import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;

/** @author John B. Matthews; distribution per GNU Public License */
public class ScaledPanel extends JPanel
    implements KeyListener, MouseListener, MouseMotionListener {

    private static final int SIZE = 8; // 8x8 board
    private static final int DIAM = SIZE * 10; // checker size
    private static final int maxX = SIZE * DIAM;
    private static final int maxY = SIZE * DIAM;
    private static final Color white = new Color(0xF0F0C0); 
    private static final Color light = new Color(0x40C040); 
    private static final Color dark  = new Color(0x404040);
    private static final Cursor hand = new Cursor(Cursor.HAND_CURSOR);
    private static final Cursor norm = new Cursor(Cursor.DEFAULT_CURSOR);
    private static final Font font = new Font("Serif", Font.BOLD, 48);
    private final Ellipse2D.Double checker = new Ellipse2D.Double();
    private final Rectangle boundary = new Rectangle();
    private int posX = 3 * DIAM; // column three
    private int posY = 3 * DIAM; // row three
    private int pressedX, pressedY;
    private int frameX, frameY;
    private boolean checkerVisible = true;
    private boolean mouseDown = false;
    
    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new ScaledPanel());
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    public ScaledPanel() {
        this.setPreferredSize(new Dimension(maxX, maxY));
        this.addKeyListener(this);
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
        this.setFocusable(true);
    }

    @Override public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2D = (Graphics2D) g;

        g2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g2D.scale(
            (double) this.getWidth() / maxX,
            (double) this.getHeight() / maxY);

        for (int row = 0; row < SIZE; row++) {
             for (int col = 0; col < SIZE; col++) {
                 g.setColor((row + col) % 2 == 0 ? light : dark);
                 g.fillRect(col * DIAM, row * DIAM, DIAM, DIAM);
             }
        }

        if (checkerVisible) {
            checker.setFrame(posX, posY, DIAM, DIAM);
            g.setColor(white);
            g2D.fill(checker);
            g.setFont(font);
            int a = g.getFontMetrics().getAscent();
            int w = g.getFontMetrics().stringWidth("\u2748");
            int bx = posX + DIAM / 2 - w / 2 + 1;
            int by = posY + DIAM / 2 + a / 2 - 1;
            g.setColor(dark);
            g.drawString("\u2748", bx, by);
        }
    }

    public void keyTyped(KeyEvent e) {}
    public void keyReleased(KeyEvent e) {}
    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_UP) moveChecker(0, -1);
        if (e.getKeyCode() == KeyEvent.VK_DOWN) moveChecker(0, 1);
        if (e.getKeyCode() == KeyEvent.VK_LEFT) moveChecker(-1, 0);
        if (e.getKeyCode() == KeyEvent.VK_RIGHT) moveChecker(1, 0);
        if (e.getKeyCode() == KeyEvent.VK_HOME) {
            eraseChecker();
            posX = 3 * DIAM;
            posY = 3 * DIAM;
            repaintChecker();
        }
    }

    private void moveChecker(int dx, int dy) {
        eraseChecker();
        posX = posX + DIAM * dx;
        posY = posY + DIAM * dy;
        repaintChecker();
    }

    public void mouseClicked(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}

    public void mousePressed(MouseEvent e) {
        if (checker.contains(scaleX(e.getX()), scaleY(e.getY()))) {
            this.setCursor(hand);
            mouseDown = true;
            Rectangle2D r = checker.getFrame();
            frameX = (int) r.getX();
            frameY = (int) r.getY();
            pressedX = e.getX(); 
            pressedY = e.getY(); 
        } else {
            mouseDown = false;
        }
    }
    
    public void mouseReleased(MouseEvent e) {
        posX = ((int) scaleX(e.getX())) / DIAM * DIAM;
        posY = ((int) scaleY(e.getY())) / DIAM * DIAM;
        this.repaint();
        this.setCursor(norm);
        mouseDown = false;
    }
    
    public void mouseMoved(MouseEvent e) {}
    public void mouseDragged(MouseEvent e) {
        if (mouseDown) {
            updateChecker(e);
        }
    }
    
    public void updateChecker(MouseEvent e) {
        eraseChecker();
        int deltaX = (int) (scaleX(e.getX() - pressedX));
        int deltaY = (int) (scaleY(e.getY() - pressedY));
        posX = frameX + deltaX;
        posY = frameY + deltaY;
        repaintChecker();
    }

    private void eraseChecker () {
        checkerVisible = false;
        repaintChecker();
    }

    private void repaintChecker() {
        checkerVisible = true;
        int rawX = (int) (unScaleX(posX));
        int rawY = (int) (unScaleY(posY));
        int rawW = (int) (unScaleX(DIAM));
        int rawH = (int) (unScaleY(DIAM));
        boundary.setRect(rawX, rawY, rawW, rawH);
        boundary.grow(2, 2);
        this.repaint(boundary);
    }

    private double scaleX(int x) {
        return ((double) x / getWidth()) * maxX;
    }

    private double scaleY(int y) {
        return ((double) y / getHeight()) * maxY;
    }

    private double unScaleX(int x) {
        return ((double) x / maxX) * getWidth();
    }

    private double unScaleY(int y) {
        return ((double) y / maxY) * getHeight();
    }
}