<?php
abstract class AbstractCar {
    public abstract function getPrice();
    public abstract function getManufacturer();
};
class Car extends AbstractCar {
    private $price = 16000;
    private $manufacturer = 'Acme Autos';
    public function getPrice() { return $this->price; }
    public function getManufacturer() { return $this->manufacturer; }
};
class CarDecorator extends AbstractCar {
    private $target;
    function __construct( Car $target ) { $this->target = $target; }
    public function getPrice() { return $target->getPrice(); }
    public function getManufacturer() { return $target->getManufacturer(); }
};
class NavigationSystem extends CarDecorator {
    public function getPrice() { return parent::getPrice()+1000; }
};

$car = new Car();
$car = new NavigationSystem( $car );
//$car = new LeatherSeats( $car );
echo $car->getPrice();