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use crate::attrs::{
is_vec_u8, parse_field_attrs, parse_repr_type, parse_type_attrs, parse_variant_attrs,
transform_expr_for_self,
};
use quote::quote;
use syn::{Data, DeriveInput, Error, Fields, Result};
pub fn derive_encode(input: &DeriveInput) -> Result<proc_macro2::TokenStream> {
let name = &input.ident;
let type_attrs = parse_type_attrs(&input.attrs)?;
match &input.data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => {
let encode_fields = fields
.named
.iter()
.map(|f| {
let field_name = &f.ident;
let field_attrs = parse_field_attrs(&f.attrs)?;
let encode_expr = if field_attrs.varint32 {
quote! {
voidmc_codec::VarI32(self.#field_name).encode(buf);
}
} else if field_attrs.varint64 {
quote! {
voidmc_codec::VarI64(self.#field_name).encode(buf);
}
} else if field_attrs.json {
quote! {
let json_str = serde_json::to_string(&self.#field_name).unwrap();
json_str.encode(buf);
}
} else if let Some(len_expr) = &field_attrs.fixed_length {
let transformed_expr = transform_expr_for_self(len_expr);
// Use optimized path for Vec<u8>
if is_vec_u8(f) {
quote! {
{
let expected_len = ((#transformed_expr) as i64) as usize;
match voidmc_codec::encode_fixed_length_vec_u8(&self.#field_name, expected_len, buf) {
Ok(_) => {},
Err(e) => panic!("{}", e),
}
}
}
} else {
quote! {
{
let expected_len = ((#transformed_expr) as i64) as usize;
match voidmc_codec::encode_fixed_length_vec(&self.#field_name, expected_len, buf) {
Ok(_) => {},
Err(e) => panic!("{}", e),
}
}
}
}
} else if field_attrs.remaining {
// Remaining attribute: consume all remaining bytes on decode
if is_vec_u8(f) {
quote! {
voidmc_codec::encode_remaining_vec_u8(&self.#field_name, buf);
}
} else {
// Error: remaining only works with Vec<u8>
return Err(Error::new_spanned(
f,
"remaining attribute only works with Vec<u8>",
));
}
} else {
quote! {
self.#field_name.encode(buf);
}
};
Ok(encode_expr)
})
.collect::<Result<Vec<_>>>()?;
let expanded = quote! {
impl voidmc_codec::Encode for #name {
fn encode(&self, buf: &mut Vec<u8>) {
#(#encode_fields)*
}
}
};
Ok(expanded)
}
Fields::Unnamed(_) => Err(Error::new_spanned(
input,
"Encode derive for tuple structs is not supported",
)),
Fields::Unit => {
let expanded = quote! {
impl voidmc_codec::Encode for #name {
fn encode(&self, _buf: &mut Vec<u8>) {}
}
};
Ok(expanded)
}
},
Data::Enum(data) => {
let repr_type = parse_repr_type(&input.attrs)?;
if type_attrs.tagged {
// Tagged enum with explicit packet IDs
let variants = data
.variants
.iter()
.map(|v| {
let variant_name = &v.ident;
let variant_attrs = parse_variant_attrs(&v.attrs)?;
let packet_id = match variant_attrs.packet_id {
Some(id) => id as u32,
None => {
return Err(Error::new_spanned(
v,
"tagged enum variant must have #[codec(packet_id = ...)] attribute",
));
}
};
Ok(match &v.fields {
Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
quote! {
Self::#variant_name(inner) => {
(#packet_id as u8).encode(buf);
inner.encode(buf);
}
}
}
_ => {
return Err(Error::new_spanned(
v,
"Enum variant must have exactly one unnamed field",
));
}
})
})
.collect::<Result<Vec<_>>>()?;
let expanded = quote! {
impl voidmc_codec::Encode for #name {
fn encode(&self, buf: &mut Vec<u8>) {
match self {
#(#variants)*
}
}
}
};
Ok(expanded)
} else if let Some(repr) = repr_type {
// Repr enum with explicit discriminants
let repr_type_ident = syn::Ident::new(&repr, proc_macro2::Span::call_site());
let variants = data
.variants
.iter()
.map(|v| {
let variant_name = &v.ident;
match &v.fields {
Fields::Unit => {
let discriminant = v
.discriminant
.as_ref()
.map(|(_, expr)| {
quote! { #expr }
})
.ok_or_else(|| {
Error::new_spanned(
v,
"repr enum variant must have explicit discriminant",
)
})?;
let encode_expr = if type_attrs.varint32 {
quote! {
voidmc_codec::VarI32(#discriminant as i32).encode(buf);
}
} else if type_attrs.varint64 {
quote! {
voidmc_codec::VarI64(#discriminant as i64).encode(buf);
}
} else {
quote! {
(#discriminant as #repr_type_ident).encode(buf);
}
};
Ok(quote! {
Self::#variant_name => {
#encode_expr
}
})
}
_ => Err(Error::new_spanned(
v,
"repr enum variant must be a unit variant",
)),
}
})
.collect::<Result<Vec<_>>>()?;
let expanded = quote! {
impl voidmc_codec::Encode for #name {
fn encode(&self, buf: &mut Vec<u8>) {
match self {
#(#variants)*
}
}
}
};
Ok(expanded)
} else {
Err(Error::new_spanned(
input,
"Enum Encode derive requires #[codec(tagged)] attribute or #[repr(...)] attribute",
))
}
}
Data::Union(_) => Err(Error::new_spanned(input, "Unions are not supported")),
}
}