[PHP5] OBSERVER DESIGN PATTERN

<?php
/**
 * defining abstract implementations
 */
if (!interface_exists ('Countable')) {
	/**
	 * Interface Countable
	 * @author: php
	 *
	 */
	interface Countable {
		
		public function count();
	}
}
if (!interface_exists ('SplObserver')) {
	/**
	 * Interface SplObserver
	 * @author: php
	 *
	 */
	interface SplObserver {
		
		public function update(SplSubject $subject);
	}
}

if (!interface_exists ('SplSubject')) {
	/**
	 * Interface SplSubject
	 * @author: php
	 *
	 */
	interface SplSubject {
		
		public function attach(SplObserver $observer);
		
		public function detach(SplObserver $observer);
		
		public function notify();
	}
}

if (!class_exists ('SplObjectStorage')) {
	/**
	 * Interface SplObjectStorage
	 * @author: php
	 *
	 */
	class SplObjectStorage implements Iterator, Countable {
		
		/**
		 * Array of objects
		 *
		 * @var array
		 */
		private $storage = array();
		/**
		 * Array of objects index
		 *
		 * @var int
		 */
		private $index = 0;
	
		/**
		 * public function rewind
		 * Rewind array pointer
		 * 
		 * @Return void
		 */
		public function rewind() {
			rewind($this->storage);
		}
	
		/**
		 * public function valid
		 * Checks if current loop iteration is valid
		 * 
		 * @Return boolean 
		 */
		public function valid() {
			return key($this->storage) !== false;
		}

		/**
		 * public function key
		 * Returns current key
		 * 
		 * @Return int 
		 */
		public function key() {
			return $this->index;
		}
		
		/**
		 * public function current
		 * Returns current array entry
		 * 
		 * @Return object 
		 */
		public function current() {
			return current($this->storage);
		}
		
		/**
		 * public function next
		 * Iterates to the next entry
		 * 
		 * @Return void 
		 */
		public public function next() {
			next($this->storage);
			$this->index++;
		}
		
		/**
		 * public function count
		 * Returns the number of entries in the array of objects
		 * 
		 * @Return int 
		 */
		public function count()  {
			return count($this->storage);
		}
		
		/**
		 * public function contains
		 * Checks if an object is in the collector array
		 * 
		 * @Param object $obj : object to check
		 * @Return boolean 
		 */
		public function contains($obj) {
			if (is_object($obj)) {
				foreach($this->storage as $object) {
					if ($object === $obj) {
						return true;
					}
				}
			}
			return false;
		}
		
		/**
		 * public function attach
		 * Attaches an object to the collector array
		 * 
		 * @Param object $obj : object to attach
		 * @Return void 
		 */
		public function attach($obj) {
			if (is_object($obj) && !$this->contains($obj)) {
				$this->storage[] = $obj;
			}
		}
		
		/**
		 * public function detach
		 * Detaches an object to the collector array
		 * 
		 * @Param object $obj : object to detach
		 * @Return void 
		 */
		public function detach($obj) {
			if (is_object($obj)) {
				foreach($this->storage as $idx => $object) {
					if ($object === $obj) {
						unset($this->storage[$idx]);
						$this->rewind();
						return;
					}
				}
			}
		}
	}
}

/**
 * starting concrete implementations
 */
/**
 * class car implements SplSubject
 * @author: Johan Barbier <johan.barbier@gmail.com>
 *
 */
class car implements SplSubject {
	
	/**
	 * Name of the car
	 *
	 * @var string
	 */
	private $sName;
	/**
	 * State of the car
	 *
	 * @var int
	 */
	private $iState = 0;
	/**
	 * Speed of the car
	 *
	 * @var int
	 */
	private $iSpeed = 0;
	/**
	 * Collector array of observers
	 *
	 * @var SplObserver
	 */
	private $aObservers;
	
	/**
	 * public function __construct
	 * constructor
	 * Initializes car's nname
	 *
	 * @param string $sName
	 */
	public function __construct ($sName) {
		$this -> sName = $sName;
		$this -> aObservers = new SplObjectStorage;
	}
	
	/**
	 * public function start
	 * Starts the car and notify observers
	 * 
	 * @Return void
	 */
	public function start () {
		$this -> iState = 1;
		$this -> notify();
	}
	
	/**
	 * public function stop
	 * Stops the car and notify observers
	 * 
	 * @Return void
	 */
	public function stop () {
		$this -> iState = 0;
		$this -> iSpeed = 0;
		$this -> notify();
	}
	
	/**
	 * public function accelerate
	 * Accelerates the car and notify the observers
	 * 
	 * @Param int $iAcceleration : how many Kmh you want to accelerate
	 * @Return void
	 */
	public function accelerate ($iAcceleration) {
		if (0 === $this -> iState) {
			throw new Exception ('You must start the car before accelerating...');
		}
		if (!is_int ($iAcceleration) || $iAcceleration < 0) {
			throw new Exception ('Wrong value for car::accelerate()');
		}
		$this -> iSpeed += $iAcceleration;
		$this -> notify();
	}

	/**
	 * public function attach
	 * Attaches an observer
	 * 
	 * @Param SplObserver $observer : the observer to attach
	 * @Return boolean
	 */
	public function attach(SplObserver $observer) {
		if(!$this->aObservers->contains($observer)) {
			$this->aObservers->attach($observer);
		}
		return true;
	}
	
	/**
	 * public function detach
	 * Detaches an observer
	 * 
	 * @Param SplObserver $observer : the observer to detach
	 * @Return boolean
	 */
	public function detach(SplObserver $observer) {
		if(!$this->aObservers->contains($observer)) {
			return false;
		}
		$this->aObservers->detach($observer);
		return true;
	}
	
	/**
	 * public function notify
	 * Notify all the observers
	 * 
	 * @Return void
	 */
	public function notify() {
		foreach($this->aObservers as $observer) {
			$observer->update($this);
		}
	}
	
	/**
	 * public function __get
	 * Get properties value
	 * 
	 * @Param string $sProp : property's name
	 * @Return mixed
	 */
	public function __get ($sProp) {
		switch ($sProp) {
			case 'STATE' : 
				return $this -> iState;
				break;
			case 'SPEED' :
				return $this -> iSpeed;
				break;
			case 'NAME' :
				return $this -> sName;
				break;
			default :
				throw new Exception ($sProp.' cannot be read');
		}
	}
	
	/**
	 * public function __set
	 * Set properties value
	 * 
	 * @Param string $sProp : property's name
	 * @Param mixed $mVal : property's value
	 * @Return void
	 */
	public function __set ($sProp, $mVal) {
		throw new Exception ($sProp.' cannot be set');
	}
}

/**
 * class carStateObserver implements SplObserve
 * @author Johan Barbier <johan.barbier@gmail.com>
 *
 */
class carStateObserver implements SplObserver {
	
	/**
	 * Stored subject's state
	 *
	 * @var int
	 */
	private $iSubjectState;
	
	/**
	 * public function update
	 * updater. Echoes subject's state (if the car is stopped or started)
	 * 
	 * @param SplSubject $subject
	 * @return void
	 */
	public function update(SplSubject $subject) {
		switch ($subject -> STATE) {
			case 0 :
				if (is_null ($this -> iSubjectState)) {
					echo $subject -> NAME.' has not been started<br />'; 
				} else {
					echo $subject -> NAME.' has been stopped<br />'; 
				}
				$this -> iSubjectState = 0;
				break;
			case 1:
				if (1 !== $this -> iSubjectState) {
					echo $subject -> NAME.' has been started<br />'; 
					$this -> iSubjectState = 1;
				}
				break;
			default :
				throw new Exception ('Unexpected error in carStateObserver::update()');
		}
	}
}

/**
 * class carSpeedObserver implements SplObserver
 * @author Johan Barbier <johan.barbier@gmail.com>
 *
 */
class carSpeedObserver implements SplObserver {
	
	/**
	 * public function update
	 * updater. Echoes subject's speed
	 * 
	 * @param SplSubject $subject
	 * @return void
	 */
	public function update(SplSubject $subject) {
		if (0 !== $subject -> STATE) {
			echo $subject -> NAME.' speed is '.$subject -> SPEED.'Kmh<br />';
		}
	}
}

/**
 * class carOverspeedObserver implements SplObserver
 * @author Johan Barbier <johan.barbier@gmail.com>
 *
 */
class carOverspeedObserver implements SplObserver {
	
	/**
	 * public function update
	 * updater. Catches the subject if it is overspeeding!
	 * 
	 * @param SplSubject $subject
	 * @return void
	 */
	public function update(SplSubject $subject) {
		if ($subject -> SPEED > 130) {
			throw new Exception ('Speed limit is 130! You lost your driver license !');
		}
	}
}
try {
	$oCar = new car ('AUDI A4');
	$oObs = new carStateObserver;
	$oObs2 = new carSpeedObserver;
	$oObs3 = new carOverspeedObserver;
	$oCar -> attach($oObs);
	$oCar -> attach($oObs2);
	$oCar -> attach($oObs3);
	
	$oCar -> start();
	$oCar -> accelerate(20);
	$oCar -> accelerate(30);
	$oCar -> stop();
	$oCar -> start();
	$oCar -> accelerate(50);
	$oCar -> accelerate(70);
	$oCar -> accelerate(100);
	$oCar -> accelerate(150);
} catch (Exception $e) {
	echo $e -> getMessage ();
}
?>