use proc_macro2::TokenStream as TokenStream2;
use quote::ToTokens;

/// We store description of the assets an application uses in the executable.
/// We use the `link_section` attribute embed an extra section in the executable.
/// We force rust to store a serialized representation of the asset description
/// inside a particular region of the binary, with the label "manganis".
/// After linking, the "manganis" sections of the different object files will be merged.
pub fn generate_link_section(asset: impl ToTokens) -> TokenStream2 {
    let position = proc_macro2::Span::call_site();
    let section_name = syn::LitStr::new(
        manganis_core::linker::LinkSection::CURRENT.link_section,
        position,
    );

    quote::quote! {
        // First serialize the asset into a constant sized buffer
        const __BUFFER: manganis::macro_helpers::const_serialize::ConstVec<u8> = manganis::macro_helpers::serialize_asset(&#asset);
        // Then pull out the byte slice
        const __BYTES: &[u8] = __BUFFER.as_ref();
        // And the length of the byte slice
        const __LEN: usize = __BYTES.len();

        // Now that we have the size of the asset, copy the bytes into a static array
        #[link_section = #section_name]
        #[used]
        static __LINK_SECTION: [u8; __LEN] = manganis::macro_helpers::copy_bytes(__BYTES);

        fn __keep_link_section() -> u8 {
            unsafe { std::ptr::read_volatile(__LINK_SECTION.as_ptr()) }
        }
    }
}