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#![recursion_limit = "128"]
extern crate proc_macro;

use proc_macro2::TokenStream;
use quote::quote;
use syn::{spanned::Spanned, *};

#[proc_macro_derive(UniformSet)]
pub fn validate_fidl_table(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input: DeriveInput = syn::parse(input).unwrap();
    let fields = if let Data::Struct(DataStruct {
        fields: syn::Fields::Named(fields),
        ..
    }) = input.data
    {
        fields
    } else {
        return Error::new(
            input.span(),
            "A uniform set may only be derived from a struct with named fields.",
        )
        .to_compile_error()
        .into();
    };

    impl_uniform_set(input.ident, fields)
}

fn impl_uniform_set(ident: Ident, fields: syn::FieldsNamed) -> proc_macro::TokenStream {
    let mut field_visits = TokenStream::new();

    field_visits.extend(fields.named.into_iter().map(|field| {
        let ident = field.ident.expect("Unwrapping name of named struct field");
        quote!(f(stringify!(#ident), &self.#ident);)
    }));

    quote!(
        impl OwnedUniforms for #ident {
            fn visit_owned_values(&self, mut f: &mut dyn FnMut(&str, &dyn IntoUniformValue)) {
                #field_visits
            }
        }
    )
    .into()
}