GOF's Adapters and Some Magic

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

namespace Scaredfingers.Adapters
{
  public interface IInjection
  {
    MethodInfo InjectionSource { get; set; }
    Type ResolutionContext { get; set; }
    IList<Assembly> References { get; }

    void Inject(ILGenerator generator, MethodBuilder method, TypeBuilder container);
  }

  public abstract class Injection : IInjection
  {
    #region IInjection Members
    protected MethodInfo mth_InjectionSource;
    public MethodInfo InjectionSource
    {
      get
      {
        return mth_InjectionSource;
      }
      set
      {
        mth_InjectionSource = value;
      }
    }

    protected Type typ_ResolutionContext;
    public Type ResolutionContext
    {
      get
      {
        return typ_ResolutionContext;
      }
      set
      {
        typ_ResolutionContext = value ;
      }
    }

    protected IList<Assembly> lst_References = new List<Assembly>();
    public IList<Assembly> References
    {
      get { return lst_References; }
    }

    public abstract void Inject(ILGenerator generator, MethodBuilder method, TypeBuilder container) ;
    #endregion
  }

  public interface IInjectionAttribute
  {
    IInjection Injection { get; }
  }

  public interface IPreInjectionAttribute
  {
    IInjection Injection { get; }
  }

  public interface IPostInjectionAttribute
  {
    IInjection Injection { get; }
  }

  public class InjectionsAdapterBuilder : AdapterBuilder
  {
    #region Creation
    public InjectionsAdapterBuilder(string assemblyName)
      : base(assemblyName)
    {

    }

    public InjectionsAdapterBuilder()
    {

    }
    #endregion

    #region Overrides
    protected override void EmitMethodBody(ILGenerator generator, FieldBuilder adapteesReferenceField, MethodBuilder methodBuilder,
      MethodInfo adapteesMethod, MethodInfo prototypeMethod, Type adapterInterfaceType, Type adapteeType, TypeBuilder adapterTypeBuilder)
    {
      foreach (IInjection injection in GetPreInjections(adapteesReferenceField, methodBuilder, adapteesMethod, prototypeMethod,
        adapterInterfaceType, adapteeType, adapterTypeBuilder))
        injection.Inject(generator, methodBuilder, adapterTypeBuilder);

      EmitMethodUninjectedMethodBody(generator, adapteesReferenceField, methodBuilder, adapteesMethod, prototypeMethod,
        adapterInterfaceType, adapteeType, adapterTypeBuilder);

      foreach (IInjection injection in GetPostInjections(adapteesReferenceField, methodBuilder, adapteesMethod, prototypeMethod,
        adapterInterfaceType, adapteeType, adapterTypeBuilder))
        injection.Inject(generator, methodBuilder, adapterTypeBuilder);
    }

    protected virtual void EmitMethodUninjectedMethodBody(ILGenerator generator, FieldBuilder adapteesReferenceField, MethodBuilder methodBuilder,
      MethodInfo adapteesMethod, MethodInfo prototypeMethod, Type adapterInterfaceType, Type adapteeType, TypeBuilder adapterTypeBuilder)
    {
      base.EmitMethodBody(generator, adapteesReferenceField, methodBuilder, adapteesMethod, prototypeMethod,
        adapterInterfaceType, adapteeType, adapterTypeBuilder);
    }
    #endregion

    #region Virtuals
    protected virtual IList<IInjection> GetPreInjections(FieldBuilder adapteesReferenceField, MethodBuilder methodBuilder,
      MethodInfo adapteesMethod, MethodInfo prototypeMethod, Type adapterInterfaceType, Type adapteeType, TypeBuilder adapterTypeBuilder)
    {
      return GetInjections(typeof(IPreInjectionAttribute), adapteesReferenceField, methodBuilder,
        adapteesMethod, prototypeMethod, adapterInterfaceType, adapteeType, adapterTypeBuilder);
    }

    protected virtual IList<IInjection> GetPostInjections(FieldBuilder adapteesReferenceField, MethodBuilder methodBuilder,
      MethodInfo adapteesMethod, MethodInfo prototypeMethod, Type adapterInterfaceType, Type adapteeType, TypeBuilder adapterTypeBuilder)
    {
      return GetInjections(typeof(IPostInjectionAttribute), adapteesReferenceField, methodBuilder,
        adapteesMethod, prototypeMethod, adapterInterfaceType, adapteeType, adapterTypeBuilder);
    }

    protected static readonly AdapterBuilder bdr_Injections = new AdapterBuilder();
    protected virtual IList<IInjection> GetInjections(Type injectionsAttributeType, FieldBuilder adapteesReferenceField, MethodBuilder methodBuilder,
      MethodInfo adapteesMethod, MethodInfo prototypeMethod, Type adapterInterfaceType, Type adapteeType, TypeBuilder adapterTypeBuilder)
    {
      List<IInjection> lst_Result = new List<IInjection>();
      foreach (object att_Injection in prototypeMethod.GetCustomAttributes(injectionsAttributeType, true))
      {
        IInjection inj_Injection = ((IInjectionAttribute)bdr_Injections.BindAdapter(typeof(IInjectionAttribute), injectionsAttributeType, 
          att_Injection)).Injection;
        inj_Injection.InjectionSource = prototypeMethod;
        inj_Injection.ResolutionContext = adapterInterfaceType;

        lst_Result.Add(inj_Injection);
      }

      foreach (object att_Injection in adapterInterfaceType.GetCustomAttributes(injectionsAttributeType, true))
      {
        IInjection inj_Injection = ((IInjectionAttribute)bdr_Injections.BindAdapter(typeof(IInjectionAttribute), injectionsAttributeType, 
          att_Injection)).Injection;
        inj_Injection.InjectionSource = prototypeMethod;
        inj_Injection.ResolutionContext = adapterInterfaceType;

        lst_Result.Add(inj_Injection);
      }

      return lst_Result;
    }
    #endregion
  }

  public abstract class InjectionAttribute : Attribute, IInjectionAttribute
  {
    #region IInjectionAttribute Members

    public abstract IInjection Injection
    {
      get;
    }

    #endregion
  }

  public class LogAttribute : Attribute, IPreInjectionAttribute, IPostInjectionAttribute
  {
    #region IInjectionAttribute Members

    IInjection IPreInjectionAttribute.Injection
    {
      get { return new LogEnter(); }
    }

    #endregion

    #region IPostInjectionAttribute Members

    IInjection IPostInjectionAttribute.Injection
    {
      get { return new LogExit() ; }
    }

    #endregion

    #region Nested Injections
    public abstract class LogInjection : Injection
    {
      protected string SignatureToString(MethodInfo method)
      {
        return string.Format("{0} {1}::{2}({3})", method.ReturnType.FullName, method.ReflectedType.FullName, 
          method.Name, ParametersToString(method.GetParameters()));
      }

      protected string ParametersToString(ParameterInfo[] formalParameters)
      {
        string result = "";
        foreach (ParameterInfo param in formalParameters)
          result += "," + param.ParameterType.FullName;

        return result.Length > 0? result.Substring(1) : "";
      }
    }

    public class LogEnter : LogInjection
    {
      public override void Inject(ILGenerator generator, MethodBuilder method, TypeBuilder container)
      {
        generator.EmitWriteLine("[Enter]" + SignatureToString(InjectionSource));
      }
    }

    public class LogExit : LogInjection
    {
      public override void Inject(ILGenerator generator, MethodBuilder method, TypeBuilder container)
      {
        generator.EmitWriteLine("[Exit]" + SignatureToString(InjectionSource));
      }
    }
    #endregion
  }
}