// OscillatingCheckerboard.java
// Solution to Short Assignment 8 Extra Credit by THC.
// Draws a checkerboard that oscillates between red and black squares
// and green and white squares.

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import javax.swing.Timer;

public class OscillatingCheckerboard extends Applet implements ActionListener {
  private final int DIMENSION = 8; // Want 8 x 8 board
  private final int SQUARE_SIZE = 30; // Each square is 30 x 30 pixels
  
  private Timer timer;  // Timer for oscillation
  private boolean redAndBlack;  // true if drawing red/black, false if green/white

  public void init() {
    // Set the size of the applet to be exactly the checkerboard size.
    setSize(DIMENSION * SQUARE_SIZE, DIMENSION * SQUARE_SIZE);
    redAndBlack = true;
    
    final int DELAY = 500;
    timer = new Timer(DELAY, this);
    timer.start();

    // Draw the checkerboard.
    repaint();
  }

  public void paint(Graphics page) {
    if (redAndBlack)
      drawCheckerboard(page, Color.black, Color.red);
    else
      drawCheckerboard(page, Color.white, Color.green);
  }
  
  // Draw a checkerboard in colors c1 and c2.
  public void drawCheckerboard(Graphics page, Color c1, Color c2) {
    // Draw all the squares.
    Color squareColor; // Color of the current square

    for (int row = 0; row < DIMENSION; row++) {
      for (int column = 0; column < DIMENSION; column++) {
        // A square is color c1 if the row and column numbers are both even
        // or both odd. Otherwise, the square is color c2.
        if (row % 2 == column % 2)
          squareColor = c1;
        else
          squareColor = c2;

        drawSquare(page, row, column, squareColor);
      }
    }
  }

  // Draw a given square of the checkerboard. Row and column numbers start
  // from 0.
  public void drawSquare(Graphics page, int row, int column, Color color) {
    page.setColor(color);
    page.fillRect(column * SQUARE_SIZE, row * SQUARE_SIZE, SQUARE_SIZE,
        SQUARE_SIZE);
  }

  // Respond to a Timer event by drawing the checkerboard.
  public void actionPerformed(ActionEvent event) {
    redAndBlack = !redAndBlack;   // oscillate
    repaint();
  }
}