouseEvent evt) {
      // When the user clicks on the applet, figure out which
      // row and column the click was in and change the
      // selected square accordingly.
      
  int col = evt.getX() / 20;   // Column where user clicked.
  int row = evt.getY() / 20;   // Row where user clicked.
  
  if (selectedRow == row && selectedCol == col) {
       // User clicked on the currently selected square.
       // Turn off the selection by setting selectedRow to -1.
     selectedRow = -1;
  }
  else {
        // Change the selection to the square the user clicked on.
     selectedRow = row;
     selectedCol = col;
  }
  repaint();

}  // end mouseDown()


public void mouseReleased(MouseEvent evt) { }
public void mouseClicked(MouseEvent evt) { }
public void mouseEntered(MouseEvent evt) { }
public void mouseExited(MouseEvent evt) { }


}   // end class