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

namespace Visitor
{
    /// <summary>

    /// MainApp startup class for Structural 

    /// Visitor Design Pattern.

    /// </summary>

    class MainApp
    {
        static void Main()
        {
            // Setup structure

            ObjectStructure o = new ObjectStructure();
            o.Attach(new ConcreteElementA());
            o.Attach(new ConcreteElementB());

            // Create visitor objects

            ConcreteVisitor1 v1 = new ConcreteVisitor1();
            ConcreteVisitor2 v2 = new ConcreteVisitor2();

            // Structure accepting visitors

            o.Accept(v1);
            o.Accept(v2);

            // Wait for user

            Console.ReadKey();
        }
    }

    /// <summary>

    /// The 'Visitor' abstract class

    /// </summary>

    abstract class Visitor
    {
        public abstract void VisitConcreteElementA(
          ConcreteElementA concreteElementA);
        public abstract void VisitConcreteElementB(
          ConcreteElementB concreteElementB);
    }

    /// <summary>

    /// A 'ConcreteVisitor' class

    /// </summary>

    class ConcreteVisitor1 : Visitor
    {
        public override void VisitConcreteElementA(
          ConcreteElementA concreteElementA)
        {
            Console.WriteLine("{0} visited by {1}",
              concreteElementA.GetType().Name, this.GetType().Name);
        }

        public override void VisitConcreteElementB(
          ConcreteElementB concreteElementB)
        {
            Console.WriteLine("{0} visited by {1}",
              concreteElementB.GetType().Name, this.GetType().Name);
        }
    }

    /// <summary>

    /// A 'ConcreteVisitor' class

    /// </summary>

    class ConcreteVisitor2 : Visitor
    {
        public override void VisitConcreteElementA(
          ConcreteElementA concreteElementA)
        {
            Console.WriteLine("{0} visited by {1}",
              concreteElementA.GetType().Name, this.GetType().Name);
        }

        public override void VisitConcreteElementB(
          ConcreteElementB concreteElementB)
        {
            Console.WriteLine("{0} visited by {1}",
              concreteElementB.GetType().Name, this.GetType().Name);
        }
    }

    /// <summary>

    /// The 'Element' abstract class

    /// </summary>

    abstract class Element
    {
        public abstract void Accept(Visitor visitor);
    }

    /// <summary>

    /// A 'ConcreteElement' class

    /// </summary>

    class ConcreteElementA : Element
    {
        public override void Accept(Visitor visitor)
        {
            visitor.VisitConcreteElementA(this);
        }

        public void OperationA()
        {
        }
    }

    /// <summary>

    /// A 'ConcreteElement' class

    /// </summary>

    class ConcreteElementB : Element
    {
        public override void Accept(Visitor visitor)
        {
            visitor.VisitConcreteElementB(this);
        }

        public void OperationB()
        {
        }
    }

    /// <summary>

    /// The 'ObjectStructure' class

    /// </summary>

    class ObjectStructure
    {
        private List<Element> _elements = new List<Element>();

        public void Attach(Element element)
        {
            _elements.Add(element);
        }

        public void Detach(Element element)
        {
            _elements.Remove(element);
        }

        public void Accept(Visitor visitor)
        {
            foreach (Element element in _elements)
            {
                element.Accept(visitor);
            }
        }
    }
}