use proc_macro2::{Literal, Span, TokenStream};
use quote::quote;
use syn::{Data, DeriveInput, GenericParam, Ident, Lifetime, LifetimeDef, Meta, NestedMeta, Type};
pub fn impl_event_reader(ast: &DeriveInput) -> TokenStream {
let event_name = &ast.ident;
let mut reader_name: Option<Ident> = None;
for meta in ast
.attrs
.iter()
.filter(|attr| attr.path.segments[0].ident == "reader")
.map(|attr| {
attr.parse_meta()
.expect("reader attribute incorrectly defined")
})
{
if let Meta::List(l) = meta {
for nested_meta in l.nested.iter() {
match nested_meta {
NestedMeta::Meta(Meta::Path(path)) => {
if let Some(ident) = path.get_ident() {
reader_name = Some(ident.clone());
} else {
panic!("reader attribute does not contain a single name");
}
}
_ => panic!("reader attribute does not contain a single name"),
}
}
};
}
let reader_name = reader_name.unwrap_or_else(|| {
panic!(
r#"
#[derive(EventReader)] requested for {}, but #[reader(SomeEventReader)] attribute is missing
Example usage:
#[derive(EventReader)]
#[reader(SomeEventReader)]
pub enum SomeEvent {{
One(Event1),
Two(Event2),
}}
"#,
event_name
)
});
let tys = collect_field_types(&ast.data);
let tys = &tys;
let names = collect_variant_names(&ast.data);
let names = &names;
let type_params_with_defaults = ast.generics.type_params();
let (_, type_generics, where_clause) = ast.generics.split_for_impl();
let mut generics = ast.generics.clone();
let reader_lifetime = Lifetime::new("'r", Span::call_site());
let reader_lifetime_iter = std::iter::repeat(reader_lifetime.clone()).take(tys.len());
generics
.params
.push(GenericParam::Lifetime(LifetimeDef::new(
reader_lifetime.clone(),
)));
let (impl_generics, _, _) = generics.split_for_impl();
let reads: Vec<_> = (0..tys.len())
.map(|n| {
let variant = &names[n];
let tuple_index = Literal::usize_unsuffixed(n);
quote! {
events.extend(
data.#tuple_index.read(
self.#tuple_index
.as_mut()
.expect("ReaderId undefined, has setup been run?")
)
.cloned()
.map(#event_name::#variant)
);
}
})
.collect();
let setups: Vec<_> = (0..tys.len())
.map(|n| {
let ty = &tys[n];
let tuple_index = Literal::usize_unsuffixed(n);
quote! {
self.#tuple_index = Some(world.fetch_mut::<EventChannel<#ty>>().register_reader());
}
})
.collect();
quote! {
#[allow(missing_docs)]
#[derive(Default)]
pub struct #reader_name <#(#type_params_with_defaults),*> (
#(Option<ReaderId<#tys>>, )*
) #where_clause;
impl #impl_generics EventReader<#reader_lifetime> for #reader_name #type_generics
#where_clause
{
type SystemData = (
#(Read<#reader_lifetime_iter, EventChannel<#tys>>),*
);
type Event = #event_name #type_generics;
fn read(&mut self, data: Self::SystemData, events: &mut Vec<#event_name #type_generics>) {
#(#reads)*
}
fn setup(&mut self, world: &mut World) {
<Self::SystemData as SystemData<#reader_lifetime>>::setup(world);
#(#setups)*
}
}
}
}
fn collect_field_types(ast: &Data) -> Vec<Type> {
let variants = match *ast {
Data::Enum(ref variants) => &variants.variants,
_ => panic!("EventReader derive only support enums"),
};
variants
.iter()
.map(|v| {
v.fields
.iter()
.next()
.expect("Event enum variant does not contain an inner event type")
.ty
.clone()
})
.collect()
}
fn collect_variant_names(ast: &Data) -> Vec<Ident> {
let variants = match *ast {
Data::Enum(ref variants) => &variants.variants,
_ => panic!("EventReader derive only support enums"),
};
variants.iter().map(|v| v.ident.clone()).collect()
}