using System;

using Microsoft.Extensions.DependencyInjection;         

public static class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

            /// <summary>

        /// Decorates a given service with another one.

        /// </summary>

        /// <typeparam name="TInterface">The interface of the service to decorate.</typeparam>

        /// <typeparam name="TDecorator">The decorator wrapping the service to decorate.</typeparam>

        /// <remarks>

        /// The service to decorate must be an existing registered service.

        /// Source: https://greatrexpectations.com/2018/10/25/decorators-in-net-core-with-dependency-injection</remarks>

        /// <param name="services"></param>

        public static void AddDecorator<TInterface, TDecorator>( this IServiceCollection services )

            where TInterface : class

            where TDecorator : class, TInterface

        {

            // grab the existing registration

            var wrappedDescriptor = services.FirstOrDefault(

                s => s.ServiceType == typeof( TInterface ) );

​

            // check it's valid

            if ( wrappedDescriptor == null )

                throw new InvalidOperationException( $"{typeof( TInterface ).Name} is not registered" );

​

            // create the object factory for our decorator type,

            // specifying that we will supply TInterface explicitly

            var objectFactory = ActivatorUtilities.CreateFactory(

                typeof( TDecorator ),

                new[] { typeof( TInterface ) } );

​

            // replace the existing registration with one

            // that passes an instance of the existing registration

            // to the object factory for the decorator

            services.Replace( ServiceDescriptor.Describe(

                typeof( TInterface ),

                s => (TInterface) objectFactory( s, new[] { s.CreateInstance( wrappedDescriptor ) } ),

                wrappedDescriptor.Lifetime )

            );

        }

}