using System;
using System.Threading;

namespace Umbraco.Core.Resolving
{
	/// <summary>
	/// base class for resolvers which declare a singleton accessor
	/// </summary>
	/// <typeparam name="TResolver"></typeparam>
	internal abstract class ResolverBase<TResolver> 
		where TResolver : class
	{
		static TResolver _resolver;

		//TODO: This is not correct, this will be the same lock for all ResolverBase classes!!
		// this will work i suppose but not really ideal
		static readonly ReaderWriterLockSlim ResolversLock = new ReaderWriterLockSlim();

		public static TResolver Current
		{
			get
			{
				using (new ReadLock(ResolversLock))
				{
					if (_resolver == null)
						throw new InvalidOperationException("Current has not been initialized. You must initialize Current before trying to read it.");
					return _resolver;
				}
			}

			set
			{
				using (new WriteLock(ResolversLock))
				{
					if (value == null)
						throw new ArgumentNullException("value");
					if (_resolver != null)
						throw new InvalidOperationException("Current has already been initialized. It is not possible to re-initialize Current once it has been initialized.");
					_resolver = value;
				}
			}
		}
	}
}