CreateOrder.cs

public async Task<Order> CreateOrderAsync(int basketId, Address shippingAddress)
{
    var basket = await _basketRepository.GetByIdAsync(basketId);

    Guard.Against.NullBasket(basketId, basket);
    Guard.Against.EmptyBasketOnCheckout(basket.Items);

    var catalogItemsSpecification = new CatalogItemsSpecification(basket.Items.Select(item => item.CatalogItemId).ToArray());
    var catalogItems = await _itemRepository.ListAsync(catalogItemsSpecification);

    var items = basket.Items.Select(basketItem =>
    {
        var catalogItem = catalogItems.First(c => c.Id == basketItem.CatalogItemId);
        var itemOrdered = new CatalogItemOrdered(catalogItem.Id, catalogItem.Name, _uriComposer.ComposePicUri(catalogItem.PictureUri));
        var orderItem = new OrderItem(itemOrdered, basketItem.UnitPrice, basketItem.Quantity);
        return orderItem;
    }).ToList();

    var now = DateTime.UtcNow;
    var order = new Order(basket.BuyerId, shippingAddress, items, now);

    await _orderRepository.AddAsync(order);

    return order;
}