<?php

/* This is a sample of Observer design pattern for PHP5.
*
* $Id: observer.php,v 1.1 2004/02/12 15:28:59 tea Exp tea $
*/

function array_remove(&$array, $element) {
    array_splice($array, array_search($element, $array), 1);
}

class DoubleAttachException
{
    function __construct(Observer $observer) {
        $this->observer = $observer;
    }
    
    public function getException() {
        return "(" . $this->observer . ") is registered already.\n";
    }
}

interface Observer
{
    abstract function update();
}

abstract class Subject
{
    function __construct() {
        $this->observers = array();
    }

    public function attach(Observer $observer) {
        if (in_array($observer, $this->observers)) {
            throw new DoubleAttachException($observer);
        }
        else {
            $this->observers[] = $observer;
        }
    }
    
    public function detach(Observer $observer) {
        if (in_array($observer, $this->observers)) {
            array_remove($this->observers, $observer);
        }
    }
    
    protected function notifyAll() {
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }
}

class Point implements Observer
{
    function __construct($name) {
        $this->name = $name;
    }

    public function update() {
        print "Point($this->name)\n";
    }
}

class Screen extends Subject
{
    function __construct($x, $y, $color) {
        parent::__construct();
        $this->x = $x;
        $this->y = $y;
        $this->color = $color;
    }
    
    public function setX($x) {
        $this->x = $x;
        $this->notifyAll();
    }

    public function setY($y) {
        $this->y = $y;
        $this->notifyAll();
    }

    public function setColor($color) {
        $this->color = $color;
        $this->notifyAll();
    }
}

try {
    $screen = new Screen(10, 20, "red");
    $screen->attach($p1 = new Point("A"));
    $screen->attach($p2 = new Point("B"));
    $screen->attach($p3 = new Point("C"));

    # Attach the same observer again.
    # This will throw DoubleAttachException.
    # $screen->attach($p1);

    print "screen set X = 10\n";
    $screen->setX(10);

    print "now detach p2 object\n";
    $screen->detach($p2);

    print "screen set color = blue\n";
    $screen->setColor("blue");
}
catch (DoubleAttachException $exception) {
    print $exception->getException();
}

?>