using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Proxy
{
    /// <summary>

    /// MainApp startup class for Structural

    /// Proxy Design Pattern.

    /// </summary>

    class MainApp
    {
        /// <summary>

        /// Entry point into console application.

        /// </summary>

        static void Main()
        {
            // Create proxy and request a service

            Proxy proxy = new Proxy();
            proxy.Request();

            // Wait for user

            Console.ReadKey();
        }
    }

    /// <summary>

    /// The 'Subject' abstract class

    /// </summary>

    abstract class Subject
    {
        public abstract void Request();
    }

    /// <summary>

    /// The 'RealSubject' class

    /// </summary>

    class RealSubject : Subject
    {
        public override void Request()
        {
            Console.WriteLine("Called RealSubject.Request()");
        }
    }

    /// <summary>

    /// The 'Proxy' class

    /// </summary>

    class Proxy : Subject
    {
        private RealSubject _realSubject;

        public override void Request()
        {
            // Use 'lazy initialization'

            if (_realSubject == null)
            {
                _realSubject = new RealSubject();
            }

            _realSubject.Request();
        }
    }
}