observer_patern.php

<?php

class Subject implements \SplSubject{
    
    public  $state;
    private $observers;
    
    public function __construct(){
        $this->observers = new \SplObjectStorage();
    }
    
    public function attach(\SplObserver $observer)
    : void{
        echo "Subject: Attached an observer.\n";
        $this->observers->attach($observer);
    }
    
    public function detach(\SplObserver $observer)
    : void{
        $this->observers->detach($observer);
        echo "Subject: Detached an observer.\n";
    }
    
    public function notify()
    : void{
        echo "Subject: Notifying observers...\n";
        foreach($this->observers as $observer){
            $observer->update($this);
        }
    }
    
    public function someBusinessLogic()
    : void{
        echo "\nSubject: I'm doing something important.\n";
        $this->state = rand(0, 100);
        
        echo "Subject: My state has just changed to: {$this->state}\n";
        $this->notify();
    }
}

class ConcreteObserverA implements \SplObserver{
    
    public function update(\SplSubject $subject)
    : void{
        if($subject->state < 3){
            echo "ConcreteObserverA: Reacted to the event.\n";
        }
    }
}

class ConcreteObserverB implements \SplObserver{
    
    public function update(\SplSubject $subject)
    : void{
        if($subject->state == 0 || $subject->state >= 2){
            echo "ConcreteObserverB: Reacted to the event.\n";
        }
    }
}

/**
 * The client code.
 */

$subject = new Subject();

$o1 = new ConcreteObserverA();
$subject->attach($o1);

$o2 = new ConcreteObserverB();
$subject->attach($o2);

//$subject->someBusinessLogic();
//$subject->someBusinessLogic();
//
//$subject->detach($o2);
////$subject->detach($o1);
//
$subject->someBusinessLogic();

echo "notity\n";
$subject->notify();