use proc_macro2::{Ident, Span, TokenStream};
use quote::quote;
use syn::DeriveInput;

use crate::{
    ffiops,
    util::{
        create_metadata_items, either_attribute_arg, extract_docstring, ident_to_string, kw,
        mod_path, wasm_single_threaded_annotation, AttributeSliceExt, UniffiAttributeArgs,
    },
    DeriveOptions,
};
use syn::{parse::ParseStream, LitStr, Token};
use uniffi_meta::ObjectImpl;

/// Handle #[uniffi(...)] attributes for objects
#[derive(Clone, Default)]
pub struct ObjectAttr {
    pub name: Option<String>,
}

impl UniffiAttributeArgs for ObjectAttr {
    fn parse_one(input: ParseStream<'_>) -> syn::Result<Self> {
        let lookahead = input.lookahead1();
        if lookahead.peek(kw::name) {
            let _: kw::name = input.parse()?;
            let _: Token![=] = input.parse()?;
            let name = Some(input.parse::<LitStr>()?.value());
            Ok(Self { name })
        } else {
            Err(syn::Error::new(
                input.span(),
                format!("attribute `{input}` is not supported here."),
            ))
        }
    }

    fn merge(self, other: Self) -> syn::Result<Self> {
        Ok(Self {
            name: either_attribute_arg(self.name, other.name)?,
        })
    }
}

/// Stores parsed data from the Derive Input for the struct/enum.
struct ObjectItem {
    ident: Ident,
    docstring: String,
    attr: ObjectAttr,
}

impl ObjectItem {
    fn new(input: DeriveInput) -> syn::Result<Self> {
        let attr = input.attrs.parse_uniffi_attr_args::<ObjectAttr>()?;
        Ok(Self {
            ident: input.ident,
            docstring: extract_docstring(&input.attrs)?,
            attr,
        })
    }

    fn ident(&self) -> &Ident {
        &self.ident
    }

    fn name(&self) -> String {
        ident_to_string(&self.ident)
    }

    fn foreign_name(&self) -> String {
        match &self.attr.name {
            Some(name) => name.clone(),
            None => self.name(),
        }
    }

    fn docstring(&self) -> &str {
        self.docstring.as_str()
    }
}

pub fn expand_object(input: DeriveInput, options: DeriveOptions) -> syn::Result<TokenStream> {
    let module_path = mod_path()?;
    let object = ObjectItem::new(input)?;
    let name = &object.foreign_name();
    let ident = object.ident();
    let clone_fn_ident = Ident::new(
        &uniffi_meta::clone_fn_symbol_name(&module_path, name),
        Span::call_site(),
    );
    let free_fn_ident = Ident::new(
        &uniffi_meta::free_fn_symbol_name(&module_path, name),
        Span::call_site(),
    );
    let meta_static_var = options.generate_metadata.then(|| {
        interface_meta_static_var(name, ObjectImpl::Struct, object.docstring())
            .unwrap_or_else(syn::Error::into_compile_error)
    });
    let interface_impl = interface_impl(&object, &options);

    Ok(quote! {
        #[doc(hidden)]
        #[unsafe(no_mangle)]
        pub unsafe extern "C" fn #clone_fn_ident(
            handle: ::uniffi::ffi::Handle,
            call_status: &mut ::uniffi::RustCallStatus
        ) -> ::uniffi::ffi::Handle {
            ::uniffi::deps::trace!("clone: {} ({:?})", #name, handle);
            ::uniffi::rust_call(call_status, || {
                unsafe {
                    handle.clone_arc_handle::<#ident>()
                };
                ::std::result::Result::Ok(handle)
            })
        }

        #[doc(hidden)]
        #[unsafe(no_mangle)]
        pub unsafe extern "C" fn #free_fn_ident(
            handle: ::uniffi::ffi::Handle,
            call_status: &mut ::uniffi::RustCallStatus
        ) {
            ::uniffi::deps::trace!("free: {} ({:?})", #name, handle);
            ::uniffi::rust_call(call_status, || {
                ::std::mem::drop(unsafe {
                    handle.into_arc::<#ident>()
                });
                ::std::result::Result::Ok(())
            });
        }

        #interface_impl
        #meta_static_var
    })
}

fn interface_impl(object: &ObjectItem, options: &DeriveOptions) -> TokenStream {
    let name = object.foreign_name();
    let ident = object.ident();
    let impl_spec = options.ffi_impl_header("FfiConverterArc", ident);
    let lower_return_impl_spec = options.ffi_impl_header("LowerReturn", ident);
    let lower_error_impl_spec = options.ffi_impl_header("LowerError", ident);
    let type_id_impl_spec = options.ffi_impl_header("TypeId", ident);
    let lift_ref_impl_spec = options.ffi_impl_header("LiftRef", ident);
    let arc_self_type = quote! { ::std::sync::Arc<Self> };
    let lower_arc = ffiops::lower(&arc_self_type);
    let type_id_meta_arc = ffiops::type_id_meta(&arc_self_type);
    let try_lift_arc = ffiops::try_lift(&arc_self_type);
    let lower_return_type_arc = ffiops::lower_return_type(&arc_self_type);
    let lower_return_arc = ffiops::lower_return(&arc_self_type);
    let lower_error_arc = ffiops::lower_error(&arc_self_type);
    let single_threaded_annotation = wasm_single_threaded_annotation();

    quote! {
        // All Object structs must be `Sync + Send`. The generated scaffolding will fail to compile
        // if they are not, but unfortunately it fails with an unactionably obscure error message.
        // By asserting the requirement explicitly, we help Rust produce a more scrutable error message
        // and thus help the user debug why the requirement isn't being met.
        #single_threaded_annotation
        ::uniffi::deps::static_assertions::assert_impl_all!(
            #ident: ::core::marker::Sync, ::core::marker::Send
        );

        // We're going to be casting raw pointers to `u64` values to pass them across the FFI.
        // Ensure that we're not on some 128-bit machine where this would overflow.
        ::uniffi::deps::static_assertions::const_assert!(::std::mem::size_of::<*const ()>() <= 8);

        #[doc(hidden)]
        #[automatically_derived]
        /// Support for passing reference-counted shared objects via the FFI.
        ///
        /// To avoid dealing with complex lifetime semantics over the FFI, any data passed
        /// by reference must be encapsulated in an `Arc`, and must be safe to share
        /// across threads.
        unsafe #impl_spec {
            type FfiType = ::uniffi::ffi::Handle;

            /// When lowering, we have an owned `Arc` and we transfer that ownership
            /// to the foreign-language code, "leaking" it out of Rust's ownership system
            /// as a raw pointer. This works safely because we have unique ownership of `self`.
            /// The foreign-language code is responsible for freeing this by calling the
            /// `ffi_object_free` FFI function provided by the corresponding UniFFI type.
            ///
            /// Safety: when freeing the resulting pointer, the foreign-language code must
            /// call the destructor function specific to the type `T`. Calling the destructor
            /// function for other types may lead to undefined behaviour.
            fn lower(obj: ::std::sync::Arc<Self>) -> Self::FfiType {
                ::uniffi::deps::trace!("lower: {} {:?}", #name, ::std::sync::Arc::as_ptr(&obj));
                let handle = ::uniffi::ffi::Handle::from_arc(obj);
                handle
            }

            /// When lifting, we receive an owned `Arc` that the foreign language code cloned.
            fn try_lift(handle: Self::FfiType) -> ::uniffi::Result<::std::sync::Arc<Self>> {
                ::uniffi::deps::trace!("lift: {} ({:?})", #name, handle);
                ::std::result::Result::Ok(unsafe { handle.into_arc() })
            }

            /// When writing as a field of a complex structure, make a clone and transfer ownership
            /// of it to the foreign-language code by writing its pointer into the buffer.
            /// The foreign-language code is responsible for freeing this by calling the
            /// `ffi_object_free` FFI function provided by the corresponding UniFFI type.
            ///
            /// Safety: when freeing the resulting pointer, the foreign-language code must
            /// call the destructor function specific to the type `T`. Calling the destructor
            /// function for other types may lead to undefined behaviour.
            fn write(obj: ::std::sync::Arc<Self>, buf: &mut ::std::vec::Vec<u8>) {
                ::uniffi::deps::bytes::BufMut::put_u64(buf, #lower_arc(obj).as_raw());
            }

            /// When reading as a field of a complex structure, we receive a "borrow" of the `Arc`
            /// that is owned by the foreign-language code, and make a clone for our own use.
            ///
            /// Safety: the buffer must contain a pointer previously obtained by calling
            /// the `lower()` or `write()` method of this impl.
            fn try_read(buf: &mut &[u8]) -> ::uniffi::Result<::std::sync::Arc<Self>> {
                ::uniffi::check_remaining(buf, 8)?;
                #try_lift_arc(::uniffi::ffi::Handle::from_raw_unchecked(::uniffi::deps::bytes::Buf::get_u64(buf)))
            }

            const TYPE_ID_META: ::uniffi::MetadataBuffer = ::uniffi::MetadataBuffer::from_code(::uniffi::metadata::codes::TYPE_INTERFACE)
                .concat_str(module_path!())
                .concat_str(#name);
        }

        unsafe #lower_return_impl_spec {
            type ReturnType = #lower_return_type_arc;

            fn lower_return(obj: Self) -> ::std::result::Result<Self::ReturnType, ::uniffi::RustCallError> {
                #lower_return_arc(::std::sync::Arc::new(obj))
            }
        }

        unsafe #lower_error_impl_spec {
            fn lower_error(obj: Self) -> ::uniffi::RustBuffer {
                #lower_error_arc(::std::sync::Arc::new(obj))
            }
        }

        unsafe #lift_ref_impl_spec {
            type LiftType = ::std::sync::Arc<Self>;
        }

        #type_id_impl_spec {
            const TYPE_ID_META: ::uniffi::MetadataBuffer = #type_id_meta_arc;
        }
    }
}

pub(crate) fn interface_meta_static_var(
    name: &str,
    imp: ObjectImpl,
    docstring: &str,
) -> syn::Result<TokenStream> {
    let code = match imp {
        ObjectImpl::Struct => quote! { ::uniffi::metadata::codes::INTERFACE },
        ObjectImpl::Trait => quote! { ::uniffi::metadata::codes::TRAIT_INTERFACE },
        ObjectImpl::CallbackTrait => quote! { ::uniffi::metadata::codes::CALLBACK_TRAIT_INTERFACE },
    };

    Ok(create_metadata_items(
        "interface",
        name,
        quote! {
            ::uniffi::MetadataBuffer::from_code(#code)
                .concat_str(module_path!())
                .concat_str(#name)
                .concat_long_str(#docstring)
        },
        None,
    ))
}