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use quote::quote;
use syn::{Data, DeriveInput, Meta};

use super::models::{FieldAttributeBuilder, TypeAttributeBuilder};
use crate::{supported_traits::Trait, trait_handlers::TraitHandler};

pub(crate) struct HashUnionHandler;

impl TraitHandler for HashUnionHandler {
    #[inline]
    fn trait_meta_handler(
        ast: &mut DeriveInput,
        token_stream: &mut proc_macro2::TokenStream,
        traits: &[Trait],
        meta: &Meta,
    ) -> syn::Result<()> {
        let type_attribute =
            TypeAttributeBuilder {
                enable_flag: true, enable_unsafe: true, enable_bound: false
            }
            .build_from_hash_meta(meta)?;

        if !type_attribute.has_unsafe {
            return Err(super::panic::union_without_unsafe(meta));
        }

        if let Data::Union(data) = &ast.data {
            for field in data.fields.named.iter() {
                let _ = FieldAttributeBuilder {
                    enable_ignore: false, enable_method: false
                }
                .build_from_attributes(&field.attrs, traits)?;
            }
        }

        let ident = &ast.ident;

        let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();

        token_stream.extend(quote! {
            impl #impl_generics ::core::hash::Hash for #ident #ty_generics #where_clause {
                #[inline]
                fn hash<H: ::core::hash::Hasher>(&self, state: &mut H) {
                    let size = ::core::mem::size_of::<Self>();
                    let data = unsafe { ::core::slice::from_raw_parts(self as *const Self as *const u8, size) };

                    ::core::hash::Hash::hash(data, state)
                }
            }
        });

        Ok(())
    }
}