abstraction shopping cart checkout

checkout.php

<?php

class Product
{
    protected $id;
    protected $name;
    
    public function __construct($id, $name)
    {
        $this->id = $id;
        $this->name = $name;
    }
}

class User
{
    protected $id;
    protected $shoppingCart;
    
    public function __construct($id, $shoppingCart)
    {
        $this->id = $id;
        $this->shoppingCart = $shoppingCart;
    }
}

class ShoppingCart
{
    protected $id;
    protected $products = [];
    
    public function __construct($id, $products)
    {
        $this->id = $id;
        $this->prododucts = $products;
    }
    
    public function checkout($payment)
    {
        if (empty($this->products)) {
            throw new \Exception('empty prodcucts');
        }
        
        if (!$payment->valid()) {
            throw new \Exception('Card not valid');
        }
        
        return $payment;
    }
}

class PaymentMethod
{
    protected $card;
    
    public function __construct($card)
    {
        $this->card = $card;
    }
    
    public function valid()
    {
        return !empty($this->card['number']);
    }
}

$u = new User(1, new ShoppingCart(1, [
    new Product(1, 'a'),
    new Product(2, 'b'),
    new Product(3, 'c'),
]));


$u->shoppingCart->checkout(new PaymentMethod([
    'number' => '123...',
    'cvv' => '123',
    'dateExp' => '01-2021',
    'name' => 'john doe'
]));