field_name 0.2.0

use darling::{ast::Data, FromDeriveInput, FromField};
use proc_macro2::TokenStream;
use quote::{quote, ToTokens};
use syn::{Generics, Ident};

#[derive(FromDeriveInput)]
#[darling(attributes(field_name), supports(struct_named))]
pub(crate) struct Receiver {
    ident: Ident,
    generics: Generics,
    data: Data<(), ReceiverField>,
}

#[derive(FromField)]
#[darling(attributes(field_name))]
struct ReceiverField {
    ident: Option<Ident>,

    #[darling(default)]
    rename: Option<String>,

    #[darling(default)]
    skip: bool,
}

impl ToTokens for Receiver {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let ident = &self.ident;
        let (impl_generics, ty_generics, where_clause) = self.generics.split_for_impl();

        let fields = self.data
            .as_ref()
            .take_struct()
            .expect("FieldNames only supports named structs")
            .into_iter()
            .filter(|f| !f.skip)
            .collect::<Vec<_>>();

        let field_values: Vec<String> = fields.iter()
            .map(|f| f.rename.clone().unwrap_or_else(|| f.ident.as_ref().unwrap().to_string()))
            .collect();

        let individual_consts = fields.iter().map(|f| {
            let field_ident = f.ident.as_ref().unwrap();

            let const_name = Ident::new(
                &field_ident.to_string().to_uppercase(),
                field_ident.span()
            );

            let const_value = f.rename.clone().unwrap_or_else(|| field_ident.to_string());

            quote! {
                pub const #const_name: &'static str = #const_value;
            }
        });

        let fields_len = field_values.len();

        tokens.extend(quote! {
            #[automatically_derived]
            impl #impl_generics #ident #ty_generics #where_clause {
                pub const FIELDS: [&'static str; #fields_len] = [
                    #(#field_values),*
                ];

                #(#individual_consts)*
            }
        });
    }
}