//
// Composite pattern. 
//
using System;
using System.Collections;
// "Component"
abstract class PageElement
{
  protected string name;
  // Constructor
  public PageElement( string name )
  {
    this.name = name;
  } 
  // Methods
  abstract public void Add(PageElement e);
  abstract public void Remove( PageElement e);
  abstract public void GetContent();
}

// "Leaf" 
class Element : PageElement
{
  public Element( string name ) : base( name ) {}
  public override void Add( PageElement e )
  {
    Console.WriteLine("Error. Can't add to leaf");
  }
  public override void Remove( PageElement e )
  {
    Console.WriteLine("Error. Can't remove from a leaf");
  }
  public override void GetContent()
  {
    Console.WriteLine( "This is content of :" + name );
  }
}

// "Composite" 

class CompositeElement : PageElement
{
  // Fields
  private ArrayList elements = new ArrayList();
  // Constructor
  public CompositeElement( string name ) 
                              : base( name ) {}
  // Methods
  public override void Add( PageElement d )
  {
    elements.Add( d );
  }

  public override void Remove( PageElement d )
  {
    elements.Remove( d );
  }

  public override void GetContent()
  {
    Console.WriteLine( "Content from composite object : "+name);

    // Display each child element on this node
    foreach( PageElement p in elements )
      p.GetContent();
  }
}

/// 

///    Summary description for Client.
/// 
public class Client
{
  public static void Main( string[] args )
  {   
    // Create a tree structure 
    CompositeElement page = new CompositeElement( "Page 1" );
    page.Add( new Element( "Tag 1" ));
    Element e2 = new Element( "Tag 2" );
    page.Add(e2);
    page.Add( new Element( "Tag 3" ));

    CompositeElement list = new CompositeElement( "List 1" );
    list.Add( new Element( "List 1, Tag 1" ) );
    list.Add( new Element( "List 1, Tag 2" ) );
    page.Add( list );
    // Add and remove a PrimitiveElement
    page.Remove(e2);
    // Recursively display nodes
    page.GetContent();
    Console.ReadLine();
  }
}