// This file is part of Substrate.

// Copyright (C) 2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use syn::spanned::Spanned;

/// Derive Clone but do not bound any generic.
pub fn derive_default_no_bound(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
	let input: syn::DeriveInput = match syn::parse(input) {
		Ok(input) => input,
		Err(e) => return e.to_compile_error().into(),
	};

	let name = &input.ident;
	let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

	let impl_ = match input.data {
		syn::Data::Struct(struct_) => match struct_.fields {
			syn::Fields::Named(named) => {
				let fields = named.named.iter()
					.map(|i| &i.ident)
					.map(|i| quote::quote_spanned!(i.span() =>
						#i: core::default::Default::default()
					));

				quote::quote!( Self { #( #fields, )* } )
			},
			syn::Fields::Unnamed(unnamed) => {
				let fields = unnamed.unnamed.iter().enumerate()
					.map(|(i, _)| syn::Index::from(i))
					.map(|i| quote::quote_spanned!(i.span() =>
						core::default::Default::default()
					));

				quote::quote!( Self ( #( #fields, )* ) )
			},
			syn::Fields::Unit => {
				quote::quote!( Self )
			}
		},
		syn::Data::Enum(enum_) => {
			if let Some(first_variant) = enum_.variants.first() {
				let variant_ident = &first_variant.ident;
				match &first_variant.fields {
					syn::Fields::Named(named) => {
						let fields = named.named.iter()
							.map(|i| &i.ident)
							.map(|i| quote::quote_spanned!(i.span() =>
								#i: core::default::Default::default()
							));

						quote::quote!( #name :: #ty_generics :: #variant_ident { #( #fields, )* } )
					},
					syn::Fields::Unnamed(unnamed) => {
						let fields = unnamed.unnamed.iter().enumerate()
							.map(|(i, _)| syn::Index::from(i))
							.map(|i| quote::quote_spanned!(i.span() =>
								core::default::Default::default()
							));

						quote::quote!( #name :: #ty_generics :: #variant_ident ( #( #fields, )* ) )
					},
					syn::Fields::Unit => quote::quote!( #name :: #ty_generics :: #variant_ident ),
				}
			} else {
				quote::quote!( Self )
			}

		},
		syn::Data::Union(_) => {
			let msg = "Union type not supported by `derive(CloneNoBound)`";
			return syn::Error::new(input.span(), msg).to_compile_error().into()
		},
	};

	quote::quote!(
		const _: () = {
			impl #impl_generics core::default::Default for #name #ty_generics #where_clause {
				fn default() -> Self {
					#impl_
				}
			}
		};
	).into()
}