/src/LinFu.AOP/Factories/AddInvocationInfoActionFactory.cs

using System;
using System.Linq;
using LinFu.AOP.Cecil.Interfaces;
using LinFu.AOP.Interfaces;
using LinFu.IoC.Configuration;
using LinFu.IoC.Interfaces;
using LinFu.Reflection.Emit;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace LinFu.AOP.Cecil.Factories
{
    /// <summary>
    ///     A factory instance that creates <see cref="Action{T}" /> delegates
    ///     that emit the necessary <see cref="IInvocationInfo" /> information
    ///     and store it in a local variable named '__invocationInfo___'.
    /// </summary>
    [Factory(typeof(Action<MethodDefinition>), ServiceName = "AddInvocationInfo")]
    public class AddInvocationInfoActionFactory : IFactory
    {
        /// <summary>
        ///     Generates the <see cref="Action{T}" /> delegate that will emit
        ///     the necessary <see cref="IInvocationInfo" /> information.
        /// </summary>
        /// <param name="request">The <see cref="IFactoryRequest" /> instance that describes the requested service type.</param>
        /// <returns>
        ///     A delegate that can emit the necessary <see cref="IInvocationInfo" /> context that will allow other developers
        ///     to infer information about the method currently being executed.
        /// </returns>
        public object CreateInstance(IFactoryRequest request)
        {
            var container = request.Container;
            Action<MethodDefinition> result =
                method =>
                {
                    var body = method.Body;

                    // Add the IInvocationInfo 
                    // instance only once
                    var localAlreadyExists = (from VariableDefinition local in body.Variables
                                                 where local.Name == "___invocationInfo___"
                                                 select local).Count() > 0;

                    if (localAlreadyExists)
                        return;

                    var variable = method.AddLocal<IInvocationInfo>();
                    variable.Name = "___invocationInfo___";

                    var emitInfo = (IEmitInvocationInfo) container.GetService(typeof(IEmitInvocationInfo));
                    emitInfo.Emit(method, method, variable);
                };

            return result;
        }
    }
}