<?php

interface ShopInterface
{
    public function getTotalPrice(): float;
}

interface ProductInterface
{
    public function getPrice(): float;
}

class Shop implements ShopInterface
{
    private $products;

    public function __construct(array $products = [])
    {
        $this->products = $products;
    }

    public function setProducts(ProductInterface $product): void
    {
        $this->products[] = $product;
    }

    public function getTotalPrice(): float
    {
        $totalPrice = 0;

        foreach ($this->products as $product) {
            $totalPrice += $product->getPrice();
        }

        return $totalPrice;
    }
}

class Product implements ProductInterface
{
    private $price;

    public function __construct(float $price)
    {
        $this->price = $price;
    }

    public function getPrice(): float
    {
        return $this->price;
    }

}

$apple = new Product(1.99);
$banana = new Product(2.99);
$lemon = new Product(3.99);

$shop = new Shop();
$shop->setProducts($apple);
$shop->setProducts($banana);
$shop->setProducts($lemon);
echo $shop->getTotalPrice() . PHP_EOL;