use proc_macro::TokenStream;
use quote::quote;

#[proc_macro_attribute]
pub fn repeat(attr: TokenStream, item: TokenStream) -> TokenStream {
    let number = syn::parse_macro_input!(attr as syn::LitInt).base10_parse::<usize>().unwrap();
    let ast = syn::parse_macro_input!(item as syn::ItemFn);
    let items = (0..number)
        .map(|i| {
            let mut new_ast = ast.clone();
            new_ast.sig.ident = syn::Ident::new(&format!("{}_{}", ast.sig.ident, i), ast.sig.ident.span());
            new_ast
        })
        .collect::<Vec<_>>();
    quote! {
        #(#items)*
    }.into()
}

#[proc_macro_attribute]
pub fn add_one(_attr: TokenStream, item: TokenStream) -> TokenStream {
    let ast = syn::parse_macro_input!(item as syn::ItemFn);
    let mut new_ast = ast.clone();
    new_ast.sig.ident = syn::Ident::new(&format!("{}_new", ast.sig.ident), ast.sig.ident.span());
    quote! {
        #ast
        #new_ast
    }.into()
}

#[proc_macro_attribute]
pub fn erase(_attr: TokenStream, _item: TokenStream) -> TokenStream {
    TokenStream::new()
}

#[proc_macro_derive(MyTrait)]
pub fn my_trait_derive(input: TokenStream) -> TokenStream {
    let ast = syn::parse_macro_input!(input as syn::DeriveInput);
    let name = &ast.ident;
    let const_ident = syn::Ident::new(&format!("CONST_{}", name), name.span());
    quote! {
        const #const_ident: u32 = 42;

        impl MyTrait for #name {
            fn my_method() -> u32 {
                #const_ident
            }
        }
    }.into()
}