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

namespace Enumに柔軟な拡張を追加する試み {
	class Program {
		enum tesyEnum {
			[Obsolete]
			a,
			[RelatedLiteral("hoge")]
			b,
		}

		enum tesyEnum2 {
			[RelatedLiteral(2)]
			c,
			[RelatedLiteral(0.5)]
			d
		}

		static void Main(string[] args) {

			//Console.WriteLine(tesyEnum.a.GetRelatedLiteral()); RelatedLiteral属性つけてないと例外発生
			Console.WriteLine(tesyEnum.b.GetRelatedLiteral());
			Console.WriteLine(tesyEnum2.c.GetRelatedLiteral());
			Console.WriteLine(tesyEnum2.d.GetRelatedLiteral());
			Console.Read();
		}
	}


	[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
	public class RelatedLiteralAttribute : Attribute {
		public RelatedLiteralAttribute(object value) {
			Value = value;
		}
		public dynamic Value { get; private set; }
	}


	/// <summary>
	/// enum拡張メソッド用クラス
	/// </summary>
	public static class EnumExtension {
		/// <summary>
		/// RelatedLiteral属性に指定したリテラルを取得します。
		/// </summary>
		/// <param name="myself"></param>
		/// <returns></returns>
		public static dynamic GetRelatedLiteral(this Enum myself) {
			Type type = myself.GetType();
			string name = Enum.GetName(type, myself);
			try {
				FieldInfo fi = type.GetField(name);
				var items = (RelatedLiteralAttribute[])fi.GetCustomAttributes(typeof(RelatedLiteralAttribute), false);
				return items[0].Value;
			}
			catch (IndexOutOfRangeException e) {
				throw new CustomAttributeFormatException(type.Name + " の " + name + " 要素にEnumAttr属性が指定されていません。");
			}
		}
	}
}