<?php
namespace Common\Observer;

use SplObjectStorage;

/**
 * The subject implement in the observer pattern.
 *
 * @author TonySeek
 *
 */
trait Subject
{
    private $observers = null;

    /**
     * Create or get existed observer object container.
     *
     * @return \SplObjectStorage;
     */
    private function getObserverStorage()
    {
        if (!$this->observers) {
            $this->observers = new SplObjectStorage();
        }
        return $this->observers;
    }

    /**
     * @return \Common\Observer\Subject
     */
    public function attachObserver(Observer $observer)
    {
        $storage = $this->getObserverStorage();
        $storage->attach($observer);
        return $this;
    }

    /**
     * @return \Common\Observer\Subject
     */
    public function detachObserver(Observer $observer)
    {
        $storage = $this->getObserverStorage();
        $storage->detach($observer);
        return $this;
    }

    /**
     * @see SplSubject::notify()
     */
    public function notify()
    {
        $storage = $this->getObserverStorage();
        foreach($storage as $observer) {
            $observer->update($this);
        }
    }
}