// patterns/visualobserver/BoxObserver.java
// (c)2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
// Demonstration of Observer pattern using
// Java's built-in observer classes.
// {TimeOut:4000} During testing
package patterns.visualobserver;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import onjava.MouseClick;

// You must inherit a new type of Observable:
class BoxObservable extends Observable {
  @Override
  public void notifyObservers(Object b) {
    // Otherwise it won't propagate changes:
    setChanged();
    super.notifyObservers(b);
  }
}

public class BoxObserver extends JFrame {
  Observable notifier = new BoxObservable();
  public BoxObserver(int grid) {
    setTitle("Demonstrates Observer pattern");
    Container cp = getContentPane();
    cp.setLayout(new GridLayout(grid, grid));
    for(int x = 0; x < grid; x++)
      for(int y = 0; y < grid; y++)
        cp.add(new OCBox(x, y, notifier));
  }
  public static void main(String[] args) {
    int grid = 8;
    if(args.length > 0)
      grid = Integer.parseInt(args[0]);
    JFrame f = new BoxObserver(grid);
    f.setSize(500, 400);
    f.setVisible(true);
    f.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
  }
}

class OCBox extends JPanel implements Observer {
  Observable notifier;
  int x, y; // Locations in grid
  Color cColor = newColor();
  static final Color[] colors = {
    Color.black, Color.blue, Color.cyan,
    Color.darkGray, Color.gray, Color.green,
    Color.lightGray, Color.magenta,
    Color.orange, Color.pink, Color.red,
    Color.white, Color.yellow
  };
  static Color newColor() {
    return colors[
      (int)(Math.random() * colors.length)
    ];
  }
  OCBox(int x, int y, Observable notifier) {
    this.x = x;
    this.y = y;
    notifier.addObserver(this);
    this.notifier = notifier;
    addMouseListener((MouseClick)
      e -> notifier.notifyObservers(OCBox.this));
  }
  @Override
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setColor(cColor);
    Dimension s = getSize();
    g.fillRect(0, 0, s.width, s.height);
  }
  @Override
  public void update(Observable o, Object arg) {
    OCBox clicked = (OCBox)arg;
    if(nextTo(clicked)) {
      cColor = clicked.cColor;
      repaint();
    }
  }
  private boolean nextTo(OCBox b) {
    return Math.abs(x - b.x) <= 1 &&
           Math.abs(y - b.y) <= 1;
  }
}