extern crate quote; // 0.6.10
extern crate proc_macro2; // 0.4.24
use quote::quote;
use proc_macro2::{Delimiter, Group, Ident, Punct, Spacing, Span};
use quote::{ToTokens, TokenStreamExt};

#[derive(Debug)]
pub struct Datum(pub u8);
#[derive(Debug)]
pub struct Data(pub Vec<Datum>);

// Taks: Implement quote::ToTokens for Data

impl ToTokens for Datum {
    fn to_tokens(&self, stream: &mut proc_macro2::TokenStream) {
       stream.append(Ident::new("Datum", Span::call_site()));
       let mut val_stream = proc_macro2::TokenStream::new();
       self.0.to_tokens(&mut val_stream);
       stream.append(Group::new(Delimiter::Parenthesis, val_stream));
    }
}

impl ToTokens for Data {
  fn to_tokens(&self, stream: &mut proc_macro2::TokenStream) {
    // target: Data( <[Datum]>::into_vec(Box::new([ (d.to_tokens ,)* ])) )
    let mut body_stream = proc_macro2::TokenStream::new();
    let mut vec_op_stream = proc_macro2::TokenStream::new();
    vec_op_stream.append(Punct::new('<', Spacing::Alone));
    let mut datum_type_stream = proc_macro2::TokenStream::new();
    datum_type_stream.append(Ident::new("Datum", Span::call_site()));
    vec_op_stream.append(Group::new(Delimiter::Bracket, datum_type_stream));
    vec_op_stream.append(Punct::new('>', Spacing::Alone));
    // done: vec_op_stream = <[datum_type_stream]> = <[Datum]>
    body_stream.append(Group::new(Delimiter::None, vec_op_stream));
    body_stream.append(Punct::new(':', Spacing::Joint));
    body_stream.append(Punct::new(':', Spacing::Alone));
    body_stream.append(Ident::new("into_vec", Span::call_site()));
    // done: body_stream = vec_op_stream::into_vec = <[Datum]>::into_vec
    let mut box_stream = proc_macro2::TokenStream::new();
    box_stream.append(Ident::new("Box", Span::call_site()));
    box_stream.append(Punct::new(':', Spacing::Joint));
    box_stream.append(Punct::new(':', Spacing::Alone));
    box_stream.append(Ident::new("new", Span::call_site()));
    // done: box_stream = Box::new
    let mut vec_arg_stream = proc_macro2::TokenStream::new();
    let mut arg_array_stream = proc_macro2::TokenStream::new();
    for (i, d) in self.0.iter().enumerate() {
      if i > 0 {
        arg_array_stream.append(Punct::new(',', Spacing::Alone));
      }
      d.to_tokens(&mut arg_array_stream);
    }
    vec_arg_stream.append(Group::new(Delimiter::Bracket, arg_array_stream));
    // done: vec_arg_stream = [arg_array_stream] = [ (d.to_tokens ,)* ]
    box_stream.append(Group::new(Delimiter::Parenthesis, vec_arg_stream));
    // done: box_stream = Box::new (vec_arg_stream) = Box::new([ (d.to_tokens ,)* ])
    body_stream.append(Group::new(Delimiter::Parenthesis, box_stream));
    // done: body_stream = vec_op_stream::into_vec(box_stream) = <[Datum]>::into_vec(Box::new([ (d.to_tokens ,)* ]))

    stream.append(Ident::new("Data", Span::call_site()));
    let group = Group::new(Delimiter::Parenthesis, body_stream);
    stream.append(group);
    // done: stream = Data(body_stream) = Data( <[Datum]>::into_vec(Box::new([ (d.to_tokens ,)* ])) )
  }
}

fn main() {
    let d : Data = Data(vec![Datum(2),Datum(4),Datum(6)]);
    println!("initial data: {:?}", d);
    println!();
    let quoted = quote!(#d);

    println!("quoted display of .to_tokens(): {}", quoted);
    println!();
    //  assuming this is printed, is it valid?
    let recovered : Data = Data (  < [ Datum ] >  :: into_vec ( Box :: new ( [ Datum ( 2u8 ) , Datum ( 4u8 ) , Datum ( 6u8 ) ] ) ) );
    println!("recovered data: {:?}", recovered);

}