using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;

namespace PlayingWithWinForms {
	public partial class Form1 : Form {
		public Form1( ) {
			InitializeComponent( );

			ICheckBoxGroup< ISport > group = new CheckBoxGroup< ISport >( );
			group.Add( checkBox1, Sport.Hockey );
			group.Add( checkBox2, Sport.BasketBall );
			group.Add( checkBox3, Sport.FootBall );
			group.Add( checkBox4, Sport.Golf );
			group.Add( checkBox5, Sport.Tennis );

			button1.Click += delegate {
			                 	StringBuilder builder = new StringBuilder( );
			                 	foreach ( ISport employee in group.GetAllEnabled( ) ) {
			                 		builder.AppendFormat( "{0}{1}", employee, Environment.NewLine );
			                 	}
			                 	MessageBox.Show( builder.ToString( ) );
			                 };
		}
	}

	internal interface ICheckBoxGroup< T > {
		void Add( CheckBox checkbox, T item );
		IEnumerable< T > GetAllEnabled( );
		IEnumerable< T > GetAllThatSatisfies( Predicate< CheckBox > condition );
	}

	public class CheckBoxGroup< T > : ICheckBoxGroup< T > {
		public CheckBoxGroup( ) {
			_checkboxes = new List< CheckBox >( );
		}

		public void Add( CheckBox checkbox, T item ) {
			checkbox.Tag = item;
			checkbox.Text = item.ToString( );
			_checkboxes.Add( checkbox );
		}

		public IEnumerable< T > GetAllEnabled( ) {
			return GetAllThatSatisfies( delegate( CheckBox box ) { return box.Checked; } );
		}

		public IEnumerable< T > GetAllThatSatisfies( Predicate< CheckBox > condition ) {
			foreach ( CheckBox checkBox in _checkboxes ) {
				if ( condition( checkBox ) ) {
					yield return ( T )checkBox.Tag;
				}
			}
		}

		private readonly IList< CheckBox > _checkboxes;
	}

	public class Sport : ISport {
		private Sport( string name ) {
			_name = name;
		}

		public static readonly ISport Hockey = new Sport( "Hockey" );
		public static readonly ISport BasketBall = new Sport( "Basket Ball" );
		public static readonly ISport FootBall = new Sport( "Football" );
		public static readonly ISport Golf = new Sport( "Golf" );
		public static readonly ISport Tennis = new Sport( "Tennis" );

		public string Name {
			get { return _name; }
		}

		public override string ToString( ) {
			return Name;
		}

		private readonly string _name;
	}

	public interface ISport {
		string Name { get; }
	}
}