سلام , 

با توجه به چیزی که متوجه شدم , کد پتر decorator رو اینجا میزارم.

امیدوارم مفید واقع بشود.

<?php
// Create your base class
interface Cost{
    public function getCost();
    public function getDescription();
    public function getTotalCost();
    public function getDetails();
}
// create all different type of costs :
class BasketCost implements cost
{
    public function getCost()
    {
        return 15000;
    }
    public function getDescription()
    {
        return self::class;
    }
    public function getTotalCost()
    {
        return self::getCost();
    }
    public function getDetails()
    {
        return [
            self::getDescription() => self::getCost()
        ];
    }
}
class TaxCost implements Cost
{ 
    public function __construct(Cost $cost)
    {
        $this->cost = $cost;
    }
    public function getCost()
    {
        return $this->cost->getTotalCost() * 0.09;
    }
    public function getDescription()
    {
        return self::class;
    }
    public function getTotalCost()
    {
        return $this->cost->getCost() + self::getCost();
    }
    public function getDetails()
    {
        return $this->cost->getDetails() + [
            self::getDescription() =>  self::getCost()
        ];
    }
}
class ShippingCost implements Cost
{
    public function __construct(Cost $cost)
    {
        $this->cost = $cost;
    }
    public function getCost()
    {
        return 5000;
    }
    public function getDescription()
    {
        return self::class;
    }
    public function getTotalCost()
    {   
        return $this->cost->getTotalCost() + self::getCost();
    }
    public function getDetails()
    {
        return $this->cost->getDetails() + [
            self::getDescription() =>  self::getCost()
        ];
    }
}
$basketCost = new BasketCost;
$basketWithTaxCost = new TaxCost(new BasketCost);
$backetWithTaxAndShippingCost = new ShippingCost($basketWithTaxCost);
# فقط قیمت کالاهای سبد خرید را برگردان
//var_dump($basketCost->getTotalCost());
# قیمت کالاهای سبد خرید + مالیات 
//var_dump($basketWithTaxCost->getTotalCost());
# قیمت کالاهای سبد خرید + مالیات + هزینه ارسال
//var_dump($backetWithTaxAndShippingCost->getTotalCost());