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extern crate proc_macro;

use crate::proc_macro::TokenStream;
use proc_macro2;
use quote::{format_ident, quote};
use syn;

#[proc_macro_derive(Identifiers)]
pub fn identifiers_derive(input: TokenStream) -> TokenStream {
    let ast = syn::parse(input).unwrap();
    impl_identifiers(&ast)
}

fn impl_identifiers(ast: &syn::DeriveInput) -> TokenStream {
    let name = &ast.ident;
    let struct_name = format_ident! {"{}Identifiers", name};
    let vis = &ast.vis;

    let methods = match &ast.data {
        syn::Data::Struct(s) => get_identifiers_methods(&s.fields, vis),
        _ => unreachable!(),
    };

    let gen = quote! {

        #vis struct #struct_name {}

        impl #name {
            #(#methods)*
        }
    };
    gen.into()
}

fn get_identifiers_methods(
    fields: &syn::Fields,
    vis: &syn::Visibility,
) -> Vec<proc_macro2::TokenStream> {
    let mut res = Vec::new();
    for field in fields.iter() {
        if let syn::Visibility::Public(_) = field.vis {
            if let Some(ident) = &field.ident {
                let fun_name = format_ident!("{}_n", ident);
                let quote_ident = format!("{}", ident);
                let fun = quote! {
                    #vis fn #fun_name() -> String {
                        String::from(#quote_ident)
                    }
                };
                res.push(fun);
            };
        };
    }
    res
}

// fn impl_field_list(ast: &syn::DeriveInput) -> TokenStream {
//     let name = &ast.ident;
//     let c_name = format_ident!("{}_field_names", name);
//     let fields = match &ast.data {
//         syn::Data::Struct(s) => {
//             let mut res = vec![];
//             for f in s.fields.iter() {
//                 if let syn::Visibility::Public(_) = f.vis {
//                     if let Some(ident) = &f.ident {
//                         res.push(format!("{}", ident));
//                     }
//                 }
//             }
//             res
//         }
//         _ => unreachable!(),
//     };
//     let gen = quote! {
//         const #c_name: &'static [&'static str] = &[#(#fields),*];
//         impl FieldList for #name {
//             fn field_list() -> &'static [&'static str] {
//                 unimplemented!()
//             }
//         }
//     };

//     gen.into()
// }

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        assert_eq!(2 + 2, 4);
    }
}