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
// 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.

//! # Bounties Module ( pallet-bounties )
//!
//! ## Bounty
//!
//! > NOTE: This pallet is tightly coupled with pallet-treasury.
//!
//! A Bounty Spending is a reward for a specified body of work - or specified set of objectives -
//! that needs to be executed for a predefined Treasury amount to be paid out. A curator is assigned
//! after the bounty is approved and funded by Council, to be delegated with the responsibility of
//! assigning a payout address once the specified set of objectives is completed.
//!
//! After the Council has activated a bounty, it delegates the work that requires expertise to a
//! curator in exchange of a deposit. Once the curator accepts the bounty, they get to close the
//! active bounty. Closing the active bounty enacts a delayed payout to the payout address, the
//! curator fee and the return of the curator deposit. The delay allows for intervention through
//! regular democracy. The Council gets to unassign the curator, resulting in a new curator
//! election. The Council also gets to cancel the bounty if deemed necessary before assigning a
//! curator or once the bounty is active or payout is pending, resulting in the slash of the
//! curator's deposit.
//!
//! This pallet may opt into using a [`ChildBountyManager`] that enables bounties to be split into
//! sub-bounties, as children of anh established bounty (called the parent in the context of it's
//! children).
//!
//! > NOTE: The parent bounty cannot be closed if it has a non-zero number of it has active child
//! > bounties associated with it.
//!
//! ### Terminology
//!
//! Bounty:
//!
//! - **Bounty spending proposal:** A proposal to reward a predefined body of work upon completion
//!   by the Treasury.
//! - **Proposer:** An account proposing a bounty spending.
//! - **Curator:** An account managing the bounty and assigning a payout address receiving the
//!   reward for the completion of work.
//! - **Deposit:** The amount held on deposit for placing a bounty proposal plus the amount held on
//!   deposit per byte within the bounty description.
//! - **Curator deposit:** The payment from a candidate willing to curate an approved bounty. The
//!   deposit is returned when/if the bounty is completed.
//! - **Bounty value:** The total amount that should be paid to the Payout Address if the bounty is
//!   rewarded.
//! - **Payout address:** The account to which the total or part of the bounty is assigned to.
//! - **Payout Delay:** The delay period for which a bounty beneficiary needs to wait before
//!   claiming.
//! - **Curator fee:** The reserved upfront payment for a curator for work related to the bounty.
//!
//! ## Interface
//!
//! ### Dispatchable Functions
//!
//! Bounty protocol:
//!
//! - `propose_bounty` - Propose a specific treasury amount to be earmarked for a predefined set of
//!   tasks and stake the required deposit.
//! - `approve_bounty` - Accept a specific treasury amount to be earmarked for a predefined body of
//!   work.
//! - `propose_curator` - Assign an account to a bounty as candidate curator.
//! - `accept_curator` - Accept a bounty assignment from the Council, setting a curator deposit.
//! - `extend_bounty_expiry` - Extend the expiry block number of the bounty and stay active.
//! - `award_bounty` - Close and pay out the specified amount for the completed work.
//! - `claim_bounty` - Claim a specific bounty amount from the Payout Address.
//! - `unassign_curator` - Unassign an accepted curator from a specific earmark.
//! - `close_bounty` - Cancel the earmark for a specific treasury amount and close the bounty.

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

mod benchmarking;
pub mod migrations;
mod tests;
pub mod weights;

use sp_std::prelude::*;

use frame_support::traits::{
	Currency, ExistenceRequirement::AllowDeath, Get, Imbalance, OnUnbalanced, ReservableCurrency,
};

use sp_runtime::{
	traits::{AccountIdConversion, BadOrigin, Saturating, StaticLookup, Zero},
	DispatchResult, Permill, RuntimeDebug,
};

use frame_support::{dispatch::DispatchResultWithPostInfo, traits::EnsureOrigin};

use frame_support::pallet_prelude::*;
use frame_system::pallet_prelude::*;
use scale_info::TypeInfo;
pub use weights::WeightInfo;

pub use pallet::*;

type BalanceOf<T, I = ()> = pallet_treasury::BalanceOf<T, I>;

type PositiveImbalanceOf<T, I = ()> = pallet_treasury::PositiveImbalanceOf<T, I>;

/// An index of a bounty. Just a `u32`.
pub type BountyIndex = u32;

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

/// A bounty proposal.
#[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug, TypeInfo, MaxEncodedLen)]
pub struct Bounty<AccountId, Balance, BlockNumber> {
	/// The account proposing it.
	proposer: AccountId,
	/// The (total) amount that should be paid if the bounty is rewarded.
	value: Balance,
	/// The curator fee. Included in value.
	fee: Balance,
	/// The deposit of curator.
	curator_deposit: Balance,
	/// The amount held on deposit (reserved) for making this proposal.
	bond: Balance,
	/// The status of this bounty.
	status: BountyStatus<AccountId, BlockNumber>,
}

impl<AccountId: PartialEq + Clone + Ord, Balance, BlockNumber: Clone>
	Bounty<AccountId, Balance, BlockNumber>
{
	/// Getter for bounty status, to be used for child bounties.
	pub fn get_status(&self) -> BountyStatus<AccountId, BlockNumber> {
		self.status.clone()
	}
}

/// The status of a bounty proposal.
#[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug, TypeInfo, MaxEncodedLen)]
pub enum BountyStatus<AccountId, BlockNumber> {
	/// The bounty is proposed and waiting for approval.
	Proposed,
	/// The bounty is approved and waiting to become active at next spend period.
	Approved,
	/// The bounty is funded and waiting for curator assignment.
	Funded,
	/// A curator has been proposed. Waiting for acceptance from the curator.
	CuratorProposed {
		/// The assigned curator of this bounty.
		curator: AccountId,
	},
	/// The bounty is active and waiting to be awarded.
	Active {
		/// The curator of this bounty.
		curator: AccountId,
		/// An update from the curator is due by this block, else they are considered inactive.
		update_due: BlockNumber,
	},
	/// The bounty is awarded and waiting to released after a delay.
	PendingPayout {
		/// The curator of this bounty.
		curator: AccountId,
		/// The beneficiary of the bounty.
		beneficiary: AccountId,
		/// When the bounty can be claimed.
		unlock_at: BlockNumber,
	},
}

/// The child bounty manager.
pub trait ChildBountyManager<Balance> {
	/// Get the active child bounties for a parent bounty.
	fn child_bounties_count(bounty_id: BountyIndex) -> BountyIndex;

	/// Get total curator fees of children-bounty curators.
	fn children_curator_fees(bounty_id: BountyIndex) -> Balance;
}

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

	const STORAGE_VERSION: StorageVersion = StorageVersion::new(4);

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

	#[pallet::config]
	pub trait Config<I: 'static = ()>: frame_system::Config + pallet_treasury::Config<I> {
		/// The amount held on deposit for placing a bounty proposal.
		#[pallet::constant]
		type BountyDepositBase: Get<BalanceOf<Self, I>>;

		/// The delay period for which a bounty beneficiary need to wait before claim the payout.
		#[pallet::constant]
		type BountyDepositPayoutDelay: Get<BlockNumberFor<Self>>;

		/// Bounty duration in blocks.
		#[pallet::constant]
		type BountyUpdatePeriod: Get<BlockNumberFor<Self>>;

		/// The curator deposit is calculated as a percentage of the curator fee.
		///
		/// This deposit has optional upper and lower bounds with `CuratorDepositMax` and
		/// `CuratorDepositMin`.
		#[pallet::constant]
		type CuratorDepositMultiplier: Get<Permill>;

		/// Maximum amount of funds that should be placed in a deposit for making a proposal.
		#[pallet::constant]
		type CuratorDepositMax: Get<Option<BalanceOf<Self, I>>>;

		/// Minimum amount of funds that should be placed in a deposit for making a proposal.
		#[pallet::constant]
		type CuratorDepositMin: Get<Option<BalanceOf<Self, I>>>;

		/// Minimum value for a bounty.
		#[pallet::constant]
		type BountyValueMinimum: Get<BalanceOf<Self, I>>;

		/// The amount held on deposit per byte within the tip report reason or bounty description.
		#[pallet::constant]
		type DataDepositPerByte: Get<BalanceOf<Self, I>>;

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

		/// Maximum acceptable reason length.
		///
		/// Benchmarks depend on this value, be sure to update weights file when changing this value
		#[pallet::constant]
		type MaximumReasonLength: Get<u32>;

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

		/// The child bounty manager.
		type ChildBountyManager: ChildBountyManager<BalanceOf<Self, I>>;
	}

	#[pallet::error]
	pub enum Error<T, I = ()> {
		/// Proposer's balance is too low.
		InsufficientProposersBalance,
		/// No proposal or bounty at that index.
		InvalidIndex,
		/// The reason given is just too big.
		ReasonTooBig,
		/// The bounty status is unexpected.
		UnexpectedStatus,
		/// Require bounty curator.
		RequireCurator,
		/// Invalid bounty value.
		InvalidValue,
		/// Invalid bounty fee.
		InvalidFee,
		/// A bounty payout is pending.
		/// To cancel the bounty, you must unassign and slash the curator.
		PendingPayout,
		/// The bounties cannot be claimed/closed because it's still in the countdown period.
		Premature,
		/// The bounty cannot be closed because it has active child bounties.
		HasActiveChildBounty,
		/// Too many approvals are already queued.
		TooManyQueued,
	}

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config<I>, I: 'static = ()> {
		/// New bounty proposal.
		BountyProposed { index: BountyIndex },
		/// A bounty proposal was rejected; funds were slashed.
		BountyRejected { index: BountyIndex, bond: BalanceOf<T, I> },
		/// A bounty proposal is funded and became active.
		BountyBecameActive { index: BountyIndex },
		/// A bounty is awarded to a beneficiary.
		BountyAwarded { index: BountyIndex, beneficiary: T::AccountId },
		/// A bounty is claimed by beneficiary.
		BountyClaimed { index: BountyIndex, payout: BalanceOf<T, I>, beneficiary: T::AccountId },
		/// A bounty is cancelled.
		BountyCanceled { index: BountyIndex },
		/// A bounty expiry is extended.
		BountyExtended { index: BountyIndex },
	}

	/// Number of bounty proposals that have been made.
	#[pallet::storage]
	#[pallet::getter(fn bounty_count)]
	pub type BountyCount<T: Config<I>, I: 'static = ()> = StorageValue<_, BountyIndex, ValueQuery>;

	/// Bounties that have been made.
	#[pallet::storage]
	#[pallet::getter(fn bounties)]
	pub type Bounties<T: Config<I>, I: 'static = ()> = StorageMap<
		_,
		Twox64Concat,
		BountyIndex,
		Bounty<T::AccountId, BalanceOf<T, I>, BlockNumberFor<T>>,
	>;

	/// The description of each bounty.
	#[pallet::storage]
	#[pallet::getter(fn bounty_descriptions)]
	pub type BountyDescriptions<T: Config<I>, I: 'static = ()> =
		StorageMap<_, Twox64Concat, BountyIndex, BoundedVec<u8, T::MaximumReasonLength>>;

	/// Bounty indices that have been approved but not yet funded.
	#[pallet::storage]
	#[pallet::getter(fn bounty_approvals)]
	pub type BountyApprovals<T: Config<I>, I: 'static = ()> =
		StorageValue<_, BoundedVec<BountyIndex, T::MaxApprovals>, ValueQuery>;

	#[pallet::call]
	impl<T: Config<I>, I: 'static> Pallet<T, I> {
		/// Propose a new bounty.
		///
		/// The dispatch origin for this call must be _Signed_.
		///
		/// Payment: `TipReportDepositBase` will be reserved from the origin account, as well as
		/// `DataDepositPerByte` for each byte in `reason`. It will be unreserved upon approval,
		/// or slashed when rejected.
		///
		/// - `curator`: The curator account whom will manage this bounty.
		/// - `fee`: The curator fee.
		/// - `value`: The total payment amount of this bounty, curator fee included.
		/// - `description`: The description of this bounty.
		#[pallet::call_index(0)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::propose_bounty(description.len() as u32))]
		pub fn propose_bounty(
			origin: OriginFor<T>,
			#[pallet::compact] value: BalanceOf<T, I>,
			description: Vec<u8>,
		) -> DispatchResult {
			let proposer = ensure_signed(origin)?;
			Self::create_bounty(proposer, description, value)?;
			Ok(())
		}

		/// Approve a bounty proposal. At a later time, the bounty will be funded and become active
		/// and the original deposit will be returned.
		///
		/// May only be called from `T::SpendOrigin`.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(1)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::approve_bounty())]
		pub fn approve_bounty(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
		) -> DispatchResult {
			let max_amount = T::SpendOrigin::ensure_origin(origin)?;
			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;
				ensure!(
					bounty.value <= max_amount,
					pallet_treasury::Error::<T, I>::InsufficientPermission
				);
				ensure!(bounty.status == BountyStatus::Proposed, Error::<T, I>::UnexpectedStatus);

				bounty.status = BountyStatus::Approved;

				BountyApprovals::<T, I>::try_append(bounty_id)
					.map_err(|()| Error::<T, I>::TooManyQueued)?;

				Ok(())
			})?;
			Ok(())
		}

		/// Assign a curator to a funded bounty.
		///
		/// May only be called from `T::SpendOrigin`.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(2)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::propose_curator())]
		pub fn propose_curator(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
			curator: AccountIdLookupOf<T>,
			#[pallet::compact] fee: BalanceOf<T, I>,
		) -> DispatchResult {
			let max_amount = T::SpendOrigin::ensure_origin(origin)?;

			let curator = T::Lookup::lookup(curator)?;
			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;
				ensure!(
					bounty.value <= max_amount,
					pallet_treasury::Error::<T, I>::InsufficientPermission
				);
				match bounty.status {
					BountyStatus::Funded => {},
					_ => return Err(Error::<T, I>::UnexpectedStatus.into()),
				};

				ensure!(fee < bounty.value, Error::<T, I>::InvalidFee);

				bounty.status = BountyStatus::CuratorProposed { curator };
				bounty.fee = fee;

				Ok(())
			})?;
			Ok(())
		}

		/// Unassign curator from a bounty.
		///
		/// This function can only be called by the `RejectOrigin` a signed origin.
		///
		/// If this function is called by the `RejectOrigin`, we assume that the curator is
		/// malicious or inactive. As a result, we will slash the curator when possible.
		///
		/// If the origin is the curator, we take this as a sign they are unable to do their job and
		/// they willingly give up. We could slash them, but for now we allow them to recover their
		/// deposit and exit without issue. (We may want to change this if it is abused.)
		///
		/// Finally, the origin can be anyone if and only if the curator is "inactive". This allows
		/// anyone in the community to call out that a curator is not doing their due diligence, and
		/// we should pick a new curator. In this case the curator should also be slashed.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(3)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::unassign_curator())]
		pub fn unassign_curator(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
		) -> DispatchResult {
			let maybe_sender = ensure_signed(origin.clone())
				.map(Some)
				.or_else(|_| T::RejectOrigin::ensure_origin(origin).map(|_| None))?;

			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;

				let slash_curator = |curator: &T::AccountId,
				                     curator_deposit: &mut BalanceOf<T, I>| {
					let imbalance = T::Currency::slash_reserved(curator, *curator_deposit).0;
					T::OnSlash::on_unbalanced(imbalance);
					*curator_deposit = Zero::zero();
				};

				match bounty.status {
					BountyStatus::Proposed | BountyStatus::Approved | BountyStatus::Funded => {
						// No curator to unassign at this point.
						return Err(Error::<T, I>::UnexpectedStatus.into())
					},
					BountyStatus::CuratorProposed { ref curator } => {
						// A curator has been proposed, but not accepted yet.
						// Either `RejectOrigin` or the proposed curator can unassign the curator.
						ensure!(maybe_sender.map_or(true, |sender| sender == *curator), BadOrigin);
					},
					BountyStatus::Active { ref curator, ref update_due } => {
						// The bounty is active.
						match maybe_sender {
							// If the `RejectOrigin` is calling this function, slash the curator.
							None => {
								slash_curator(curator, &mut bounty.curator_deposit);
								// Continue to change bounty status below...
							},
							Some(sender) => {
								// If the sender is not the curator, and the curator is inactive,
								// slash the curator.
								if sender != *curator {
									let block_number = frame_system::Pallet::<T>::block_number();
									if *update_due < block_number {
										slash_curator(curator, &mut bounty.curator_deposit);
									// Continue to change bounty status below...
									} else {
										// Curator has more time to give an update.
										return Err(Error::<T, I>::Premature.into())
									}
								} else {
									// Else this is the curator, willingly giving up their role.
									// Give back their deposit.
									let err_amount =
										T::Currency::unreserve(curator, bounty.curator_deposit);
									debug_assert!(err_amount.is_zero());
									bounty.curator_deposit = Zero::zero();
									// Continue to change bounty status below...
								}
							},
						}
					},
					BountyStatus::PendingPayout { ref curator, .. } => {
						// The bounty is pending payout, so only council can unassign a curator.
						// By doing so, they are claiming the curator is acting maliciously, so
						// we slash the curator.
						ensure!(maybe_sender.is_none(), BadOrigin);
						slash_curator(curator, &mut bounty.curator_deposit);
						// Continue to change bounty status below...
					},
				};

				bounty.status = BountyStatus::Funded;
				Ok(())
			})?;
			Ok(())
		}

		/// Accept the curator role for a bounty.
		/// A deposit will be reserved from curator and refund upon successful payout.
		///
		/// May only be called from the curator.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(4)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::accept_curator())]
		pub fn accept_curator(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
		) -> DispatchResult {
			let signer = ensure_signed(origin)?;

			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;

				match bounty.status {
					BountyStatus::CuratorProposed { ref curator } => {
						ensure!(signer == *curator, Error::<T, I>::RequireCurator);

						let deposit = Self::calculate_curator_deposit(&bounty.fee);
						T::Currency::reserve(curator, deposit)?;
						bounty.curator_deposit = deposit;

						let update_due = frame_system::Pallet::<T>::block_number() +
							T::BountyUpdatePeriod::get();
						bounty.status =
							BountyStatus::Active { curator: curator.clone(), update_due };

						Ok(())
					},
					_ => Err(Error::<T, I>::UnexpectedStatus.into()),
				}
			})?;
			Ok(())
		}

		/// Award bounty to a beneficiary account. The beneficiary will be able to claim the funds
		/// after a delay.
		///
		/// The dispatch origin for this call must be the curator of this bounty.
		///
		/// - `bounty_id`: Bounty ID to award.
		/// - `beneficiary`: The beneficiary account whom will receive the payout.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(5)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::award_bounty())]
		pub fn award_bounty(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
			beneficiary: AccountIdLookupOf<T>,
		) -> DispatchResult {
			let signer = ensure_signed(origin)?;
			let beneficiary = T::Lookup::lookup(beneficiary)?;

			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;

				// Ensure no active child bounties before processing the call.
				ensure!(
					T::ChildBountyManager::child_bounties_count(bounty_id) == 0,
					Error::<T, I>::HasActiveChildBounty
				);

				match &bounty.status {
					BountyStatus::Active { curator, .. } => {
						ensure!(signer == *curator, Error::<T, I>::RequireCurator);
					},
					_ => return Err(Error::<T, I>::UnexpectedStatus.into()),
				}
				bounty.status = BountyStatus::PendingPayout {
					curator: signer,
					beneficiary: beneficiary.clone(),
					unlock_at: frame_system::Pallet::<T>::block_number() +
						T::BountyDepositPayoutDelay::get(),
				};

				Ok(())
			})?;

			Self::deposit_event(Event::<T, I>::BountyAwarded { index: bounty_id, beneficiary });
			Ok(())
		}

		/// Claim the payout from an awarded bounty after payout delay.
		///
		/// The dispatch origin for this call must be the beneficiary of this bounty.
		///
		/// - `bounty_id`: Bounty ID to claim.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(6)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::claim_bounty())]
		pub fn claim_bounty(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
		) -> DispatchResult {
			let _ = ensure_signed(origin)?; // anyone can trigger claim

			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.take().ok_or(Error::<T, I>::InvalidIndex)?;
				if let BountyStatus::PendingPayout { curator, beneficiary, unlock_at } =
					bounty.status
				{
					ensure!(
						frame_system::Pallet::<T>::block_number() >= unlock_at,
						Error::<T, I>::Premature
					);
					let bounty_account = Self::bounty_account_id(bounty_id);
					let balance = T::Currency::free_balance(&bounty_account);
					let fee = bounty.fee.min(balance); // just to be safe
					let payout = balance.saturating_sub(fee);
					let err_amount = T::Currency::unreserve(&curator, bounty.curator_deposit);
					debug_assert!(err_amount.is_zero());

					// Get total child bounties curator fees, and subtract it from the parent
					// curator fee (the fee in present referenced bounty, `self`).
					let children_fee = T::ChildBountyManager::children_curator_fees(bounty_id);
					debug_assert!(children_fee <= fee);

					let final_fee = fee.saturating_sub(children_fee);
					let res =
						T::Currency::transfer(&bounty_account, &curator, final_fee, AllowDeath); // should not fail
					debug_assert!(res.is_ok());
					let res =
						T::Currency::transfer(&bounty_account, &beneficiary, payout, AllowDeath); // should not fail
					debug_assert!(res.is_ok());

					*maybe_bounty = None;

					BountyDescriptions::<T, I>::remove(bounty_id);

					Self::deposit_event(Event::<T, I>::BountyClaimed {
						index: bounty_id,
						payout,
						beneficiary,
					});
					Ok(())
				} else {
					Err(Error::<T, I>::UnexpectedStatus.into())
				}
			})?;
			Ok(())
		}

		/// Cancel a proposed or active bounty. All the funds will be sent to treasury and
		/// the curator deposit will be unreserved if possible.
		///
		/// Only `T::RejectOrigin` is able to cancel a bounty.
		///
		/// - `bounty_id`: Bounty ID to cancel.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(7)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::close_bounty_proposed()
			.max(<T as Config<I>>::WeightInfo::close_bounty_active()))]
		pub fn close_bounty(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
		) -> DispatchResultWithPostInfo {
			T::RejectOrigin::ensure_origin(origin)?;

			Bounties::<T, I>::try_mutate_exists(
				bounty_id,
				|maybe_bounty| -> DispatchResultWithPostInfo {
					let bounty = maybe_bounty.as_ref().ok_or(Error::<T, I>::InvalidIndex)?;

					// Ensure no active child bounties before processing the call.
					ensure!(
						T::ChildBountyManager::child_bounties_count(bounty_id) == 0,
						Error::<T, I>::HasActiveChildBounty
					);

					match &bounty.status {
						BountyStatus::Proposed => {
							// The reject origin would like to cancel a proposed bounty.
							BountyDescriptions::<T, I>::remove(bounty_id);
							let value = bounty.bond;
							let imbalance = T::Currency::slash_reserved(&bounty.proposer, value).0;
							T::OnSlash::on_unbalanced(imbalance);
							*maybe_bounty = None;

							Self::deposit_event(Event::<T, I>::BountyRejected {
								index: bounty_id,
								bond: value,
							});
							// Return early, nothing else to do.
							return Ok(
								Some(<T as Config<I>>::WeightInfo::close_bounty_proposed()).into()
							)
						},
						BountyStatus::Approved => {
							// For weight reasons, we don't allow a council to cancel in this phase.
							// We ask for them to wait until it is funded before they can cancel.
							return Err(Error::<T, I>::UnexpectedStatus.into())
						},
						BountyStatus::Funded | BountyStatus::CuratorProposed { .. } => {
							// Nothing extra to do besides the removal of the bounty below.
						},
						BountyStatus::Active { curator, .. } => {
							// Cancelled by council, refund deposit of the working curator.
							let err_amount =
								T::Currency::unreserve(curator, bounty.curator_deposit);
							debug_assert!(err_amount.is_zero());
							// Then execute removal of the bounty below.
						},
						BountyStatus::PendingPayout { .. } => {
							// Bounty is already pending payout. If council wants to cancel
							// this bounty, it should mean the curator was acting maliciously.
							// So the council should first unassign the curator, slashing their
							// deposit.
							return Err(Error::<T, I>::PendingPayout.into())
						},
					}

					let bounty_account = Self::bounty_account_id(bounty_id);

					BountyDescriptions::<T, I>::remove(bounty_id);

					let balance = T::Currency::free_balance(&bounty_account);
					let res = T::Currency::transfer(
						&bounty_account,
						&Self::account_id(),
						balance,
						AllowDeath,
					); // should not fail
					debug_assert!(res.is_ok());
					*maybe_bounty = None;

					Self::deposit_event(Event::<T, I>::BountyCanceled { index: bounty_id });
					Ok(Some(<T as Config<I>>::WeightInfo::close_bounty_active()).into())
				},
			)
		}

		/// Extend the expiry time of an active bounty.
		///
		/// The dispatch origin for this call must be the curator of this bounty.
		///
		/// - `bounty_id`: Bounty ID to extend.
		/// - `remark`: additional information.
		///
		/// ## Complexity
		/// - O(1).
		#[pallet::call_index(8)]
		#[pallet::weight(<T as Config<I>>::WeightInfo::extend_bounty_expiry())]
		pub fn extend_bounty_expiry(
			origin: OriginFor<T>,
			#[pallet::compact] bounty_id: BountyIndex,
			_remark: Vec<u8>,
		) -> DispatchResult {
			let signer = ensure_signed(origin)?;

			Bounties::<T, I>::try_mutate_exists(bounty_id, |maybe_bounty| -> DispatchResult {
				let bounty = maybe_bounty.as_mut().ok_or(Error::<T, I>::InvalidIndex)?;

				match bounty.status {
					BountyStatus::Active { ref curator, ref mut update_due } => {
						ensure!(*curator == signer, Error::<T, I>::RequireCurator);
						*update_due = (frame_system::Pallet::<T>::block_number() +
							T::BountyUpdatePeriod::get())
						.max(*update_due);
					},
					_ => return Err(Error::<T, I>::UnexpectedStatus.into()),
				}

				Ok(())
			})?;

			Self::deposit_event(Event::<T, I>::BountyExtended { index: bounty_id });
			Ok(())
		}
	}
}

impl<T: Config<I>, I: 'static> Pallet<T, I> {
	pub fn calculate_curator_deposit(fee: &BalanceOf<T, I>) -> BalanceOf<T, I> {
		let mut deposit = T::CuratorDepositMultiplier::get() * *fee;

		if let Some(max_deposit) = T::CuratorDepositMax::get() {
			deposit = deposit.min(max_deposit)
		}

		if let Some(min_deposit) = T::CuratorDepositMin::get() {
			deposit = deposit.max(min_deposit)
		}

		deposit
	}

	/// The account ID of the treasury pot.
	///
	/// This actually does computation. If you need to keep using it, then make sure you cache the
	/// value and only call this once.
	pub fn account_id() -> T::AccountId {
		T::PalletId::get().into_account_truncating()
	}

	/// The account ID of a bounty account
	pub fn bounty_account_id(id: BountyIndex) -> T::AccountId {
		// only use two byte prefix to support 16 byte account id (used by test)
		// "modl" ++ "py/trsry" ++ "bt" is 14 bytes, and two bytes remaining for bounty index
		T::PalletId::get().into_sub_account_truncating(("bt", id))
	}

	fn create_bounty(
		proposer: T::AccountId,
		description: Vec<u8>,
		value: BalanceOf<T, I>,
	) -> DispatchResult {
		let bounded_description: BoundedVec<_, _> =
			description.try_into().map_err(|_| Error::<T, I>::ReasonTooBig)?;
		ensure!(value >= T::BountyValueMinimum::get(), Error::<T, I>::InvalidValue);

		let index = Self::bounty_count();

		// reserve deposit for new bounty
		let bond = T::BountyDepositBase::get() +
			T::DataDepositPerByte::get() * (bounded_description.len() as u32).into();
		T::Currency::reserve(&proposer, bond)
			.map_err(|_| Error::<T, I>::InsufficientProposersBalance)?;

		BountyCount::<T, I>::put(index + 1);

		let bounty = Bounty {
			proposer,
			value,
			fee: 0u32.into(),
			curator_deposit: 0u32.into(),
			bond,
			status: BountyStatus::Proposed,
		};

		Bounties::<T, I>::insert(index, &bounty);
		BountyDescriptions::<T, I>::insert(index, bounded_description);

		Self::deposit_event(Event::<T, I>::BountyProposed { index });

		Ok(())
	}
}

impl<T: Config<I>, I: 'static> pallet_treasury::SpendFunds<T, I> for Pallet<T, I> {
	fn spend_funds(
		budget_remaining: &mut BalanceOf<T, I>,
		imbalance: &mut PositiveImbalanceOf<T, I>,
		total_weight: &mut Weight,
		missed_any: &mut bool,
	) {
		let bounties_len = BountyApprovals::<T, I>::mutate(|v| {
			let bounties_approval_len = v.len() as u32;
			v.retain(|&index| {
				Bounties::<T, I>::mutate(index, |bounty| {
					// Should always be true, but shouldn't panic if false or we're screwed.
					if let Some(bounty) = bounty {
						if bounty.value <= *budget_remaining {
							*budget_remaining -= bounty.value;

							bounty.status = BountyStatus::Funded;

							// return their deposit.
							let err_amount = T::Currency::unreserve(&bounty.proposer, bounty.bond);
							debug_assert!(err_amount.is_zero());

							// fund the bounty account
							imbalance.subsume(T::Currency::deposit_creating(
								&Self::bounty_account_id(index),
								bounty.value,
							));

							Self::deposit_event(Event::<T, I>::BountyBecameActive { index });
							false
						} else {
							*missed_any = true;
							true
						}
					} else {
						false
					}
				})
			});
			bounties_approval_len
		});

		*total_weight += <T as pallet::Config<I>>::WeightInfo::spend_funds(bounties_len);
	}
}

// Default impl for when ChildBounties is not being used in the runtime.
impl<Balance: Zero> ChildBountyManager<Balance> for () {
	fn child_bounties_count(_bounty_id: BountyIndex) -> BountyIndex {
		Default::default()
	}

	fn children_curator_fees(_bounty_id: BountyIndex) -> Balance {
		Zero::zero()
	}
}