interface IChargeable 
{
	public function getPrice();
}

class ShopProduct implements IChargeable
{
	private $title;
	private $producerMainName;
	private $producerFirstName;
	protected $price;
	
	function __construct($title, $firstName, $mainName, $price) {
		$this->title = $title;
		$this->producerMainName = $mainName;
		$this->producerFirstName = $firstName;
		$this->price = $price;
	}
	
	public function getPrice () {
		return $this->price;
	}
	
	public function getProducerMainName() {
		return $this->producerMainName;
	}
	
	public function getProducerFirstName() {
		return $this->producerFirstName;
	}
	
	public function setDiscount( $num ) {
		$this->discount=$num;
	}

    public function getDiscount() {
		return $this->discount;
    }

    public function getTitle() {
		return $this->title;
    }
	
	public function getProducer() {
		return "{$this->producerFirstName} {$this->producerMainName}";	
	}	
	
	function getSummaryLine() {
		$base = "{$this->title} ({$this->producerMainName}, {$this->producerFirstName})";
		return $base;
	}
}

class CDProduct extends ShopProduct
{
	private $playLength = 0;
	
	function __construct ($title, $firstName, $mainName, $price, $playLength) {
		parent::__construct($title, $firstName, $mainName, $price);
		$this->playLength = $playLength;
	}
	
	function getPlayLength() {
		return $this->playLength;
	}
	
	function getSummaryLine() {
		$base = parent::getSummaryLine().": Продолжительность - {$this->playLength}";
		return $base;
	}
}

class BookProduct extends ShopProduct
{
	private $numPages = 0;
	
	function __construct ($title, $firstName, $mainName, $price, $numPages) {
		parent::__construct($title, $firstName, $mainName, $price);
		$this->numPages = $numPages;
	}
	
	function getNumberOfPages() {
		return $this->numPages;
	}
	
	function getSummaryLine() {
		$base = parent::getSummaryLine().": {$this->numPages} стр.";
		return $base;
	}
}

abstract class ShopProductWriter 
{
	protected $products = array();
	
	public function addProduct(ShopProduct $shopProduct) {
		$this->products[] = $shopProduct;
	}
	
	abstract public function write();
}

class XmlShopProductWriter extends ShopProductWriter{
    public function write() {
        $str = '<?xml version="1.0" encoding="UTF-8"?>'."\n";
        $str .= "<products>\n";
         foreach ( $this->products as $product ) {
            $str .= "\t<product title=\"{$product->getTitle()}\">\n";
            $str .= "\t\t<summary>\n";
            $str .= "\t\t{$product->getSummaryLine()}\n";
            $str .= "\t\t</summary>\n";
            $str .= "\t</product>\n";
        }
        $str .= "</products>\n";   
        print $str;
    }
}

class TextShopProductWriter extends ShopProductWriter{
    public function write() {
        $str = "ТОВАРЫ: ";
		foreach ($this->products as $product)
		{
			$str .= "{$product->getTitle()}: <b>{$product->getProducer()}</b>, {$product->getPrice()}$<br>";
		}
		echo $str;
    }
}