using System;
using System.Collections.Generic;
using System.Text;
using System.Web;

namespace ScrambledBrains.Nuggets
{
   // immutable modification of singleton-per-request pattern
   public class ImmutableRequestSingleton<ImmutableType> where ImmutableType : IIdentifiable, new()
   {
      protected static string _identifier = "ImmutableRequestSingleton<";
      private ImmutableRequestSingleton() { }
      public static void Initialize(ImmutableType immutableReferenceMember)
      {
         if (HttpContext.Current.Items[_identifier + (new ImmutableType()).TypeIdentity] == null) // then ImmutableRequestSingleton is uninitialized
         {
            HttpContext.Current.Items[_identifier + new ImmutableType().TypeIdentity] = new ImmutableRequestSingleton<ImmutableType>();
            ((ImmutableRequestSingleton<ImmutableType>)(HttpContext.Current.Items[_identifier + new ImmutableType().TypeIdentity]))._immutableReferenceMember = immutableReferenceMember;
         }
         else
            throw new Exception(_identifier + new ImmutableType().TypeIdentity + "> already initialized.");
      }
      public static ImmutableRequestSingleton<ImmutableType> Current
      {
         get
         {
            if (HttpContext.Current.Items[_identifier + new ImmutableType().TypeIdentity] == null)
               return (ImmutableRequestSingleton<ImmutableType>)null; // throw new Exception("ImmutableRequestSingleton not initialized.");
            else
               return (ImmutableRequestSingleton<ImmutableType>)HttpContext.Current.Items[_identifier + new ImmutableType().TypeIdentity];
         }
      }
      // note: readonly modifier is not used, but writing is controlled conditionally within Initialize()
      private ImmutableType _immutableReferenceMember;
      public ImmutableType ImmutableReferenceMember
      {
         get { return _immutableReferenceMember; }
      }
   }
   public interface IIdentifiable
   {
      string TypeIdentity { get; }
   }
}