using System;
namespace DependencyInjection
{
    public interface IDependent
    {
        void DoSomething();
    }

    public class Dependent1 : IDependent
    {
        public void DoSomething()
        {
            Console.WriteLine("Hello from Dependent1");
        }
    }

    public class Dependent2 : IDependent
    {
        public void DoSomething()
        {
            Console.WriteLine("Hello from Dependent2");
        }
    }

    public class MainClass
    {
        private IDependent _dependent;

        public void SetDependency(IDependent dependent)
        {
            _dependent = dependent 
                         ?? throw new ArgumentNullException(nameof(dependent), "Argument cannot be null");
        }

        public void DoSomething()
        {
            _dependent.DoSomething();
        }
    }

    internal static class Program
    {
        private static void Main()
        {
            // Get the correct dependency
            var dependency = GetCorrectDependency();

            // Create class 
            var mainClass = new MainClass();

            //Inject the dependency
            mainClass.SetDependency(dependency);

            mainClass.DoSomething();

            Console.ReadLine();
        }

        private static IDependent GetCorrectDependency()
        {
            return new Dependent1();
        }
    }
}