static void Main(string[] args)
{
// Observer Example
var customer = new Customer("Eliot Anderson");
var customer2 = new Customer("Andrei Keks");
var shop = new OnlineShop();
var mobile = new Product("Xiaomi MI 9", 600);
shop.Subscribe(customer);
shop.Subscribe(customer2);
shop.AddProduct(mobile);
// Template pattern example
var mkvVideo = new MkvVideoPlayer();
var mp4Video = new MP4VideoPlayer();
mkvVideo.PlayVideo("funny-cats.mkv");
mp4Video.PlayVideo("funny-dogs.mp4");
// Strategy pattern
var order = new Order(126);
var calculator = new ShippingCalculator();
var shippingCostDHL = calculator.CalculateShipping(new DHLShippingStrategy(), order);
var shippingCostUPS = calculator.CalculateShipping(new UpsShippingStrategy(), order);
Console.WriteLine($"Shipping prices:\n DHL price: {shippingCostDHL}$\n UPS Price: {shippingCostUPS}$");
Console.ReadLine();
}