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#![feature(box_syntax)]

extern crate proc_macro;

use syn::*;
use syn::visit_mut::*;

use quote::{
    quote, quote_spanned, ToTokens,
};

#[proc_macro_attribute]
pub fn suspend(_metadata: proc_macro::TokenStream, input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    if let Ok(ref mut item) = syn::parse::<ItemImpl>(input.clone()) {
        Vis {}.visit_item_impl_mut(item);
        quote!(#item).into()
    } else if let Ok(ref mut method) = syn::parse(input) {
        Vis {}.visit_impl_item_method_mut(method);
        panic!("method : {}", method.to_token_stream());
        //quote!(#method).into()
    } else {
        panic!("Need an impl or a method item")
    }
}

struct Vis {}

impl VisitMut for Vis {
    fn visit_expr_mut(&mut self, base_expr: &mut Expr) {
        if let Expr::Await(ref mut expr) = base_expr {
            self.visit_expr_mut(&mut expr.base);
            let base = &expr.base;
            let syntax = quote_spanned! {
                expr.await_token.span => {
                        let _fut = #base;
                        let (mut _tmp, _res) =  self.suspend(_fut).await;
                        self = _tmp;
                        _res
                    }
                };

            let block = parse2::<Block>(syntax).unwrap();
            *base_expr = Expr::Block(ExprBlock {
                block,
                label: None,
                attrs: vec![],
            });
        } else {
            visit_expr_mut(self, base_expr);
        }
    }
}

#[test]
fn test_suspending() {
    let code = r##"
#[suspend::suspend]
async fn handle(self: &mut Context<Self>, msg: TestMessage) -> i32 {
    self.x += 1;
    let res = delay_for(Duration::from_secs((2 * x) as _)).await.await;
    self.x -= 1;
    return self.x;
}
"##;

    let generated = suspend_impl(syn::parse_str(code).unwrap());
    panic!("Generated : {:?}", generated.to_string())
}