laatzen/Common/CommonConsole/ServiceProvider.cs

namespace CommonConsole
{
    using System;
    using System.Collections.Concurrent;
    using System.Linq;
    using System.Reflection;

    public partial class Program
    {
        class Outer
        {
            private readonly Middle middle;

            Outer(Middle middle)
            {
                Console.WriteLine($"{nameof(Outer)}: I am transient!");

                this.middle = middle;
            }

            internal string Text => $"{nameof(Outer)}.{nameof(Text)} => {this.middle.Text}";
        }

        class Middle
        {
            private readonly Inner inner;

            Middle(Inner inner)
            {
                Console.WriteLine($"{nameof(Middle)}: I am transient!");

                this.inner = inner;
            }

            internal string Text => $"{nameof(Middle)}.{nameof(Text)} => {this.inner.Text}";
        }

        class Inner
        {
            private readonly string text;

            internal Inner(string text)
            {
                Console.WriteLine($"{nameof(Inner)}: I am singleton!");

                this.text = text;
            }

            internal string Text => $"{nameof(Inner)}.{nameof(Text)} => {this.text}";
        }

        public static void DependencyInjectionTest()
        {
            ServiceProvider
                .ServiceCollection
                .AddSingleton(new Inner("It works!"));

            var outer = ServiceProvider.GetService<Outer>();

            Console.WriteLine(outer.Text);
        }
    }

    public interface IServiceCollection
    {
        IServiceCollection AddSingleton<T>(T instance);
    }

    public class ServiceProvider : IServiceProvider, IServiceCollection
    {
        private static readonly ServiceProvider serviceProvider = new ServiceProvider();

        private readonly ConcurrentDictionary<Type, object> services;

        private ServiceProvider()
        {
            this.services = new ConcurrentDictionary<Type, object>();
        }

        public IServiceCollection AddSingleton<T>(T instance)
        {
            services.AddOrUpdate(typeof(T), instance, (t, i) => instance);

            return this;
        }

        public object GetService(Type serviceType)
        {
            return services.GetOrAdd(serviceType, default(object));
        }

        public static IServiceCollection ServiceCollection
        {
            get => serviceProvider;
        }

        public static T GetService<T>()
        {
            var serviceType = typeof(T);
            var serviceInstance = default(T);

            if (serviceProvider.GetService(serviceType) is T existingInstance)
            {
                serviceInstance = existingInstance;
            }
            else if (CreateInstance(serviceType) is T newInstance)
            {
                serviceInstance = newInstance;
            }

            return serviceInstance;
        }

        private static object CreateInstance(Type instanceType)
        {
            var instance = default(object);
            var constructors = instanceType
                .GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)
                .OrderByDescending(x => x.GetParameters().Length);

            foreach (var constructor in constructors)
            {
                var parameters = constructor.GetParameters();
                var parametersLength = parameters.Length;
                var createParameters = new object[parametersLength];

                for (int i = 0; i < parametersLength; i++)
                {
                    var parameterType = parameters[i].ParameterType;
                    var parameter = serviceProvider.GetService(parameterType);

                    if (parameter is null)
                    {
                        parameter = CreateInstance(parameterType);
                    }

                    createParameters[i] = parameter;
                }

                try
                {
                    instance = constructor.Invoke(createParameters);

                    if (instance != null)
                    {
                        break;
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                }
            }

            return instance;
        }
    }
}