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use proc_macro2::{Ident, TokenStream};
use quote::quote;
use syn::Result;
use syn::{DeriveInput, ImplGenerics, TypeGenerics, WhereClause};

pub struct DeriveInputContext<'a> {
    pub input: &'a DeriveInput,
    pub impl_generics: ImplGenerics<'a>,
    pub ty_generics: TypeGenerics<'a>,
    pub where_clause: Option<&'a WhereClause>,
    pub trait_ty: Option<Ident>,
    pub target_ty: Ident,
}

impl<'a> DeriveInputContext<'a> {
    pub fn new(input: &'a DeriveInput, trait_ty: Option<Ident>, target_ty: Ident) -> Self {
        let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
        Self {
            input,
            impl_generics,
            ty_generics,
            where_clause,
            trait_ty,
            target_ty,
        }
    }

    pub fn impl_token(
        self,
        block_fn: impl Fn(&DeriveInputContext<'a>) -> Result<TokenStream>,
    ) -> TokenStream {
        let impl_generics = &self.impl_generics;
        let ty_generics = &self.ty_generics;
        let where_clause = &self.where_clause;
        let block = block_fn(&self).unwrap_or_else(|err| err.into_compile_error());
        let target_ty = &self.target_ty;
        match self.trait_ty {
            Some(trait_ty) => {
                quote! {
                    impl #impl_generics #trait_ty for #target_ty #ty_generics #where_clause {
                        #block
                    }
                }
            }
            None => {
                quote! {
                    impl #impl_generics #target_ty #ty_generics #where_clause {
                        #block
                    }
                }
            }
        }
    }
}