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extern crate proc_macro;

use proc_macro::TokenStream;
use proc_macro2::{Ident, Span as Span2};
use quote::quote;

#[proc_macro_attribute]
pub fn middleware_fn(attr: TokenStream, item: TokenStream) -> TokenStream {
    if let syn::Item::Fn(mut function_item) = syn::parse(item.clone()).unwrap() {
        let name = function_item.ident.clone();
        let new_name = Ident::new(&format!("__async_{}", name.clone()), Span2::call_site());
        function_item.ident = new_name.clone();

        let visibility = function_item.vis.clone();
        let arguments = function_item.decl.inputs.clone();
        let generics = function_item.decl.generics.clone();

        let context_type = match &arguments[0] {
            syn::FnArg::Captured(cap) => &cap.ty,
            _ => panic!("Expected the first argument to be a context type"),
        };
        let new_return_type = Ident::new(&format!("__MiddlewareReturnValue_{}", name.clone()), Span2::call_site());
        let crate_path = match attr.to_string().as_str() {
            "_internal" => quote! {
                crate::core::{ MiddlewareReturnValue as #new_return_type }
            },
            _ => quote! {
                thruster::{ MiddlewareReturnValue as #new_return_type }
            },
        };

        let gen = quote! {
            #function_item

            use #crate_path;
            #visibility fn #name#generics(ctx: #context_type, next: MiddlewareNext<#context_type>) -> #new_return_type<#context_type> {
                Box::pin(#new_name(ctx, next))
            }
        };

        // proc_macro::Span::call_site()
        //     .note("Thruster code output")
        //     .note(gen.to_string())
        //     .emit();

        gen.into()
    } else {
        item
    }
}