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// Copyright 2019-2020 Parity Technologies (UK) Ltd. // This file is part of Substrate. // Substrate is free software: you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation, either version 3 of the License, or // (at your option) any later version. // Substrate is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // You should have received a copy of the GNU General Public License // along with Substrate. If not, see <http://www.gnu.org/licenses/>. //! # Scored Pool Module //! //! The module maintains a scored membership pool. Each entity in the //! pool can be attributed a `Score`. From this pool a set `Members` //! is constructed. This set contains the `MemberCount` highest //! scoring entities. Unscored entities are never part of `Members`. //! //! If an entity wants to be part of the pool a deposit is required. //! The deposit is returned when the entity withdraws or when it //! is removed by an entity with the appropriate authority. //! //! Every `Period` blocks the set of `Members` is refreshed from the //! highest scoring members in the pool and, no matter if changes //! occurred, `T::MembershipChanged::set_members_sorted` is invoked. //! On first load `T::MembershipInitialized::initialize_members` is //! invoked with the initial `Members` set. //! //! It is possible to withdraw candidacy/resign your membership at any //! time. If an entity is currently a member, this results in removal //! from the `Pool` and `Members`; the entity is immediately replaced //! by the next highest scoring candidate in the pool, if available. //! //! - [`scored_pool::Trait`](./trait.Trait.html) //! - [`Call`](./enum.Call.html) //! - [`Module`](./struct.Module.html) //! //! ## Interface //! //! ### Public Functions //! //! - `submit_candidacy` - Submit candidacy to become a member. Requires a deposit. //! - `withdraw_candidacy` - Withdraw candidacy. Deposit is returned. //! - `score` - Attribute a quantitative score to an entity. //! - `kick` - Remove an entity from the pool and members. Deposit is returned. //! - `change_member_count` - Changes the amount of candidates taken into `Members`. //! //! ## Usage //! //! ``` //! use frame_support::{decl_module, dispatch}; //! use frame_system::{self as system, ensure_signed}; //! use pallet_scored_pool::{self as scored_pool}; //! //! pub trait Trait: scored_pool::Trait {} //! //! decl_module! { //! pub struct Module<T: Trait> for enum Call where origin: T::Origin { //! pub fn candidate(origin) -> dispatch::DispatchResult { //! let who = ensure_signed(origin)?; //! //! let _ = <scored_pool::Module<T>>::submit_candidacy( //! T::Origin::from(Some(who.clone()).into()) //! ); //! Ok(()) //! } //! } //! } //! //! # fn main() { } //! ``` //! //! ## Dependencies //! //! This module depends on the [System module](../frame_system/index.html). // Ensure we're `no_std` when compiling for Wasm. #![cfg_attr(not(feature = "std"), no_std)] #[cfg(test)] mod mock; #[cfg(test)] mod tests; use codec::FullCodec; use sp_std::{ fmt::Debug, prelude::*, }; use frame_support::{ decl_module, decl_storage, decl_event, ensure, decl_error, traits::{ChangeMembers, InitializeMembers, Currency, Get, ReservableCurrency}, }; use frame_system::{self as system, ensure_root, ensure_signed}; use sp_runtime::{ traits::{EnsureOrigin, AtLeast32Bit, MaybeSerializeDeserialize, Zero, StaticLookup}, }; type BalanceOf<T, I> = <<T as Trait<I>>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::Balance; type PoolT<T, I> = Vec<(<T as frame_system::Trait>::AccountId, Option<<T as Trait<I>>::Score>)>; /// The enum is supplied when refreshing the members set. /// Depending on the enum variant the corresponding associated /// type function will be invoked. enum ChangeReceiver { /// Should call `T::MembershipInitialized`. MembershipInitialized, /// Should call `T::MembershipChanged`. MembershipChanged, } pub trait Trait<I=DefaultInstance>: frame_system::Trait { /// The currency used for deposits. type Currency: Currency<Self::AccountId> + ReservableCurrency<Self::AccountId>; /// The score attributed to a member or candidate. type Score: AtLeast32Bit + Clone + Copy + Default + FullCodec + MaybeSerializeDeserialize + Debug; /// The overarching event type. type Event: From<Event<Self, I>> + Into<<Self as frame_system::Trait>::Event>; // The deposit which is reserved from candidates if they want to // start a candidacy. The deposit gets returned when the candidacy is // withdrawn or when the candidate is kicked. type CandidateDeposit: Get<BalanceOf<Self, I>>; /// Every `Period` blocks the `Members` are filled with the highest scoring /// members in the `Pool`. type Period: Get<Self::BlockNumber>; /// The receiver of the signal for when the membership has been initialized. /// This happens pre-genesis and will usually be the same as `MembershipChanged`. /// If you need to do something different on initialization, then you can change /// this accordingly. type MembershipInitialized: InitializeMembers<Self::AccountId>; /// The receiver of the signal for when the members have changed. type MembershipChanged: ChangeMembers<Self::AccountId>; /// Allows a configurable origin type to set a score to a candidate in the pool. type ScoreOrigin: EnsureOrigin<Self::Origin>; /// Required origin for removing a member (though can always be Root). /// Configurable origin which enables removing an entity. If the entity /// is part of the `Members` it is immediately replaced by the next /// highest scoring candidate, if available. type KickOrigin: EnsureOrigin<Self::Origin>; } decl_storage! { trait Store for Module<T: Trait<I>, I: Instance=DefaultInstance> as ScoredPool { /// The current pool of candidates, stored as an ordered Vec /// (ordered descending by score, `None` last, highest first). Pool get(fn pool) config(): PoolT<T, I>; /// A Map of the candidates. The information in this Map is redundant /// to the information in the `Pool`. But the Map enables us to easily /// check if a candidate is already in the pool, without having to /// iterate over the entire pool (the `Pool` is not sorted by /// `T::AccountId`, but by `T::Score` instead). CandidateExists get(fn candidate_exists): map hasher(blake2_256) T::AccountId => bool; /// The current membership, stored as an ordered Vec. Members get(fn members): Vec<T::AccountId>; /// Size of the `Members` set. MemberCount get(fn member_count) config(): u32; } add_extra_genesis { config(members): Vec<T::AccountId>; config(phantom): sp_std::marker::PhantomData<I>; build(|config| { let mut pool = config.pool.clone(); // reserve balance for each candidate in the pool. // panicking here is ok, since this just happens one time, pre-genesis. pool .iter() .for_each(|(who, _)| { T::Currency::reserve(&who, T::CandidateDeposit::get()) .expect("balance too low to create candidacy"); <CandidateExists<T, I>>::insert(who, true); }); /// Sorts the `Pool` by score in a descending order. Entities which /// have a score of `None` are sorted to the beginning of the vec. pool.sort_by_key(|(_, maybe_score)| Reverse(maybe_score.unwrap_or_default()) ); <Pool<T, I>>::put(&pool); <Module<T, I>>::refresh_members(pool, ChangeReceiver::MembershipInitialized); }) } } decl_event!( pub enum Event<T, I=DefaultInstance> where <T as frame_system::Trait>::AccountId, { /// The given member was removed. See the transaction for who. MemberRemoved, /// An entity has issued a candidacy. See the transaction for who. CandidateAdded, /// An entity withdrew candidacy. See the transaction for who. CandidateWithdrew, /// The candidacy was forcefully removed for an entity. /// See the transaction for who. CandidateKicked, /// A score was attributed to the candidate. /// See the transaction for who. CandidateScored, /// Phantom member, never used. Dummy(sp_std::marker::PhantomData<(AccountId, I)>), } ); decl_error! { /// Error for the scored-pool module. pub enum Error for Module<T: Trait<I>, I: Instance> { /// Already a member. AlreadyInPool, /// Index out of bounds. InvalidIndex, /// Index does not match requested account. WrongAccountIndex, } } decl_module! { pub struct Module<T: Trait<I>, I: Instance=DefaultInstance> for enum Call where origin: T::Origin { type Error = Error<T, I>; fn deposit_event() = default; /// Every `Period` blocks the `Members` set is refreshed from the /// highest scoring members in the pool. fn on_initialize(n: T::BlockNumber) { if n % T::Period::get() == Zero::zero() { let pool = <Pool<T, I>>::get(); <Module<T, I>>::refresh_members(pool, ChangeReceiver::MembershipChanged); } } /// Add `origin` to the pool of candidates. /// /// This results in `CandidateDeposit` being reserved from /// the `origin` account. The deposit is returned once /// candidacy is withdrawn by the candidate or the entity /// is kicked by `KickOrigin`. /// /// The dispatch origin of this function must be signed. /// /// The `index` parameter of this function must be set to /// the index of the transactor in the `Pool`. pub fn submit_candidacy(origin) { let who = ensure_signed(origin)?; ensure!(!<CandidateExists<T, I>>::contains_key(&who), Error::<T, I>::AlreadyInPool); let deposit = T::CandidateDeposit::get(); T::Currency::reserve(&who, deposit)?; // can be inserted as last element in pool, since entities with // `None` are always sorted to the end. if let Err(e) = <Pool<T, I>>::append(&[(who.clone(), None)]) { T::Currency::unreserve(&who, deposit); Err(e)? } <CandidateExists<T, I>>::insert(&who, true); Self::deposit_event(RawEvent::CandidateAdded); } /// An entity withdraws candidacy and gets its deposit back. /// /// If the entity is part of the `Members`, then the highest member /// of the `Pool` that is not currently in `Members` is immediately /// placed in the set instead. /// /// The dispatch origin of this function must be signed. /// /// The `index` parameter of this function must be set to /// the index of the transactor in the `Pool`. pub fn withdraw_candidacy( origin, index: u32 ) { let who = ensure_signed(origin)?; let pool = <Pool<T, I>>::get(); Self::ensure_index(&pool, &who, index)?; Self::remove_member(pool, who, index)?; Self::deposit_event(RawEvent::CandidateWithdrew); } /// Kick a member `who` from the set. /// /// May only be called from `KickOrigin` or root. /// /// The `index` parameter of this function must be set to /// the index of `dest` in the `Pool`. pub fn kick( origin, dest: <T::Lookup as StaticLookup>::Source, index: u32 ) { T::KickOrigin::try_origin(origin) .map(|_| ()) .or_else(ensure_root)?; let who = T::Lookup::lookup(dest)?; let pool = <Pool<T, I>>::get(); Self::ensure_index(&pool, &who, index)?; Self::remove_member(pool, who, index)?; Self::deposit_event(RawEvent::CandidateKicked); } /// Score a member `who` with `score`. /// /// May only be called from `ScoreOrigin` or root. /// /// The `index` parameter of this function must be set to /// the index of the `dest` in the `Pool`. pub fn score( origin, dest: <T::Lookup as StaticLookup>::Source, index: u32, score: T::Score ) { T::ScoreOrigin::try_origin(origin) .map(|_| ()) .or_else(ensure_root)?; let who = T::Lookup::lookup(dest)?; let mut pool = <Pool<T, I>>::get(); Self::ensure_index(&pool, &who, index)?; pool.remove(index as usize); // we binary search the pool (which is sorted descending by score). // if there is already an element with `score`, we insert // right before that. if not, the search returns a location // where we can insert while maintaining order. let item = (who.clone(), Some(score.clone())); let location = pool .binary_search_by_key( &Reverse(score), |(_, maybe_score)| Reverse(maybe_score.unwrap_or_default()) ) .unwrap_or_else(|l| l); pool.insert(location, item); <Pool<T, I>>::put(&pool); Self::deposit_event(RawEvent::CandidateScored); } /// Dispatchable call to change `MemberCount`. /// /// This will only have an effect the next time a refresh happens /// (this happens each `Period`). /// /// May only be called from root. pub fn change_member_count(origin, count: u32) { ensure_root(origin)?; <MemberCount<I>>::put(&count); } } } impl<T: Trait<I>, I: Instance> Module<T, I> { /// Fetches the `MemberCount` highest scoring members from /// `Pool` and puts them into `Members`. /// /// The `notify` parameter is used to deduct which associated /// type function to invoke at the end of the method. fn refresh_members( pool: PoolT<T, I>, notify: ChangeReceiver ) { let count = <MemberCount<I>>::get(); let mut new_members: Vec<T::AccountId> = pool .into_iter() .filter(|(_, score)| score.is_some()) .take(count as usize) .map(|(account_id, _)| account_id) .collect(); new_members.sort(); let old_members = <Members<T, I>>::get(); <Members<T, I>>::put(&new_members); match notify { ChangeReceiver::MembershipInitialized => T::MembershipInitialized::initialize_members(&new_members), ChangeReceiver::MembershipChanged => T::MembershipChanged::set_members_sorted( &new_members[..], &old_members[..], ), } } /// Removes an entity `remove` at `index` from the `Pool`. /// /// If the entity is a member it is also removed from `Members` and /// the deposit is returned. fn remove_member( mut pool: PoolT<T, I>, remove: T::AccountId, index: u32 ) -> Result<(), Error<T, I>> { // all callers of this function in this module also check // the index for validity before calling this function. // nevertheless we check again here, to assert that there was // no mistake when invoking this sensible function. Self::ensure_index(&pool, &remove, index)?; pool.remove(index as usize); <Pool<T, I>>::put(&pool); // remove from set, if it was in there let members = <Members<T, I>>::get(); if members.binary_search(&remove).is_ok() { Self::refresh_members(pool, ChangeReceiver::MembershipChanged); } <CandidateExists<T, I>>::remove(&remove); T::Currency::unreserve(&remove, T::CandidateDeposit::get()); Self::deposit_event(RawEvent::MemberRemoved); Ok(()) } /// Checks if `index` is a valid number and if the element found /// at `index` in `Pool` is equal to `who`. fn ensure_index( pool: &PoolT<T, I>, who: &T::AccountId, index: u32 ) -> Result<(), Error<T, I>> { ensure!(index < pool.len() as u32, Error::<T, I>::InvalidIndex); let (index_who, _index_score) = &pool[index as usize]; ensure!(index_who == who, Error::<T, I>::WrongAccountIndex); Ok(()) } }