open System
open System.Linq
open System.Net
open System.Reflection
open System.Reflection.Emit
open System.Collections.Generic

[<AttributeUsage(AttributeTargets.Class, AllowMultiple = false)>]
type public LoggingAttributeAttribute (t : Type) =
    inherit Attribute()
    member public this.AttachedType
        with get() = t

[<LoggingAttribute(typeof<MyClass>)>]
type public MyClass () =
    class
        abstract member DoStuff : unit -> string
        default this.DoStuff () =
            "hello world"
    end

type ExtendedMyClassDoStuffDelegate =
    delegate of unit -> string

(*
let GenerateLogging (attrs : LoggingAttributeAttribute seq) =

    let types = Seq.map (fun (attr : LoggingAttributeAttribute) -> attr.AttachedType) attrs

    let asmName = new AssemblyName "myAssembly"
    let ab = AppDomain.CurrentDomain.DefineDynamicAssembly (asmName, AssemblyBuilderAccess.Run)
    let mb = ab.DefineDynamicModule asmName.Name

    for t in types do
        let name = t.Name
        let methods = t.GetMethods (BindingFlags.Public ||| BindingFlags.DeclaredOnly ||| BindingFlags)
        let tb = mb.DefineType ("Extended" + name, TypeAttributes.Public, t)
        let cb = tb.DefineConstructor (MethodAttributes.Public, CallingConventions.Standard, Array.empty)
        let cbIl = cb.GetILGenerator ()
        cbIl.Emit OpCodes.Ldarg_0
        cbIl.Emit (OpCodes.Call, typeof<MyClass>.GetConstructor Type.EmptyTypes)
        cbIl.Emit OpCodes.Ret
        for m in methods do
            let methodName = m.Name
            let mb = tb.DefineMethod (methodName, MethodAttributes.Public ||| MethodAttributes.HideBySig ||| MethodAttributes.Virtual ||| MethodAttributes.NewSlot, m.




    0

*)
[<EntryPoint>]
let main args =

    let attrs =  [|
                    for x in (Attribute.GetCustomAttributes(Assembly.GetEntryAssembly(), typeof<LoggingAttributeAttribute>))
                        do yield x :?> LoggingAttributeAttribute
                 |]


    let asmName = new AssemblyName "myAssembly"
    let ab = AppDomain.CurrentDomain.DefineDynamicAssembly (asmName, AssemblyBuilderAccess.Run)
    let mb = ab.DefineDynamicModule asmName.Name
    let tb = mb.DefineType ("ExtendedMyClass", TypeAttributes.Public, typeof<MyClass>)

    let cb = tb.DefineConstructor (MethodAttributes.Public, CallingConventions.Standard, Array.empty)
    let cbIl = cb.GetILGenerator ()
    cbIl.Emit OpCodes.Ldarg_0
    cbIl.Emit (OpCodes.Call, typeof<MyClass>.GetConstructor Type.EmptyTypes)
    cbIl.Emit OpCodes.Ret


    let mbDoStuff =
        tb.DefineMethod ("DoStuff", MethodAttributes.Public ||| MethodAttributes.HideBySig ||| MethodAttributes.Virtual ||| MethodAttributes.NewSlot, typeof<string>, Type.EmptyTypes)
    let ilDoStuff = mbDoStuff.GetILGenerator ()

    ilDoStuff.Emit OpCodes.Ldarg_0
    ilDoStuff.Emit(OpCodes.Ldstr, "Calling base `DoStuff'")
    ilDoStuff.Emit (OpCodes.Call, typeof<Console>.GetMethod ("WriteLine", [| typeof<string> |]) )
    ilDoStuff.Emit (OpCodes.Callvirt, typeof<MyClass>.GetMethod "DoStuff")
    ilDoStuff.Emit OpCodes.Ret

    let myDynamicType = tb.CreateType ()
    let extendedMyClass = Activator.CreateInstance myDynamicType

    let del = Delegate.CreateDelegate (typeof<ExtendedMyClassDoStuffDelegate>, extendedMyClass, "DoStuff")
    let extendedMyClassDoStuff = del :?> ExtendedMyClassDoStuffDelegate

    let myClass = new MyClass ()


    [myClass.DoStuff; extendedMyClassDoStuff.Invoke]
    |> List.map (fun del -> del() )
    |> List.iter (fun str -> printfn "%s" str)


    0