//! Procedural macros for `rkyv_dyn`.

#![deny(
    rustdoc::broken_intra_doc_links,
    missing_docs,
    rustdoc::missing_crate_level_docs
)]

extern crate proc_macro;

use quote::quote;
use syn::{
    parse::{Parse, ParseStream, Result},
    parse_macro_input,
    spanned::Spanned,
    Attribute, Error, Ident, ItemImpl, ItemTrait, LitStr, Token, Visibility,
};

enum Input {
    Impl(ItemImpl),
    Trait(ItemTrait),
}

impl Parse for Input {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut attrs = Attribute::parse_outer(input)?;

        let ahead = input.fork();
        ahead.parse::<Visibility>()?;
        ahead.parse::<Option<Token![unsafe]>>()?;

        if ahead.peek(Token![trait]) {
            let mut item: ItemTrait = input.parse()?;
            attrs.extend(item.attrs);
            item.attrs = attrs;
            Ok(Input::Trait(item))
        } else if ahead.peek(Token![impl]) {
            let mut item: ItemImpl = input.parse()?;
            if item.trait_.is_none() {
                let impl_token = item.impl_token;
                let ty = item.self_ty;
                let span = quote!(#impl_token #ty);
                let msg = "expected impl Trait for Type";
                return Err(Error::new_spanned(span, msg));
            }
            attrs.extend(item.attrs);
            item.attrs = attrs;
            Ok(Input::Impl(item))
        } else {
            Err(input.error("expected trait or impl block"))
        }
    }
}

struct Args {
    serialize: Option<LitStr>,
    deserialize: Option<Option<LitStr>>,
}

impl Parse for Args {
    fn parse(input: ParseStream) -> Result<Self> {
        mod kw {
            syn::custom_keyword!(serialize);
            syn::custom_keyword!(deserialize);
        }

        let mut serialize = None;
        let mut deserialize = None;

        let mut needs_punct = false;
        while !input.is_empty() {
            if needs_punct {
                input.parse::<Token![,]>()?;
            }

            if input.peek(kw::serialize) {
                if serialize.is_some() {
                    return Err(input.error("duplicate serialize argument"));
                }

                input.parse::<kw::serialize>()?;
                input.parse::<Token![=]>()?;
                serialize = Some(input.parse::<LitStr>()?);
            } else if input.peek(kw::deserialize) {
                if deserialize.is_some() {
                    return Err(input.error("duplicate deserialize argument"));
                }

                input.parse::<kw::deserialize>()?;
                if input.peek(Token![=]) {
                    input.parse::<Token![=]>()?;
                    deserialize = Some(Some(input.parse::<LitStr>()?));
                } else {
                    deserialize = Some(None);
                }
            } else {
                return Err(
                    input.error("expected serialize = \"...\" or deserialize = \"...\" parameters")
                );
            }

            needs_punct = true;
        }

        Ok(Args {
            serialize,
            deserialize,
        })
    }
}

/// Creates archivable trait objects and registers implementations.
///
/// Prepend to trait definitions and implementations. For generic implementations, you may need to
/// manually register impls with the trait object system. See `register_impl` for more information.
///
/// See `ArchiveDyn` for usage information and examples.
///
/// # Parameters
///
/// - `serialize = "..."`: Chooses the name of the serialize trait. By default, it will be named
///   "Serialize" + your trait name.
/// - `deserialize`, `deserialize = "..."`: Adds deserialization support to the archived trait.
///   Similarly to the `name` parameter, you can choose the name of the deserialize trait and by
///   default it will be named "Deserialize" + your trait name.
#[proc_macro_attribute]
pub fn archive_dyn(
    attr: proc_macro::TokenStream,
    item: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    let input = parse_macro_input!(item as Input);

    let args = parse_macro_input!(attr as Args);

    let input_impl = match input {
        Input::Impl(ref input) => {
            if !input.generics.params.is_empty() {
                Error::new(input.generics.span(), "#[archive_dyn] can only register non-generic impls; call register_impl! with the concrete types to register and manually implement DeserializeDyn for archived types if necessary").to_compile_error()
            } else if let Some((_, ref trait_, _)) = input.trait_ {
                let ty = &input.self_ty;

                let mut serialize_trait = trait_.clone();
                let last = serialize_trait.segments.last_mut().unwrap();
                if let Some(ar_name) = args.serialize {
                    last.ident = Ident::new(&ar_name.value(), ar_name.span());
                } else {
                    last.ident = Ident::new(&format!("Serialize{}", last.ident), trait_.span());
                };

                let (deserialize_trait, deserialize_impl) = if let Some(deserialize) =
                    args.deserialize
                {
                    let mut deserialize_trait = trait_.clone();
                    let last = deserialize_trait.segments.last_mut().unwrap();
                    if let Some(ua_name) = deserialize {
                        last.ident = Ident::new(&ua_name.value(), ua_name.span());
                    } else {
                        last.ident =
                            Ident::new(&format!("Deserialize{}", last.ident), trait_.span());
                    };

                    (
                        deserialize_trait,
                        quote! {
                            impl DeserializeDyn<dyn #serialize_trait> for Archived<#ty>
                            where
                                Archived<#ty>: for<'a> Deserialize<#ty, (dyn DynDeserializer + 'a)>,
                            {
                                unsafe fn deserialize_dyn(&self, deserializer: &mut dyn DynDeserializer, alloc: &mut dyn FnMut(Layout) -> *mut u8) -> Result<*mut (), DynError> {
                                    let result = alloc(core::alloc::Layout::new::<#ty>()).cast::<#ty>();
                                    assert!(!result.is_null());
                                    result.write(self.deserialize(deserializer)?);
                                    Ok(result as *mut ())
                                }

                                fn deserialize_dyn_metadata(&self, deserializer: &mut dyn DynDeserializer) -> Result<<dyn #serialize_trait as ptr_meta::Pointee>::Metadata, DynError> {
                                    unsafe {
                                        Ok(core::mem::transmute(
                                            ptr_meta::metadata(core::ptr::null::<#ty>() as *const dyn #serialize_trait)
                                        ))
                                    }
                                }
                            }
                        },
                    )
                } else {
                    (trait_.clone(), quote! {})
                };

                quote! {
                    #input

                    const _: () = {
                        use core::alloc::{Layout, LayoutError};
                        use rkyv::{
                            Archived,
                            Deserialize,
                        };
                        use rkyv_dyn::{
                            DeserializeDyn,
                            DynDeserializer,
                            DynError,
                        };

                        rkyv_dyn::register_impl!(Archived<#ty> as dyn #deserialize_trait);

                        #deserialize_impl
                    };
                }
            } else {
                Error::new(
                    input.span(),
                    "#[archive_dyn] is only valid on trait implementations",
                )
                .to_compile_error()
            }
        }
        Input::Trait(input) => {
            let vis = &input.vis;

            let generic_params = input.generics.params.iter().map(|p| quote! { #p });
            let generic_params = quote! { #(#generic_params),* };

            let generic_args = input.generics.type_params().map(|p| {
                let name = &p.ident;
                quote! { #name }
            });
            let generic_args = quote! { #(#generic_args),* };

            let name = &input.ident;
            let serialize_trait = args
                .serialize
                .map(|ar_name| Ident::new(&ar_name.value(), ar_name.span()))
                .unwrap_or_else(|| Ident::new(&format!("Serialize{}", name), name.span()));

            let type_name_wheres = input.generics.type_params().map(|p| {
                let name = &p.ident;
                quote! { #name: TypeName }
            });
            let type_name_wheres = quote! { #(#type_name_wheres,)* };

            let (deserialize_trait, deserialize_trait_def, deserialize_trait_impl, pointee_input) =
                if let Some(deserialize) = args.deserialize {
                    let deserialize_trait = if let Some(ua_name) = deserialize {
                        Ident::new(&ua_name.value(), ua_name.span())
                    } else {
                        Ident::new(&format!("Deserialize{}", name), name.span())
                    };

                    (
                        deserialize_trait.clone(),
                        quote! {
                            #[ptr_meta::pointee]
                            #vis trait #deserialize_trait<#generic_params>: #name<#generic_args> + rkyv_dyn::DeserializeDyn<dyn #serialize_trait<#generic_args>> {}
                        },
                        quote! {
                            impl<__T: #name<#generic_args> + DeserializeDyn<dyn #serialize_trait<#generic_args>>, #generic_params> #deserialize_trait<#generic_args> for __T {}

                            impl<__D: Fallible + ?Sized, #generic_params> DeserializeUnsized<dyn #serialize_trait<#generic_args>, __D> for dyn #deserialize_trait<#generic_args> {
                                unsafe fn deserialize_unsized(&self, mut deserializer: &mut __D, mut alloc: impl FnMut(Layout) -> *mut u8) -> Result<*mut (), __D::Error> {
                                    self.deserialize_dyn(&mut deserializer, &mut alloc).map_err(|e| *e.downcast().unwrap())
                                }

                                fn deserialize_metadata(&self, mut deserializer: &mut __D) -> Result<<dyn #serialize_trait<#generic_args> as ptr_meta::Pointee>::Metadata, __D::Error> {
                                    self.deserialize_dyn_metadata(&mut deserializer).map_err(|e| *e.downcast().unwrap())
                                }
                            }
                        },
                        quote! {},
                    )
                } else {
                    (
                        name.clone(),
                        quote! {},
                        quote! {},
                        quote! { #[ptr_meta::pointee] },
                    )
                };

            let build_type_name = if !input.generics.params.is_empty() {
                let dyn_name = format!("dyn {}<", deserialize_trait);
                let mut results = input.generics.type_params().map(|p| {
                    let name = &p.ident;
                    quote! { #name::build_type_name(&mut f) }
                });
                let first = results.next().unwrap();
                quote! {
                    f(#dyn_name);
                    #first;
                    #(f(", "); #results;)*
                    f(">");
                }
            } else {
                quote! { f(stringify!(dyn #deserialize_trait)); }
            };

            #[cfg(feature = "validation")]
            let validation_impl = quote! {
                use bytecheck::CheckBytes;
                use rkyv::validation::LayoutRaw;
                use rkyv_dyn::validation::{CHECK_BYTES_REGISTRY, CheckDynError, DynContext};

                impl<#generic_params> LayoutRaw for (dyn #deserialize_trait<#generic_args> + '_) {
                    fn layout_raw(metadata: <Self as ptr_meta::Pointee>::Metadata) -> Result<Layout, LayoutError> {
                        Ok(metadata.layout())
                    }
                }

                impl<#generic_params> CheckBytes<dyn DynContext + '_> for (dyn #deserialize_trait<#generic_args> + '_) {
                    type Error = CheckDynError;

                    #[inline]
                    unsafe fn check_bytes<'a>(value: *const Self, context: &mut (dyn DynContext + '_)) -> Result<&'a Self, Self::Error> {
                        let vtable = core::mem::transmute(ptr_meta::metadata(value));
                        if let Some(validation) = CHECK_BYTES_REGISTRY.get(vtable) {
                            (validation.check_bytes_dyn)(value.cast(), context)?;
                            Ok(&*value)
                        } else {
                            Err(CheckDynError::InvalidMetadata(vtable as usize as u64))
                        }
                    }
                }

                impl<__C: DynContext, #generic_params> CheckBytes<__C> for (dyn #deserialize_trait<#generic_args> + '_) {
                    type Error = CheckDynError;

                    #[inline]
                    unsafe fn check_bytes<'a>(value: *const Self, context: &mut __C) -> Result<&'a Self, Self::Error> {
                        Self::check_bytes(value, context as &mut dyn DynContext)
                    }
                }
            };

            #[cfg(not(feature = "validation"))]
            let validation_impl = quote! {};

            quote! {
                #pointee_input
                #input

                #[ptr_meta::pointee]
                #vis trait #serialize_trait<#generic_params>: #name<#generic_args> + rkyv_dyn::SerializeDyn {}

                #deserialize_trait_def

                const _: ()  = {
                    use core::alloc::{Layout, LayoutError};
                    use rkyv::{
                        ser::{ScratchSpace, Serializer},
                        Archive,
                        Archived,
                        ArchivedMetadata,
                        ArchivePointee,
                        ArchiveUnsized,
                        DeserializeUnsized,
                        Fallible,
                        SerializeUnsized,
                    };
                    use rkyv_dyn::{
                        ArchivedDynMetadata,
                        DynDeserializer,
                        RegisteredImpl,
                        SerializeDyn,
                        DeserializeDyn,
                        DynSerializer,
                    };
                    use rkyv_typename::TypeName;

                    impl<__T: Archive + SerializeDyn + #name<#generic_args>, #generic_params> #serialize_trait<#generic_args> for __T
                    where
                        __T::Archived: RegisteredImpl<dyn #deserialize_trait<#generic_args>>
                    {}

                    #deserialize_trait_impl

                    impl<#generic_params> TypeName for dyn #deserialize_trait<#generic_args> + '_
                    where
                        #type_name_wheres
                    {
                        fn build_type_name<F: FnMut(&str)>(mut f: F) {
                            #build_type_name
                        }
                    }

                    impl<#generic_params> ArchiveUnsized for dyn #serialize_trait<#generic_args> {
                        type Archived = dyn #deserialize_trait<#generic_args>;
                        type MetadataResolver = ();

                        unsafe fn resolve_metadata(&self, _: usize, _: Self::MetadataResolver, out: *mut ArchivedMetadata<Self>) {
                            ArchivedDynMetadata::emplace(self.archived_type_id(), out);
                        }
                    }

                    impl<#generic_params> ArchivePointee for dyn #deserialize_trait<#generic_args> {
                        type ArchivedMetadata = ArchivedDynMetadata<Self>;

                        fn pointer_metadata(archived: &Self::ArchivedMetadata) -> <Self as ptr_meta::Pointee>::Metadata {
                            archived.pointer_metadata()
                        }
                    }

                    impl<__S: ScratchSpace + Serializer + ?Sized, #generic_params> SerializeUnsized<__S> for dyn #serialize_trait<#generic_args> {
                        fn serialize_unsized(&self, mut serializer: &mut __S) -> Result<usize, __S::Error> {
                            self.serialize_dyn(&mut serializer).map_err(|e| *e.downcast::<__S::Error>().unwrap())
                        }

                        fn serialize_metadata(&self, _: &mut __S) -> Result<Self::MetadataResolver, __S::Error> {
                            Ok(())
                        }
                    }

                    #validation_impl
                };
            }
        }
    };

    proc_macro::TokenStream::from(input_impl)
}