// This file is part of Substrate.

// Copyright (C) 2018-2022 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.

//! Macros that define an Event types. Events can be used to easily report changes or conditions
//! in your runtime to external entities like users, chain explorers, or dApps.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

/// Implement the `Event` for a module.
///
/// # Simple Event Example:
///
/// ```rust
/// frame_support::decl_event!(
///    pub enum Event {
///       Success,
///       Failure(String),
///    }
/// );
///
/// # fn main() {}
/// ```
///
/// # Generic Event Example:
///
/// ```rust
/// trait Config {
///     type Balance;
///     type Token;
/// }
///
/// mod event1 {
///     // Event that specifies the generic parameter explicitly (`Balance`).
///     frame_support::decl_event!(
///        pub enum Event<T> where Balance = <T as super::Config>::Balance {
///           Message(Balance),
///        }
///     );
/// }
///
/// mod event2 {
///     // Event that uses the generic parameter `Balance`.
///     // If no name for the generic parameter is specified explicitly,
///     // the name will be taken from the type name of the trait.
///     frame_support::decl_event!(
///        pub enum Event<T> where <T as super::Config>::Balance {
///           Message(Balance),
///        }
///     );
/// }
///
/// mod event3 {
///     // And we even support declaring multiple generic parameters!
///     frame_support::decl_event!(
///        pub enum Event<T> where <T as super::Config>::Balance, <T as super::Config>::Token {
///           Message(Balance, Token),
///        }
///     );
/// }
///
/// # fn main() {}
/// ```
///
/// The syntax for generic events requires the `where`.
///
/// # Generic Event with Instance Example:
///
/// ```rust
/// # struct DefaultInstance;
/// # trait Instance {}
/// # impl Instance for DefaultInstance {}
/// trait Config<I: Instance=DefaultInstance> {
///     type Balance;
///     type Token;
/// }
///
/// // For module with instances, DefaultInstance is optional
/// frame_support::decl_event!(
///    pub enum Event<T, I: Instance = DefaultInstance> where
///       <T as Config>::Balance,
///       <T as Config>::Token
///    {
///       Message(Balance, Token),
///    }
/// );
/// # fn main() {}
/// ```
#[macro_export]
macro_rules! decl_event {
	(
		$(#[$attr:meta])*
		pub enum Event<$evt_generic_param:ident $(, $instance:ident $(: $instantiable:ident)? $( = $event_default_instance:path)? )?> where
			$( $tt:tt )*
	) => {
		$crate::__decl_generic_event!(
			$( #[ $attr ] )*;
			$evt_generic_param;
			$($instance $( = $event_default_instance)? )?;
			{ $( $tt )* };
		);
	};
	(
		$(#[$attr:meta])*
		pub enum Event {
			$(
				$events:tt
			)*
		}
	) => {
		// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
		#[derive(
			Clone, PartialEq, Eq,
			$crate::codec::Encode,
			$crate::codec::Decode,
			$crate::scale_info::TypeInfo,
			$crate::RuntimeDebug,
		)]
		#[scale_info(capture_docs = "always")]
		/// Events for this module.
		///
		$(#[$attr])*
		pub enum Event {
			$(
				$events
			)*
		}
		impl From<Event> for () {
			fn from(_: Event) -> () { () }
		}
	}
}

#[macro_export]
#[doc(hidden)]
// This parsing to retrieve last ident on unnamed generic could be improved.
// but user can still name it if the parsing fails. And improving parsing seems difficult.
macro_rules! __decl_generic_event {
	(
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $( $tt:tt )* };
	) => {
		$crate::__decl_generic_event!(@format_generic
			$( #[ $attr ] )*;
			$event_generic_param;
			$($instance $( = $event_default_instance)? )?;
			{ $( $tt )* };
			{};
		);
	};
	// Finish formatting on an unnamed one
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ <$generic:ident as $trait:path>::$trait_type:ident $(,)? { $( $events:tt )* } };
		{$( $parsed:tt)*};
	) => {
		$crate::__decl_generic_event!(@generate
			$( #[ $attr ] )*;
			$event_generic_param;
			$($instance $( = $event_default_instance)? )?;
			{ $($events)* };
			{ $($parsed)*, $trait_type = <$generic as $trait>::$trait_type };
		);
	};
	// Finish formatting on a named one
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $generic_rename:ident = $generic_type:ty $(,)? { $( $events:tt )* } };
		{ $($parsed:tt)* };
	) => {
		$crate::__decl_generic_event!(@generate
			$(#[$attr])*;
			$event_generic_param;
			$($instance $( = $event_default_instance)? )?;
			{ $($events)* };
			{ $($parsed)*, $generic_rename = $generic_type };
		);
	};
	// Parse named
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $generic_rename:ident = $generic_type:ty, $($rest:tt)* };
		{$( $parsed:tt)*};
	) => {
		$crate::__decl_generic_event!(@format_generic
			$( #[ $attr ] )*;
			$event_generic_param;
			$( $instance $( = $event_default_instance)? )?;
			{ $($rest)* };
			{ $($parsed)*, $generic_rename = $generic_type };
		);
	};
	// Parse unnamed
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ <$generic:ident as $trait:path>::$trait_type:ident, $($rest:tt)* };
		{$($parsed:tt)*};
	) => {
		$crate::__decl_generic_event!(@format_generic
			$( #[ $attr ] )*;
			$event_generic_param;
			$($instance $( = $event_default_instance)? )?;
			{ $($rest)* };
			{ $($parsed)*, $trait_type = <$generic as $trait>::$trait_type };
		);
	};
	// Unnamed type can't be parsed
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $generic_type:ty, $($rest:tt)* };
		{ $($parsed:tt)* };
	) => {
		$crate::__decl_generic_event!(@cannot_parse $generic_type);
	};
	// Final unnamed type can't be parsed
	(@format_generic
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $generic_type:ty { $( $events:tt )* } };
		{$( $parsed:tt)*};
	) => {
		$crate::__decl_generic_event!(@cannot_parse $generic_type);
	};
	(@generate
		$(#[$attr:meta])*;
		$event_generic_param:ident;
		$($instance:ident $( = $event_default_instance:path)? )?;
		{ $( $events:tt )* };
		{ ,$( $generic_param:ident = $generic_type:ty ),* };
	) => {
		/// [`RawEvent`] specialized for the configuration [`Config`]
		///
		/// [`RawEvent`]: enum.RawEvent.html
		/// [`Config`]: trait.Config.html
		pub type Event<$event_generic_param $(, $instance $( = $event_default_instance)? )?> = RawEvent<$( $generic_type ),* $(, $instance)? >;

		#[derive(
			Clone, PartialEq, Eq,
			$crate::codec::Encode,
			$crate::codec::Decode,
			$crate::scale_info::TypeInfo,
			$crate::RuntimeDebug,
		)]
		#[scale_info(capture_docs = "always")]
		/// Events for this module.
		///
		$(#[$attr])*
		pub enum RawEvent<$( $generic_param ),* $(, $instance)? > {
			$(
				$events
			)*
			$(
				#[doc(hidden)]
				#[codec(skip)]
				PhantomData($crate::sp_std::marker::PhantomData<$instance>),
			)?
		}
		impl<$( $generic_param ),* $(, $instance)? > From<RawEvent<$( $generic_param ),* $(, $instance)?>> for () {
			fn from(_: RawEvent<$( $generic_param ),* $(, $instance)?>) -> () { () }
		}
	};
	(@cannot_parse $ty:ty) => {
		compile_error!(concat!("The type `", stringify!($ty), "` can't be parsed as an unnamed one, please name it `Name = ", stringify!($ty), "`"));
	}
}
