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// Copyright 2020 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

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

//! A pallet for managing validators on Rococo.

use sp_staking::SessionIndex;
use sp_std::vec::Vec;

pub use pallet::*;

type Session<T> = pallet_session::Pallet<T>;

#[frame_support::pallet]
pub mod pallet {
	use super::*;
	use frame_support::{dispatch::DispatchResult, pallet_prelude::*, traits::EnsureOrigin};
	use frame_system::pallet_prelude::*;

	#[pallet::pallet]
	#[pallet::without_storage_info]
	pub struct Pallet<T>(_);

	/// Configuration for the parachain proposer.
	#[pallet::config]
	pub trait Config: frame_system::Config + pallet_session::Config {
		/// The overreaching event type.
		type Event: From<Event<Self>> + IsType<<Self as frame_system::Config>::Event>;

		/// Privileged origin that can add or remove validators.
		type PrivilegedOrigin: EnsureOrigin<<Self as frame_system::Config>::Origin>;
	}

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config> {
		/// New validators were added to the set.
		ValidatorsRegistered(Vec<T::ValidatorId>),
		/// Validators were removed from the set.
		ValidatorsDeregistered(Vec<T::ValidatorId>),
	}

	/// Validators that should be retired, because their Parachain was deregistered.
	#[pallet::storage]
	pub(crate) type ValidatorsToRetire<T: Config> =
		StorageValue<_, Vec<T::ValidatorId>, ValueQuery>;

	/// Validators that should be added.
	#[pallet::storage]
	pub(crate) type ValidatorsToAdd<T: Config> = StorageValue<_, Vec<T::ValidatorId>, ValueQuery>;

	#[pallet::call]
	impl<T: Config> Pallet<T> {
		/// Add new validators to the set.
		///
		/// The new validators will be active from current session + 2.
		#[pallet::weight(100_000)]
		pub fn register_validators(
			origin: OriginFor<T>,
			validators: Vec<T::ValidatorId>,
		) -> DispatchResult {
			T::PrivilegedOrigin::ensure_origin(origin)?;

			validators.clone().into_iter().for_each(|v| ValidatorsToAdd::<T>::append(v));

			Self::deposit_event(Event::ValidatorsRegistered(validators));
			Ok(())
		}

		/// Remove validators from the set.
		///
		/// The removed validators will be deactivated from current session + 2.
		#[pallet::weight(100_000)]
		pub fn deregister_validators(
			origin: OriginFor<T>,
			validators: Vec<T::ValidatorId>,
		) -> DispatchResult {
			T::PrivilegedOrigin::ensure_origin(origin)?;

			validators.clone().into_iter().for_each(|v| ValidatorsToRetire::<T>::append(v));

			Self::deposit_event(Event::ValidatorsDeregistered(validators));
			Ok(())
		}
	}
}

impl<T: Config> pallet_session::SessionManager<T::ValidatorId> for Pallet<T> {
	fn new_session(new_index: SessionIndex) -> Option<Vec<T::ValidatorId>> {
		if new_index <= 1 {
			return None
		}

		let mut validators = Session::<T>::validators();

		ValidatorsToRetire::<T>::take().iter().for_each(|v| {
			if let Some(pos) = validators.iter().position(|r| r == v) {
				validators.swap_remove(pos);
			}
		});

		ValidatorsToAdd::<T>::take().into_iter().for_each(|v| {
			if !validators.contains(&v) {
				validators.push(v);
			}
		});

		Some(validators)
	}

	fn end_session(_: SessionIndex) {}

	fn start_session(_start_index: SessionIndex) {}
}

impl<T: Config> pallet_session::historical::SessionManager<T::ValidatorId, ()> for Pallet<T> {
	fn new_session(new_index: SessionIndex) -> Option<Vec<(T::ValidatorId, ())>> {
		<Self as pallet_session::SessionManager<_>>::new_session(new_index)
			.map(|r| r.into_iter().map(|v| (v, Default::default())).collect())
	}

	fn start_session(start_index: SessionIndex) {
		<Self as pallet_session::SessionManager<_>>::start_session(start_index)
	}

	fn end_session(end_index: SessionIndex) {
		<Self as pallet_session::SessionManager<_>>::end_session(end_index)
	}
}