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use proc_macro2::TokenStream;
use syn::spanned::Spanned;
use syn::ItemImpl;

use quote::{quote, quote_spanned};

use crate::args::Flag;
use crate::gen_caster::generate_caster;
use std::collections::HashSet;

pub fn process(flags: &HashSet<Flag>, input: ItemImpl) -> TokenStream {
    let ItemImpl {
        ref self_ty,
        ref trait_,
        ..
    } = input;

    let generated = match trait_ {
        None => quote_spanned! {
            self_ty.span() => compile_error!("#[cast_to] should only be on an impl of a trait");
        },
        Some(trait_) => match trait_ {
            (Some(bang), _, _) => quote_spanned! {
                bang.span() => compile_error!("#[cast_to] is not for !Trait impl");
            },
            (None, path, _) => generate_caster(self_ty, path, flags.contains(&Flag::Sync)),
        },
    };

    quote! {
        #input
        #generated
    }
}