TypeBuilderLib, a Library to Build Dynamic Types Easily

using System;
using System.Reflection;

namespace TypeBuilderLib.AOP
{
	/// <summary>Group interceptors together and exposes <see cref="IInterceptor"/>.</summary>
	/// <remarks>Useful when we want to chain interceptors.</remarks>
	public class InterceptorGroup : IInterceptor
	{
		#region Inner types
		private class GroupMethodInvoker : IMethodInvoker
		{
			private readonly IMethodInvoker realInvoker;
			private readonly IInterceptor[] interceptors;
			private readonly int currentInterceptorIndex;

			/// <summary>Construct a group invoker.</summary>
			/// <param name="realInvoker"></param>
			/// <param name="interceptors"></param>
			/// <param name="currentInterceptorIndex"></param>
			public GroupMethodInvoker(
				IMethodInvoker realInvoker,
				IInterceptor[] interceptors,
				int currentInterceptorIndex)
			{
				this.realInvoker = realInvoker;
				this.interceptors = interceptors;
				this.currentInterceptorIndex = currentInterceptorIndex;
			}

			#region IMethodInvoker Members
			MethodBase IMethodInvoker.Method
			{
				get { return realInvoker.Method; }
			}

			object[] IMethodInvoker.Parameters
			{
				get { return realInvoker.Parameters; }
			}

			object IMethodInvoker.Invoke()
			{
				IMethodInvoker invoker;

				if (currentInterceptorIndex + 1 < interceptors.Length)
				{
					invoker =
						new GroupMethodInvoker(realInvoker, interceptors, currentInterceptorIndex + 1);
				}
				else
				{
					invoker = realInvoker;
				}

				return interceptors[currentInterceptorIndex].InterceptCall(invoker);
			}
			#endregion
		}
		#endregion

		private IInterceptor[] interceptors;

		#region IInterceptor Members
		object IInterceptor.InterceptCall(IMethodInvoker methodInvoker)
		{
			IMethodInvoker groupMethodInvoker = new GroupMethodInvoker(methodInvoker, Interceptors, 0);

			return groupMethodInvoker.Invoke();
		}
		#endregion

		/// <summary>Exposes a list of interceptor.</summary>
		public IInterceptor[] Interceptors
		{
			get { return interceptors; }
			set { interceptors = value; }
		}

		/// <summary>
		/// Returns <see cref="Interceptors"/> or a default implementation if the list is empty.
		/// </summary>
		protected IInterceptor[] NonEmptyInterceptors
		{
			get
			{
				if (Interceptors == null || Interceptors.Length == 0)
				{
					return new IInterceptor[] { new DefaultInterceptor() };
				}
				else
				{
					return Interceptors;
				}
			}
		}
	}
}