lib.rs

// This file is part of Substrate.

// Copyright (C) 2017-2022 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! # Balances Pallet
//!
//! The Balances pallet provides functionality for handling accounts and balances.
//!
//! - [`Config`]
//! - [`Call`]
//! - [`Pallet`]
//!
//! ## Overview
//!
//! The Balances pallet provides functions for:
//!
//! - Getting and setting free balances.
//! - Retrieving total, reserved and unreserved balances.
//! - Repatriating a reserved balance to a beneficiary account that exists.
//! - Transferring a balance between accounts (when not reserved).
//! - Slashing an account balance.
//! - Account creation and removal.
//! - Managing total issuance.
//! - Setting and managing locks.
//!
//! ### Terminology
//!
//! - **Existential Deposit:** The minimum balance required to create or keep an account open. This
//!   prevents "dust accounts" from filling storage. When the free plus the reserved balance (i.e.
//!   the total balance) fall below this, then the account is said to be dead; and it loses its
//!   functionality as well as any prior history and all information on it is removed from the
//!   chain's state. No account should ever have a total balance that is strictly between 0 and the
//!   existential deposit (exclusive). If this ever happens, it indicates either a bug in this
//!   pallet or an erroneous raw mutation of storage.
//!
//! - **Total Issuance:** The total number of units in existence in a system.
//!
//! - **Reaping an account:** The act of removing an account by resetting its nonce. Happens after
//!   its
//! total balance has become zero (or, strictly speaking, less than the Existential Deposit).
//!
//! - **Free Balance:** The portion of a balance that is not reserved. The free balance is the only
//!   balance that matters for most operations.
//!
//! - **Reserved Balance:** Reserved balance still belongs to the account holder, but is suspended.
//!   Reserved balance can still be slashed, but only after all the free balance has been slashed.
//!
//! - **Imbalance:** A condition when some funds were credited or debited without equal and opposite
//!   accounting
//! (i.e. a difference between total issuance and account balances). Functions that result in an
//! imbalance will return an object of the `Imbalance` trait that can be managed within your runtime
//! logic. (If an imbalance is simply dropped, it should automatically maintain any book-keeping
//! such as total issuance.)
//!
//! - **Lock:** A freeze on a specified amount of an account's free balance until a specified block
//!   number. Multiple
//! locks always operate over the same funds, so they "overlay" rather than "stack".
//!
//! ### Implementations
//!
//! The Balances pallet provides implementations for the following traits. If these traits provide
//! the functionality that you need, then you can avoid coupling with the Balances pallet.
//!
//! - [`Currency`](frame_support::traits::Currency): Functions for dealing with a
//! fungible assets system.
//! - [`ReservableCurrency`](frame_support::traits::ReservableCurrency):
//! - [`NamedReservableCurrency`](frame_support::traits::NamedReservableCurrency):
//! Functions for dealing with assets that can be reserved from an account.
//! - [`LockableCurrency`](frame_support::traits::LockableCurrency): Functions for
//! dealing with accounts that allow liquidity restrictions.
//! - [`Imbalance`](frame_support::traits::Imbalance): Functions for handling
//! imbalances between total issuance in the system and account balances. Must be used when a
//! function creates new funds (e.g. a reward) or destroys some funds (e.g. a system fee).
//!
//! ## Interface
//!
//! ### Dispatchable Functions
//!
//! - `transfer` - Transfer some liquid free balance to another account.
//! - `set_balance` - Set the balances of a given account. The origin of this call must be root.
//!
//! ## Usage
//!
//! The following examples show how to use the Balances pallet in your custom pallet.
//!
//! ### Examples from the FRAME
//!
//! The Contract pallet uses the `Currency` trait to handle gas payment, and its types inherit from
//! `Currency`:
//!
//! ```
//! use frame_support::traits::Currency;
//! # pub trait Config: frame_system::Config {
//! # 	type Currency: Currency<Self::AccountId>;
//! # }
//!
//! pub type BalanceOf<T> = <<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance;
//! pub type NegativeImbalanceOf<T> = <<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::NegativeImbalance;
//!
//! # fn main() {}
//! ```
//!
//! The Staking pallet uses the `LockableCurrency` trait to lock a stash account's funds:
//!
//! ```
//! use frame_support::traits::{WithdrawReasons, LockableCurrency};
//! use sp_runtime::traits::Bounded;
//! pub trait Config: frame_system::Config {
//! 	type Currency: LockableCurrency<Self::AccountId, Moment=Self::BlockNumber>;
//! }
//! # struct StakingLedger<T: Config> {
//! # 	stash: <T as frame_system::Config>::AccountId,
//! # 	total: <<T as Config>::Currency as frame_support::traits::Currency<<T as frame_system::Config>::AccountId>>::Balance,
//! # 	phantom: std::marker::PhantomData<T>,
//! # }
//! # const STAKING_ID: [u8; 8] = *b"staking ";
//!
//! fn update_ledger<T: Config>(
//! 	controller: &T::AccountId,
//! 	ledger: &StakingLedger<T>
//! ) {
//! 	T::Currency::set_lock(
//! 		STAKING_ID,
//! 		&ledger.stash,
//! 		ledger.total,
//! 		WithdrawReasons::all()
//! 	);
//! 	// <Ledger<T>>::insert(controller, ledger); // Commented out as we don't have access to Staking's storage here.
//! }
//! # fn main() {}
//! ```
//!
//! ## Genesis config
//!
//! The Balances pallet depends on the [`GenesisConfig`].
//!
//! ## Assumptions
//!
//! * Total issued balanced of all accounts should be less than `Config::Balance::max_value()`.

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

#[macro_use]
mod tests;
mod benchmarking;
mod tests_composite;
mod tests_local;
#[cfg(test)]
mod tests_reentrancy;
pub mod weights;

pub use self::imbalances::{NegativeImbalance, PositiveImbalance};
use codec::{Codec, Decode, Encode, MaxEncodedLen};
#[cfg(feature = "std")]
use frame_support::traits::GenesisBuild;
use frame_support::{
	ensure,
	pallet_prelude::DispatchResult,
	traits::{
		tokens::{fungible, BalanceStatus as Status, DepositConsequence, WithdrawConsequence},
		Currency, DefensiveSaturating, ExistenceRequirement,
		ExistenceRequirement::{AllowDeath, KeepAlive},
		Get, Imbalance, LockIdentifier, LockableCurrency, NamedReservableCurrency, OnUnbalanced,
		ReservableCurrency, SignedImbalance, StoredMap, TryDrop, WithdrawReasons,
	},
	WeakBoundedVec,
};
use frame_system as system;
use scale_info::TypeInfo;
use sp_runtime::{
	traits::{
		AtLeast32BitUnsigned, Bounded, CheckedAdd, CheckedSub, MaybeSerializeDeserialize,
		Saturating, StaticLookup, Zero,
	},
	ArithmeticError, DispatchError, FixedPointOperand, RuntimeDebug,
};
use sp_std::{cmp, fmt::Debug, mem, ops::BitOr, prelude::*, result};
pub use weights::WeightInfo;

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::*;

	#[pallet::config]
	pub trait Config<I: 'static = ()>: frame_system::Config {
		/// The balance of an account.
		type Balance: Parameter
			+ Member
			+ AtLeast32BitUnsigned
			+ Codec
			+ Default
			+ Copy
			+ MaybeSerializeDeserialize
			+ Debug
			+ MaxEncodedLen
			+ TypeInfo
			+ FixedPointOperand;

		/// Handler for the unbalanced reduction when removing a dust account.
		type DustRemoval: OnUnbalanced<NegativeImbalance<Self, I>>;

		/// The overarching event type.
		type RuntimeEvent: From<Event<Self, I>>
			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;

		/// The minimum amount required to keep an account open.
		#[pallet::constant]
		type ExistentialDeposit: Get<Self::Balance>;

		/// The means of storing the balances of an account.
		type AccountStore: StoredMap<Self::AccountId, AccountData<Self::Balance>>;

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

		/// The maximum number of locks that should exist on an account.
		/// Not strictly enforced, but used for weight estimation.
		#[pallet::constant]
		type MaxLocks: Get<u32>;

		/// The maximum number of named reserves that can exist on an account.
		#[pallet::constant]
		type MaxReserves: Get<u32>;

		/// The id type for named reserves.
		type ReserveIdentifier: Parameter + Member + MaxEncodedLen + Ord + Copy;
	}

	#[pallet::pallet]
	#[pallet::generate_store(pub(super) trait Store)]
	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);

	#[pallet::call]
	impl<T: Config<I>, I: 'static> Pallet<T, I> {
		/// Transfer some liquid free balance to another account.
		///
		/// `transfer` will set the `FreeBalance` of the sender and receiver.
		/// If the sender's account is below the existential deposit as a result
		/// of the transfer, the account will be reaped.
		///
		/// The dispatch origin for this call must be `Signed` by the transactor.
		///
		/// # <weight>
		/// - Dependent on arguments but not critical, given proper implementations for input config
		///   types. See related functions below.
		/// - It contains a limited number of reads and writes internally and no complex
		///   computation.
		///
		/// Related functions:
		///
		///   - `ensure_can_withdraw` is always called internally but has a bounded complexity.
		///   - Transferring balances to accounts that did not exist before will cause
		///     `T::OnNewAccount::on_new_account` to be called.
		///   - Removing enough funds from an account will trigger `T::DustRemoval::on_unbalanced`.
		///   - `transfer_keep_alive` works the same way as `transfer`, but has an additional check
		///     that the transfer will not kill the origin account.
		/// ---------------------------------
		/// - Origin account is already in memory, so no DB operations for them.
		/// # </weight>
		#[pallet::weight(T::WeightInfo::transfer())]
		pub fn transfer(
			origin: OriginFor<T>,
			dest: AccountIdLookupOf<T>,
			#[pallet::compact] value: T::Balance,
		) -> DispatchResultWithPostInfo {
			let transactor = ensure_signed(origin)?;
			let dest = T::Lookup::lookup(dest)?;
			<Self as Currency<_>>::transfer(
				&transactor,
				&dest,
				value,
				ExistenceRequirement::AllowDeath,
			)?;
			Ok(().into())
		}

		/// Set the balances of a given account.
		///
		/// This will alter `FreeBalance` and `ReservedBalance` in storage. it will
		/// also alter the total issuance of the system (`TotalIssuance`) appropriately.
		/// If the new free or reserved balance is below the existential deposit,
		/// it will reset the account nonce (`frame_system::AccountNonce`).
		///
		/// The dispatch origin for this call is `root`.
		#[pallet::weight(
			T::WeightInfo::set_balance_creating() // Creates a new account.
				.max(T::WeightInfo::set_balance_killing()) // Kills an existing account.
		)]
		pub fn set_balance(
			origin: OriginFor<T>,
			who: AccountIdLookupOf<T>,
			#[pallet::compact] new_free: T::Balance,
			#[pallet::compact] new_reserved: T::Balance,
		) -> DispatchResultWithPostInfo {
			ensure_root(origin)?;
			let who = T::Lookup::lookup(who)?;
			let existential_deposit = T::ExistentialDeposit::get();

			let wipeout = new_free + new_reserved < existential_deposit;
			let new_free = if wipeout { Zero::zero() } else { new_free };
			let new_reserved = if wipeout { Zero::zero() } else { new_reserved };

			// First we try to modify the account's balance to the forced balance.
			let (old_free, old_reserved) = Self::mutate_account(&who, |account| {
				let old_free = account.free;
				let old_reserved = account.reserved;

				account.free = new_free;
				account.reserved = new_reserved;

				(old_free, old_reserved)
			})?;

			// This will adjust the total issuance, which was not done by the `mutate_account`
			// above.
			if new_free > old_free {
				mem::drop(PositiveImbalance::<T, I>::new(new_free - old_free));
			} else if new_free < old_free {
				mem::drop(NegativeImbalance::<T, I>::new(old_free - new_free));
			}

			if new_reserved > old_reserved {
				mem::drop(PositiveImbalance::<T, I>::new(new_reserved - old_reserved));
			} else if new_reserved < old_reserved {
				mem::drop(NegativeImbalance::<T, I>::new(old_reserved - new_reserved));
			}

			Self::deposit_event(Event::BalanceSet { who, free: new_free, reserved: new_reserved });
			Ok(().into())
		}

		/// Exactly as `transfer`, except the origin must be root and the source account may be
		/// specified.
		/// # <weight>
		/// - Same as transfer, but additional read and write because the source account is not
		///   assumed to be in the overlay.
		/// # </weight>
		#[pallet::weight(T::WeightInfo::force_transfer())]
		pub fn force_transfer(
			origin: OriginFor<T>,
			source: AccountIdLookupOf<T>,
			dest: AccountIdLookupOf<T>,
			#[pallet::compact] value: T::Balance,
		) -> DispatchResultWithPostInfo {
			ensure_root(origin)?;
			let source = T::Lookup::lookup(source)?;
			let dest = T::Lookup::lookup(dest)?;
			<Self as Currency<_>>::transfer(
				&source,
				&dest,
				value,
				ExistenceRequirement::AllowDeath,
			)?;
			Ok(().into())
		}

		/// Same as the [`transfer`] call, but with a check that the transfer will not kill the
		/// origin account.
		///
		/// 99% of the time you want [`transfer`] instead.
		///
		/// [`transfer`]: struct.Pallet.html#method.transfer
		#[pallet::weight(T::WeightInfo::transfer_keep_alive())]
		pub fn transfer_keep_alive(
			origin: OriginFor<T>,
			dest: AccountIdLookupOf<T>,
			#[pallet::compact] value: T::Balance,
		) -> DispatchResultWithPostInfo {
			let transactor = ensure_signed(origin)?;
			let dest = T::Lookup::lookup(dest)?;
			<Self as Currency<_>>::transfer(&transactor, &dest, value, KeepAlive)?;
			Ok(().into())
		}

		/// Transfer the entire transferable balance from the caller account.
		///
		/// NOTE: This function only attempts to transfer _transferable_ balances. This means that
		/// any locked, reserved, or existential deposits (when `keep_alive` is `true`), will not be
		/// transferred by this function. To ensure that this function results in a killed account,
		/// you might need to prepare the account by removing any reference counters, storage
		/// deposits, etc...
		///
		/// The dispatch origin of this call must be Signed.
		///
		/// - `dest`: The recipient of the transfer.
		/// - `keep_alive`: A boolean to determine if the `transfer_all` operation should send all
		///   of the funds the account has, causing the sender account to be killed (false), or
		///   transfer everything except at least the existential deposit, which will guarantee to
		///   keep the sender account alive (true). # <weight>
		/// - O(1). Just like transfer, but reading the user's transferable balance first.
		///   #</weight>
		#[pallet::weight(T::WeightInfo::transfer_all())]
		pub fn transfer_all(
			origin: OriginFor<T>,
			dest: AccountIdLookupOf<T>,
			keep_alive: bool,
		) -> DispatchResult {
			use fungible::Inspect;
			let transactor = ensure_signed(origin)?;
			let reducible_balance = Self::reducible_balance(&transactor, keep_alive);
			let dest = T::Lookup::lookup(dest)?;
			let keep_alive = if keep_alive { KeepAlive } else { AllowDeath };
			<Self as Currency<_>>::transfer(&transactor, &dest, reducible_balance, keep_alive)?;
			Ok(())
		}

		/// Unreserve some balance from a user by force.
		///
		/// Can only be called by ROOT.
		#[pallet::weight(T::WeightInfo::force_unreserve())]
		pub fn force_unreserve(
			origin: OriginFor<T>,
			who: AccountIdLookupOf<T>,
			amount: T::Balance,
		) -> DispatchResult {
			ensure_root(origin)?;
			let who = T::Lookup::lookup(who)?;
			let _leftover = <Self as ReservableCurrency<_>>::unreserve(&who, amount);
			Ok(())
		}
	}

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config<I>, I: 'static = ()> {
		/// An account was created with some free balance.
		Endowed { account: T::AccountId, free_balance: T::Balance },
		/// An account was removed whose balance was non-zero but below ExistentialDeposit,
		/// resulting in an outright loss.
		DustLost { account: T::AccountId, amount: T::Balance },
		/// Transfer succeeded.
		Transfer { from: T::AccountId, to: T::AccountId, amount: T::Balance },
		/// A balance was set by root.
		BalanceSet { who: T::AccountId, free: T::Balance, reserved: T::Balance },
		/// Some balance was reserved (moved from free to reserved).
		Reserved { who: T::AccountId, amount: T::Balance },
		/// Some balance was unreserved (moved from reserved to free).
		Unreserved { who: T::AccountId, amount: T::Balance },
		/// Some balance was moved from the reserve of the first account to the second account.
		/// Final argument indicates the destination balance type.
		ReserveRepatriated {
			from: T::AccountId,
			to: T::AccountId,
			amount: T::Balance,
			destination_status: Status,
		},
		/// Some amount was deposited (e.g. for transaction fees).
		Deposit { who: T::AccountId, amount: T::Balance },
		/// Some amount was withdrawn from the account (e.g. for transaction fees).
		Withdraw { who: T::AccountId, amount: T::Balance },
		/// Some amount was removed from the account (e.g. for misbehavior).
		Slashed { who: T::AccountId, amount: T::Balance },
	}

	#[pallet::error]
	pub enum Error<T, I = ()> {
		/// Vesting balance too high to send value
		VestingBalance,
		/// Account liquidity restrictions prevent withdrawal
		LiquidityRestrictions,
		/// Balance too low to send value
		InsufficientBalance,
		/// Value too low to create account due to existential deposit
		ExistentialDeposit,
		/// Transfer/payment would kill account
		KeepAlive,
		/// A vesting schedule already exists for this account
		ExistingVestingSchedule,
		/// Beneficiary account must pre-exist
		DeadAccount,
		/// Number of named reserves exceed MaxReserves
		TooManyReserves,
	}

	/// The total units issued in the system.
	#[pallet::storage]
	#[pallet::getter(fn total_issuance)]
	#[pallet::whitelist_storage]
	pub type TotalIssuance<T: Config<I>, I: 'static = ()> = StorageValue<_, T::Balance, ValueQuery>;

	/// The Balances pallet example of storing the balance of an account.
	///
	/// # Example
	///
	/// ```nocompile
	///  impl pallet_balances::Config for Runtime {
	///    type AccountStore = StorageMapShim<Self::Account<Runtime>, frame_system::Provider<Runtime>, AccountId, Self::AccountData<Balance>>
	///  }
	/// ```
	///
	/// You can also store the balance of an account in the `System` pallet.
	///
	/// # Example
	///
	/// ```nocompile
	///  impl pallet_balances::Config for Runtime {
	///   type AccountStore = System
	///  }
	/// ```
	///
	/// But this comes with tradeoffs, storing account balances in the system pallet stores
	/// `frame_system` data alongside the account data contrary to storing account balances in the
	/// `Balances` pallet, which uses a `StorageMap` to store balances data only.
	/// NOTE: This is only used in the case that this pallet is used to store balances.
	#[pallet::storage]
	pub type Account<T: Config<I>, I: 'static = ()> =
		StorageMap<_, Blake2_128Concat, T::AccountId, AccountData<T::Balance>, ValueQuery>;

	/// Any liquidity locks on some account balances.
	/// NOTE: Should only be accessed when setting, changing and freeing a lock.
	#[pallet::storage]
	#[pallet::getter(fn locks)]
	pub type Locks<T: Config<I>, I: 'static = ()> = StorageMap<
		_,
		Blake2_128Concat,
		T::AccountId,
		WeakBoundedVec<BalanceLock<T::Balance>, T::MaxLocks>,
		ValueQuery,
	>;

	/// Named reserves on some account balances.
	#[pallet::storage]
	#[pallet::getter(fn reserves)]
	pub type Reserves<T: Config<I>, I: 'static = ()> = StorageMap<
		_,
		Blake2_128Concat,
		T::AccountId,
		BoundedVec<ReserveData<T::ReserveIdentifier, T::Balance>, T::MaxReserves>,
		ValueQuery,
	>;

	/// Storage version of the pallet.
	///
	/// This is set to v2.0.0 for new networks.
	#[pallet::storage]
	pub(super) type StorageVersion<T: Config<I>, I: 'static = ()> =
		StorageValue<_, Releases, ValueQuery>;

	#[pallet::genesis_config]
	pub struct GenesisConfig<T: Config<I>, I: 'static = ()> {
		pub balances: Vec<(T::AccountId, T::Balance)>,
	}

	#[cfg(feature = "std")]
	impl<T: Config<I>, I: 'static> Default for GenesisConfig<T, I> {
		fn default() -> Self {
			Self { balances: Default::default() }
		}
	}

	#[pallet::genesis_build]
	impl<T: Config<I>, I: 'static> GenesisBuild<T, I> for GenesisConfig<T, I> {
		fn build(&self) {
			let total = self.balances.iter().fold(Zero::zero(), |acc: T::Balance, &(_, n)| acc + n);
			<TotalIssuance<T, I>>::put(total);

			<StorageVersion<T, I>>::put(Releases::V2_0_0);

			for (_, balance) in &self.balances {
				assert!(
					*balance >= <T as Config<I>>::ExistentialDeposit::get(),
					"the balance of any account should always be at least the existential deposit.",
				)
			}

			// ensure no duplicates exist.
			let endowed_accounts = self
				.balances
				.iter()
				.map(|(x, _)| x)
				.cloned()
				.collect::<std::collections::BTreeSet<_>>();

			assert!(
				endowed_accounts.len() == self.balances.len(),
				"duplicate balances in genesis."
			);

			for &(ref who, free) in self.balances.iter() {
				assert!(T::AccountStore::insert(who, AccountData { free, ..Default::default() })
					.is_ok());
			}
		}
	}
}

#[cfg(feature = "std")]
impl<T: Config<I>, I: 'static> GenesisConfig<T, I> {
	/// Direct implementation of `GenesisBuild::build_storage`.
	///
	/// Kept in order not to break dependency.
	pub fn build_storage(&self) -> Result<sp_runtime::Storage, String> {
		<Self as GenesisBuild<T, I>>::build_storage(self)
	}

	/// Direct implementation of `GenesisBuild::assimilate_storage`.
	///
	/// Kept in order not to break dependency.
	pub fn assimilate_storage(&self, storage: &mut sp_runtime::Storage) -> Result<(), String> {
		<Self as GenesisBuild<T, I>>::assimilate_storage(self, storage)
	}
}

/// Simplified reasons for withdrawing balance.
#[derive(Encode, Decode, Clone, Copy, PartialEq, Eq, RuntimeDebug, MaxEncodedLen, TypeInfo)]
pub enum Reasons {
	/// Paying system transaction fees.
	Fee = 0,
	/// Any reason other than paying system transaction fees.
	Misc = 1,
	/// Any reason at all.
	All = 2,
}

impl From<WithdrawReasons> for Reasons {
	fn from(r: WithdrawReasons) -> Reasons {
		if r == WithdrawReasons::TRANSACTION_PAYMENT {
			Reasons::Fee
		} else if r.contains(WithdrawReasons::TRANSACTION_PAYMENT) {
			Reasons::All
		} else {
			Reasons::Misc
		}
	}
}

impl BitOr for Reasons {
	type Output = Reasons;
	fn bitor(self, other: Reasons) -> Reasons {
		if self == other {
			return self
		}
		Reasons::All
	}
}

/// A single lock on a balance. There can be many of these on an account and they "overlap", so the
/// same balance is frozen by multiple locks.
#[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug, MaxEncodedLen, TypeInfo)]
pub struct BalanceLock<Balance> {
	/// An identifier for this lock. Only one lock may be in existence for each identifier.
	pub id: LockIdentifier,
	/// The amount which the free balance may not drop below when this lock is in effect.
	pub amount: Balance,
	/// If true, then the lock remains in effect even for payment of transaction fees.
	pub reasons: Reasons,
}

/// Store named reserved balance.
#[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug, MaxEncodedLen, TypeInfo)]
pub struct ReserveData<ReserveIdentifier, Balance> {
	/// The identifier for the named reserve.
	pub id: ReserveIdentifier,
	/// The amount of the named reserve.
	pub amount: Balance,
}

/// All balance information for an account.
#[derive(Encode, Decode, Clone, PartialEq, Eq, Default, RuntimeDebug, MaxEncodedLen, TypeInfo)]
pub struct AccountData<Balance> {
	/// Non-reserved part of the balance. There may still be restrictions on this, but it is the
	/// total pool what may in principle be transferred, reserved and used for tipping.
	///
	/// This is the only balance that matters in terms of most operations on tokens. It
	/// alone is used to determine the balance when in the contract execution environment.
	pub free: Balance,
	/// Balance which is reserved and may not be used at all.
	///
	/// This can still get slashed, but gets slashed last of all.
	///
	/// This balance is a 'reserve' balance that other subsystems use in order to set aside tokens
	/// that are still 'owned' by the account holder, but which are suspendable.
	/// This includes named reserve and unnamed reserve.
	pub reserved: Balance,
	/// The amount that `free` may not drop below when withdrawing for *anything except transaction
	/// fee payment*.
	pub misc_frozen: Balance,
	/// The amount that `free` may not drop below when withdrawing specifically for transaction
	/// fee payment.
	pub fee_frozen: Balance,
}

impl<Balance: Saturating + Copy + Ord> AccountData<Balance> {
	/// How much this account's balance can be reduced for the given `reasons`.
	fn usable(&self, reasons: Reasons) -> Balance {
		self.free.saturating_sub(self.frozen(reasons))
	}
	/// The amount that this account's free balance may not be reduced beyond for the given
	/// `reasons`.
	fn frozen(&self, reasons: Reasons) -> Balance {
		match reasons {
			Reasons::All => self.misc_frozen.max(self.fee_frozen),
			Reasons::Misc => self.misc_frozen,
			Reasons::Fee => self.fee_frozen,
		}
	}
	/// The total balance in this account including any that is reserved and ignoring any frozen.
	fn total(&self) -> Balance {
		self.free.saturating_add(self.reserved)
	}
}

// A value placed in storage that represents the current version of the Balances storage.
// This value is used by the `on_runtime_upgrade` logic to determine whether we run
// storage migration logic. This should match directly with the semantic versions of the Rust crate.
#[derive(Encode, Decode, Clone, Copy, PartialEq, Eq, RuntimeDebug, MaxEncodedLen, TypeInfo)]
enum Releases {
	V1_0_0,
	V2_0_0,
}

impl Default for Releases {
	fn default() -> Self {
		Releases::V1_0_0
	}
}

pub struct DustCleaner<T: Config<I>, I: 'static = ()>(
	Option<(T::AccountId, NegativeImbalance<T, I>)>,
);

impl<T: Config<I>, I: 'static> Drop for DustCleaner<T, I> {
	fn drop(&mut self) {
		if let Some((who, dust)) = self.0.take() {
			Pallet::<T, I>::deposit_event(Event::DustLost { account: who, amount: dust.peek() });
			T::DustRemoval::on_unbalanced(dust);
		}
	}
}

impl<T: Config<I>, I: 'static> Pallet<T, I> {
	/// Get the free balance of an account.
	pub fn free_balance(who: impl sp_std::borrow::Borrow<T::AccountId>) -> T::Balance {
		Self::account(who.borrow()).free
	}

	/// Get the balance of an account that can be used for transfers, reservations, or any other
	/// non-locking, non-transaction-fee activity. Will be at most `free_balance`.
	pub fn usable_balance(who: impl sp_std::borrow::Borrow<T::AccountId>) -> T::Balance {
		Self::account(who.borrow()).usable(Reasons::Misc)
	}

	/// Get the balance of an account that can be used for paying transaction fees (not tipping,
	/// or any other kind of fees, though). Will be at most `free_balance`.
	pub fn usable_balance_for_fees(who: impl sp_std::borrow::Borrow<T::AccountId>) -> T::Balance {
		Self::account(who.borrow()).usable(Reasons::Fee)
	}

	/// Get the reserved balance of an account.
	pub fn reserved_balance(who: impl sp_std::borrow::Borrow<T::AccountId>) -> T::Balance {
		Self::account(who.borrow()).reserved
	}

	/// Get both the free and reserved balances of an account.
	fn account(who: &T::AccountId) -> AccountData<T::Balance> {
		T::AccountStore::get(who)
	}

	/// Handles any steps needed after mutating an account.
	///
	/// This includes DustRemoval unbalancing, in the case than the `new` account's total balance
	/// is non-zero but below ED.
	///
	/// Returns two values:
	/// - `Some` containing the the `new` account, iff the account has sufficient balance.
	/// - `Some` containing the dust to be dropped, iff some dust should be dropped.
	fn post_mutation(
		_who: &T::AccountId,
		new: AccountData<T::Balance>,
	) -> (Option<AccountData<T::Balance>>, Option<NegativeImbalance<T, I>>) {
		let total = new.total();
		if total < T::ExistentialDeposit::get() {
			if total.is_zero() {
				(None, None)
			} else {
				(None, Some(NegativeImbalance::new(total)))
			}
		} else {
			(Some(new), None)
		}
	}

	fn deposit_consequence(
		_who: &T::AccountId,
		amount: T::Balance,
		account: &AccountData<T::Balance>,
		mint: bool,
	) -> DepositConsequence {
		if amount.is_zero() {
			return DepositConsequence::Success
		}

		if mint && TotalIssuance::<T, I>::get().checked_add(&amount).is_none() {
			return DepositConsequence::Overflow
		}

		let new_total_balance = match account.total().checked_add(&amount) {
			Some(x) => x,
			None => return DepositConsequence::Overflow,
		};

		if new_total_balance < T::ExistentialDeposit::get() {
			return DepositConsequence::BelowMinimum
		}

		// NOTE: We assume that we are a provider, so don't need to do any checks in the
		// case of account creation.

		DepositConsequence::Success
	}

	fn withdraw_consequence(
		who: &T::AccountId,
		amount: T::Balance,
		account: &AccountData<T::Balance>,
	) -> WithdrawConsequence<T::Balance> {
		if amount.is_zero() {
			return WithdrawConsequence::Success
		}

		if TotalIssuance::<T, I>::get().checked_sub(&amount).is_none() {
			return WithdrawConsequence::Underflow
		}

		let new_total_balance = match account.total().checked_sub(&amount) {
			Some(x) => x,
			None => return WithdrawConsequence::NoFunds,
		};

		// Provider restriction - total account balance cannot be reduced to zero if it cannot
		// sustain the loss of a provider reference.
		// NOTE: This assumes that the pallet is a provider (which is true). Is this ever changes,
		// then this will need to adapt accordingly.
		let ed = T::ExistentialDeposit::get();
		let success = if new_total_balance < ed {
			if frame_system::Pallet::<T>::can_dec_provider(who) {
				WithdrawConsequence::ReducedToZero(new_total_balance)
			} else {
				return WithdrawConsequence::WouldDie
			}
		} else {
			WithdrawConsequence::Success
		};

		// Enough free funds to have them be reduced.
		let new_free_balance = match account.free.checked_sub(&amount) {
			Some(b) => b,
			None => return WithdrawConsequence::NoFunds,
		};

		// Eventual free funds must be no less than the frozen balance.
		let min_balance = account.frozen(Reasons::All);
		if new_free_balance < min_balance {
			return WithdrawConsequence::Frozen
		}

		success
	}

	/// Mutate an account to some new value, or delete it entirely with `None`. Will enforce
	/// `ExistentialDeposit` law, annulling the account as needed.
	///
	/// NOTE: Doesn't do any preparatory work for creating a new account, so should only be used
	/// when it is known that the account already exists.
	///
	/// NOTE: LOW-LEVEL: This will not attempt to maintain total issuance. It is expected that
	/// the caller will do this.
	pub fn mutate_account<R>(
		who: &T::AccountId,
		f: impl FnOnce(&mut AccountData<T::Balance>) -> R,
	) -> Result<R, DispatchError> {
		Self::try_mutate_account(who, |a, _| -> Result<R, DispatchError> { Ok(f(a)) })
	}

	/// Mutate an account to some new value, or delete it entirely with `None`. Will enforce
	/// `ExistentialDeposit` law, annulling the account as needed. This will do nothing if the
	/// result of `f` is an `Err`.
	///
	/// NOTE: Doesn't do any preparatory work for creating a new account, so should only be used
	/// when it is known that the account already exists.
	///
	/// NOTE: LOW-LEVEL: This will not attempt to maintain total issuance. It is expected that
	/// the caller will do this.
	fn try_mutate_account<R, E: From<DispatchError>>(
		who: &T::AccountId,
		f: impl FnOnce(&mut AccountData<T::Balance>, bool) -> Result<R, E>,
	) -> Result<R, E> {
		Self::try_mutate_account_with_dust(who, f).map(|(result, dust_cleaner)| {
			drop(dust_cleaner);
			result
		})
	}

	/// Mutate an account to some new value, or delete it entirely with `None`. Will enforce
	/// `ExistentialDeposit` law, annulling the account as needed. This will do nothing if the
	/// result of `f` is an `Err`.
	///
	/// It returns both the result from the closure, and an optional `DustCleaner` instance which
	/// should be dropped once it is known that all nested mutates that could affect storage items
	/// what the dust handler touches have completed.
	///
	/// NOTE: Doesn't do any preparatory work for creating a new account, so should only be used
	/// when it is known that the account already exists.
	///
	/// NOTE: LOW-LEVEL: This will not attempt to maintain total issuance. It is expected that
	/// the caller will do this.
	fn try_mutate_account_with_dust<R, E: From<DispatchError>>(
		who: &T::AccountId,
		f: impl FnOnce(&mut AccountData<T::Balance>, bool) -> Result<R, E>,
	) -> Result<(R, DustCleaner<T, I>), E> {
		let result = T::AccountStore::try_mutate_exists(who, |maybe_account| {
			let is_new = maybe_account.is_none();
			let mut account = maybe_account.take().unwrap_or_default();
			f(&mut account, is_new).map(move |result| {
				let maybe_endowed = if is_new { Some(account.free) } else { None };
				let maybe_account_maybe_dust = Self::post_mutation(who, account);
				*maybe_account = maybe_account_maybe_dust.0;
				(maybe_endowed, maybe_account_maybe_dust.1, result)
			})
		});
		result.map(|(maybe_endowed, maybe_dust, result)| {
			if let Some(endowed) = maybe_endowed {
				Self::deposit_event(Event::Endowed { account: who.clone(), free_balance: endowed });
			}
			let dust_cleaner = DustCleaner(maybe_dust.map(|dust| (who.clone(), dust)));
			(result, dust_cleaner)
		})
	}

	/// Update the account entry for `who`, given the locks.
	fn update_locks(who: &T::AccountId, locks: &[BalanceLock<T::Balance>]) {
		let bounded_locks = WeakBoundedVec::<_, T::MaxLocks>::force_from(
			locks.to_vec(),
			Some("Balances Update Locks"),
		);

		if locks.len() as u32 > T::MaxLocks::get() {
			log::warn!(
				target: "runtime::balances",
				"Warning: A user has more currency locks than expected. \
				A runtime configuration adjustment may be needed."
			);
		}
		// No way this can fail since we do not alter the existential balances.
		let res = Self::mutate_account(who, |b| {
			b.misc_frozen = Zero::zero();
			b.fee_frozen = Zero::zero();
			for l in locks.iter() {
				if l.reasons == Reasons::All || l.reasons == Reasons::Misc {
					b.misc_frozen = b.misc_frozen.max(l.amount);
				}
				if l.reasons == Reasons::All || l.reasons == Reasons::Fee {
					b.fee_frozen = b.fee_frozen.max(l.amount);
				}
			}
		});
		debug_assert!(res.is_ok());

		let existed = Locks::<T, I>::contains_key(who);
		if locks.is_empty() {
			Locks::<T, I>::remove(who);
			if existed {
				// TODO: use Locks::<T, I>::hashed_key
				// https://github.com/paritytech/substrate/issues/4969
				system::Pallet::<T>::dec_consumers(who);
			}
		} else {
			Locks::<T, I>::insert(who, bounded_locks);
			if !existed && system::Pallet::<T>::inc_consumers_without_limit(who).is_err() {
				// No providers for the locks. This is impossible under normal circumstances
				// since the funds that are under the lock will themselves be stored in the
				// account and therefore will need a reference.
				log::warn!(
					target: "runtime::balances",
					"Warning: Attempt to introduce lock consumer reference, yet no providers. \
					This is unexpected but should be safe."
				);
			}
		}
	}

	/// Move the reserved balance of one account into the balance of another, according to `status`.
	///
	/// Is a no-op if:
	/// - the value to be moved is zero; or
	/// - the `slashed` id equal to `beneficiary` and the `status` is `Reserved`.
	///
	/// NOTE: returns actual amount of transferred value in `Ok` case.
	fn do_transfer_reserved(
		slashed: &T::AccountId,
		beneficiary: &T::AccountId,
		value: T::Balance,
		best_effort: bool,
		status: Status,
	) -> Result<T::Balance, DispatchError> {
		if value.is_zero() {
			return Ok(Zero::zero())
		}

		if slashed == beneficiary {
			return match status {
				Status::Free => Ok(value.saturating_sub(Self::unreserve(slashed, value))),
				Status::Reserved => Ok(value.saturating_sub(Self::reserved_balance(slashed))),
			}
		}

		let ((actual, _maybe_one_dust), _maybe_other_dust) = Self::try_mutate_account_with_dust(
			beneficiary,
			|to_account, is_new| -> Result<(T::Balance, DustCleaner<T, I>), DispatchError> {
				ensure!(!is_new, Error::<T, I>::DeadAccount);
				Self::try_mutate_account_with_dust(
					slashed,
					|from_account, _| -> Result<T::Balance, DispatchError> {
						let actual = cmp::min(from_account.reserved, value);
						ensure!(best_effort || actual == value, Error::<T, I>::InsufficientBalance);
						match status {
							Status::Free =>
								to_account.free = to_account
									.free
									.checked_add(&actual)
									.ok_or(ArithmeticError::Overflow)?,
							Status::Reserved =>
								to_account.reserved = to_account
									.reserved
									.checked_add(&actual)
									.ok_or(ArithmeticError::Overflow)?,
						}
						from_account.reserved -= actual;
						Ok(actual)
					},
				)
			},
		)?;

		Self::deposit_event(Event::ReserveRepatriated {
			from: slashed.clone(),
			to: beneficiary.clone(),
			amount: actual,
			destination_status: status,
		});
		Ok(actual)
	}
}

impl<T: Config<I>, I: 'static> fungible::Inspect<T::AccountId> for Pallet<T, I> {
	type Balance = T::Balance;

	fn total_issuance() -> Self::Balance {
		TotalIssuance::<T, I>::get()
	}
	fn minimum_balance() -> Self::Balance {
		T::ExistentialDeposit::get()
	}
	fn balance(who: &T::AccountId) -> Self::Balance {
		Self::account(who).total()
	}
	fn reducible_balance(who: &T::AccountId, keep_alive: bool) -> Self::Balance {
		let a = Self::account(who);
		// Liquid balance is what is neither reserved nor locked/frozen.
		let liquid = a.free.saturating_sub(a.fee_frozen.max(a.misc_frozen));
		if frame_system::Pallet::<T>::can_dec_provider(who) && !keep_alive {
			liquid
		} else {
			// `must_remain_to_exist` is the part of liquid balance which must remain to keep total
			// over ED.
			let must_remain_to_exist =
				T::ExistentialDeposit::get().saturating_sub(a.total() - liquid);
			liquid.saturating_sub(must_remain_to_exist)
		}
	}
	fn can_deposit(who: &T::AccountId, amount: Self::Balance, mint: bool) -> DepositConsequence {
		Self::deposit_consequence(who, amount, &Self::account(who), mint)
	}
	fn can_withdraw(
		who: &T::AccountId,
		amount: Self::Balance,
	) -> WithdrawConsequence<Self::Balance> {
		Self::withdraw_consequence(who, amount, &Self::account(who))
	}
}

impl<T: Config<I>, I: 'static> fungible::Mutate<T::AccountId> for Pallet<T, I> {
	fn mint_into(who: &T::AccountId, amount: Self::Balance) -> DispatchResult {
		if amount.is_zero() {
			return Ok(())
		}
		Self::try_mutate_account(who, |account, _is_new| -> DispatchResult {
			Self::deposit_consequence(who, amount, account, true).into_result()?;
			account.free += amount;
			Ok(())
		})?;
		TotalIssuance::<T, I>::mutate(|t| *t += amount);
		Self::deposit_event(Event::Deposit { who: who.clone(), amount });
		Ok(())
	}

	fn burn_from(
		who: &T::AccountId,
		amount: Self::Balance,
	) -> Result<Self::Balance, DispatchError> {
		if amount.is_zero() {
			return Ok(Self::Balance::zero())
		}
		let actual = Self::try_mutate_account(
			who,
			|account, _is_new| -> Result<T::Balance, DispatchError> {
				let extra = Self::withdraw_consequence(who, amount, account).into_result()?;
				let actual = amount + extra;
				account.free -= actual;
				Ok(actual)
			},
		)?;
		TotalIssuance::<T, I>::mutate(|t| *t -= actual);
		Self::deposit_event(Event::Withdraw { who: who.clone(), amount });
		Ok(actual)
	}
}

impl<T: Config<I>, I: 'static> fungible::Transfer<T::AccountId> for Pallet<T, I> {
	fn transfer(
		source: &T::AccountId,
		dest: &T::AccountId,
		amount: T::Balance,
		keep_alive: bool,
	) -> Result<T::Balance, DispatchError> {
		let er = if keep_alive { KeepAlive } else { AllowDeath };
		<Self as Currency<T::AccountId>>::transfer(source, dest, amount, er).map(|_| amount)
	}
}

impl<T: Config<I>, I: 'static> fungible::Unbalanced<T::AccountId> for Pallet<T, I> {
	fn set_balance(who: &T::AccountId, amount: Self::Balance) -> DispatchResult {
		Self::mutate_account(who, |account| {
			account.free = amount;
			Self::deposit_event(Event::BalanceSet {
				who: who.clone(),
				free: account.free,
				reserved: account.reserved,
			});
		})?;
		Ok(())
	}

	fn set_total_issuance(amount: Self::Balance) {
		TotalIssuance::<T, I>::mutate(|t| *t = amount);
	}
}

impl<T: Config<I>, I: 'static> fungible::InspectHold<T::AccountId> for Pallet<T, I> {
	fn balance_on_hold(who: &T::AccountId) -> T::Balance {
		Self::account(who).reserved
	}
	fn can_hold(who: &T::AccountId, amount: T::Balance) -> bool {
		let a = Self::account(who);
		let min_balance = T::ExistentialDeposit::get().max(a.frozen(Reasons::All));
		if a.reserved.checked_add(&amount).is_none() {
			return false
		}
		// We require it to be min_balance + amount to ensure that the full reserved funds may be
		// slashed without compromising locked funds or destroying the account.
		let required_free = match min_balance.checked_add(&amount) {
			Some(x) => x,
			None => return false,
		};
		a.free >= required_free
	}
}
impl<T: Config<I>, I: 'static> fungible::MutateHold<T::AccountId> for Pallet<T, I> {
	fn hold(who: &T::AccountId, amount: Self::Balance) -> DispatchResult {
		if amount.is_zero() {
			return Ok(())
		}
		ensure!(Self::can_reserve(who, amount), Error::<T, I>::InsufficientBalance);
		Self::mutate_account(who, |a| {
			a.free -= amount;
			a.reserved += amount;
		})?;
		Ok(())
	}
	fn release(
		who: &T::AccountId,
		amount: Self::Balance,
		best_effort: bool,
	) -> Result<T::Balance, DispatchError> {
		if amount.is_zero() {
			return Ok(amount)
		}
		// Done on a best-effort basis.
		Self::try_mutate_account(who, |a, _| {
			let new_free = a.free.saturating_add(amount.min(a.reserved));
			let actual = new_free - a.free;
			ensure!(best_effort || actual == amount, Error::<T, I>::InsufficientBalance);
			// ^^^ Guaranteed to be <= amount and <= a.reserved
			a.free = new_free;
			a.reserved = a.reserved.saturating_sub(actual);
			Ok(actual)
		})
	}
	fn transfer_held(
		source: &T::AccountId,
		dest: &T::AccountId,
		amount: Self::Balance,
		best_effort: bool,
		on_hold: bool,
	) -> Result<Self::Balance, DispatchError> {
		let status = if on_hold { Status::Reserved } else { Status::Free };
		Self::do_transfer_reserved(source, dest, amount, best_effort, status)
	}
}

// wrapping these imbalances in a private module is necessary to ensure absolute privacy
// of the inner member.
mod imbalances {
	use super::{result, Config, Imbalance, RuntimeDebug, Saturating, TryDrop, Zero};
	use frame_support::traits::SameOrOther;
	use sp_std::mem;

	/// Opaque, move-only struct with private fields that serves as a token denoting that
	/// funds have been created without any equal and opposite accounting.
	#[must_use]
	#[derive(RuntimeDebug, PartialEq, Eq)]
	pub struct PositiveImbalance<T: Config<I>, I: 'static = ()>(T::Balance);

	impl<T: Config<I>, I: 'static> PositiveImbalance<T, I> {
		/// Create a new positive imbalance from a balance.
		pub fn new(amount: T::Balance) -> Self {
			PositiveImbalance(amount)
		}
	}

	/// Opaque, move-only struct with private fields that serves as a token denoting that
	/// funds have been destroyed without any equal and opposite accounting.
	#[must_use]
	#[derive(RuntimeDebug, PartialEq, Eq)]
	pub struct NegativeImbalance<T: Config<I>, I: 'static = ()>(T::Balance);

	impl<T: Config<I>, I: 'static> NegativeImbalance<T, I> {
		/// Create a new negative imbalance from a balance.
		pub fn new(amount: T::Balance) -> Self {
			NegativeImbalance(amount)
		}
	}

	impl<T: Config<I>, I: 'static> TryDrop for PositiveImbalance<T, I> {
		fn try_drop(self) -> result::Result<(), Self> {
			self.drop_zero()
		}
	}

	impl<T: Config<I>, I: 'static> Default for PositiveImbalance<T, I> {
		fn default() -> Self {
			Self::zero()
		}
	}

	impl<T: Config<I>, I: 'static> Imbalance<T::Balance> for PositiveImbalance<T, I> {
		type Opposite = NegativeImbalance<T, I>;

		fn zero() -> Self {
			Self(Zero::zero())
		}
		fn drop_zero(self) -> result::Result<(), Self> {
			if self.0.is_zero() {
				Ok(())
			} else {
				Err(self)
			}
		}
		fn split(self, amount: T::Balance) -> (Self, Self) {
			let first = self.0.min(amount);
			let second = self.0 - first;

			mem::forget(self);
			(Self(first), Self(second))
		}
		fn merge(mut self, other: Self) -> Self {
			self.0 = self.0.saturating_add(other.0);
			mem::forget(other);

			self
		}
		fn subsume(&mut self, other: Self) {
			self.0 = self.0.saturating_add(other.0);
			mem::forget(other);
		}
		fn offset(self, other: Self::Opposite) -> SameOrOther<Self, Self::Opposite> {
			let (a, b) = (self.0, other.0);
			mem::forget((self, other));

			if a > b {
				SameOrOther::Same(Self(a - b))
			} else if b > a {
				SameOrOther::Other(NegativeImbalance::new(b - a))
			} else {
				SameOrOther::None
			}
		}
		fn peek(&self) -> T::Balance {
			self.0
		}
	}

	impl<T: Config<I>, I: 'static> TryDrop for NegativeImbalance<T, I> {
		fn try_drop(self) -> result::Result<(), Self> {
			self.drop_zero()
		}
	}

	impl<T: Config<I>, I: 'static> Default for NegativeImbalance<T, I> {
		fn default() -> Self {
			Self::zero()
		}
	}

	impl<T: Config<I>, I: 'static> Imbalance<T::Balance> for NegativeImbalance<T, I> {
		type Opposite = PositiveImbalance<T, I>;

		fn zero() -> Self {
			Self(Zero::zero())
		}
		fn drop_zero(self) -> result::Result<(), Self> {
			if self.0.is_zero() {
				Ok(())
			} else {
				Err(self)
			}
		}
		fn split(self, amount: T::Balance) -> (Self, Self) {
			let first = self.0.min(amount);
			let second = self.0 - first;

			mem::forget(self);
			(Self(first), Self(second))
		}
		fn merge(mut self, other: Self) -> Self {
			self.0 = self.0.saturating_add(other.0);
			mem::forget(other);

			self
		}
		fn subsume(&mut self, other: Self) {
			self.0 = self.0.saturating_add(other.0);
			mem::forget(other);
		}
		fn offset(self, other: Self::Opposite) -> SameOrOther<Self, Self::Opposite> {
			let (a, b) = (self.0, other.0);
			mem::forget((self, other));

			if a > b {
				SameOrOther::Same(Self(a - b))
			} else if b > a {
				SameOrOther::Other(PositiveImbalance::new(b - a))
			} else {
				SameOrOther::None
			}
		}
		fn peek(&self) -> T::Balance {
			self.0
		}
	}

	impl<T: Config<I>, I: 'static> Drop for PositiveImbalance<T, I> {
		/// Basic drop handler will just square up the total issuance.
		fn drop(&mut self) {
			<super::TotalIssuance<T, I>>::mutate(|v| *v = v.saturating_add(self.0));
		}
	}

	impl<T: Config<I>, I: 'static> Drop for NegativeImbalance<T, I> {
		/// Basic drop handler will just square up the total issuance.
		fn drop(&mut self) {
			<super::TotalIssuance<T, I>>::mutate(|v| *v = v.saturating_sub(self.0));
		}
	}
}

impl<T: Config<I>, I: 'static> Currency<T::AccountId> for Pallet<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	type Balance = T::Balance;
	type PositiveImbalance = PositiveImbalance<T, I>;
	type NegativeImbalance = NegativeImbalance<T, I>;

	fn total_balance(who: &T::AccountId) -> Self::Balance {
		Self::account(who).total()
	}

	// Check if `value` amount of free balance can be slashed from `who`.
	fn can_slash(who: &T::AccountId, value: Self::Balance) -> bool {
		if value.is_zero() {
			return true
		}
		Self::free_balance(who) >= value
	}

	fn total_issuance() -> Self::Balance {
		<TotalIssuance<T, I>>::get()
	}

	fn minimum_balance() -> Self::Balance {
		T::ExistentialDeposit::get()
	}

	// Burn funds from the total issuance, returning a positive imbalance for the amount burned.
	// Is a no-op if amount to be burned is zero.
	fn burn(mut amount: Self::Balance) -> Self::PositiveImbalance {
		if amount.is_zero() {
			return PositiveImbalance::zero()
		}
		<TotalIssuance<T, I>>::mutate(|issued| {
			*issued = issued.checked_sub(&amount).unwrap_or_else(|| {
				amount = *issued;
				Zero::zero()
			});
		});
		PositiveImbalance::new(amount)
	}

	// Create new funds into the total issuance, returning a negative imbalance
	// for the amount issued.
	// Is a no-op if amount to be issued it zero.
	fn issue(mut amount: Self::Balance) -> Self::NegativeImbalance {
		if amount.is_zero() {
			return NegativeImbalance::zero()
		}
		<TotalIssuance<T, I>>::mutate(|issued| {
			*issued = issued.checked_add(&amount).unwrap_or_else(|| {
				amount = Self::Balance::max_value() - *issued;
				Self::Balance::max_value()
			})
		});
		NegativeImbalance::new(amount)
	}

	fn free_balance(who: &T::AccountId) -> Self::Balance {
		Self::account(who).free
	}

	// Ensure that an account can withdraw from their free balance given any existing withdrawal
	// restrictions like locks and vesting balance.
	// Is a no-op if amount to be withdrawn is zero.
	//
	// # <weight>
	// Despite iterating over a list of locks, they are limited by the number of
	// lock IDs, which means the number of runtime pallets that intend to use and create locks.
	// # </weight>
	fn ensure_can_withdraw(
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
		new_balance: T::Balance,
	) -> DispatchResult {
		if amount.is_zero() {
			return Ok(())
		}
		let min_balance = Self::account(who).frozen(reasons.into());
		ensure!(new_balance >= min_balance, Error::<T, I>::LiquidityRestrictions);
		Ok(())
	}

	// Transfer some free balance from `transactor` to `dest`, respecting existence requirements.
	// Is a no-op if value to be transferred is zero or the `transactor` is the same as `dest`.
	fn transfer(
		transactor: &T::AccountId,
		dest: &T::AccountId,
		value: Self::Balance,
		existence_requirement: ExistenceRequirement,
	) -> DispatchResult {
		if value.is_zero() || transactor == dest {
			return Ok(())
		}

		Self::try_mutate_account_with_dust(
			dest,
			|to_account, _| -> Result<DustCleaner<T, I>, DispatchError> {
				Self::try_mutate_account_with_dust(
					transactor,
					|from_account, _| -> DispatchResult {
						from_account.free = from_account
							.free
							.checked_sub(&value)
							.ok_or(Error::<T, I>::InsufficientBalance)?;

						// NOTE: total stake being stored in the same type means that this could
						// never overflow but better to be safe than sorry.
						to_account.free =
							to_account.free.checked_add(&value).ok_or(ArithmeticError::Overflow)?;

						let ed = T::ExistentialDeposit::get();
						ensure!(to_account.total() >= ed, Error::<T, I>::ExistentialDeposit);

						Self::ensure_can_withdraw(
							transactor,
							value,
							WithdrawReasons::TRANSFER,
							from_account.free,
						)
						.map_err(|_| Error::<T, I>::LiquidityRestrictions)?;

						// TODO: This is over-conservative. There may now be other providers, and
						// this pallet may not even be a provider.
						let allow_death = existence_requirement == ExistenceRequirement::AllowDeath;
						let allow_death =
							allow_death && system::Pallet::<T>::can_dec_provider(transactor);
						ensure!(
							allow_death || from_account.total() >= ed,
							Error::<T, I>::KeepAlive
						);

						Ok(())
					},
				)
				.map(|(_, maybe_dust_cleaner)| maybe_dust_cleaner)
			},
		)?;

		// Emit transfer event.
		Self::deposit_event(Event::Transfer {
			from: transactor.clone(),
			to: dest.clone(),
			amount: value,
		});

		Ok(())
	}

	/// Slash a target account `who`, returning the negative imbalance created and any left over
	/// amount that could not be slashed.
	///
	/// Is a no-op if `value` to be slashed is zero or the account does not exist.
	///
	/// NOTE: `slash()` prefers free balance, but assumes that reserve balance can be drawn
	/// from in extreme circumstances. `can_slash()` should be used prior to `slash()` to avoid
	/// having to draw from reserved funds, however we err on the side of punishment if things are
	/// inconsistent or `can_slash` wasn't used appropriately.
	fn slash(who: &T::AccountId, value: Self::Balance) -> (Self::NegativeImbalance, Self::Balance) {
		if value.is_zero() {
			return (NegativeImbalance::zero(), Zero::zero())
		}
		if Self::total_balance(who).is_zero() {
			return (NegativeImbalance::zero(), value)
		}

		for attempt in 0..2 {
			match Self::try_mutate_account(
				who,
				|account,
				 _is_new|
				 -> Result<(Self::NegativeImbalance, Self::Balance), DispatchError> {
					// Best value is the most amount we can slash following liveness rules.
					let best_value = match attempt {
						// First attempt we try to slash the full amount, and see if liveness issues
						// happen.
						0 => value,
						// If acting as a critical provider (i.e. first attempt failed), then slash
						// as much as possible while leaving at least at ED.
						_ => value.min(
							(account.free + account.reserved)
								.saturating_sub(T::ExistentialDeposit::get()),
						),
					};

					let free_slash = cmp::min(account.free, best_value);
					account.free -= free_slash; // Safe because of above check
					let remaining_slash = best_value - free_slash; // Safe because of above check

					if !remaining_slash.is_zero() {
						// If we have remaining slash, take it from reserved balance.
						let reserved_slash = cmp::min(account.reserved, remaining_slash);
						account.reserved -= reserved_slash; // Safe because of above check
						Ok((
							NegativeImbalance::new(free_slash + reserved_slash),
							value - free_slash - reserved_slash, /* Safe because value is gt or
							                                      * eq total slashed */
						))
					} else {
						// Else we are done!
						Ok((
							NegativeImbalance::new(free_slash),
							value - free_slash, // Safe because value is gt or eq to total slashed
						))
					}
				},
			) {
				Ok((imbalance, not_slashed)) => {
					Self::deposit_event(Event::Slashed {
						who: who.clone(),
						amount: value.saturating_sub(not_slashed),
					});
					return (imbalance, not_slashed)
				},
				Err(_) => (),
			}
		}

		// Should never get here. But we'll be defensive anyway.
		(Self::NegativeImbalance::zero(), value)
	}

	/// Deposit some `value` into the free balance of an existing target account `who`.
	///
	/// Is a no-op if the `value` to be deposited is zero.
	fn deposit_into_existing(
		who: &T::AccountId,
		value: Self::Balance,
	) -> Result<Self::PositiveImbalance, DispatchError> {
		if value.is_zero() {
			return Ok(PositiveImbalance::zero())
		}

		Self::try_mutate_account(
			who,
			|account, is_new| -> Result<Self::PositiveImbalance, DispatchError> {
				ensure!(!is_new, Error::<T, I>::DeadAccount);
				account.free = account.free.checked_add(&value).ok_or(ArithmeticError::Overflow)?;
				Self::deposit_event(Event::Deposit { who: who.clone(), amount: value });
				Ok(PositiveImbalance::new(value))
			},
		)
	}

	/// Deposit some `value` into the free balance of `who`, possibly creating a new account.
	///
	/// This function is a no-op if:
	/// - the `value` to be deposited is zero; or
	/// - the `value` to be deposited is less than the required ED and the account does not yet
	///   exist; or
	/// - the deposit would necessitate the account to exist and there are no provider references;
	///   or
	/// - `value` is so large it would cause the balance of `who` to overflow.
	fn deposit_creating(who: &T::AccountId, value: Self::Balance) -> Self::PositiveImbalance {
		if value.is_zero() {
			return Self::PositiveImbalance::zero()
		}

		Self::try_mutate_account(
			who,
			|account, is_new| -> Result<Self::PositiveImbalance, DispatchError> {
				let ed = T::ExistentialDeposit::get();
				ensure!(value >= ed || !is_new, Error::<T, I>::ExistentialDeposit);

				// defensive only: overflow should never happen, however in case it does, then this
				// operation is a no-op.
				account.free = match account.free.checked_add(&value) {
					Some(x) => x,
					None => return Ok(Self::PositiveImbalance::zero()),
				};

				Self::deposit_event(Event::Deposit { who: who.clone(), amount: value });
				Ok(PositiveImbalance::new(value))
			},
		)
		.unwrap_or_else(|_| Self::PositiveImbalance::zero())
	}

	/// Withdraw some free balance from an account, respecting existence requirements.
	///
	/// Is a no-op if value to be withdrawn is zero.
	fn withdraw(
		who: &T::AccountId,
		value: Self::Balance,
		reasons: WithdrawReasons,
		liveness: ExistenceRequirement,
	) -> result::Result<Self::NegativeImbalance, DispatchError> {
		if value.is_zero() {
			return Ok(NegativeImbalance::zero())
		}

		Self::try_mutate_account(
			who,
			|account, _| -> Result<Self::NegativeImbalance, DispatchError> {
				let new_free_account =
					account.free.checked_sub(&value).ok_or(Error::<T, I>::InsufficientBalance)?;

				// bail if we need to keep the account alive and this would kill it.
				let ed = T::ExistentialDeposit::get();
				let would_be_dead = new_free_account + account.reserved < ed;
				let would_kill = would_be_dead && account.free + account.reserved >= ed;
				ensure!(liveness == AllowDeath || !would_kill, Error::<T, I>::KeepAlive);

				Self::ensure_can_withdraw(who, value, reasons, new_free_account)?;

				account.free = new_free_account;

				Self::deposit_event(Event::Withdraw { who: who.clone(), amount: value });
				Ok(NegativeImbalance::new(value))
			},
		)
	}

	/// Force the new free balance of a target account `who` to some new value `balance`.
	fn make_free_balance_be(
		who: &T::AccountId,
		value: Self::Balance,
	) -> SignedImbalance<Self::Balance, Self::PositiveImbalance> {
		Self::try_mutate_account(
			who,
			|account,
			 is_new|
			 -> Result<SignedImbalance<Self::Balance, Self::PositiveImbalance>, DispatchError> {
				let ed = T::ExistentialDeposit::get();
				let total = value.saturating_add(account.reserved);
				// If we're attempting to set an existing account to less than ED, then
				// bypass the entire operation. It's a no-op if you follow it through, but
				// since this is an instance where we might account for a negative imbalance
				// (in the dust cleaner of set_account) before we account for its actual
				// equal and opposite cause (returned as an Imbalance), then in the
				// instance that there's no other accounts on the system at all, we might
				// underflow the issuance and our arithmetic will be off.
				ensure!(total >= ed || !is_new, Error::<T, I>::ExistentialDeposit);

				let imbalance = if account.free <= value {
					SignedImbalance::Positive(PositiveImbalance::new(value - account.free))
				} else {
					SignedImbalance::Negative(NegativeImbalance::new(account.free - value))
				};
				account.free = value;
				Self::deposit_event(Event::BalanceSet {
					who: who.clone(),
					free: account.free,
					reserved: account.reserved,
				});
				Ok(imbalance)
			},
		)
		.unwrap_or_else(|_| SignedImbalance::Positive(Self::PositiveImbalance::zero()))
	}
}

impl<T: Config<I>, I: 'static> ReservableCurrency<T::AccountId> for Pallet<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	/// Check if `who` can reserve `value` from their free balance.
	///
	/// Always `true` if value to be reserved is zero.
	fn can_reserve(who: &T::AccountId, value: Self::Balance) -> bool {
		if value.is_zero() {
			return true
		}
		Self::account(who).free.checked_sub(&value).map_or(false, |new_balance| {
			Self::ensure_can_withdraw(who, value, WithdrawReasons::RESERVE, new_balance).is_ok()
		})
	}

	fn reserved_balance(who: &T::AccountId) -> Self::Balance {
		Self::account(who).reserved
	}

	/// Move `value` from the free balance from `who` to their reserved balance.
	///
	/// Is a no-op if value to be reserved is zero.
	fn reserve(who: &T::AccountId, value: Self::Balance) -> DispatchResult {
		if value.is_zero() {
			return Ok(())
		}

		Self::try_mutate_account(who, |account, _| -> DispatchResult {
			account.free =
				account.free.checked_sub(&value).ok_or(Error::<T, I>::InsufficientBalance)?;
			account.reserved =
				account.reserved.checked_add(&value).ok_or(ArithmeticError::Overflow)?;
			Self::ensure_can_withdraw(&who, value, WithdrawReasons::RESERVE, account.free)
		})?;

		Self::deposit_event(Event::Reserved { who: who.clone(), amount: value });
		Ok(())
	}

	/// Unreserve some funds, returning any amount that was unable to be unreserved.
	///
	/// Is a no-op if the value to be unreserved is zero or the account does not exist.
	///
	/// NOTE: returns amount value which wasn't successfully unreserved.
	fn unreserve(who: &T::AccountId, value: Self::Balance) -> Self::Balance {
		if value.is_zero() {
			return Zero::zero()
		}
		if Self::total_balance(who).is_zero() {
			return value
		}

		let actual = match Self::mutate_account(who, |account| {
			let actual = cmp::min(account.reserved, value);
			account.reserved -= actual;
			// defensive only: this can never fail since total issuance which is at least
			// free+reserved fits into the same data type.
			account.free = account.free.defensive_saturating_add(actual);
			actual
		}) {
			Ok(x) => x,
			Err(_) => {
				// This should never happen since we don't alter the total amount in the account.
				// If it ever does, then we should fail gracefully though, indicating that nothing
				// could be done.
				return value
			},
		};

		Self::deposit_event(Event::Unreserved { who: who.clone(), amount: actual });
		value - actual
	}

	/// Slash from reserved balance, returning the negative imbalance created,
	/// and any amount that was unable to be slashed.
	///
	/// Is a no-op if the value to be slashed is zero or the account does not exist.
	fn slash_reserved(
		who: &T::AccountId,
		value: Self::Balance,
	) -> (Self::NegativeImbalance, Self::Balance) {
		if value.is_zero() {
			return (NegativeImbalance::zero(), Zero::zero())
		}
		if Self::total_balance(who).is_zero() {
			return (NegativeImbalance::zero(), value)
		}

		// NOTE: `mutate_account` may fail if it attempts to reduce the balance to the point that an
		//   account is attempted to be illegally destroyed.

		for attempt in 0..2 {
			match Self::mutate_account(who, |account| {
				let best_value = match attempt {
					0 => value,
					// If acting as a critical provider (i.e. first attempt failed), then ensure
					// slash leaves at least the ED.
					_ => value.min(
						(account.free + account.reserved)
							.saturating_sub(T::ExistentialDeposit::get()),
					),
				};

				let actual = cmp::min(account.reserved, best_value);
				account.reserved -= actual;

				// underflow should never happen, but it if does, there's nothing to be done here.
				(NegativeImbalance::new(actual), value - actual)
			}) {
				Ok((imbalance, not_slashed)) => {
					Self::deposit_event(Event::Slashed {
						who: who.clone(),
						amount: value.saturating_sub(not_slashed),
					});
					return (imbalance, not_slashed)
				},
				Err(_) => (),
			}
		}
		// Should never get here as we ensure that ED is left in the second attempt.
		// In case we do, though, then we fail gracefully.
		(Self::NegativeImbalance::zero(), value)
	}

	/// Move the reserved balance of one account into the balance of another, according to `status`.
	///
	/// Is a no-op if:
	/// - the value to be moved is zero; or
	/// - the `slashed` id equal to `beneficiary` and the `status` is `Reserved`.
	fn repatriate_reserved(
		slashed: &T::AccountId,
		beneficiary: &T::AccountId,
		value: Self::Balance,
		status: Status,
	) -> Result<Self::Balance, DispatchError> {
		let actual = Self::do_transfer_reserved(slashed, beneficiary, value, true, status)?;
		Ok(value.saturating_sub(actual))
	}
}

impl<T: Config<I>, I: 'static> NamedReservableCurrency<T::AccountId> for Pallet<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	type ReserveIdentifier = T::ReserveIdentifier;

	fn reserved_balance_named(id: &Self::ReserveIdentifier, who: &T::AccountId) -> Self::Balance {
		let reserves = Self::reserves(who);
		reserves
			.binary_search_by_key(id, |data| data.id)
			.map(|index| reserves[index].amount)
			.unwrap_or_default()
	}

	/// Move `value` from the free balance from `who` to a named reserve balance.
	///
	/// Is a no-op if value to be reserved is zero.
	fn reserve_named(
		id: &Self::ReserveIdentifier,
		who: &T::AccountId,
		value: Self::Balance,
	) -> DispatchResult {
		if value.is_zero() {
			return Ok(())
		}

		Reserves::<T, I>::try_mutate(who, |reserves| -> DispatchResult {
			match reserves.binary_search_by_key(id, |data| data.id) {
				Ok(index) => {
					// this add can't overflow but just to be defensive.
					reserves[index].amount = reserves[index].amount.defensive_saturating_add(value);
				},
				Err(index) => {
					reserves
						.try_insert(index, ReserveData { id: *id, amount: value })
						.map_err(|_| Error::<T, I>::TooManyReserves)?;
				},
			};
			<Self as ReservableCurrency<_>>::reserve(who, value)?;
			Ok(())
		})
	}

	/// Unreserve some funds, returning any amount that was unable to be unreserved.
	///
	/// Is a no-op if the value to be unreserved is zero.
	fn unreserve_named(
		id: &Self::ReserveIdentifier,
		who: &T::AccountId,
		value: Self::Balance,
	) -> Self::Balance {
		if value.is_zero() {
			return Zero::zero()
		}

		Reserves::<T, I>::mutate_exists(who, |maybe_reserves| -> Self::Balance {
			if let Some(reserves) = maybe_reserves.as_mut() {
				match reserves.binary_search_by_key(id, |data| data.id) {
					Ok(index) => {
						let to_change = cmp::min(reserves[index].amount, value);

						let remain = <Self as ReservableCurrency<_>>::unreserve(who, to_change);

						// remain should always be zero but just to be defensive here.
						let actual = to_change.defensive_saturating_sub(remain);

						// `actual <= to_change` and `to_change <= amount`; qed;
						reserves[index].amount -= actual;

						if reserves[index].amount.is_zero() {
							if reserves.len() == 1 {
								// no more named reserves
								*maybe_reserves = None;
							} else {
								// remove this named reserve
								reserves.remove(index);
							}
						}

						value - actual
					},
					Err(_) => value,
				}
			} else {
				value
			}
		})
	}

	/// Slash from reserved balance, returning the negative imbalance created,
	/// and any amount that was unable to be slashed.
	///
	/// Is a no-op if the value to be slashed is zero.
	fn slash_reserved_named(
		id: &Self::ReserveIdentifier,
		who: &T::AccountId,
		value: Self::Balance,
	) -> (Self::NegativeImbalance, Self::Balance) {
		if value.is_zero() {
			return (NegativeImbalance::zero(), Zero::zero())
		}

		Reserves::<T, I>::mutate(who, |reserves| -> (Self::NegativeImbalance, Self::Balance) {
			match reserves.binary_search_by_key(id, |data| data.id) {
				Ok(index) => {
					let to_change = cmp::min(reserves[index].amount, value);

					let (imb, remain) =
						<Self as ReservableCurrency<_>>::slash_reserved(who, to_change);

					// remain should always be zero but just to be defensive here.
					let actual = to_change.defensive_saturating_sub(remain);

					// `actual <= to_change` and `to_change <= amount`; qed;
					reserves[index].amount -= actual;

					Self::deposit_event(Event::Slashed { who: who.clone(), amount: actual });
					(imb, value - actual)
				},
				Err(_) => (NegativeImbalance::zero(), value),
			}
		})
	}

	/// Move the reserved balance of one account into the balance of another, according to `status`.
	/// If `status` is `Reserved`, the balance will be reserved with given `id`.
	///
	/// Is a no-op if:
	/// - the value to be moved is zero; or
	/// - the `slashed` id equal to `beneficiary` and the `status` is `Reserved`.
	fn repatriate_reserved_named(
		id: &Self::ReserveIdentifier,
		slashed: &T::AccountId,
		beneficiary: &T::AccountId,
		value: Self::Balance,
		status: Status,
	) -> Result<Self::Balance, DispatchError> {
		if value.is_zero() {
			return Ok(Zero::zero())
		}

		if slashed == beneficiary {
			return match status {
				Status::Free => Ok(Self::unreserve_named(id, slashed, value)),
				Status::Reserved =>
					Ok(value.saturating_sub(Self::reserved_balance_named(id, slashed))),
			}
		}

		Reserves::<T, I>::try_mutate(slashed, |reserves| -> Result<Self::Balance, DispatchError> {
			match reserves.binary_search_by_key(id, |data| data.id) {
				Ok(index) => {
					let to_change = cmp::min(reserves[index].amount, value);

					let actual = if status == Status::Reserved {
						// make it the reserved under same identifier
						Reserves::<T, I>::try_mutate(
							beneficiary,
							|reserves| -> Result<T::Balance, DispatchError> {
								match reserves.binary_search_by_key(id, |data| data.id) {
									Ok(index) => {
										let remain =
											<Self as ReservableCurrency<_>>::repatriate_reserved(
												slashed,
												beneficiary,
												to_change,
												status,
											)?;

										// remain should always be zero but just to be defensive
										// here.
										let actual = to_change.defensive_saturating_sub(remain);

										// this add can't overflow but just to be defensive.
										reserves[index].amount =
											reserves[index].amount.defensive_saturating_add(actual);

										Ok(actual)
									},
									Err(index) => {
										let remain =
											<Self as ReservableCurrency<_>>::repatriate_reserved(
												slashed,
												beneficiary,
												to_change,
												status,
											)?;

										// remain should always be zero but just to be defensive
										// here
										let actual = to_change.defensive_saturating_sub(remain);

										reserves
											.try_insert(
												index,
												ReserveData { id: *id, amount: actual },
											)
											.map_err(|_| Error::<T, I>::TooManyReserves)?;

										Ok(actual)
									},
								}
							},
						)?
					} else {
						let remain = <Self as ReservableCurrency<_>>::repatriate_reserved(
							slashed,
							beneficiary,
							to_change,
							status,
						)?;

						// remain should always be zero but just to be defensive here
						to_change.defensive_saturating_sub(remain)
					};

					// `actual <= to_change` and `to_change <= amount`; qed;
					reserves[index].amount -= actual;

					Ok(value - actual)
				},
				Err(_) => Ok(value),
			}
		})
	}
}

impl<T: Config<I>, I: 'static> LockableCurrency<T::AccountId> for Pallet<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	type Moment = T::BlockNumber;

	type MaxLocks = T::MaxLocks;

	// Set a lock on the balance of `who`.
	// Is a no-op if lock amount is zero or `reasons` `is_none()`.
	fn set_lock(
		id: LockIdentifier,
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
	) {
		if amount.is_zero() || reasons.is_empty() {
			return
		}
		let mut new_lock = Some(BalanceLock { id, amount, reasons: reasons.into() });
		let mut locks = Self::locks(who)
			.into_iter()
			.filter_map(|l| if l.id == id { new_lock.take() } else { Some(l) })
			.collect::<Vec<_>>();
		if let Some(lock) = new_lock {
			locks.push(lock)
		}
		Self::update_locks(who, &locks[..]);
	}

	// Extend a lock on the balance of `who`.
	// Is a no-op if lock amount is zero or `reasons` `is_none()`.
	fn extend_lock(
		id: LockIdentifier,
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
	) {
		if amount.is_zero() || reasons.is_empty() {
			return
		}
		let mut new_lock = Some(BalanceLock { id, amount, reasons: reasons.into() });
		let mut locks = Self::locks(who)
			.into_iter()
			.filter_map(|l| {
				if l.id == id {
					new_lock.take().map(|nl| BalanceLock {
						id: l.id,
						amount: l.amount.max(nl.amount),
						reasons: l.reasons | nl.reasons,
					})
				} else {
					Some(l)
				}
			})
			.collect::<Vec<_>>();
		if let Some(lock) = new_lock {
			locks.push(lock)
		}
		Self::update_locks(who, &locks[..]);
	}

	fn remove_lock(id: LockIdentifier, who: &T::AccountId) {
		let mut locks = Self::locks(who);
		locks.retain(|l| l.id != id);
		Self::update_locks(who, &locks[..]);
	}
}