referrerpolicy=no-referrer-when-downgrade
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
// 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.

//! Implementations for the `Currency` family of traits.
//!
//! Note that `WithdrawReasons` are intentionally not used for anything in this implementation and
//! are expected to be removed in the near future, once migration to `fungible::*` traits is done.

use super::*;
use frame_support::{
	ensure,
	pallet_prelude::DispatchResult,
	traits::{
		tokens::{fungible, BalanceStatus as Status, Fortitude::Polite, Precision::BestEffort},
		Currency, DefensiveSaturating, ExistenceRequirement,
		ExistenceRequirement::AllowDeath,
		Get, Imbalance, InspectLockableCurrency, LockIdentifier, LockableCurrency,
		NamedReservableCurrency, ReservableCurrency, SignedImbalance, TryDrop, WithdrawReasons,
	},
};
use frame_system::pallet_prelude::BlockNumberFor;
pub use imbalances::{NegativeImbalance, PositiveImbalance};
use sp_runtime::traits::Bounded;

// wrapping these imbalances in a private module is necessary to ensure absolute privacy
// of the inner member.
mod imbalances {
	use super::*;
	use core::mem;
	use frame_support::traits::{tokens::imbalance::TryMerge, SameOrOther};

	/// 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 extract(&mut self, amount: T::Balance) -> Self {
			let new = self.0.min(amount);
			self.0 = self.0 - new;
			Self(new)
		}
		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> TryMerge for PositiveImbalance<T, I> {
		fn try_merge(self, other: Self) -> Result<Self, (Self, Self)> {
			Ok(self.merge(other))
		}
	}

	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 extract(&mut self, amount: T::Balance) -> Self {
			let new = self.0.min(amount);
			self.0 = self.0 - new;
			Self(new)
		}
		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> TryMerge for NegativeImbalance<T, I> {
		fn try_merge(self, other: Self) -> Result<Self, (Self, Self)> {
			Ok(self.merge(other))
		}
	}

	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) {
			if !self.0.is_zero() {
				<super::TotalIssuance<T, I>>::mutate(|v| *v = v.saturating_add(self.0));
				Pallet::<T, I>::deposit_event(Event::<T, I>::Issued { amount: 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) {
			if !self.0.is_zero() {
				<super::TotalIssuance<T, I>>::mutate(|v| *v = v.saturating_sub(self.0));
				Pallet::<T, I>::deposit_event(Event::<T, I>::Rescinded { amount: 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 active_issuance() -> Self::Balance {
		<Self as fungible::Inspect<_>>::active_issuance()
	}

	fn deactivate(amount: Self::Balance) {
		<Self as fungible::Unbalanced<_>>::deactivate(amount);
	}

	fn reactivate(amount: Self::Balance) {
		<Self as fungible::Unbalanced<_>>::reactivate(amount);
	}

	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()
			});
		});

		Pallet::<T, I>::deposit_event(Event::<T, I>::Rescinded { amount });
		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()
			})
		});

		Pallet::<T, I>::deposit_event(Event::<T, I>::Issued { amount });
		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.
	fn ensure_can_withdraw(
		who: &T::AccountId,
		amount: T::Balance,
		_reasons: WithdrawReasons,
		new_balance: T::Balance,
	) -> DispatchResult {
		if amount.is_zero() {
			return Ok(())
		}
		ensure!(new_balance >= Self::account(who).frozen, 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(())
		}
		let keep_alive = match existence_requirement {
			ExistenceRequirement::KeepAlive => Preserve,
			ExistenceRequirement::AllowDeath => Expendable,
		};
		<Self as fungible::Mutate<_>>::transfer(transactor, dest, value, keep_alive)?;
		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)
		}

		let result = match Self::try_mutate_account_handling_dust(
			who,
			|account, _is_new| -> Result<(Self::NegativeImbalance, Self::Balance), DispatchError> {
				// Best value is the most amount we can slash following liveness rules.
				let ed = T::ExistentialDeposit::get();
				let actual = match system::Pallet::<T>::can_dec_provider(who) {
					true => value.min(account.free),
					false => value.min(account.free.saturating_sub(ed)),
				};
				account.free.saturating_reduce(actual);
				let remaining = value.saturating_sub(actual);
				Ok((NegativeImbalance::new(actual), remaining))
			},
		) {
			Ok((imbalance, remaining)) => {
				Self::deposit_event(Event::Slashed {
					who: who.clone(),
					amount: value.saturating_sub(remaining),
				});
				(imbalance, remaining)
			},
			Err(_) => (Self::NegativeImbalance::zero(), value),
		};
		result
	}

	/// 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_handling_dust(
			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_handling_dust(
			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_handling_dust(
			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 < ed;
				let would_kill = would_be_dead && account.free >= ed;
				ensure!(liveness == AllowDeath || !would_kill, Error::<T, I>::Expendability);

				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_handling_dust(
			who,
			|account,
			 is_new|
			 -> Result<SignedImbalance<Self::Balance, Self::PositiveImbalance>, DispatchError> {
				let ed = T::ExistentialDeposit::get();
				// 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!(value >= 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 });
				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| {
			new_balance >= T::ExistentialDeposit::get() &&
				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_handling_dust(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_handling_dust(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.

		match Self::mutate_account_handling_dust(who, |account| {
			let actual = value.min(account.reserved);
			account.reserved.saturating_reduce(actual);

			// underflow should never happen, but it if does, there's nothing to be done here.
			(NegativeImbalance::new(actual), value.saturating_sub(actual))
		}) {
			Ok((imbalance, not_slashed)) => {
				Self::deposit_event(Event::Slashed {
					who: who.clone(),
					amount: value.saturating_sub(not_slashed),
				});
				(imbalance, not_slashed)
			},
			Err(_) => (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`.
	///
	/// This is `Polite` and thus will not repatriate any funds which would lead the total balance
	/// to be less than the frozen amount. Returns `Ok` with the actual amount of funds moved,
	/// which may be less than `value` since the operation is done an a `BestEffort` basis.
	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, BestEffort, Polite, 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 = BlockNumberFor<T>;

	type MaxLocks = T::MaxLocks;

	// Set or alter a lock on the balance of `who`.
	fn set_lock(
		id: LockIdentifier,
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
	) {
		if reasons.is_empty() || amount.is_zero() {
			Self::remove_lock(id, who);
			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[..]);
	}
}

impl<T: Config<I>, I: 'static> InspectLockableCurrency<T::AccountId> for Pallet<T, I> {
	fn balance_locked(id: LockIdentifier, who: &T::AccountId) -> Self::Balance {
		Self::locks(who)
			.into_iter()
			.filter(|l| l.id == id)
			.fold(Zero::zero(), |acc, l| acc + l.amount)
	}
}