public abstract class MethodInterceptor
{
    public abstract object Invoke(object instance, MethodInfo methodInfo, object[] parameters, object returnValue);
}

public static class ProxyGenerator
{
    private static ModuleBuilder moduleBuilder;
    private static MethodInfo getMethodMethod = typeof(MethodBase).GetMethod("GetMethodFromHandle", new[] { typeof(RuntimeMethodHandle) });
    private static MethodInfo invoke = typeof(MethodInterceptor).GetMethod("Invoke");
    static ProxyGenerator()
    {
        var asmBuilder = AssemblyBuilder.DefineDynamicAssembly(new AssemblyName("EmitAopDemoTest"), AssemblyBuilderAccess.RunAndCollect);
        moduleBuilder = asmBuilder.DefineDynamicModule("Proxy");
    }
    public static T Generate<T>(Type methodInterceptorType)
    {
        var proxyType = GenerateProxyType(typeof(T), methodInterceptorType);
        return (T)Activator.CreateInstance(proxyType);
    }
    public static Type GenerateProxyType(Type type, Type methodInterceptorType)
    {
        var typeBuilder = moduleBuilder.DefineType($"{type.Name}Proxy", TypeAttributes.Class | TypeAttributes.Public, type);
        foreach (var m in type.GetTypeInfo().DeclaredMethods)
        {
            var ps = m.GetParameters().Select(i => i.ParameterType).ToArray();
            var newM = typeBuilder.DefineMethod(m.Name, MethodAttributes.HideBySig | MethodAttributes.NewSlot | MethodAttributes.Virtual, m.CallingConvention, m.ReturnType, ps);
            CreateProxyMethod(methodInterceptorType, m, ps, newM);
            typeBuilder.DefineMethodOverride(newM, m);
        }
        return typeBuilder.CreateType();
    }
    private static void CreateProxyMethod(Type methodInterceptorType, MethodInfo m, Type[] ps, MethodBuilder newM)
    {
        var il = newM.GetILGenerator();
        var argsLocal = il.DeclareLocal(typeof(object[]));
        var returnLocal = il.DeclareLocal(typeof(object));
        // 初始化参数集合
        il.Emit(OpCodes.Ldc_I4, ps.Length);
        il.Emit(OpCodes.Newarr, typeof(object));
        for (var i = 0; i < ps.Length; i++)
        {
            il.Emit(OpCodes.Dup);
            il.Emit(OpCodes.Ldc_I4, i);
            il.Emit(OpCodes.Ldarg, i + 1);
            il.Emit(OpCodes.Box, ps[i]);
            il.Emit(OpCodes.Stelem_Ref);
        }
        il.Emit(OpCodes.Stloc, argsLocal);
        // 调用被代理方法
        il.Emit(OpCodes.Ldarg, 0); // load this
        for (var i = 0; i < ps.Length; i++)
        {
            il.Emit(OpCodes.Ldarg, i + 1);
        }
        il.Emit(OpCodes.Call, m);
        il.Emit(OpCodes.Box, newM.ReturnType);
        il.Emit(OpCodes.Stloc, returnLocal);
        //调用方法后拦截器
        il.Emit(OpCodes.Newobj, methodInterceptorType.GetConstructors().First());
        il.Emit(OpCodes.Ldarg, 0); // load this
        //加载方法信息参数
        il.Emit(OpCodes.Ldtoken, m);
        il.Emit(OpCodes.Call, getMethodMethod);
        il.Emit(OpCodes.Castclass, typeof(MethodInfo));
        il.Emit(OpCodes.Ldloc, argsLocal);
        il.Emit(OpCodes.Ldloc, returnLocal);
        il.Emit(OpCodes.Callvirt, invoke);
        il.Emit(OpCodes.Stloc, returnLocal);
        // return
        il.Emit(OpCodes.Ldloc, returnLocal);
        il.Emit(OpCodes.Unbox_Any, newM.ReturnType);
        il.Emit(OpCodes.Ret);
    }
}

 internal class Program
 {
     private static void Main(string[] args)
     {
         RealClass proxy = ProxyGenerator.Generate<RealClass>(typeof(AddOneInterceptor));
         var i = 5;
         var j = 10;
         Console.WriteLine($"{i} + {j} = {(i + j)}, but proxy is {proxy.Add(i, j)}");
     }
 }