// This file is part of Substrate.

// Copyright (C) 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.

//! # Phragmén Election Module.
//!
//! An election module based on sequential phragmen.
//!
//! ### Term and Round
//!
//! The election happens in _rounds_: every `N` blocks, all previous members are retired and a new
//! set is elected (which may or may not have an intersection with the previous set). Each round
//! lasts for some number of blocks defined by [`Config::TermDuration`]. The words _term_ and
//! _round_ can be used interchangeably in this context.
//!
//! [`Config::TermDuration`] might change during a round. This can shorten or extend the length of
//! the round. The next election round's block number is never stored but rather always checked on
//! the fly. Based on the current block number and [`Config::TermDuration`], the condition
//! `BlockNumber % TermDuration == 0` being satisfied will always trigger a new election round.
//!
//! ### Bonds and Deposits
//!
//! Both voting and being a candidate requires deposits to be taken, in exchange for the data that
//! needs to be kept on-chain. The terms *bond* and *deposit* can be used interchangeably in this
//! context.
//!
//! Bonds will be unreserved only upon adhering to the protocol laws. Failing to do so will cause in
//! the bond to slashed.
//!
//! ### Voting
//!
//! Voters can vote for a limited number of the candidates by providing a list of account ids,
//! bounded by [`Config::MaxVotesPerVoter`]. Invalid votes (voting for non-candidates) and duplicate
//! votes are ignored during election. Yet, a voter _might_ vote for a future candidate. Voters
//! reserve a bond as they vote. Each vote defines a `value`. This amount is locked from the account
//! of the voter and indicates the weight of the vote. Voters can update their votes at any time by
//! calling `vote()` again. This can update the vote targets (which might update the deposit) or
//! update the vote's stake ([`Voter::stake`]). After a round, votes are kept and might still be
//! valid for further rounds. A voter is responsible for calling `remove_voter` once they are done
//! to have their bond back and remove the lock.
//!
//! See [`Call::vote`], [`Call::remove_voter`].
//!
//! ### Defunct Voter
//!
//! A voter is defunct once all of the candidates that they have voted for are not a valid candidate
//! (as seen further below, members and runners-up are also always candidates). Defunct voters can
//! be removed via a root call ([`Call::clean_defunct_voters`]). Upon being removed, their bond is
//! returned. This is an administrative operation and can be called only by the root origin in the
//! case of state bloat.
//!
//! ### Candidacy and Members
//!
//! Candidates also reserve a bond as they submit candidacy. A candidate can end up in one of the
//! below situations:
//!   - **Members**: A winner is kept as a _member_. They must still have a bond in reserve and they
//!     are automatically counted as a candidate for the next election. The number of desired
//!     members is set by [`Config::DesiredMembers`].
//!   - **Runner-up**: Runners-up are the best candidates immediately after the winners. The number
//!     of runners up to keep is set by [`Config::DesiredRunnersUp`]. Runners-up are used, in the
//!     same order as they are elected, as replacements when a candidate is kicked by
//!     [`Call::remove_member`], or when an active member renounces their candidacy. Runners are
//!     automatically counted as a candidate for the next election.
//!   - **Loser**: Any of the candidate who are not member/runner-up are left as losers. A loser
//!     might be an _outgoing member or runner-up_, meaning that they are an active member who
//!     failed to keep their spot. **An outgoing candidate/member/runner-up will always lose their
//!     bond**.
//!
//! #### Renouncing candidacy.
//!
//! All candidates, elected or not, can renounce their candidacy. A call to
//! [`Call::renounce_candidacy`] will always cause the candidacy bond to be refunded.
//!
//! Note that with the members being the default candidates for the next round and votes persisting
//! in storage, the election system is entirely stable given no further input. This means that if
//! the system has a particular set of candidates `C` and voters `V` that lead to a set of members
//! `M` being elected, as long as `V` and `C` don't remove their candidacy and votes, `M` will keep
//! being re-elected at the end of each round.
//!
//! ### Module Information
//!
//! - [`Config`]
//! - [`Call`]
//! - [`Module`]

#![cfg_attr(not(feature = "std"), no_std)]

use codec::{Decode, Encode};
use frame_support::{
	traits::{
		defensive_prelude::*, ChangeMembers, Contains, ContainsLengthBound, Currency, Get,
		InitializeMembers, LockIdentifier, LockableCurrency, OnUnbalanced, ReservableCurrency,
		SortedMembers, WithdrawReasons,
	},
	weights::Weight,
};
use log;
use scale_info::TypeInfo;
use sp_npos_elections::{ElectionResult, ExtendedBalance};
use sp_runtime::{
	traits::{Saturating, StaticLookup, Zero},
	DispatchError, Perbill, RuntimeDebug,
};
use sp_staking::currency_to_vote::CurrencyToVote;
use sp_std::{cmp::Ordering, prelude::*};

#[cfg(any(feature = "try-runtime", test))]
use sp_runtime::TryRuntimeError;

mod benchmarking;
pub mod weights;
pub use weights::WeightInfo;

/// All migrations.
pub mod migrations;

const LOG_TARGET: &str = "runtime::elections-phragmen";

type BalanceOf<T> =
	<<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance;
type NegativeImbalanceOf<T> = <<T as Config>::Currency as Currency<
	<T as frame_system::Config>::AccountId,
>>::NegativeImbalance;

/// An indication that the renouncing account currently has which of the below roles.
#[derive(Encode, Decode, Clone, PartialEq, RuntimeDebug, TypeInfo)]
pub enum Renouncing {
	/// A member is renouncing.
	Member,
	/// A runner-up is renouncing.
	RunnerUp,
	/// A candidate is renouncing, while the given total number of candidates exists.
	Candidate(#[codec(compact)] u32),
}

/// An active voter.
#[derive(Encode, Decode, Clone, RuntimeDebug, PartialEq, TypeInfo)]
pub struct Voter<AccountId, Balance> {
	/// The members being backed.
	pub votes: Vec<AccountId>,
	/// The amount of stake placed on this vote.
	pub stake: Balance,
	/// The amount of deposit reserved for this vote.
	///
	/// To be unreserved upon removal.
	pub deposit: Balance,
}

impl<AccountId, Balance: Default> Default for Voter<AccountId, Balance> {
	fn default() -> Self {
		Self { votes: vec![], stake: Default::default(), deposit: Default::default() }
	}
}

/// A holder of a seat as either a member or a runner-up.
#[derive(Encode, Decode, Clone, Default, RuntimeDebug, PartialEq, TypeInfo)]
pub struct SeatHolder<AccountId, Balance> {
	/// The holder.
	pub who: AccountId,
	/// The total backing stake.
	pub stake: Balance,
	/// The amount of deposit held on-chain.
	///
	/// To be unreserved upon renouncing, or slashed upon being a loser.
	pub deposit: Balance,
}

pub use pallet::*;

type AccountIdLookupOf<T> = <<T as frame_system::Config>::Lookup as StaticLookup>::Source;

#[frame_support::pallet]
pub mod pallet {
	use super::*;
	use frame_support::pallet_prelude::*;
	use frame_system::pallet_prelude::*;

	/// The current storage version.
	const STORAGE_VERSION: StorageVersion = StorageVersion::new(4);

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

	#[pallet::config]
	pub trait Config: frame_system::Config {
		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;

		/// Identifier for the elections-phragmen pallet's lock
		#[pallet::constant]
		type PalletId: Get<LockIdentifier>;

		/// The currency that people are electing with.
		type Currency: LockableCurrency<Self::AccountId, Moment = BlockNumberFor<Self>>
			+ ReservableCurrency<Self::AccountId>;

		/// What to do when the members change.
		type ChangeMembers: ChangeMembers<Self::AccountId>;

		/// What to do with genesis members
		type InitializeMembers: InitializeMembers<Self::AccountId>;

		/// Convert a balance into a number used for election calculation.
		/// This must fit into a `u64` but is allowed to be sensibly lossy.
		type CurrencyToVote: CurrencyToVote<BalanceOf<Self>>;

		/// How much should be locked up in order to submit one's candidacy.
		#[pallet::constant]
		type CandidacyBond: Get<BalanceOf<Self>>;

		/// Base deposit associated with voting.
		///
		/// This should be sensibly high to economically ensure the pallet cannot be attacked by
		/// creating a gigantic number of votes.
		#[pallet::constant]
		type VotingBondBase: Get<BalanceOf<Self>>;

		/// The amount of bond that need to be locked for each vote (32 bytes).
		#[pallet::constant]
		type VotingBondFactor: Get<BalanceOf<Self>>;

		/// Handler for the unbalanced reduction when a candidate has lost (and is not a runner-up)
		type LoserCandidate: OnUnbalanced<NegativeImbalanceOf<Self>>;

		/// Handler for the unbalanced reduction when a member has been kicked.
		type KickedMember: OnUnbalanced<NegativeImbalanceOf<Self>>;

		/// Number of members to elect.
		#[pallet::constant]
		type DesiredMembers: Get<u32>;

		/// Number of runners_up to keep.
		#[pallet::constant]
		type DesiredRunnersUp: Get<u32>;

		/// How long each seat is kept. This defines the next block number at which an election
		/// round will happen. If set to zero, no elections are ever triggered and the module will
		/// be in passive mode.
		#[pallet::constant]
		type TermDuration: Get<BlockNumberFor<Self>>;

		/// The maximum number of candidates in a phragmen election.
		///
		/// Warning: This impacts the size of the election which is run onchain. Chose wisely, and
		/// consider how it will impact `T::WeightInfo::election_phragmen`.
		///
		/// When this limit is reached no more candidates are accepted in the election.
		#[pallet::constant]
		type MaxCandidates: Get<u32>;

		/// The maximum number of voters to allow in a phragmen election.
		///
		/// Warning: This impacts the size of the election which is run onchain. Chose wisely, and
		/// consider how it will impact `T::WeightInfo::election_phragmen`.
		///
		/// When the limit is reached the new voters are ignored.
		#[pallet::constant]
		type MaxVoters: Get<u32>;

		/// Maximum numbers of votes per voter.
		///
		/// Warning: This impacts the size of the election which is run onchain. Chose wisely, and
		/// consider how it will impact `T::WeightInfo::election_phragmen`.
		#[pallet::constant]
		type MaxVotesPerVoter: Get<u32>;

		/// Weight information for extrinsics in this pallet.
		type WeightInfo: WeightInfo;
	}

	#[pallet::hooks]
	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
		/// What to do at the end of each block.
		///
		/// Checks if an election needs to happen or not.
		fn on_initialize(n: BlockNumberFor<T>) -> Weight {
			let term_duration = T::TermDuration::get();
			if !term_duration.is_zero() && (n % term_duration).is_zero() {
				Self::do_phragmen()
			} else {
				Weight::zero()
			}
		}

		fn integrity_test() {
			let block_weight = T::BlockWeights::get().max_block;
			// mind the order.
			let election_weight = T::WeightInfo::election_phragmen(
				T::MaxCandidates::get(),
				T::MaxVoters::get(),
				T::MaxVotesPerVoter::get() * T::MaxVoters::get(),
			);

			let to_seconds = |w: &Weight| {
				w.ref_time() as f32 /
					frame_support::weights::constants::WEIGHT_REF_TIME_PER_SECOND as f32
			};

			log::debug!(
				target: LOG_TARGET,
				"election weight {}s ({:?}) // chain's block weight {}s ({:?})",
				to_seconds(&election_weight),
				election_weight,
				to_seconds(&block_weight),
				block_weight,
			);
			assert!(
				election_weight.all_lt(block_weight),
				"election weight {}s ({:?}) will exceed a {}s chain's block weight ({:?}) (MaxCandidates {}, MaxVoters {}, MaxVotesPerVoter {} -- tweak these parameters)",
				election_weight,
				to_seconds(&election_weight),
				to_seconds(&block_weight),
				block_weight,
				T::MaxCandidates::get(),
				T::MaxVoters::get(),
				T::MaxVotesPerVoter::get(),
			);
		}

		#[cfg(feature = "try-runtime")]
		fn try_state(_n: BlockNumberFor<T>) -> Result<(), TryRuntimeError> {
			Self::do_try_state()
		}
	}

	#[pallet::call]
	impl<T: Config> Pallet<T> {
		/// Vote for a set of candidates for the upcoming round of election. This can be called to
		/// set the initial votes, or update already existing votes.
		///
		/// Upon initial voting, `value` units of `who`'s balance is locked and a deposit amount is
		/// reserved. The deposit is based on the number of votes and can be updated over time.
		///
		/// The `votes` should:
		///   - not be empty.
		///   - be less than the number of possible candidates. Note that all current members and
		///     runners-up are also automatically candidates for the next round.
		///
		/// If `value` is more than `who`'s free balance, then the maximum of the two is used.
		///
		/// The dispatch origin of this call must be signed.
		///
		/// ### Warning
		///
		/// It is the responsibility of the caller to **NOT** place all of their balance into the
		/// lock and keep some for further operations.
		#[pallet::call_index(0)]
		#[pallet::weight(
			T::WeightInfo::vote_more(votes.len() as u32)
			.max(T::WeightInfo::vote_less(votes.len() as u32))
			.max(T::WeightInfo::vote_equal(votes.len() as u32))
		)]
		pub fn vote(
			origin: OriginFor<T>,
			votes: Vec<T::AccountId>,
			#[pallet::compact] value: BalanceOf<T>,
		) -> DispatchResultWithPostInfo {
			let who = ensure_signed(origin)?;

			ensure!(
				votes.len() <= T::MaxVotesPerVoter::get() as usize,
				Error::<T>::MaximumVotesExceeded
			);
			ensure!(!votes.is_empty(), Error::<T>::NoVotes);

			let candidates_count = <Candidates<T>>::decode_len().unwrap_or(0);
			let members_count = <Members<T>>::decode_len().unwrap_or(0);
			let runners_up_count = <RunnersUp<T>>::decode_len().unwrap_or(0);

			// can never submit a vote of there are no members, and cannot submit more votes than
			// all potential vote targets.
			// addition is valid: candidates, members and runners-up will never overlap.
			let allowed_votes =
				candidates_count.saturating_add(members_count).saturating_add(runners_up_count);
			ensure!(!allowed_votes.is_zero(), Error::<T>::UnableToVote);
			ensure!(votes.len() <= allowed_votes, Error::<T>::TooManyVotes);

			ensure!(value > T::Currency::minimum_balance(), Error::<T>::LowBalance);

			// Reserve bond.
			let new_deposit = Self::deposit_of(votes.len());
			let Voter { deposit: old_deposit, .. } = <Voting<T>>::get(&who);
			match new_deposit.cmp(&old_deposit) {
				Ordering::Greater => {
					// Must reserve a bit more.
					let to_reserve = new_deposit - old_deposit;
					T::Currency::reserve(&who, to_reserve)
						.map_err(|_| Error::<T>::UnableToPayBond)?;
				},
				Ordering::Equal => {},
				Ordering::Less => {
					// Must unreserve a bit.
					let to_unreserve = old_deposit - new_deposit;
					let _remainder = T::Currency::unreserve(&who, to_unreserve);
					debug_assert!(_remainder.is_zero());
				},
			};

			// Amount to be locked up.
			let locked_stake = value.min(T::Currency::free_balance(&who));
			T::Currency::set_lock(T::PalletId::get(), &who, locked_stake, WithdrawReasons::all());

			Voting::<T>::insert(&who, Voter { votes, deposit: new_deposit, stake: locked_stake });
			Ok(None::<Weight>.into())
		}

		/// Remove `origin` as a voter.
		///
		/// This removes the lock and returns the deposit.
		///
		/// The dispatch origin of this call must be signed and be a voter.
		#[pallet::call_index(1)]
		#[pallet::weight(T::WeightInfo::remove_voter())]
		pub fn remove_voter(origin: OriginFor<T>) -> DispatchResult {
			let who = ensure_signed(origin)?;
			ensure!(Self::is_voter(&who), Error::<T>::MustBeVoter);
			Self::do_remove_voter(&who);
			Ok(())
		}

		/// Submit oneself for candidacy. A fixed amount of deposit is recorded.
		///
		/// All candidates are wiped at the end of the term. They either become a member/runner-up,
		/// or leave the system while their deposit is slashed.
		///
		/// The dispatch origin of this call must be signed.
		///
		/// ### Warning
		///
		/// Even if a candidate ends up being a member, they must call [`Call::renounce_candidacy`]
		/// to get their deposit back. Losing the spot in an election will always lead to a slash.
		///
		/// The number of current candidates must be provided as witness data.
		/// ## Complexity
		/// O(C + log(C)) where C is candidate_count.
		#[pallet::call_index(2)]
		#[pallet::weight(T::WeightInfo::submit_candidacy(*candidate_count))]
		pub fn submit_candidacy(
			origin: OriginFor<T>,
			#[pallet::compact] candidate_count: u32,
		) -> DispatchResult {
			let who = ensure_signed(origin)?;

			let actual_count = <Candidates<T>>::decode_len().unwrap_or(0) as u32;
			ensure!(actual_count <= candidate_count, Error::<T>::InvalidWitnessData);
			ensure!(
				actual_count <= <T as Config>::MaxCandidates::get(),
				Error::<T>::TooManyCandidates
			);

			let index = Self::is_candidate(&who).err().ok_or(Error::<T>::DuplicatedCandidate)?;

			ensure!(!Self::is_member(&who), Error::<T>::MemberSubmit);
			ensure!(!Self::is_runner_up(&who), Error::<T>::RunnerUpSubmit);

			T::Currency::reserve(&who, T::CandidacyBond::get())
				.map_err(|_| Error::<T>::InsufficientCandidateFunds)?;

			<Candidates<T>>::mutate(|c| c.insert(index, (who, T::CandidacyBond::get())));
			Ok(())
		}

		/// Renounce one's intention to be a candidate for the next election round. 3 potential
		/// outcomes exist:
		///
		/// - `origin` is a candidate and not elected in any set. In this case, the deposit is
		///   unreserved, returned and origin is removed as a candidate.
		/// - `origin` is a current runner-up. In this case, the deposit is unreserved, returned and
		///   origin is removed as a runner-up.
		/// - `origin` is a current member. In this case, the deposit is unreserved and origin is
		///   removed as a member, consequently not being a candidate for the next round anymore.
		///   Similar to [`remove_member`](Self::remove_member), if replacement runners exists, they
		///   are immediately used. If the prime is renouncing, then no prime will exist until the
		///   next round.
		///
		/// The dispatch origin of this call must be signed, and have one of the above roles.
		/// The type of renouncing must be provided as witness data.
		///
		/// ## Complexity
		///   - Renouncing::Candidate(count): O(count + log(count))
		///   - Renouncing::Member: O(1)
		///   - Renouncing::RunnerUp: O(1)
		#[pallet::call_index(3)]
		#[pallet::weight(match *renouncing {
			Renouncing::Candidate(count) => T::WeightInfo::renounce_candidacy_candidate(count),
			Renouncing::Member => T::WeightInfo::renounce_candidacy_members(),
			Renouncing::RunnerUp => T::WeightInfo::renounce_candidacy_runners_up(),
		})]
		pub fn renounce_candidacy(origin: OriginFor<T>, renouncing: Renouncing) -> DispatchResult {
			let who = ensure_signed(origin)?;
			match renouncing {
				Renouncing::Member => {
					let _ = Self::remove_and_replace_member(&who, false)
						.map_err(|_| Error::<T>::InvalidRenouncing)?;
					Self::deposit_event(Event::Renounced { candidate: who });
				},
				Renouncing::RunnerUp => {
					<RunnersUp<T>>::try_mutate::<_, Error<T>, _>(|runners_up| {
						let index = runners_up
							.iter()
							.position(|SeatHolder { who: r, .. }| r == &who)
							.ok_or(Error::<T>::InvalidRenouncing)?;
						// can't fail anymore.
						let SeatHolder { deposit, .. } = runners_up.remove(index);
						let _remainder = T::Currency::unreserve(&who, deposit);
						debug_assert!(_remainder.is_zero());
						Self::deposit_event(Event::Renounced { candidate: who });
						Ok(())
					})?;
				},
				Renouncing::Candidate(count) => {
					<Candidates<T>>::try_mutate::<_, Error<T>, _>(|candidates| {
						ensure!(count >= candidates.len() as u32, Error::<T>::InvalidWitnessData);
						let index = candidates
							.binary_search_by(|(c, _)| c.cmp(&who))
							.map_err(|_| Error::<T>::InvalidRenouncing)?;
						let (_removed, deposit) = candidates.remove(index);
						let _remainder = T::Currency::unreserve(&who, deposit);
						debug_assert!(_remainder.is_zero());
						Self::deposit_event(Event::Renounced { candidate: who });
						Ok(())
					})?;
				},
			};
			Ok(())
		}

		/// Remove a particular member from the set. This is effective immediately and the bond of
		/// the outgoing member is slashed.
		///
		/// If a runner-up is available, then the best runner-up will be removed and replaces the
		/// outgoing member. Otherwise, if `rerun_election` is `true`, a new phragmen election is
		/// started, else, nothing happens.
		///
		/// If `slash_bond` is set to true, the bond of the member being removed is slashed. Else,
		/// it is returned.
		///
		/// The dispatch origin of this call must be root.
		///
		/// Note that this does not affect the designated block number of the next election.
		///
		/// ## Complexity
		/// - Check details of remove_and_replace_member() and do_phragmen().
		#[pallet::call_index(4)]
		#[pallet::weight(if *rerun_election {
			T::WeightInfo::remove_member_without_replacement()
		} else {
			T::WeightInfo::remove_member_with_replacement()
		})]
		pub fn remove_member(
			origin: OriginFor<T>,
			who: AccountIdLookupOf<T>,
			slash_bond: bool,
			rerun_election: bool,
		) -> DispatchResult {
			ensure_root(origin)?;
			let who = T::Lookup::lookup(who)?;

			let _ = Self::remove_and_replace_member(&who, slash_bond)?;
			Self::deposit_event(Event::MemberKicked { member: who });

			if rerun_election {
				Self::do_phragmen();
			}

			// no refund needed.
			Ok(())
		}

		/// Clean all voters who are defunct (i.e. they do not serve any purpose at all). The
		/// deposit of the removed voters are returned.
		///
		/// This is an root function to be used only for cleaning the state.
		///
		/// The dispatch origin of this call must be root.
		///
		/// ## Complexity
		/// - Check is_defunct_voter() details.
		#[pallet::call_index(5)]
		#[pallet::weight(T::WeightInfo::clean_defunct_voters(*num_voters, *num_defunct))]
		pub fn clean_defunct_voters(
			origin: OriginFor<T>,
			num_voters: u32,
			num_defunct: u32,
		) -> DispatchResult {
			let _ = ensure_root(origin)?;

			<Voting<T>>::iter()
				.take(num_voters as usize)
				.filter(|(_, x)| Self::is_defunct_voter(&x.votes))
				.take(num_defunct as usize)
				.for_each(|(dv, _)| Self::do_remove_voter(&dv));

			Ok(())
		}
	}

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config> {
		/// A new term with new_members. This indicates that enough candidates existed to run
		/// the election, not that enough have has been elected. The inner value must be examined
		/// for this purpose. A `NewTerm(\[\])` indicates that some candidates got their bond
		/// slashed and none were elected, whilst `EmptyTerm` means that no candidates existed to
		/// begin with.
		NewTerm { new_members: Vec<(<T as frame_system::Config>::AccountId, BalanceOf<T>)> },
		/// No (or not enough) candidates existed for this round. This is different from
		/// `NewTerm(\[\])`. See the description of `NewTerm`.
		EmptyTerm,
		/// Internal error happened while trying to perform election.
		ElectionError,
		/// A member has been removed. This should always be followed by either `NewTerm` or
		/// `EmptyTerm`.
		MemberKicked { member: <T as frame_system::Config>::AccountId },
		/// Someone has renounced their candidacy.
		Renounced { candidate: <T as frame_system::Config>::AccountId },
		/// A candidate was slashed by amount due to failing to obtain a seat as member or
		/// runner-up.
		///
		/// Note that old members and runners-up are also candidates.
		CandidateSlashed { candidate: <T as frame_system::Config>::AccountId, amount: BalanceOf<T> },
		/// A seat holder was slashed by amount by being forcefully removed from the set.
		SeatHolderSlashed {
			seat_holder: <T as frame_system::Config>::AccountId,
			amount: BalanceOf<T>,
		},
	}

	#[pallet::error]
	pub enum Error<T> {
		/// Cannot vote when no candidates or members exist.
		UnableToVote,
		/// Must vote for at least one candidate.
		NoVotes,
		/// Cannot vote more than candidates.
		TooManyVotes,
		/// Cannot vote more than maximum allowed.
		MaximumVotesExceeded,
		/// Cannot vote with stake less than minimum balance.
		LowBalance,
		/// Voter can not pay voting bond.
		UnableToPayBond,
		/// Must be a voter.
		MustBeVoter,
		/// Duplicated candidate submission.
		DuplicatedCandidate,
		/// Too many candidates have been created.
		TooManyCandidates,
		/// Member cannot re-submit candidacy.
		MemberSubmit,
		/// Runner cannot re-submit candidacy.
		RunnerUpSubmit,
		/// Candidate does not have enough funds.
		InsufficientCandidateFunds,
		/// Not a member.
		NotMember,
		/// The provided count of number of candidates is incorrect.
		InvalidWitnessData,
		/// The provided count of number of votes is incorrect.
		InvalidVoteCount,
		/// The renouncing origin presented a wrong `Renouncing` parameter.
		InvalidRenouncing,
		/// Prediction regarding replacement after member removal is wrong.
		InvalidReplacement,
	}

	/// The current elected members.
	///
	/// Invariant: Always sorted based on account id.
	#[pallet::storage]
	#[pallet::getter(fn members)]
	pub type Members<T: Config> =
		StorageValue<_, Vec<SeatHolder<T::AccountId, BalanceOf<T>>>, ValueQuery>;

	/// The current reserved runners-up.
	///
	/// Invariant: Always sorted based on rank (worse to best). Upon removal of a member, the
	/// last (i.e. _best_) runner-up will be replaced.
	#[pallet::storage]
	#[pallet::getter(fn runners_up)]
	pub type RunnersUp<T: Config> =
		StorageValue<_, Vec<SeatHolder<T::AccountId, BalanceOf<T>>>, ValueQuery>;

	/// The present candidate list. A current member or runner-up can never enter this vector
	/// and is always implicitly assumed to be a candidate.
	///
	/// Second element is the deposit.
	///
	/// Invariant: Always sorted based on account id.
	#[pallet::storage]
	#[pallet::getter(fn candidates)]
	pub type Candidates<T: Config> = StorageValue<_, Vec<(T::AccountId, BalanceOf<T>)>, ValueQuery>;

	/// The total number of vote rounds that have happened, excluding the upcoming one.
	#[pallet::storage]
	#[pallet::getter(fn election_rounds)]
	pub type ElectionRounds<T: Config> = StorageValue<_, u32, ValueQuery>;

	/// Votes and locked stake of a particular voter.
	///
	/// TWOX-NOTE: SAFE as `AccountId` is a crypto hash.
	#[pallet::storage]
	#[pallet::getter(fn voting)]
	pub type Voting<T: Config> =
		StorageMap<_, Twox64Concat, T::AccountId, Voter<T::AccountId, BalanceOf<T>>, ValueQuery>;

	#[pallet::genesis_config]
	#[derive(frame_support::DefaultNoBound)]
	pub struct GenesisConfig<T: Config> {
		pub members: Vec<(T::AccountId, BalanceOf<T>)>,
	}

	#[pallet::genesis_build]
	impl<T: Config> BuildGenesisConfig for GenesisConfig<T> {
		fn build(&self) {
			assert!(
				self.members.len() as u32 <= T::DesiredMembers::get(),
				"Cannot accept more than DesiredMembers genesis member",
			);
			let members = self
				.members
				.iter()
				.map(|(ref member, ref stake)| {
					// make sure they have enough stake.
					assert!(
						T::Currency::free_balance(member) >= *stake,
						"Genesis member does not have enough stake.",
					);

					// Note: all members will only vote for themselves, hence they must be given
					// exactly their own stake as total backing. Any sane election should behave as
					// such. Nonetheless, stakes will be updated for term 1 onwards according to the
					// election.
					Members::<T>::mutate(|members| {
						match members.binary_search_by(|m| m.who.cmp(member)) {
							Ok(_) => {
								panic!(
									"Duplicate member in elections-phragmen genesis: {:?}",
									member
								)
							},
							Err(pos) => members.insert(
								pos,
								SeatHolder {
									who: member.clone(),
									stake: *stake,
									deposit: Zero::zero(),
								},
							),
						}
					});

					// set self-votes to make persistent. Genesis voters don't have any bond, nor do
					// they have any lock. NOTE: this means that we will still try to remove a lock
					// once this genesis voter is removed, and for now it is okay because
					// remove_lock is noop if lock is not there.
					<Voting<T>>::insert(
						&member,
						Voter { votes: vec![member.clone()], stake: *stake, deposit: Zero::zero() },
					);

					member.clone()
				})
				.collect::<Vec<T::AccountId>>();

			// report genesis members to upstream, if any.
			T::InitializeMembers::initialize_members(&members);
		}
	}
}

impl<T: Config> Pallet<T> {
	/// The deposit value of `count` votes.
	fn deposit_of(count: usize) -> BalanceOf<T> {
		T::VotingBondBase::get()
			.saturating_add(T::VotingBondFactor::get().saturating_mul((count as u32).into()))
	}

	/// Attempts to remove a member `who`. If a runner-up exists, it is used as the replacement.
	///
	/// Returns:
	///
	/// - `Ok(true)` if the member was removed and a replacement was found.
	/// - `Ok(false)` if the member was removed and but no replacement was found.
	/// - `Err(_)` if the member was no found.
	///
	/// Both `Members` and `RunnersUp` storage is updated accordingly. `T::ChangeMember` is called
	/// if needed. If `slash` is true, the deposit of the potentially removed member is slashed,
	/// else, it is unreserved.
	///
	/// ### Note: Prime preservation
	///
	/// This function attempts to preserve the prime. If the removed members is not the prime, it is
	/// set again via [`Config::ChangeMembers`].
	fn remove_and_replace_member(who: &T::AccountId, slash: bool) -> Result<bool, DispatchError> {
		// closure will return:
		// - `Ok(Option(replacement))` if member was removed and replacement was replaced.
		// - `Ok(None)` if member was removed but no replacement was found
		// - `Err(_)` if who is not a member.
		let maybe_replacement = <Members<T>>::try_mutate::<_, Error<T>, _>(|members| {
			let remove_index = members
				.binary_search_by(|m| m.who.cmp(who))
				.map_err(|_| Error::<T>::NotMember)?;
			// we remove the member anyhow, regardless of having a runner-up or not.
			let removed = members.remove(remove_index);

			// slash or unreserve
			if slash {
				let (imbalance, _remainder) = T::Currency::slash_reserved(who, removed.deposit);
				debug_assert!(_remainder.is_zero());
				T::LoserCandidate::on_unbalanced(imbalance);
				Self::deposit_event(Event::SeatHolderSlashed {
					seat_holder: who.clone(),
					amount: removed.deposit,
				});
			} else {
				T::Currency::unreserve(who, removed.deposit);
			}

			let maybe_next_best = <RunnersUp<T>>::mutate(|r| r.pop()).map(|next_best| {
				// defensive-only: Members and runners-up are disjoint. This will always be err and
				// give us an index to insert.
				if let Err(index) = members.binary_search_by(|m| m.who.cmp(&next_best.who)) {
					members.insert(index, next_best.clone());
				} else {
					// overlap. This can never happen. If so, it seems like our intended replacement
					// is already a member, so not much more to do.
					log::error!(target: LOG_TARGET, "A member seems to also be a runner-up.");
				}
				next_best
			});
			Ok(maybe_next_best)
		})?;

		let remaining_member_ids_sorted =
			Self::members().into_iter().map(|x| x.who).collect::<Vec<_>>();
		let outgoing = &[who.clone()];
		let maybe_current_prime = T::ChangeMembers::get_prime();
		let return_value = match maybe_replacement {
			// member ids are already sorted, other two elements have one item.
			Some(incoming) => {
				T::ChangeMembers::change_members_sorted(
					&[incoming.who],
					outgoing,
					&remaining_member_ids_sorted[..],
				);
				true
			},
			None => {
				T::ChangeMembers::change_members_sorted(
					&[],
					outgoing,
					&remaining_member_ids_sorted[..],
				);
				false
			},
		};

		// if there was a prime before and they are not the one being removed, then set them
		// again.
		if let Some(current_prime) = maybe_current_prime {
			if &current_prime != who {
				T::ChangeMembers::set_prime(Some(current_prime));
			}
		}

		Ok(return_value)
	}

	/// Check if `who` is a candidate. It returns the insert index if the element does not exists as
	/// an error.
	fn is_candidate(who: &T::AccountId) -> Result<(), usize> {
		Self::candidates().binary_search_by(|c| c.0.cmp(who)).map(|_| ())
	}

	/// Check if `who` is a voter. It may or may not be a _current_ one.
	fn is_voter(who: &T::AccountId) -> bool {
		Voting::<T>::contains_key(who)
	}

	/// Check if `who` is currently an active member.
	fn is_member(who: &T::AccountId) -> bool {
		Self::members().binary_search_by(|m| m.who.cmp(who)).is_ok()
	}

	/// Check if `who` is currently an active runner-up.
	fn is_runner_up(who: &T::AccountId) -> bool {
		Self::runners_up().iter().any(|r| &r.who == who)
	}

	/// Get the members' account ids.
	pub(crate) fn members_ids() -> Vec<T::AccountId> {
		Self::members().into_iter().map(|m| m.who).collect::<Vec<T::AccountId>>()
	}

	/// Get a concatenation of previous members and runners-up and their deposits.
	///
	/// These accounts are essentially treated as candidates.
	fn implicit_candidates_with_deposit() -> Vec<(T::AccountId, BalanceOf<T>)> {
		// invariant: these two are always without duplicates.
		Self::members()
			.into_iter()
			.map(|m| (m.who, m.deposit))
			.chain(Self::runners_up().into_iter().map(|r| (r.who, r.deposit)))
			.collect::<Vec<_>>()
	}

	/// Check if `votes` will correspond to a defunct voter. As no origin is part of the inputs,
	/// this function does not check the origin at all.
	///
	/// O(NLogM) with M candidates and `who` having voted for `N` of them.
	/// Reads Members, RunnersUp, Candidates and Voting(who) from database.
	fn is_defunct_voter(votes: &[T::AccountId]) -> bool {
		votes.iter().all(|v| {
			!Self::is_member(v) && !Self::is_runner_up(v) && Self::is_candidate(v).is_err()
		})
	}

	/// Remove a certain someone as a voter.
	fn do_remove_voter(who: &T::AccountId) {
		let Voter { deposit, .. } = <Voting<T>>::take(who);

		// remove storage, lock and unreserve.
		T::Currency::remove_lock(T::PalletId::get(), who);

		// NOTE: we could check the deposit amount before removing and skip if zero, but it will be
		// a noop anyhow.
		let _remainder = T::Currency::unreserve(who, deposit);
		debug_assert!(_remainder.is_zero());
	}

	/// Run the phragmen election with all required side processes and state updates, if election
	/// succeeds. Else, it will emit an `ElectionError` event.
	///
	/// Calls the appropriate [`ChangeMembers`] function variant internally.
	fn do_phragmen() -> Weight {
		let desired_seats = T::DesiredMembers::get() as usize;
		let desired_runners_up = T::DesiredRunnersUp::get() as usize;
		let num_to_elect = desired_runners_up + desired_seats;

		let mut candidates_and_deposit = Self::candidates();
		// add all the previous members and runners-up as candidates as well.
		candidates_and_deposit.append(&mut Self::implicit_candidates_with_deposit());

		if candidates_and_deposit.len().is_zero() {
			Self::deposit_event(Event::EmptyTerm);
			return T::DbWeight::get().reads(3)
		}

		// All of the new winners that come out of phragmen will thus have a deposit recorded.
		let candidate_ids =
			candidates_and_deposit.iter().map(|(x, _)| x).cloned().collect::<Vec<_>>();

		// helper closures to deal with balance/stake.
		let total_issuance = T::Currency::total_issuance();
		let to_votes = |b: BalanceOf<T>| T::CurrencyToVote::to_vote(b, total_issuance);
		let to_balance = |e: ExtendedBalance| T::CurrencyToVote::to_currency(e, total_issuance);

		let mut num_edges: u32 = 0;

		let max_voters = <T as Config>::MaxVoters::get() as usize;
		// used for prime election.
		let mut voters_and_stakes = Vec::new();
		match Voting::<T>::iter().try_for_each(|(voter, Voter { stake, votes, .. })| {
			if voters_and_stakes.len() < max_voters {
				voters_and_stakes.push((voter, stake, votes));
				Ok(())
			} else {
				Err(())
			}
		}) {
			Ok(_) => (),
			Err(_) => {
				log::error!(
					target: LOG_TARGET,
					"Failed to run election. Number of voters exceeded",
				);
				Self::deposit_event(Event::ElectionError);
				return T::DbWeight::get().reads(3 + max_voters as u64)
			},
		}

		// used for phragmen.
		let voters_and_votes = voters_and_stakes
			.iter()
			.cloned()
			.map(|(voter, stake, votes)| {
				num_edges = num_edges.saturating_add(votes.len() as u32);
				(voter, to_votes(stake), votes)
			})
			.collect::<Vec<_>>();

		let weight_candidates = candidates_and_deposit.len() as u32;
		let weight_voters = voters_and_votes.len() as u32;
		let weight_edges = num_edges;
		let _ =
			sp_npos_elections::seq_phragmen(num_to_elect, candidate_ids, voters_and_votes, None)
				.map(|ElectionResult::<T::AccountId, Perbill> { winners, assignments: _ }| {
					// this is already sorted by id.
					let old_members_ids_sorted = <Members<T>>::take()
						.into_iter()
						.map(|m| m.who)
						.collect::<Vec<T::AccountId>>();
					// this one needs a sort by id.
					let mut old_runners_up_ids_sorted = <RunnersUp<T>>::take()
						.into_iter()
						.map(|r| r.who)
						.collect::<Vec<T::AccountId>>();
					old_runners_up_ids_sorted.sort();

					// filter out those who end up with no backing stake.
					let mut new_set_with_stake = winners
						.into_iter()
						.filter_map(
							|(m, b)| if b.is_zero() { None } else { Some((m, to_balance(b))) },
						)
						.collect::<Vec<(T::AccountId, BalanceOf<T>)>>();

					// OPTIMIZATION NOTE: we could bail out here if `new_set.len() == 0`. There
					// isn't much left to do. Yet, re-arranging the code would require duplicating
					// the slashing of exposed candidates, cleaning any previous members, and so on.
					// For now, in favor of readability and veracity, we keep it simple.

					// split new set into winners and runners up.
					let split_point = desired_seats.min(new_set_with_stake.len());
					let mut new_members_sorted_by_id =
						new_set_with_stake.drain(..split_point).collect::<Vec<_>>();
					new_members_sorted_by_id.sort_by(|i, j| i.0.cmp(&j.0));

					// all the rest will be runners-up
					new_set_with_stake.reverse();
					let new_runners_up_sorted_by_rank = new_set_with_stake;
					let mut new_runners_up_ids_sorted = new_runners_up_sorted_by_rank
						.iter()
						.map(|(r, _)| r.clone())
						.collect::<Vec<_>>();
					new_runners_up_ids_sorted.sort();

					// Now we select a prime member using a [Borda
					// count](https://en.wikipedia.org/wiki/Borda_count). We weigh everyone's vote for
					// that new member by a multiplier based on the order of the votes. i.e. the
					// first person a voter votes for gets a 16x multiplier, the next person gets a
					// 15x multiplier, an so on... (assuming `T::MaxVotesPerVoter` = 16)
					let mut prime_votes = new_members_sorted_by_id
						.iter()
						.map(|c| (&c.0, BalanceOf::<T>::zero()))
						.collect::<Vec<_>>();
					for (_, stake, votes) in voters_and_stakes.into_iter() {
						for (vote_multiplier, who) in
							votes.iter().enumerate().map(|(vote_position, who)| {
								((T::MaxVotesPerVoter::get() as usize - vote_position) as u32, who)
							}) {
							if let Ok(i) = prime_votes.binary_search_by_key(&who, |k| k.0) {
								prime_votes[i].1 = prime_votes[i]
									.1
									.saturating_add(stake.saturating_mul(vote_multiplier.into()));
							}
						}
					}
					// We then select the new member with the highest weighted stake. In the case of
					// a tie, the last person in the list with the tied score is selected. This is
					// the person with the "highest" account id based on the sort above.
					let prime = prime_votes.into_iter().max_by_key(|x| x.1).map(|x| x.0.clone());

					// new_members_sorted_by_id is sorted by account id.
					let new_members_ids_sorted = new_members_sorted_by_id
						.iter()
						.map(|(m, _)| m.clone())
						.collect::<Vec<T::AccountId>>();

					// report member changes. We compute diff because we need the outgoing list.
					let (incoming, outgoing) = T::ChangeMembers::compute_members_diff_sorted(
						&new_members_ids_sorted,
						&old_members_ids_sorted,
					);
					T::ChangeMembers::change_members_sorted(
						&incoming,
						&outgoing,
						&new_members_ids_sorted,
					);
					T::ChangeMembers::set_prime(prime);

					// All candidates/members/runners-up who are no longer retaining a position as a
					// seat holder will lose their bond.
					candidates_and_deposit.iter().for_each(|(c, d)| {
						if new_members_ids_sorted.binary_search(c).is_err() &&
							new_runners_up_ids_sorted.binary_search(c).is_err()
						{
							let (imbalance, _) = T::Currency::slash_reserved(c, *d);
							T::LoserCandidate::on_unbalanced(imbalance);
							Self::deposit_event(Event::CandidateSlashed {
								candidate: c.clone(),
								amount: *d,
							});
						}
					});

					// write final values to storage.
					let deposit_of_candidate = |x: &T::AccountId| -> BalanceOf<T> {
						// defensive-only. This closure is used against the new members and new
						// runners-up, both of which are phragmen winners and thus must have
						// deposit.
						candidates_and_deposit
							.iter()
							.find_map(|(c, d)| if c == x { Some(*d) } else { None })
							.defensive_unwrap_or_default()
					};
					// fetch deposits from the one recorded one. This will make sure that a
					// candidate who submitted candidacy before a change to candidacy deposit will
					// have the correct amount recorded.
					<Members<T>>::put(
						new_members_sorted_by_id
							.iter()
							.map(|(who, stake)| SeatHolder {
								deposit: deposit_of_candidate(who),
								who: who.clone(),
								stake: *stake,
							})
							.collect::<Vec<_>>(),
					);
					<RunnersUp<T>>::put(
						new_runners_up_sorted_by_rank
							.into_iter()
							.map(|(who, stake)| SeatHolder {
								deposit: deposit_of_candidate(&who),
								who,
								stake,
							})
							.collect::<Vec<_>>(),
					);

					// clean candidates.
					<Candidates<T>>::kill();

					Self::deposit_event(Event::NewTerm { new_members: new_members_sorted_by_id });
					<ElectionRounds<T>>::mutate(|v| *v += 1);
				})
				.map_err(|e| {
					log::error!(target: LOG_TARGET, "Failed to run election [{:?}].", e,);
					Self::deposit_event(Event::ElectionError);
				});

		T::WeightInfo::election_phragmen(weight_candidates, weight_voters, weight_edges)
	}
}

impl<T: Config> Contains<T::AccountId> for Pallet<T> {
	fn contains(who: &T::AccountId) -> bool {
		Self::is_member(who)
	}
}

impl<T: Config> SortedMembers<T::AccountId> for Pallet<T> {
	fn contains(who: &T::AccountId) -> bool {
		Self::is_member(who)
	}

	fn sorted_members() -> Vec<T::AccountId> {
		Self::members_ids()
	}

	// A special function to populate members in this pallet for passing Origin
	// checks in runtime benchmarking.
	#[cfg(feature = "runtime-benchmarks")]
	fn add(who: &T::AccountId) {
		Members::<T>::mutate(|members| match members.binary_search_by(|m| m.who.cmp(who)) {
			Ok(_) => (),
			Err(pos) => {
				let s = SeatHolder {
					who: who.clone(),
					stake: Default::default(),
					deposit: Default::default(),
				};
				members.insert(pos, s)
			},
		})
	}
}

impl<T: Config> ContainsLengthBound for Pallet<T> {
	fn min_len() -> usize {
		0
	}

	/// Implementation uses a parameter type so calling is cost-free.
	fn max_len() -> usize {
		T::DesiredMembers::get() as usize
	}
}

#[cfg(any(feature = "try-runtime", test))]
impl<T: Config> Pallet<T> {
	fn do_try_state() -> Result<(), TryRuntimeError> {
		Self::try_state_members()?;
		Self::try_state_runners_up()?;
		Self::try_state_candidates()?;
		Self::try_state_candidates_runners_up_disjoint()?;
		Self::try_state_members_disjoint()?;
		Self::try_state_members_approval_stake()
	}

	/// [`Members`] state checks. Invariants:
	///  - Members are always sorted based on account ID.
	fn try_state_members() -> Result<(), TryRuntimeError> {
		let mut members = Members::<T>::get().clone();
		members.sort_by_key(|m| m.who.clone());

		if Members::<T>::get() == members {
			Ok(())
		} else {
			Err("try_state checks: Members must be always sorted by account ID".into())
		}
	}

	// [`RunnersUp`] state checks. Invariants:
	//  - Elements are sorted based on weight (worst to best).
	fn try_state_runners_up() -> Result<(), TryRuntimeError> {
		let mut sorted = RunnersUp::<T>::get();
		// worst stake first
		sorted.sort_by(|a, b| a.stake.cmp(&b.stake));

		if RunnersUp::<T>::get() == sorted {
			Ok(())
		} else {
			Err("try_state checks: Runners Up must always be sorted by stake (worst to best)"
				.into())
		}
	}

	// [`Candidates`] state checks. Invariants:
	//  - Always sorted based on account ID.
	fn try_state_candidates() -> Result<(), TryRuntimeError> {
		let mut candidates = Candidates::<T>::get().clone();
		candidates.sort_by_key(|(c, _)| c.clone());

		if Candidates::<T>::get() == candidates {
			Ok(())
		} else {
			Err("try_state checks: Candidates must be always sorted by account ID".into())
		}
	}
	// [`Candidates`] and [`RunnersUp`] state checks. Invariants:
	//  - Candidates and runners-ups sets are disjoint.
	fn try_state_candidates_runners_up_disjoint() -> Result<(), TryRuntimeError> {
		match Self::intersects(&Self::candidates_ids(), &Self::runners_up_ids()) {
			true => Err("Candidates and runners up sets should always be disjoint".into()),
			false => Ok(()),
		}
	}

	// [`Members`], [`Candidates`] and [`RunnersUp`] state checks. Invariants:
	//  - Members and candidates sets are disjoint;
	//  - Members and runners-ups sets are disjoint.
	fn try_state_members_disjoint() -> Result<(), TryRuntimeError> {
		match Self::intersects(&Pallet::<T>::members_ids(), &Self::candidates_ids()) &&
			Self::intersects(&Pallet::<T>::members_ids(), &Self::runners_up_ids())
		{
			true =>
				Err("Members set should be disjoint from candidates and runners-up sets".into()),
			false => Ok(()),
		}
	}

	// [`Members`], [`RunnersUp`] and approval stake state checks. Invariants:
	// - Selected members should have approval stake;
	// - Selected RunnersUp should have approval stake.
	fn try_state_members_approval_stake() -> Result<(), TryRuntimeError> {
		match Members::<T>::get()
			.iter()
			.chain(RunnersUp::<T>::get().iter())
			.all(|s| s.stake != BalanceOf::<T>::zero())
		{
			true => Ok(()),
			false => Err("Members and RunnersUp must have approval stake".into()),
		}
	}

	fn intersects<P: PartialEq>(a: &[P], b: &[P]) -> bool {
		a.iter().any(|e| b.contains(e))
	}

	fn candidates_ids() -> Vec<T::AccountId> {
		Pallet::<T>::candidates().iter().map(|(x, _)| x).cloned().collect::<Vec<_>>()
	}

	fn runners_up_ids() -> Vec<T::AccountId> {
		Pallet::<T>::runners_up().into_iter().map(|r| r.who).collect::<Vec<_>>()
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use crate as elections_phragmen;
	use frame_support::{
		assert_noop, assert_ok,
		dispatch::DispatchResultWithPostInfo,
		parameter_types,
		traits::{ConstU32, ConstU64, OnInitialize},
	};
	use frame_system::ensure_signed;
	use sp_core::H256;
	use sp_runtime::{
		testing::Header,
		traits::{BlakeTwo256, IdentityLookup},
		BuildStorage,
	};
	use substrate_test_utils::assert_eq_uvec;

	impl frame_system::Config for Test {
		type BaseCallFilter = frame_support::traits::Everything;
		type BlockWeights = ();
		type BlockLength = ();
		type DbWeight = ();
		type RuntimeOrigin = RuntimeOrigin;
		type Nonce = u64;
		type RuntimeCall = RuntimeCall;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type AccountId = u64;
		type Lookup = IdentityLookup<Self::AccountId>;
		type Block = Block;
		type RuntimeEvent = RuntimeEvent;
		type BlockHashCount = ConstU64<250>;
		type Version = ();
		type PalletInfo = PalletInfo;
		type AccountData = pallet_balances::AccountData<u64>;
		type OnNewAccount = ();
		type OnKilledAccount = ();
		type SystemWeightInfo = ();
		type SS58Prefix = ();
		type OnSetCode = ();
		type MaxConsumers = ConstU32<16>;
	}

	impl pallet_balances::Config for Test {
		type Balance = u64;
		type RuntimeEvent = RuntimeEvent;
		type DustRemoval = ();
		type ExistentialDeposit = ConstU64<1>;
		type AccountStore = frame_system::Pallet<Test>;
		type MaxLocks = ();
		type MaxReserves = ();
		type ReserveIdentifier = [u8; 8];
		type WeightInfo = ();
		type FreezeIdentifier = ();
		type MaxFreezes = ();
		type RuntimeHoldReason = ();
		type RuntimeFreezeReason = ();
		type MaxHolds = ();
	}

	frame_support::parameter_types! {
		pub static VotingBondBase: u64 = 2;
		pub static VotingBondFactor: u64 = 0;
		pub static CandidacyBond: u64 = 3;
		pub static DesiredMembers: u32 = 2;
		pub static DesiredRunnersUp: u32 = 0;
		pub static TermDuration: u64 = 5;
		pub static Members: Vec<u64> = vec![];
		pub static Prime: Option<u64> = None;
	}

	pub struct TestChangeMembers;
	impl ChangeMembers<u64> for TestChangeMembers {
		fn change_members_sorted(incoming: &[u64], outgoing: &[u64], new: &[u64]) {
			// new, incoming, outgoing must be sorted.
			let mut new_sorted = new.to_vec();
			new_sorted.sort();
			assert_eq!(new, &new_sorted[..]);

			let mut incoming_sorted = incoming.to_vec();
			incoming_sorted.sort();
			assert_eq!(incoming, &incoming_sorted[..]);

			let mut outgoing_sorted = outgoing.to_vec();
			outgoing_sorted.sort();
			assert_eq!(outgoing, &outgoing_sorted[..]);

			// incoming and outgoing must be disjoint
			for x in incoming.iter() {
				assert!(outgoing.binary_search(x).is_err());
			}

			let mut old_plus_incoming = MEMBERS.with(|m| m.borrow().to_vec());
			old_plus_incoming.extend_from_slice(incoming);
			old_plus_incoming.sort();

			let mut new_plus_outgoing = new.to_vec();
			new_plus_outgoing.extend_from_slice(outgoing);
			new_plus_outgoing.sort();

			assert_eq!(old_plus_incoming, new_plus_outgoing, "change members call is incorrect!");

			MEMBERS.with(|m| *m.borrow_mut() = new.to_vec());
			PRIME.with(|p| *p.borrow_mut() = None);
		}

		fn set_prime(who: Option<u64>) {
			PRIME.with(|p| *p.borrow_mut() = who);
		}

		fn get_prime() -> Option<u64> {
			PRIME.with(|p| *p.borrow())
		}
	}

	parameter_types! {
		pub const ElectionsPhragmenPalletId: LockIdentifier = *b"phrelect";
		pub const PhragmenMaxVoters: u32 = 1000;
		pub const PhragmenMaxCandidates: u32 = 100;
	}

	impl Config for Test {
		type PalletId = ElectionsPhragmenPalletId;
		type RuntimeEvent = RuntimeEvent;
		type Currency = Balances;
		type CurrencyToVote = ();
		type ChangeMembers = TestChangeMembers;
		type InitializeMembers = ();
		type CandidacyBond = CandidacyBond;
		type VotingBondBase = VotingBondBase;
		type VotingBondFactor = VotingBondFactor;
		type TermDuration = TermDuration;
		type DesiredMembers = DesiredMembers;
		type DesiredRunnersUp = DesiredRunnersUp;
		type LoserCandidate = ();
		type KickedMember = ();
		type WeightInfo = ();
		type MaxVoters = PhragmenMaxVoters;
		type MaxVotesPerVoter = ConstU32<16>;
		type MaxCandidates = PhragmenMaxCandidates;
	}

	pub type Block = sp_runtime::generic::Block<Header, UncheckedExtrinsic>;
	pub type UncheckedExtrinsic =
		sp_runtime::generic::UncheckedExtrinsic<u32, u64, RuntimeCall, ()>;

	frame_support::construct_runtime!(
		pub enum Test
		{
			System: frame_system::{Pallet, Call, Event<T>},
			Balances: pallet_balances::{Pallet, Call, Event<T>, Config<T>},
			Elections: elections_phragmen::{Pallet, Call, Event<T>, Config<T>},
		}
	);

	pub struct ExtBuilder {
		balance_factor: u64,
		genesis_members: Vec<(u64, u64)>,
	}

	impl Default for ExtBuilder {
		fn default() -> Self {
			Self { balance_factor: 1, genesis_members: vec![] }
		}
	}

	impl ExtBuilder {
		pub fn voter_bond(self, bond: u64) -> Self {
			VOTING_BOND_BASE.with(|v| *v.borrow_mut() = bond);
			self
		}
		pub fn voter_bond_factor(self, bond: u64) -> Self {
			VOTING_BOND_FACTOR.with(|v| *v.borrow_mut() = bond);
			self
		}
		pub fn desired_runners_up(self, count: u32) -> Self {
			DESIRED_RUNNERS_UP.with(|v| *v.borrow_mut() = count);
			self
		}
		pub fn term_duration(self, duration: u64) -> Self {
			TERM_DURATION.with(|v| *v.borrow_mut() = duration);
			self
		}
		pub fn genesis_members(mut self, members: Vec<(u64, u64)>) -> Self {
			MEMBERS.with(|m| *m.borrow_mut() = members.iter().map(|(m, _)| *m).collect::<Vec<_>>());
			self.genesis_members = members;
			self
		}
		pub fn desired_members(self, count: u32) -> Self {
			DESIRED_MEMBERS.with(|m| *m.borrow_mut() = count);
			self
		}
		pub fn balance_factor(mut self, factor: u64) -> Self {
			self.balance_factor = factor;
			self
		}
		pub fn build_and_execute(self, test: impl FnOnce() -> ()) {
			sp_tracing::try_init_simple();
			MEMBERS.with(|m| {
				*m.borrow_mut() = self.genesis_members.iter().map(|(m, _)| *m).collect::<Vec<_>>()
			});
			let mut ext: sp_io::TestExternalities = RuntimeGenesisConfig {
				balances: pallet_balances::GenesisConfig::<Test> {
					balances: vec![
						(1, 10 * self.balance_factor),
						(2, 20 * self.balance_factor),
						(3, 30 * self.balance_factor),
						(4, 40 * self.balance_factor),
						(5, 50 * self.balance_factor),
						(6, 60 * self.balance_factor),
					],
				},
				elections: elections_phragmen::GenesisConfig::<Test> {
					members: self.genesis_members,
				},
			}
			.build_storage()
			.unwrap()
			.into();
			ext.execute_with(pre_conditions);
			ext.execute_with(test);

			#[cfg(feature = "try-runtime")]
			ext.execute_with(|| {
				assert_ok!(<Elections as frame_support::traits::Hooks<u64>>::try_state(
					System::block_number()
				));
			});
		}
	}

	fn candidate_ids() -> Vec<u64> {
		Elections::candidates().into_iter().map(|(c, _)| c).collect::<Vec<_>>()
	}

	fn candidate_deposit(who: &u64) -> u64 {
		Elections::candidates()
			.into_iter()
			.find_map(|(c, d)| if c == *who { Some(d) } else { None })
			.unwrap_or_default()
	}

	fn voter_deposit(who: &u64) -> u64 {
		Elections::voting(who).deposit
	}

	fn runners_up_ids() -> Vec<u64> {
		Elections::runners_up().into_iter().map(|r| r.who).collect::<Vec<_>>()
	}

	fn members_ids() -> Vec<u64> {
		Elections::members_ids()
	}

	fn members_and_stake() -> Vec<(u64, u64)> {
		Elections::members().into_iter().map(|m| (m.who, m.stake)).collect::<Vec<_>>()
	}

	fn runners_up_and_stake() -> Vec<(u64, u64)> {
		Elections::runners_up()
			.into_iter()
			.map(|r| (r.who, r.stake))
			.collect::<Vec<_>>()
	}

	fn all_voters() -> Vec<u64> {
		Voting::<Test>::iter().map(|(v, _)| v).collect::<Vec<u64>>()
	}

	fn balances(who: &u64) -> (u64, u64) {
		(Balances::free_balance(who), Balances::reserved_balance(who))
	}

	fn has_lock(who: &u64) -> u64 {
		Balances::locks(who)
			.get(0)
			.cloned()
			.map(|lock| {
				assert_eq!(lock.id, ElectionsPhragmenPalletId::get());
				lock.amount
			})
			.unwrap_or_default()
	}

	fn locked_stake_of(who: &u64) -> u64 {
		Voting::<Test>::get(who).stake
	}

	fn pre_conditions() {
		System::set_block_number(1);
		Elections::do_try_state().unwrap();
	}

	fn submit_candidacy(origin: RuntimeOrigin) -> sp_runtime::DispatchResult {
		Elections::submit_candidacy(origin, Elections::candidates().len() as u32)
	}

	fn vote(origin: RuntimeOrigin, votes: Vec<u64>, stake: u64) -> DispatchResultWithPostInfo {
		// historical note: helper function was created in a period of time in which the API of vote
		// call was changing. Currently it is a wrapper for the original call and does not do much.
		// Nonetheless, totally harmless.
		ensure_signed(origin.clone()).expect("vote origin must be signed");
		Elections::vote(origin, votes, stake)
	}

	fn votes_of(who: &u64) -> Vec<u64> {
		Voting::<Test>::get(who).votes
	}

	#[test]
	fn params_should_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(<Test as Config>::DesiredMembers::get(), 2);
			assert_eq!(<Test as Config>::DesiredRunnersUp::get(), 0);
			assert_eq!(<Test as Config>::VotingBondBase::get(), 2);
			assert_eq!(<Test as Config>::VotingBondFactor::get(), 0);
			assert_eq!(<Test as Config>::CandidacyBond::get(), 3);
			assert_eq!(<Test as Config>::TermDuration::get(), 5);
			assert_eq!(Elections::election_rounds(), 0);

			assert!(Elections::members().is_empty());
			assert!(Elections::runners_up().is_empty());

			assert!(candidate_ids().is_empty());
			assert_eq!(<Candidates<Test>>::decode_len(), None);
			assert!(Elections::is_candidate(&1).is_err());

			assert!(all_voters().is_empty());
			assert!(votes_of(&1).is_empty());
		});
	}

	#[test]
	fn genesis_members_should_work() {
		ExtBuilder::default()
			.genesis_members(vec![(1, 10), (2, 20)])
			.build_and_execute(|| {
				System::set_block_number(1);
				assert_eq!(
					Elections::members(),
					vec![
						SeatHolder { who: 1, stake: 10, deposit: 0 },
						SeatHolder { who: 2, stake: 20, deposit: 0 }
					]
				);

				assert_eq!(
					Elections::voting(1),
					Voter { stake: 10u64, votes: vec![1], deposit: 0 }
				);
				assert_eq!(
					Elections::voting(2),
					Voter { stake: 20u64, votes: vec![2], deposit: 0 }
				);

				// they will persist since they have self vote.
				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![1, 2]);
			})
	}

	#[test]
	fn genesis_voters_can_remove_lock() {
		ExtBuilder::default()
			.genesis_members(vec![(1, 10), (2, 20)])
			.build_and_execute(|| {
				System::set_block_number(1);

				assert_eq!(
					Elections::voting(1),
					Voter { stake: 10u64, votes: vec![1], deposit: 0 }
				);
				assert_eq!(
					Elections::voting(2),
					Voter { stake: 20u64, votes: vec![2], deposit: 0 }
				);

				assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(1)));
				assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(2)));

				assert_eq!(Elections::voting(1), Default::default());
				assert_eq!(Elections::voting(2), Default::default());
			})
	}

	#[test]
	fn genesis_members_unsorted_should_work() {
		ExtBuilder::default()
			.genesis_members(vec![(2, 20), (1, 10)])
			.build_and_execute(|| {
				System::set_block_number(1);
				assert_eq!(
					Elections::members(),
					vec![
						SeatHolder { who: 1, stake: 10, deposit: 0 },
						SeatHolder { who: 2, stake: 20, deposit: 0 },
					]
				);

				assert_eq!(
					Elections::voting(1),
					Voter { stake: 10u64, votes: vec![1], deposit: 0 }
				);
				assert_eq!(
					Elections::voting(2),
					Voter { stake: 20u64, votes: vec![2], deposit: 0 }
				);

				// they will persist since they have self vote.
				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![1, 2]);
			})
	}

	#[test]
	#[should_panic = "Genesis member does not have enough stake"]
	fn genesis_members_cannot_over_stake_0() {
		// 10 cannot lock 20 as their stake and extra genesis will panic.
		ExtBuilder::default()
			.genesis_members(vec![(1, 20), (2, 20)])
			.build_and_execute(|| {});
	}

	#[test]
	#[should_panic = "Duplicate member in elections-phragmen genesis: 2"]
	fn genesis_members_cannot_be_duplicate() {
		ExtBuilder::default()
			.desired_members(3)
			.genesis_members(vec![(1, 10), (2, 10), (2, 10)])
			.build_and_execute(|| {});
	}

	#[test]
	#[should_panic = "Cannot accept more than DesiredMembers genesis member"]
	fn genesis_members_cannot_too_many() {
		ExtBuilder::default()
			.genesis_members(vec![(1, 10), (2, 10), (3, 30)])
			.desired_members(2)
			.build_and_execute(|| {});
	}

	#[test]
	fn term_duration_zero_is_passive() {
		ExtBuilder::default().term_duration(0).build_and_execute(|| {
			assert_eq!(<Test as Config>::TermDuration::get(), 0);
			assert_eq!(<Test as Config>::DesiredMembers::get(), 2);
			assert_eq!(Elections::election_rounds(), 0);

			assert!(members_ids().is_empty());
			assert!(Elections::runners_up().is_empty());
			assert!(candidate_ids().is_empty());

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert!(members_ids().is_empty());
			assert!(Elections::runners_up().is_empty());
			assert!(candidate_ids().is_empty());
		});
	}

	#[test]
	fn simple_candidate_submission_should_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());
			assert!(Elections::is_candidate(&1).is_err());
			assert!(Elections::is_candidate(&2).is_err());

			assert_eq!(balances(&1), (10, 0));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(1)));
			assert_eq!(balances(&1), (7, 3));

			assert_eq!(candidate_ids(), vec![1]);

			assert!(Elections::is_candidate(&1).is_ok());
			assert!(Elections::is_candidate(&2).is_err());

			assert_eq!(balances(&2), (20, 0));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
			assert_eq!(balances(&2), (17, 3));

			assert_eq!(candidate_ids(), vec![1, 2]);

			assert!(Elections::is_candidate(&1).is_ok());
			assert!(Elections::is_candidate(&2).is_ok());

			assert_eq!(candidate_deposit(&1), 3);
			assert_eq!(candidate_deposit(&2), 3);
			assert_eq!(candidate_deposit(&3), 0);
		});
	}

	#[test]
	fn updating_candidacy_bond_works() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_eq!(Elections::candidates(), vec![(5, 3)]);

			// a runtime upgrade changes the bond.
			CANDIDACY_BOND.with(|v| *v.borrow_mut() = 4);

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_eq!(Elections::candidates(), vec![(4, 4), (5, 3)]);

			// once elected, they each hold their candidacy bond, no more.
			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(balances(&4), (34, 6));
			assert_eq!(balances(&5), (45, 5));
			assert_eq!(
				Elections::members(),
				vec![
					SeatHolder { who: 4, stake: 34, deposit: 4 },
					SeatHolder { who: 5, stake: 45, deposit: 3 },
				]
			);
		})
	}

	#[test]
	fn candidates_are_always_sorted() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_eq!(candidate_ids(), vec![3]);
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(1)));
			assert_eq!(candidate_ids(), vec![1, 3]);
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
			assert_eq!(candidate_ids(), vec![1, 2, 3]);
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_eq!(candidate_ids(), vec![1, 2, 3, 4]);
		});
	}

	#[test]
	fn dupe_candidate_submission_should_not_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(1)));
			assert_eq!(candidate_ids(), vec![1]);
			assert_noop!(
				submit_candidacy(RuntimeOrigin::signed(1)),
				Error::<Test>::DuplicatedCandidate
			);
		});
	}

	#[test]
	fn member_candidacy_submission_should_not_work() {
		// critically important to make sure that outgoing candidates and losers are not mixed up.
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![5]);
			assert!(Elections::runners_up().is_empty());
			assert!(candidate_ids().is_empty());

			assert_noop!(submit_candidacy(RuntimeOrigin::signed(5)), Error::<Test>::MemberSubmit);
		});
	}

	#[test]
	fn runner_candidate_submission_should_not_work() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5, 4], 20));
			assert_ok!(vote(RuntimeOrigin::signed(1), vec![3], 10));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![3]);

			assert_noop!(submit_candidacy(RuntimeOrigin::signed(3)), Error::<Test>::RunnerUpSubmit);
		});
	}

	#[test]
	fn poor_candidate_submission_should_not_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());
			assert_noop!(
				submit_candidacy(RuntimeOrigin::signed(7)),
				Error::<Test>::InsufficientCandidateFunds,
			);
		});
	}

	#[test]
	fn simple_voting_should_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());
			assert_eq!(balances(&2), (20, 0));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));

			assert_eq!(balances(&2), (18, 2));
			assert_eq!(has_lock(&2), 18);
		});
	}

	#[test]
	fn can_vote_with_custom_stake() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(candidate_ids(), Vec::<u64>::new());
			assert_eq!(balances(&2), (20, 0));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 12));

			assert_eq!(balances(&2), (18, 2));
			assert_eq!(has_lock(&2), 12);
		});
	}

	#[test]
	fn can_update_votes_and_stake() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(balances(&2), (20, 0));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));

			// User only locks up to their free balance.
			assert_eq!(balances(&2), (18, 2));
			assert_eq!(has_lock(&2), 18);
			assert_eq!(locked_stake_of(&2), 18);

			// can update; different stake; different lock and reserve.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5, 4], 15));
			assert_eq!(balances(&2), (18, 2));
			assert_eq!(has_lock(&2), 15);
			assert_eq!(locked_stake_of(&2), 15);
		});
	}

	#[test]
	fn updated_voting_bond_works() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_eq!(balances(&2), (20, 0));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 5));
			assert_eq!(balances(&2), (18, 2));
			assert_eq!(voter_deposit(&2), 2);

			// a runtime upgrade lowers the voting bond to 1. This guy still un-reserves 2 when
			// leaving.
			VOTING_BOND_BASE.with(|v| *v.borrow_mut() = 1);

			// proof that bond changed.
			assert_eq!(balances(&1), (10, 0));
			assert_ok!(vote(RuntimeOrigin::signed(1), vec![5], 5));
			assert_eq!(balances(&1), (9, 1));
			assert_eq!(voter_deposit(&1), 1);

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(2)));
			assert_eq!(balances(&2), (20, 0));
		})
	}

	#[test]
	fn voting_reserves_bond_per_vote() {
		ExtBuilder::default().voter_bond_factor(1).build_and_execute(|| {
			assert_eq!(balances(&2), (20, 0));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			// initial vote.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 10));

			// 2 + 1
			assert_eq!(balances(&2), (17, 3));
			assert_eq!(Elections::voting(&2).deposit, 3);
			assert_eq!(has_lock(&2), 10);
			assert_eq!(locked_stake_of(&2), 10);

			// can update; different stake; different lock and reserve.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5, 4], 15));
			// 2 + 2
			assert_eq!(balances(&2), (16, 4));
			assert_eq!(Elections::voting(&2).deposit, 4);
			assert_eq!(has_lock(&2), 15);
			assert_eq!(locked_stake_of(&2), 15);

			// stay at two votes with different stake.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5, 3], 18));
			// 2 + 2
			assert_eq!(balances(&2), (16, 4));
			assert_eq!(Elections::voting(&2).deposit, 4);
			assert_eq!(has_lock(&2), 16);
			assert_eq!(locked_stake_of(&2), 16);

			// back to 1 vote.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![4], 12));
			// 2 + 1
			assert_eq!(balances(&2), (17, 3));
			assert_eq!(Elections::voting(&2).deposit, 3);
			assert_eq!(has_lock(&2), 12);
			assert_eq!(locked_stake_of(&2), 12);
		});
	}

	#[test]
	fn cannot_vote_for_no_candidate() {
		ExtBuilder::default().build_and_execute(|| {
			assert_noop!(vote(RuntimeOrigin::signed(2), vec![], 20), Error::<Test>::NoVotes);
		});
	}

	#[test]
	fn can_vote_for_old_members_even_when_no_new_candidates() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![4, 5], 20));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert!(candidate_ids().is_empty());

			assert_ok!(vote(RuntimeOrigin::signed(3), vec![4, 5], 10));
		});
	}

	#[test]
	fn prime_works() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(1), vec![4, 3], 10));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![4], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert!(candidate_ids().is_empty());

			assert_ok!(vote(RuntimeOrigin::signed(3), vec![4, 5], 10));
			assert_eq!(PRIME.with(|p| *p.borrow()), Some(4));
		});
	}

	#[test]
	fn prime_votes_for_exiting_members_are_removed() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(1), vec![4, 3], 10));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![4], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(4),
				Renouncing::Candidate(3)
			));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![3, 5]);
			assert!(candidate_ids().is_empty());

			assert_eq!(PRIME.with(|p| *p.borrow()), Some(5));
		});
	}

	#[test]
	fn prime_is_kept_if_other_members_leave() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(PRIME.with(|p| *p.borrow()), Some(5));
			assert_ok!(Elections::renounce_candidacy(RuntimeOrigin::signed(4), Renouncing::Member));

			assert_eq!(members_ids(), vec![5]);
			assert_eq!(PRIME.with(|p| *p.borrow()), Some(5));
		})
	}

	#[test]
	fn prime_is_gone_if_renouncing() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(PRIME.with(|p| *p.borrow()), Some(5));
			assert_ok!(Elections::renounce_candidacy(RuntimeOrigin::signed(5), Renouncing::Member));

			assert_eq!(members_ids(), vec![4]);
			assert_eq!(PRIME.with(|p| *p.borrow()), None);
		})
	}

	#[test]
	fn cannot_vote_for_more_than_candidates_and_members_and_runners() {
		ExtBuilder::default()
			.desired_runners_up(1)
			.balance_factor(10)
			.build_and_execute(|| {
				// when we have only candidates
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

				assert_noop!(
					// content of the vote is irrelevant.
					vote(RuntimeOrigin::signed(1), vec![9, 99, 999, 9999], 5),
					Error::<Test>::TooManyVotes,
				);

				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				// now we have 2 members, 1 runner-up, and 1 new candidate
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_ok!(vote(RuntimeOrigin::signed(1), vec![9, 99, 999, 9999], 5));
				assert_noop!(
					vote(RuntimeOrigin::signed(1), vec![9, 99, 999, 9_999, 99_999], 5),
					Error::<Test>::TooManyVotes,
				);
			});
	}

	#[test]
	fn cannot_vote_for_less_than_ed() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_noop!(vote(RuntimeOrigin::signed(2), vec![4], 1), Error::<Test>::LowBalance);
		})
	}

	#[test]
	fn can_vote_for_more_than_free_balance_but_moot() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			// User has 100 free and 50 reserved.
			assert_ok!(Balances::force_set_balance(RuntimeOrigin::root(), 2, 150));
			assert_ok!(Balances::reserve(&2, 50));
			// User tries to vote with 150 tokens.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![4, 5], 150));
			// We truncate to only their free balance, after reserving additional for voting.
			assert_eq!(locked_stake_of(&2), 98);
			assert_eq!(has_lock(&2), 98);
		});
	}

	#[test]
	fn remove_voter_should_work() {
		ExtBuilder::default().voter_bond(8).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![5], 30));

			assert_eq_uvec!(all_voters(), vec![2, 3]);
			assert_eq!(balances(&2), (12, 8));
			assert_eq!(locked_stake_of(&2), 12);
			assert_eq!(balances(&3), (22, 8));
			assert_eq!(locked_stake_of(&3), 22);
			assert_eq!(votes_of(&2), vec![5]);
			assert_eq!(votes_of(&3), vec![5]);

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(2)));

			assert_eq_uvec!(all_voters(), vec![3]);
			assert!(votes_of(&2).is_empty());
			assert_eq!(locked_stake_of(&2), 0);

			assert_eq!(balances(&2), (20, 0));
			assert_eq!(Balances::locks(&2).len(), 0);
		});
	}

	#[test]
	fn non_voter_remove_should_not_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_noop!(
				Elections::remove_voter(RuntimeOrigin::signed(3)),
				Error::<Test>::MustBeVoter
			);
		});
	}

	#[test]
	fn dupe_remove_should_fail() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(2)));
			assert!(all_voters().is_empty());

			assert_noop!(
				Elections::remove_voter(RuntimeOrigin::signed(2)),
				Error::<Test>::MustBeVoter
			);
		});
	}

	#[test]
	fn removed_voter_should_not_be_counted() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(4)));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![3, 5]);
		});
	}

	#[test]
	fn simple_voting_rounds_should_work() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 15));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			assert_eq_uvec!(all_voters(), vec![2, 3, 4]);

			assert_eq!(votes_of(&2), vec![5]);
			assert_eq!(votes_of(&3), vec![3]);
			assert_eq!(votes_of(&4), vec![4]);

			assert_eq!(candidate_ids(), vec![3, 4, 5]);
			assert_eq!(<Candidates<Test>>::decode_len().unwrap(), 3);

			assert_eq!(Elections::election_rounds(), 0);

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(balances(&3), (25, 5));
			// votes for 5
			assert_eq!(balances(&2), (18, 2));
			assert_eq!(members_and_stake(), vec![(3, 25), (5, 18)]);
			assert!(Elections::runners_up().is_empty());

			assert_eq_uvec!(all_voters(), vec![2, 3, 4]);
			assert!(candidate_ids().is_empty());
			assert_eq!(<Candidates<Test>>::decode_len(), None);

			assert_eq!(Elections::election_rounds(), 1);
		});
	}

	#[test]
	fn empty_term() {
		ExtBuilder::default().build_and_execute(|| {
			// no candidates, no nothing.
			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			System::assert_last_event(RuntimeEvent::Elections(super::Event::EmptyTerm));
		})
	}

	#[test]
	fn all_outgoing() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			System::assert_last_event(RuntimeEvent::Elections(super::Event::NewTerm {
				new_members: vec![(4, 35), (5, 45)],
			}));

			assert_eq!(members_and_stake(), vec![(4, 35), (5, 45)]);
			assert_eq!(runners_up_and_stake(), vec![]);

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(5)));
			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(4)));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			System::assert_last_event(RuntimeEvent::Elections(super::Event::NewTerm {
				new_members: vec![],
			}));

			// outgoing have lost their bond.
			assert_eq!(balances(&4), (37, 0));
			assert_eq!(balances(&5), (47, 0));
		});
	}

	#[test]
	fn defunct_voter_will_be_counted() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			// This guy's vote is pointless for this round.
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![4], 30));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_and_stake(), vec![(5, 45)]);
			assert_eq!(Elections::election_rounds(), 1);

			// but now it has a valid target.
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			// candidate 4 is affected by an old vote.
			assert_eq!(members_and_stake(), vec![(4, 28), (5, 45)]);
			assert_eq!(Elections::election_rounds(), 2);
			assert_eq_uvec!(all_voters(), vec![3, 5]);
		});
	}

	#[test]
	fn only_desired_seats_are_chosen() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(Elections::election_rounds(), 1);
			assert_eq!(members_ids(), vec![4, 5]);
		});
	}

	#[test]
	fn phragmen_should_not_self_vote() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert!(candidate_ids().is_empty());
			assert_eq!(Elections::election_rounds(), 1);
			assert!(members_ids().is_empty());

			System::assert_last_event(RuntimeEvent::Elections(super::Event::NewTerm {
				new_members: vec![],
			}));
		});
	}

	#[test]
	fn runners_up_should_be_kept() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![3], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![2], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![5], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![4], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			// sorted based on account id.
			assert_eq!(members_ids(), vec![4, 5]);
			// sorted based on merit (least -> most)
			assert_eq!(runners_up_ids(), vec![3, 2]);

			// runner ups are still locked.
			assert_eq!(balances(&4), (35, 5));
			assert_eq!(balances(&5), (45, 5));
			assert_eq!(balances(&3), (25, 5));
		});
	}

	#[test]
	fn runners_up_should_be_next_candidates() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_and_stake(), vec![(4, 35), (5, 45)]);
			assert_eq!(runners_up_and_stake(), vec![(2, 15), (3, 25)]);

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 10));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_and_stake(), vec![(3, 25), (4, 35)]);
			assert_eq!(runners_up_and_stake(), vec![(5, 10), (2, 15)]);
		});
	}

	#[test]
	fn runners_up_lose_bond_once_outgoing() {
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![2]);
			assert_eq!(balances(&2), (15, 5));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			assert_eq!(runners_up_ids(), vec![3]);
			assert_eq!(balances(&2), (15, 2));
		});
	}

	#[test]
	fn members_lose_bond_once_outgoing() {
		ExtBuilder::default().build_and_execute(|| {
			assert_eq!(balances(&5), (50, 0));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_eq!(balances(&5), (47, 3));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_eq!(balances(&5), (45, 5));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_ids(), vec![5]);

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(5)));
			assert_eq!(balances(&5), (47, 3));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());
			assert!(members_ids().is_empty());

			assert_eq!(balances(&5), (47, 0));
		});
	}

	#[test]
	fn candidates_lose_the_bond_when_outgoing() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![5], 40));

			assert_eq!(balances(&5), (47, 3));
			assert_eq!(balances(&3), (27, 3));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![5]);

			// winner
			assert_eq!(balances(&5), (47, 3));
			// loser
			assert_eq!(balances(&3), (27, 0));
		});
	}

	#[test]
	fn current_members_are_always_next_candidate() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(Elections::election_rounds(), 1);

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(4)));

			// 5 will persist as candidates despite not being in the list.
			assert_eq!(candidate_ids(), vec![2, 3]);

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			// 4 removed; 5 and 3 are the new best.
			assert_eq!(members_ids(), vec![3, 5]);
		});
	}

	#[test]
	fn election_state_is_uninterrupted() {
		// what I mean by uninterrupted:
		// given no input or stimulants the same members are re-elected.
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

			let check_at_block = |b: u32| {
				System::set_block_number(b.into());
				Elections::on_initialize(System::block_number());
				// we keep re-electing the same folks.
				assert_eq!(members_and_stake(), vec![(4, 35), (5, 45)]);
				assert_eq!(runners_up_and_stake(), vec![(2, 15), (3, 25)]);
				// no new candidates but old members and runners-up are always added.
				assert!(candidate_ids().is_empty());
				assert_eq!(Elections::election_rounds(), b / 5);
				assert_eq_uvec!(all_voters(), vec![2, 3, 4, 5]);
			};

			// this state will always persist when no further input is given.
			check_at_block(5);
			check_at_block(10);
			check_at_block(15);
			check_at_block(20);
		});
	}

	#[test]
	fn remove_members_triggers_election() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(Elections::election_rounds(), 1);

			// a new candidate
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			assert_ok!(Elections::remove_member(RuntimeOrigin::root(), 4, true, true));

			assert_eq!(balances(&4), (35, 2)); // slashed
			assert_eq!(Elections::election_rounds(), 2); // new election round
			assert_eq!(members_ids(), vec![3, 5]); // new members
		});
	}

	#[test]
	fn seats_should_be_released_when_no_vote() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![3], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			assert_eq!(<Candidates<Test>>::decode_len().unwrap(), 3);

			assert_eq!(Elections::election_rounds(), 0);

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_ids(), vec![3, 5]);
			assert_eq!(Elections::election_rounds(), 1);

			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(2)));
			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(3)));
			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(4)));
			assert_ok!(Elections::remove_voter(RuntimeOrigin::signed(5)));

			// meanwhile, no one cares to become a candidate again.
			System::set_block_number(10);
			Elections::on_initialize(System::block_number());
			assert!(members_ids().is_empty());
			assert_eq!(Elections::election_rounds(), 2);
		});
	}

	#[test]
	fn incoming_outgoing_are_reported() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));

			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			assert_eq!(members_ids(), vec![4, 5]);

			assert_ok!(submit_candidacy(RuntimeOrigin::signed(1)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			// 5 will change their vote and becomes an `outgoing`
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![4], 8));
			// 4 will stay in the set
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			// 3 will become a winner
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			// these two are losers.
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));
			assert_ok!(vote(RuntimeOrigin::signed(1), vec![1], 10));

			System::set_block_number(10);
			Elections::on_initialize(System::block_number());

			// 3, 4 are new members, must still be bonded, nothing slashed.
			assert_eq!(members_and_stake(), vec![(3, 25), (4, 43)]);
			assert_eq!(balances(&3), (25, 5));
			assert_eq!(balances(&4), (35, 5));

			// 1 is a loser, slashed by 3.
			assert_eq!(balances(&1), (5, 2));

			// 5 is an outgoing loser. will also get slashed.
			assert_eq!(balances(&5), (45, 2));

			System::assert_has_event(RuntimeEvent::Elections(super::Event::NewTerm {
				new_members: vec![(4, 35), (5, 45)],
			}));
		})
	}

	#[test]
	fn invalid_votes_are_moot() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![10], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq_uvec!(members_ids(), vec![3, 4]);
			assert_eq!(Elections::election_rounds(), 1);
		});
	}

	#[test]
	fn members_are_sorted_based_on_id_runners_on_merit() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![3], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![2], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![5], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![4], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());
			// id: low -> high.
			assert_eq!(members_and_stake(), vec![(4, 45), (5, 35)]);
			// merit: low -> high.
			assert_eq!(runners_up_and_stake(), vec![(3, 15), (2, 25)]);
		});
	}

	#[test]
	fn runner_up_replacement_maintains_members_order() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![2], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![2, 4]);
			assert_ok!(Elections::remove_member(RuntimeOrigin::root(), 2, true, false));
			assert_eq!(members_ids(), vec![4, 5]);
		});
	}

	#[test]
	fn can_renounce_candidacy_member_with_runners_bond_is_refunded() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![2, 3]);

			assert_ok!(Elections::renounce_candidacy(RuntimeOrigin::signed(4), Renouncing::Member));
			assert_eq!(balances(&4), (38, 2)); // 2 is voting bond.

			assert_eq!(members_ids(), vec![3, 5]);
			assert_eq!(runners_up_ids(), vec![2]);
		})
	}

	#[test]
	fn can_renounce_candidacy_member_without_runners_bond_is_refunded() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert!(runners_up_ids().is_empty());

			assert_ok!(Elections::renounce_candidacy(RuntimeOrigin::signed(4), Renouncing::Member));
			assert_eq!(balances(&4), (38, 2)); // 2 is voting bond.

			// no replacement
			assert_eq!(members_ids(), vec![5]);
			assert!(runners_up_ids().is_empty());
		})
	}

	#[test]
	fn can_renounce_candidacy_runner_up() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![4], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![5], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![2, 3]);

			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(3),
				Renouncing::RunnerUp
			));
			assert_eq!(balances(&3), (28, 2)); // 2 is voting bond.

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![2]);
		})
	}

	#[test]
	fn runner_up_replacement_works_when_out_of_order() {
		ExtBuilder::default().desired_runners_up(2).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

			assert_ok!(vote(RuntimeOrigin::signed(2), vec![5], 20));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![2], 50));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![2, 4]);
			assert_eq!(runners_up_ids(), vec![5, 3]);
			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(3),
				Renouncing::RunnerUp
			));
			assert_eq!(members_ids(), vec![2, 4]);
			assert_eq!(runners_up_ids(), vec![5]);
		});
	}

	#[test]
	fn can_renounce_candidacy_candidate() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_eq!(balances(&5), (47, 3));
			assert_eq!(candidate_ids(), vec![5]);

			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(5),
				Renouncing::Candidate(1)
			));
			assert_eq!(balances(&5), (50, 0));
			assert!(candidate_ids().is_empty());
		})
	}

	#[test]
	fn wrong_renounce_candidacy_should_fail() {
		ExtBuilder::default().build_and_execute(|| {
			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(5), Renouncing::Candidate(0)),
				Error::<Test>::InvalidRenouncing,
			);
			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(5), Renouncing::Member),
				Error::<Test>::InvalidRenouncing,
			);
			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(5), Renouncing::RunnerUp),
				Error::<Test>::InvalidRenouncing,
			);
		})
	}

	#[test]
	fn non_member_renounce_member_should_fail() {
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![3]);

			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(3), Renouncing::Member),
				Error::<Test>::InvalidRenouncing,
			);
		})
	}

	#[test]
	fn non_runner_up_renounce_runner_up_should_fail() {
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![3]);

			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(4), Renouncing::RunnerUp),
				Error::<Test>::InvalidRenouncing,
			);
		})
	}

	#[test]
	fn wrong_candidate_count_renounce_should_fail() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_noop!(
				Elections::renounce_candidacy(RuntimeOrigin::signed(4), Renouncing::Candidate(2)),
				Error::<Test>::InvalidWitnessData,
			);

			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(4),
				Renouncing::Candidate(3)
			));
		})
	}

	#[test]
	fn renounce_candidacy_count_can_overestimate() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			// while we have only 3 candidates.
			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(4),
				Renouncing::Candidate(4)
			));
		})
	}

	#[test]
	fn unsorted_runners_up_are_detected() {
		ExtBuilder::default()
			.desired_runners_up(2)
			.desired_members(1)
			.build_and_execute(|| {
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

				assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 5));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 15));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![5]);
				assert_eq!(runners_up_ids(), vec![4, 3]);

				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 10));

				System::set_block_number(10);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![5]);
				assert_eq!(runners_up_ids(), vec![2, 3]);

				// 4 is outgoing runner-up. Slash candidacy bond.
				assert_eq!(balances(&4), (35, 2));
				// 3 stays.
				assert_eq!(balances(&3), (25, 5));
			})
	}

	#[test]
	fn member_to_runner_up_wont_slash() {
		ExtBuilder::default()
			.desired_runners_up(2)
			.desired_members(1)
			.build_and_execute(|| {
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![4]);
				assert_eq!(runners_up_ids(), vec![2, 3]);

				assert_eq!(balances(&4), (35, 5));
				assert_eq!(balances(&3), (25, 5));
				assert_eq!(balances(&2), (15, 5));

				// this guy will shift everyone down.
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
				assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));

				System::set_block_number(10);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![5]);
				assert_eq!(runners_up_ids(), vec![3, 4]);

				// 4 went from member to runner-up -- don't slash.
				assert_eq!(balances(&4), (35, 5));
				// 3 stayed runner-up -- don't slash.
				assert_eq!(balances(&3), (25, 5));
				// 2 was removed -- slash.
				assert_eq!(balances(&2), (15, 2));
			});
	}

	#[test]
	fn runner_up_to_member_wont_slash() {
		ExtBuilder::default()
			.desired_runners_up(2)
			.desired_members(1)
			.build_and_execute(|| {
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![4]);
				assert_eq!(runners_up_ids(), vec![2, 3]);

				assert_eq!(balances(&4), (35, 5));
				assert_eq!(balances(&3), (25, 5));
				assert_eq!(balances(&2), (15, 5));

				// swap some votes.
				assert_ok!(vote(RuntimeOrigin::signed(4), vec![2], 40));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![4], 20));

				System::set_block_number(10);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![2]);
				assert_eq!(runners_up_ids(), vec![4, 3]);

				// 2 went from runner to member, don't slash
				assert_eq!(balances(&2), (15, 5));
				// 4 went from member to runner, don't slash
				assert_eq!(balances(&4), (35, 5));
				// 3 stayed the same
				assert_eq!(balances(&3), (25, 5));
			});
	}

	#[test]
	fn remove_and_replace_member_works() {
		let setup = || {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5], 50));
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![4, 5]);
			assert_eq!(runners_up_ids(), vec![3]);
		};

		// member removed, replacement found.
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			setup();
			assert_eq!(Elections::remove_and_replace_member(&4, false), Ok(true));

			assert_eq!(members_ids(), vec![3, 5]);
			assert_eq!(runners_up_ids().len(), 0);
		});

		// member removed, no replacement found.
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			setup();
			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(3),
				Renouncing::RunnerUp
			));
			assert_eq!(Elections::remove_and_replace_member(&4, false), Ok(false));

			assert_eq!(members_ids(), vec![5]);
			assert_eq!(runners_up_ids().len(), 0);
		});

		// wrong member to remove.
		ExtBuilder::default().desired_runners_up(1).build_and_execute(|| {
			setup();
			assert!(matches!(Elections::remove_and_replace_member(&2, false), Err(_)));
		});
	}

	#[test]
	fn no_desired_members() {
		// not interested in anything
		ExtBuilder::default()
			.desired_members(0)
			.desired_runners_up(0)
			.build_and_execute(|| {
				assert_eq!(Elections::candidates().len(), 0);

				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_eq!(Elections::candidates().len(), 3);

				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids().len(), 0);
				assert_eq!(runners_up_ids().len(), 0);
				assert_eq!(all_voters().len(), 3);
				assert_eq!(Elections::candidates().len(), 0);
			});

		// not interested in members
		ExtBuilder::default()
			.desired_members(0)
			.desired_runners_up(2)
			.build_and_execute(|| {
				assert_eq!(Elections::candidates().len(), 0);

				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_eq!(Elections::candidates().len(), 3);

				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids().len(), 0);
				assert_eq!(runners_up_ids(), vec![3, 4]);
				assert_eq!(all_voters().len(), 3);
				assert_eq!(Elections::candidates().len(), 0);
			});

		// not interested in runners-up
		ExtBuilder::default()
			.desired_members(2)
			.desired_runners_up(0)
			.build_and_execute(|| {
				assert_eq!(Elections::candidates().len(), 0);

				assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
				assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));

				assert_eq!(Elections::candidates().len(), 3);

				assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 40));
				assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));
				assert_ok!(vote(RuntimeOrigin::signed(2), vec![2], 20));

				System::set_block_number(5);
				Elections::on_initialize(System::block_number());

				assert_eq!(members_ids(), vec![3, 4]);
				assert_eq!(runners_up_ids().len(), 0);
				assert_eq!(all_voters().len(), 3);
				assert_eq!(Elections::candidates().len(), 0);
			});
	}

	#[test]
	fn dupe_vote_is_moot() {
		ExtBuilder::default().desired_members(1).build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(2)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(1)));

			// all these duplicate votes will not cause 2 to win.
			assert_ok!(vote(RuntimeOrigin::signed(1), vec![2, 2, 2, 2], 5));
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![2, 2, 2, 2], 20));

			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 30));

			System::set_block_number(5);
			Elections::on_initialize(System::block_number());

			assert_eq!(members_ids(), vec![3]);
		})
	}

	#[test]
	fn remove_defunct_voter_works() {
		ExtBuilder::default().build_and_execute(|| {
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(5)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(4)));
			assert_ok!(submit_candidacy(RuntimeOrigin::signed(3)));

			// defunct
			assert_ok!(vote(RuntimeOrigin::signed(5), vec![5, 4], 5));
			// defunct
			assert_ok!(vote(RuntimeOrigin::signed(4), vec![4], 5));
			// ok
			assert_ok!(vote(RuntimeOrigin::signed(3), vec![3], 5));
			// ok
			assert_ok!(vote(RuntimeOrigin::signed(2), vec![3, 4], 5));

			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(5),
				Renouncing::Candidate(3)
			));
			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(4),
				Renouncing::Candidate(2)
			));
			assert_ok!(Elections::renounce_candidacy(
				RuntimeOrigin::signed(3),
				Renouncing::Candidate(1)
			));

			assert_ok!(Elections::clean_defunct_voters(RuntimeOrigin::root(), 4, 2));
		})
	}
}