assert_type_match 0.1.1

use crate::args::Args;
use crate::utils::{
    create_member, extract_cfg_attrs, extract_field_args, extract_variant_args, try_unzip,
};
use proc_macro2::TokenStream;
use quote::{format_ident, quote, ToTokens};
use syn::{DataEnum, DeriveInput, Error, TypePath, Variant};

pub(crate) fn enum_assert(
    data: &DataEnum,
    input: &DeriveInput,
    args: &Args,
) -> syn::Result<TokenStream> {
    let ident = &input.ident;
    let foreign_ty = args.foreign_ty();
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let this = format_ident!("this");

    let (fn_name, this_ty) = if args.skip_types() {
        (
            format_ident!("__assert_untyped_variants_match"),
            foreign_ty.to_token_stream(),
        )
    } else {
        (
            format_ident!("__assert_typed_variants_match"),
            ident.to_token_stream(),
        )
    };

    let this_to_foreign = assert_fields_match(data, foreign_ty, &this_ty)?;
    let foreign_to_this = assert_variants_exist(data, foreign_ty)?;

    Ok(quote! {
        fn #fn_name #impl_generics(#this: #this_ty #ty_generics) -> #foreign_ty #ty_generics #where_clause {
             match #this {
                #this_to_foreign
            }
        }

        // This test is needed to ensure that all variants in the foreign enum exist in the input enum
        fn __assert_all_variants_exist #impl_generics(#this: #foreign_ty #ty_generics) #where_clause {
             match #this {
                #foreign_to_this
            }
        }
    })
}

pub(crate) fn enum_from(
    data: &DataEnum,
    input: &DeriveInput,
    args: &Args,
) -> syn::Result<TokenStream> {
    let ident = &input.ident;
    let foreign_ty = args.foreign_ty();
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let make_match_arms = |from_ty: TokenStream| {
        data.variants.iter().map(move |variant| {
            let variant_ident = &variant.ident;
            let attrs = extract_cfg_attrs(&variant.attrs);

            let (field_decls, field_ctors) = variant
                .fields
                .iter()
                .enumerate()
                .map(|(index, field)| {
                    let member = create_member(field, index);
                    let attrs = extract_cfg_attrs(&field.attrs)
                        .map(ToTokens::to_token_stream)
                        .collect::<TokenStream>();

                    let alias = format_ident!("__{}", member);

                    (
                        quote!(#attrs #member: #alias,),
                        quote!(#attrs #member: #alias.into(),),
                    )
                })
                .unzip::<_, _, TokenStream, TokenStream>();

            quote! {
                #( #attrs )*
                #from_ty::#variant_ident { #field_decls .. } => Self::#variant_ident { #field_ctors }
            }
        })
    };

    let from_this = make_match_arms(ident.to_token_stream());
    let from_foreign = make_match_arms(foreign_ty.to_token_stream());

    Ok(quote! {
        impl #impl_generics ::core::convert::From<#ident #ty_generics> for #foreign_ty #ty_generics #where_clause {
            #[inline]
            fn from(this: #ident #ty_generics) -> Self {
                match this {
                    #( #from_this ),*
                }
            }
        }

        impl #impl_generics ::core::convert::From<#foreign_ty #ty_generics> for #ident #ty_generics #where_clause {
            #[inline]
            fn from(this: #foreign_ty #ty_generics) -> Self {
                match this {
                    #( #from_foreign ),*
                }
            }
        }
    })
}

fn assert_fields_match(
    data: &DataEnum,
    foreign_ty: &TypePath,
    this_ty: &TokenStream,
) -> Result<TokenStream, Error> {
    data.variants
        .iter()
        .map(|variant| {
            let variant_ident = &variant.ident;
            let attrs = extract_cfg_attrs(&variant.attrs);

            let variant_args = extract_variant_args(&variant.attrs)?;

            let (field_decls, field_ctors): (TokenStream, TokenStream) =
                try_unzip(filter_fields(variant))?;

            let ctor = if variant_args.skip() {
                quote! { unreachable!() }
            } else {
                quote! {#foreign_ty::#variant_ident { #field_ctors }}
            };

            Ok(quote! {
                #( #attrs )*
                #this_ty::#variant_ident { #field_decls .. } => #ctor,
            })
        })
        .collect::<syn::Result<TokenStream>>()
}

fn filter_fields(
    variant: &Variant,
) -> impl Iterator<Item = syn::Result<(TokenStream, TokenStream)>> + '_ {
    variant
        .fields
        .iter()
        .enumerate()
        .filter_map(|(index, field)| {
            let member = create_member(field, index);
            let decl_attrs = extract_cfg_attrs(&field.attrs);
            let ctor_attrs = extract_cfg_attrs(&field.attrs);

            let field_args = match extract_field_args(&field.attrs) {
                Ok(args) => args,
                Err(err) => return Some(Err(err)),
            };

            if field_args.skip() {
                return None;
            }

            let alias = format_ident!("__{}", member);

            let value = if field_args.skip_type() {
                quote! { (|| { unreachable!() })() }
            } else {
                quote! { #alias }
            };

            Some(Ok((
                quote!(#( #decl_attrs )* #member: #alias,),
                quote! {
                    #( #ctor_attrs )*
                    #member: #value,
                },
            )))
        })
}

fn assert_variants_exist(data: &DataEnum, foreign_ty: &TypePath) -> syn::Result<TokenStream> {
    let foreign_to_this = data
        .variants
        .iter()
        .filter_map(|variant| {
            let variant_ident = &variant.ident;
            let attrs = extract_cfg_attrs(&variant.attrs);

            let variant_args = match extract_variant_args(&variant.attrs) {
                Ok(args) => args,
                Err(err) => return Some(Err(err)),
            };

            if variant_args.skip() {
                return None;
            }

            Some(Ok(quote! {
                #( #attrs )*
                #foreign_ty::#variant_ident { .. } => {},
            }))
        })
        .collect::<syn::Result<TokenStream>>()?;
    Ok(foreign_to_this)
}