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// This file is part of Substrate.

// Copyright (C) 2020-2021 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 crate::pallet::Def;

struct ConstDef {
	/// Name of the associated type.
	pub ident: syn::Ident,
	/// The type in Get, e.g. `u32` in `type Foo: Get<u32>;`, but `Self` is replaced by `T`
	pub type_: syn::Type,
	/// The doc associated
	pub doc: Vec<syn::Lit>,
	/// default_byte implementation
	pub default_byte_impl: proc_macro2::TokenStream,
	/// Constant name for Metadata (optional)
	pub metadata_name: Option<syn::Ident>,
}

///
/// * Impl fn module_constant_metadata for pallet.
pub fn expand_constants(def: &mut Def) -> proc_macro2::TokenStream {
	let frame_support = &def.frame_support;
	let type_impl_gen = &def.type_impl_generics(proc_macro2::Span::call_site());
	let type_use_gen = &def.type_use_generics(proc_macro2::Span::call_site());
	let pallet_ident = &def.pallet_struct.pallet;
	let trait_use_gen = &def.trait_use_generics(proc_macro2::Span::call_site());

	let mut where_clauses = vec![&def.config.where_clause];
	where_clauses.extend(def.extra_constants.iter().map(|d| &d.where_clause));
	let completed_where_clause = super::merge_where_clauses(&where_clauses);

	let config_consts = def.config.consts_metadata.iter().map(|const_| {
		let ident = &const_.ident;
		let const_type = &const_.type_;

		ConstDef {
			ident: const_.ident.clone(),
			type_: const_.type_.clone(),
			doc: const_.doc.clone(),
			default_byte_impl: quote::quote!(
				let value = <<T as Config #trait_use_gen>::#ident as
					#frame_support::traits::Get<#const_type>>::get();
				#frame_support::codec::Encode::encode(&value)
			),
			metadata_name: None,
		}
	});

	let extra_consts = def.extra_constants.iter().flat_map(|d| &d.extra_constants).map(|const_| {
		let ident = &const_.ident;

		ConstDef {
			ident: const_.ident.clone(),
			type_: const_.type_.clone(),
			doc: const_.doc.clone(),
			default_byte_impl: quote::quote!(
				let value = <Pallet<#type_use_gen>>::#ident();
				#frame_support::codec::Encode::encode(&value)
			),
			metadata_name: const_.metadata_name.clone(),
		}
	});

	let consts = config_consts.chain(extra_consts).map(|const_| {
		let const_type = &const_.type_;
		let ident_str = format!("{}", const_.metadata_name.unwrap_or(const_.ident));

		let doc = const_.doc.clone().into_iter();
		let default_byte_impl = &const_.default_byte_impl;

		quote::quote!({
			#frame_support::metadata::PalletConstantMetadata {
				name: #ident_str,
				ty: #frame_support::scale_info::meta_type::<#const_type>(),
				value: { #default_byte_impl },
				docs: #frame_support::sp_std::vec![ #( #doc ),* ],
			}
		})
	});

	quote::quote!(
		impl<#type_impl_gen> #pallet_ident<#type_use_gen> #completed_where_clause{

			#[doc(hidden)]
			pub fn pallet_constants_metadata()
				-> #frame_support::sp_std::vec::Vec<#frame_support::metadata::PalletConstantMetadata>
			{
				#frame_support::sp_std::vec![ #( #consts ),* ]
			}
		}
	)
}