Kentico modular system for e-products

CustomEProductManager.cs

using System;
using System.Collections.Generic;
using System.Linq;
using CMS.Ecommerce;
using CMS.Helpers;

namespace CustomEProducts
{
    public static class CustomEProductManager
    {
        private static readonly Dictionary<string, ICustomEProduct> _EProducts = new Dictionary<string, ICustomEProduct>();

        public static void RegisterEProduct(string skuNumber, ICustomEProduct customEProduct)
        {
            // Ensure that the parameters are provided
            if (skuNumber == null)
            {
                throw new ArgumentNullException(nameof(skuNumber));
            }

            if (customEProduct == null)
            {
                throw new ArgumentNullException(nameof(customEProduct));
            }

            _EProducts[skuNumber] = customEProduct;
        }

        private static void ProcessCustomEProducts(OrderInfo oi)
        {
            // Get shopping cart items
            var sci = ShoppingCartInfoProvider.GetShoppingCartInfoFromOrder(oi.OrderID);
            if (sci == null)
                return;

            var customProcessingData = oi.OrderCustomData.GetValue("CustomProcessing") as string;

            var existingValues = new ContainerCustomData();
            existingValues.LoadData(customProcessingData);

            foreach (var i in sci.CartItems.Where(x => existingValues[x.SKU.SKUNumber] == null))
            {
                if (!_EProducts.ContainsKey(i.SKU.SKUNumber))
                    continue;

                _EProducts[i.SKU.SKUNumber].ProcessPaidProduct(i);

                existingValues[i.SKU.SKUNumber] = true;
            }

            oi.OrderCustomData.SetValue("CustomProcessing", existingValues.GetData());
            oi.Update();
        }

        public static void OrderPaid(object sender, OrderPaidEventArgs e)
        {
            ProcessCustomEProducts(e.Order);
        }
    }
}

CustomEProductsModule.cs

using CMS;
using CMS.DataEngine;
using CMS.Ecommerce;
using CustomEProducts;

[assembly: RegisterModule(typeof(CustomEProductsModule))]
namespace CustomEProducts
{
    public class CustomEProductsModule : Module
    {
        public CustomEProductsModule() : base("CustomEProducts")
        {
        }

        protected override void OnInit()
        {
            EcommerceEvents.OrderPaid.Execute += CustomEProductManager.OrderPaid;
        }
    }
}

ICustomEProduct.cs

using CMS.Ecommerce;

namespace CustomEProducts
{
    public interface ICustomEProduct
    {
        void ProcessPaidProduct(ShoppingCartItemInfo cartItem);
    }
}

MySpecialProduct.cs

using CMS.Ecommerce;
using CMS.EventLog;
using CustomEProducts;
using MyCustomEProducts;

[assembly: RegisterCustomEProduct("MySpecialProduct", typeof(MySpecialProduct))]
namespace MyCustomEProducts
{
    public class MySpecialProduct : ICustomEProduct
    {
        public void ProcessPaidProduct(ShoppingCartItemInfo cartItem)
        {
            EventLogProvider.LogInformation("CustomEProducts", "Purchased", string.Format("Someone has purchased {0} unit(s) of the product!", cartItem.CartItemUnits));
        }
    }
}

RegisterCustomEProductAttribute.cs

using System;
using CMS;

namespace CustomEProducts
{
    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
    public class RegisterCustomEProductAttribute : Attribute, IPreInitAttribute
    {
        public Type MarkedType { get; private set; }
        private readonly string _skuNumber;

        public RegisterCustomEProductAttribute(string skuNumber, Type customEProduct)
        {
            if (skuNumber == null)
                throw new ArgumentNullException(nameof(skuNumber));

            if (customEProduct == null)
                throw new ArgumentNullException(nameof(customEProduct));

            if (!typeof(ICustomEProduct).IsAssignableFrom(customEProduct))
                throw new ArgumentException("Provided type does not implement ICustomEProduct interface.", nameof(customEProduct));

            _skuNumber = skuNumber;
            MarkedType = customEProduct;
        }

        public void PreInit()
        {
            CustomEProductManager.RegisterEProduct(_skuNumber, (ICustomEProduct)Activator.CreateInstance(MarkedType));
        }
    }
}