// IProductCatalogService.cs

public interface IProductCatalogService {

List GetProducts();

}

// IShoppingCartService.cs

public interface IShoppingCartService {

void AddToCart(Product product);

List GetCartItems();

}

// IOrderProcessingService.cs

public interface IOrderProcessingService {

void ProcessOrder(List cartItems);

}

// ProductCatalogService.cs

public class ProductCatalogService : IProductCatalogService {

public List GetProducts() {

// Fetch products from a database or external API

// For simplicity, returning sample data here

return new List { new Product { Id = 1, Name = "Product 1", Price = 10.99 }, new Product { Id = 2, Name = "Product 2", Price = 19.99 },

// ... other products

}; } }

// ShoppingCartService.cs

public class ShoppingCartService : IShoppingCartService {

private List _cartItems = new List();

public void AddToCart(Product product) {

_cartItems.Add(product);

}

public List GetCartItems() {

return _cartItems;

} }

// OrderProcessingService.cs

public class OrderProcessingService : IOrderProcessingService {

public void ProcessOrder(List cartItems) {

// Perform order processing, payment, etc.

// For simplicity, printing order details here Console.WriteLine("Processing order with items:");

foreach (var item in cartItems) {

Console.WriteLine($" - {item.Name}, Price: {item.Price:C}");

} Console.WriteLine("Order processed successfully.");

}

}