numbat-codec-derive 0.0.9

use proc_macro::TokenStream;
use quote::quote;

use crate::nested_en_derive::{dep_encode_or_exit_snippet, dep_encode_snippet};
use crate::util::*;

pub fn variant_top_encode_snippets(
	name: &syn::Ident,
	data_enum: &syn::DataEnum,
) -> Vec<proc_macro2::TokenStream> {
	data_enum
		.variants
		.iter()
		.enumerate()
		.map(|(variant_index, variant)| {
			let variant_index_u8 = variant_index as u8;
			let variant_ident = &variant.ident;
			if variant.fields.is_empty() {
				// top-encode discriminant directly
				quote! {
					#name::#variant_ident =>
						numbat_codec::TopEncode::top_encode(&#variant_index_u8, output),
				}
			} else {
				// dep-encode to buffer first
				let local_var_declarations =
					fields_decl_syntax(&variant.fields, local_variable_for_field);
				let variant_field_snippets = fields_snippets(&variant.fields, |index, field| {
					dep_encode_snippet(&local_variable_for_field(index, field))
				});
				quote! {
					#name::#variant_ident #local_var_declarations => {
						let mut buffer = numbat_codec::Vec::<u8>::new();
						let dest = &mut buffer;
						numbat_codec::NestedEncode::dep_encode(&#variant_index_u8, dest)?;
						#(#variant_field_snippets)*
						output.set_slice_u8(&buffer[..]);
						core::result::Result::Ok(())
					},
				}
			}
		})
		.collect()
}

pub fn variant_top_encode_or_exit_snippets(
	name: &syn::Ident,
	data_enum: &syn::DataEnum,
) -> Vec<proc_macro2::TokenStream> {
	data_enum
		.variants
		.iter()
		.enumerate()
		.map(|(variant_index, variant)| {
			let variant_index_u8 = variant_index as u8;
			let variant_ident = &variant.ident;
			if variant.fields.is_empty() {
				// top-encode discriminant directly
				quote! {
					#name::#variant_ident =>
						numbat_codec::TopEncode::top_encode_or_exit(&#variant_index_u8, output, c.clone(), exit),
				}
			} else {
				// dep-encode to buffer first
				let local_var_declarations =
					fields_decl_syntax(&variant.fields, local_variable_for_field);
				let variant_field_snippets = fields_snippets(&variant.fields, |index, field| {
					dep_encode_or_exit_snippet(&local_variable_for_field(index, field))
				});
				quote! {
					#name::#variant_ident #local_var_declarations => {
						let mut buffer = numbat_codec::Vec::<u8>::new();
						let dest = &mut buffer;
						numbat_codec::NestedEncode::dep_encode_or_exit(&#variant_index_u8, dest, c.clone(), exit);
						#(#variant_field_snippets)*
						output.set_slice_u8(&buffer[..]);
					},
				}
			}
		})
		.collect()
}

/// Only returns the trait implementation method bodies, without the impl or method definitions.
fn top_encode_method_bodies(
	ast: &syn::DeriveInput,
) -> (proc_macro2::TokenStream, proc_macro2::TokenStream) {
	let name = &ast.ident;
	match &ast.data {
		syn::Data::Struct(data_struct) => {
			let field_dep_encode_snippets = fields_snippets(&data_struct.fields, |index, field| {
				dep_encode_snippet(&self_field_expr(index, field))
			});
			let field_dep_encode_or_exit_snippets =
				fields_snippets(&data_struct.fields, |index, field| {
					dep_encode_or_exit_snippet(&self_field_expr(index, field))
				});
			let top_encode_body = quote! {
				let mut buffer = numbat_codec::Vec::<u8>::new();
				let dest = &mut buffer;
				#(#field_dep_encode_snippets)*
				output.set_slice_u8(&buffer[..]);
				core::result::Result::Ok(())
			};
			let top_encode_or_exit_body = quote! {
				let mut buffer = numbat_codec::Vec::<u8>::new();
				let dest = &mut buffer;
				#(#field_dep_encode_or_exit_snippets)*
				output.set_slice_u8(&buffer[..]);
			};
			(top_encode_body, top_encode_or_exit_body)
		},
		syn::Data::Enum(data_enum) => {
			assert!(
				data_enum.variants.len() < 256,
				"enums with more than 256 variants not supported"
			);
			let variant_top_encode_snippets = variant_top_encode_snippets(&name, &data_enum);
			let variant_top_encode_or_exit_snippets =
				variant_top_encode_or_exit_snippets(&name, &data_enum);

			let top_encode_body = quote! {
				match self {
					#(#variant_top_encode_snippets)*
				}
			};
			let top_encode_or_exit_body = quote! {
				match self {
					#(#variant_top_encode_or_exit_snippets)*
				}
			};
			(top_encode_body, top_encode_or_exit_body)
		},
		syn::Data::Union(_) => panic!("Union not supported"),
	}
}

pub fn top_encode_impl(ast: &syn::DeriveInput) -> TokenStream {
	let name = &ast.ident;
	let (impl_generics, ty_generics, where_clause) = &ast.generics.split_for_impl();
	let (top_encode_body, top_encode_or_exit_body) = top_encode_method_bodies(ast);

	let gen = quote! {
		impl #impl_generics numbat_codec::TopEncode for #name #ty_generics #where_clause {
			fn top_encode<O: numbat_codec::TopEncodeOutput>(&self, output: O) -> core::result::Result<(), numbat_codec::EncodeError> {
				#top_encode_body
			}

			fn top_encode_or_exit<O: numbat_codec::TopEncodeOutput, ExitCtx: Clone>(
				&self,
				output: O,
				c: ExitCtx,
				exit: fn(ExitCtx, numbat_codec::EncodeError) -> !,
			) {
				#top_encode_or_exit_body
			}
		}
	};
	gen.into()
}

pub fn top_encode_or_default_impl(ast: &syn::DeriveInput) -> TokenStream {
	let name = &ast.ident;
	let (impl_generics, ty_generics, where_clause) = &ast.generics.split_for_impl();
	let (top_encode_body, top_encode_or_exit_body) = top_encode_method_bodies(ast);

	let gen = quote! {
		impl #impl_generics numbat_codec::TopEncode for #name #ty_generics #where_clause {
			fn top_encode<O: numbat_codec::TopEncodeOutput>(&self, output: O) -> core::result::Result<(), numbat_codec::EncodeError> {
				if numbat_codec::EncodeDefault::is_default(self) {
					output.set_slice_u8(&[]);
					Ok(())
				} else {
					#top_encode_body
				}
			}

			fn top_encode_or_exit<O: numbat_codec::TopEncodeOutput, ExitCtx: Clone>(
				&self,
				output: O,
				c: ExitCtx,
				exit: fn(ExitCtx, numbat_codec::EncodeError) -> !,
			) {
				if numbat_codec::EncodeDefault::is_default(self) {
					output.set_slice_u8(&[]);
				} else {
					#top_encode_or_exit_body
				}
			}
		}
	};
	gen.into()
}