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
// This file is part of Substrate.

// Copyright (C) 2019-2022 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.

//! The traits for putting holds within a single fungible token class.

use crate::{
	ensure,
	traits::tokens::{
		DepositConsequence::Success,
		Fortitude::{self, Force},
		Precision::{self, BestEffort, Exact},
		Preservation::{self, Protect},
		Provenance::Extant,
		Restriction::{self, Free, OnHold},
	},
};
use scale_info::TypeInfo;
use sp_arithmetic::{
	traits::{CheckedAdd, CheckedSub, Zero},
	ArithmeticError,
};
use sp_runtime::{DispatchError, DispatchResult, Saturating, TokenError};

use super::*;

/// Trait for inspecting a fungible asset whose accounts support partitioning and slashing.
pub trait Inspect<AccountId>: super::Inspect<AccountId> {
	/// An identifier for a hold. Used for disambiguating different holds so that
	/// they can be individually replaced or removed and funds from one hold don't accidentally
	/// become unreserved or slashed for another.
	type Reason: codec::Encode + TypeInfo + 'static;

	/// Amount of funds on hold (for all hold reasons) of `who`.
	fn total_balance_on_hold(who: &AccountId) -> Self::Balance;

	/// Get the maximum amount that the `total_balance_on_hold` of `who` can be reduced successfully
	/// based on whether we are willing to force the reduction and potentially go below user-level
	/// restrictions on the minimum amount of the account. Note: This cannot bring the account into
	/// an inconsistent state with regards any required existential deposit.
	///
	/// Never more than `total_balance_on_hold()`.
	fn reducible_total_balance_on_hold(who: &AccountId, _force: Fortitude) -> Self::Balance {
		Self::total_balance_on_hold(who)
	}

	/// Amount of funds on hold (for the given reason) of `who`.
	fn balance_on_hold(reason: &Self::Reason, who: &AccountId) -> Self::Balance;

	/// Returns `true` if it's possible to place (additional) funds under a hold of a given
	/// `reason`. This may fail if the account has exhausted a limited number of concurrent
	/// holds or if it cannot be made to exist (e.g. there is no provider reference).
	///
	/// NOTE: This does not take into account changes which could be made to the account of `who`
	/// (such as removing a provider reference) after this call is made. Any usage of this should
	/// therefore ensure the account is already in the appropriate state prior to calling it.
	fn hold_available(_reason: &Self::Reason, _who: &AccountId) -> bool {
		true
	}

	/// Check to see if some `amount` of funds of `who` may be placed on hold with the given
	/// `reason`. Reasons why this may not be true:
	///
	/// - The implementor supports only a limited number of concurrent holds on an account which is
	///   the possible values of `reason`;
	/// - The total balance of the account is less than `amount`;
	/// - Removing `amount` from the total balance would kill the account and remove the only
	///   provider reference.
	///
	/// Note: we pass `true` as the third argument to `reducible_balance` since we assume that if
	/// needed the balance can slashed. If we are using a simple non-forcing reserve-transfer, then
	/// we really ought to check that we are not reducing the funds below the freeze-limit (if any).
	///
	/// NOTE: This does not take into account changes which could be made to the account of `who`
	/// (such as removing a provider reference) after this call is made. Any usage of this should
	/// therefore ensure the account is already in the appropriate state prior to calling it.
	fn ensure_can_hold(
		reason: &Self::Reason,
		who: &AccountId,
		amount: Self::Balance,
	) -> DispatchResult {
		ensure!(Self::hold_available(reason, who), TokenError::CannotCreateHold);
		ensure!(
			amount <= Self::reducible_balance(who, Protect, Force),
			TokenError::FundsUnavailable
		);
		Ok(())
	}

	/// Check to see if some `amount` of funds of `who` may be placed on hold for the given
	/// `reason`. Reasons why this may not be true:
	///
	/// - The implementor supports only a limited number of concurrent holds on an account which is
	///   the possible values of `reason`;
	/// - The main balance of the account is less than `amount`;
	/// - Removing `amount` from the main balance would kill the account and remove the only
	///   provider reference.
	///
	/// NOTE: This does not take into account changes which could be made to the account of `who`
	/// (such as removing a provider reference) after this call is made. Any usage of this should
	/// therefore ensure the account is already in the appropriate state prior to calling it.
	fn can_hold(reason: &Self::Reason, who: &AccountId, amount: Self::Balance) -> bool {
		Self::ensure_can_hold(reason, who, amount).is_ok()
	}
}

/// A fungible, holdable token class where the balance on hold can be set arbitrarily.
///
/// **WARNING**
/// Do not use this directly unless you want trouble, since it allows you to alter account balances
/// without keeping the issuance up to date. It has no safeguards against accidentally creating
/// token imbalances in your system leading to accidental inflation or deflation. It's really just
/// for the underlying datatype to implement so the user gets the much safer `Balanced` trait to
/// use.
pub trait Unbalanced<AccountId>: Inspect<AccountId> {
	/// Forcefully set the balance on hold of `who` to `amount`. This is independent of any other
	/// balances on hold or the main ("free") balance.
	///
	/// If this call executes successfully, you can `assert_eq!(Self::balance_on_hold(), amount);`.
	///
	/// This function does its best to force the balance change through, but will not break system
	/// invariants such as any Existential Deposits needed or overflows/underflows.
	/// If this cannot be done for some reason (e.g. because the account doesn't exist) then an
	/// `Err` is returned.
	// Implementation note: This should increment the consumer refs if it moves total on hold from
	// zero to non-zero and decrement in the opposite direction.
	//
	// Since this was not done in the previous logic, this will need either a migration or a
	// state item which tracks whether the account is on the old logic or new.
	fn set_balance_on_hold(
		reason: &Self::Reason,
		who: &AccountId,
		amount: Self::Balance,
	) -> DispatchResult;

	/// Reduce the balance on hold of `who` by `amount`.
	///
	/// If `precision` is `Exact` and it cannot be reduced by that amount for
	/// some reason, return `Err` and don't reduce it at all. If `precision` is `BestEffort`, then
	/// reduce the balance of `who` by the most that is possible, up to `amount`.
	///
	/// In either case, if `Ok` is returned then the inner is the amount by which is was reduced.
	fn decrease_balance_on_hold(
		reason: &Self::Reason,
		who: &AccountId,
		mut amount: Self::Balance,
		precision: Precision,
	) -> Result<Self::Balance, DispatchError> {
		let old_balance = Self::balance_on_hold(reason, who);
		if let BestEffort = precision {
			amount = amount.min(old_balance);
		}
		let new_balance = old_balance.checked_sub(&amount).ok_or(TokenError::FundsUnavailable)?;
		Self::set_balance_on_hold(reason, who, new_balance)?;
		Ok(amount)
	}

	/// Increase the balance on hold of `who` by `amount`.
	///
	/// If it cannot be increased by that amount for some reason, return `Err` and don't increase
	/// it at all. If Ok, return the imbalance.
	fn increase_balance_on_hold(
		reason: &Self::Reason,
		who: &AccountId,
		amount: Self::Balance,
		precision: Precision,
	) -> Result<Self::Balance, DispatchError> {
		let old_balance = Self::balance_on_hold(reason, who);
		let new_balance = if let BestEffort = precision {
			old_balance.saturating_add(amount)
		} else {
			old_balance.checked_add(&amount).ok_or(ArithmeticError::Overflow)?
		};
		let amount = new_balance.saturating_sub(old_balance);
		if !amount.is_zero() {
			Self::set_balance_on_hold(reason, who, new_balance)?;
		}
		Ok(amount)
	}
}

/// Trait for mutating a fungible asset which can be placed on hold.
pub trait Mutate<AccountId>:
	Inspect<AccountId> + super::Unbalanced<AccountId> + Unbalanced<AccountId>
{
	/// Hold some funds in an account. If a hold for `reason` is already in place, then this
	/// will increase it.
	fn hold(reason: &Self::Reason, who: &AccountId, amount: Self::Balance) -> DispatchResult {
		// NOTE: This doesn't change the total balance of the account so there's no need to
		// check liquidity.

		Self::ensure_can_hold(reason, who, amount)?;
		// Should be infallible now, but we proceed softly anyway.
		Self::decrease_balance(who, amount, Exact, Protect, Force)?;
		Self::increase_balance_on_hold(reason, who, amount, BestEffort)?;
		Self::done_hold(reason, who, amount);
		Ok(())
	}

	/// Release up to `amount` held funds in an account.
	///
	/// The actual amount released is returned with `Ok`.
	///
	/// If `precision` is `BestEffort`, then the amount actually unreserved and returned as the
	/// inner value of `Ok` may be smaller than the `amount` passed.
	///
	/// NOTE! The inner of the `Ok` result variant returns the *actual* amount released. This is the
	/// opposite of the `ReservableCurrency::unreserve()` result, which gives the amount not able
	/// to be released!
	fn release(
		reason: &Self::Reason,
		who: &AccountId,
		amount: Self::Balance,
		precision: Precision,
	) -> Result<Self::Balance, DispatchError> {
		// NOTE: This doesn't change the total balance of the account so there's no need to
		// check liquidity.

		// We want to make sure we can deposit the amount in advance. If we can't then something is
		// very wrong.
		ensure!(Self::can_deposit(who, amount, Extant) == Success, TokenError::CannotCreate);
		// Get the amount we can actually take from the hold. This might be less than what we want
		// if we're only doing a best-effort.
		let amount = Self::decrease_balance_on_hold(reason, who, amount, precision)?;
		// Increase the main balance by what we took. We always do a best-effort here because we
		// already checked that we can deposit before.
		let actual = Self::increase_balance(who, amount, BestEffort)?;
		Self::done_release(reason, who, actual);
		Ok(actual)
	}

	/// Attempt to decrease the balance of `who` which is held for the given `reason` by `amount`.
	///
	/// If `precision` is `BestEffort`, then as much as possible is reduced, up to `amount`, and the
	/// amount of tokens reduced is returned. Otherwise, if the total amount can be reduced, then it
	/// is and the amount returned, and if not, then nothing changes and `Err` is returned.
	///
	/// If `force` is `Force`, then locks/freezes will be ignored. This should only be used when
	/// conducting slashing or other activity which materially disadvantages the account holder
	/// since it could provide a means of circumventing freezes.
	fn burn_held(
		reason: &Self::Reason,
		who: &AccountId,
		mut amount: Self::Balance,
		precision: Precision,
		force: Fortitude,
	) -> Result<Self::Balance, DispatchError> {
		// We must check total-balance requirements if `!force`.
		let liquid = Self::reducible_total_balance_on_hold(who, force);
		if let BestEffort = precision {
			amount = amount.min(liquid);
		} else {
			ensure!(amount <= liquid, TokenError::Frozen);
		}
		let amount = Self::decrease_balance_on_hold(reason, who, amount, precision)?;
		Self::set_total_issuance(Self::total_issuance().saturating_sub(amount));
		Self::done_burn_held(reason, who, amount);
		Ok(amount)
	}

	/// Transfer held funds into a destination account.
	///
	/// If `mode` is `OnHold`, then the destination account must already exist and the assets
	/// transferred will still be on hold in the destination account. If not, then the destination
	/// account need not already exist, but must be creatable.
	///
	/// If `precision` is `BestEffort`, then an amount less than `amount` may be transferred without
	/// error.
	///
	/// If `force` is `Force`, then other fund-locking mechanisms may be disregarded. It should be
	/// left as `Polite` in most circumstances, but when you want the same power as a `slash`, it
	/// may be `Force`.
	///
	/// The actual amount transferred is returned, or `Err` in the case of error and nothing is
	/// changed.
	fn transfer_on_hold(
		reason: &Self::Reason,
		source: &AccountId,
		dest: &AccountId,
		mut amount: Self::Balance,
		precision: Precision,
		mode: Restriction,
		force: Fortitude,
	) -> Result<Self::Balance, DispatchError> {
		// We must check total-balance requirements if `force` is `Fortitude::Polite`.
		let have = Self::balance_on_hold(reason, source);
		let liquid = Self::reducible_total_balance_on_hold(source, force);
		if let BestEffort = precision {
			amount = amount.min(liquid).min(have);
		} else {
			ensure!(amount <= liquid, TokenError::Frozen);
			ensure!(amount <= have, TokenError::FundsUnavailable);
		}

		// We want to make sure we can deposit the amount in advance. If we can't then something is
		// very wrong.
		ensure!(Self::can_deposit(dest, amount, Extant) == Success, TokenError::CannotCreate);
		ensure!(mode == Free || Self::hold_available(reason, dest), TokenError::CannotCreateHold);

		let amount = Self::decrease_balance_on_hold(reason, source, amount, precision)?;
		let actual = if mode == OnHold {
			Self::increase_balance_on_hold(reason, dest, amount, precision)?
		} else {
			Self::increase_balance(dest, amount, precision)?
		};
		Self::done_transfer_on_hold(reason, source, dest, actual);
		Ok(actual)
	}

	/// Transfer some `amount` of free balance from `source` to become owned by `dest` but on hold
	/// for `reason`.
	///
	/// If `precision` is `BestEffort`, then an amount less than `amount` may be transferred without
	/// error.
	///
	/// `source` must obey the requirements of `keep_alive`.
	///
	/// If `force` is `Force`, then other fund-locking mechanisms may be disregarded. It should be
	/// left as `Polite` in most circumstances, but when you want the same power as a `slash`, it
	/// may be `Force`.
	///
	/// The amount placed on hold is returned or `Err` in the case of error and nothing is changed.
	///
	/// WARNING: This may return an error after a partial storage mutation. It should be used only
	/// inside a transactional storage context and an `Err` result must imply a storage rollback.
	fn transfer_and_hold(
		reason: &Self::Reason,
		source: &AccountId,
		dest: &AccountId,
		amount: Self::Balance,
		precision: Precision,
		expendability: Preservation,
		force: Fortitude,
	) -> Result<Self::Balance, DispatchError> {
		ensure!(Self::hold_available(reason, dest), TokenError::CannotCreateHold);
		ensure!(Self::can_deposit(dest, amount, Extant) == Success, TokenError::CannotCreate);
		let actual = Self::decrease_balance(source, amount, precision, expendability, force)?;
		Self::increase_balance_on_hold(reason, dest, actual, precision)?;
		Self::done_transfer_on_hold(reason, source, dest, actual);
		Ok(actual)
	}

	fn done_hold(_reason: &Self::Reason, _who: &AccountId, _amount: Self::Balance) {}
	fn done_release(_reason: &Self::Reason, _who: &AccountId, _amount: Self::Balance) {}
	fn done_burn_held(_reason: &Self::Reason, _who: &AccountId, _amount: Self::Balance) {}
	fn done_transfer_on_hold(
		_reason: &Self::Reason,
		_source: &AccountId,
		_dest: &AccountId,
		_amount: Self::Balance,
	) {
	}
	fn done_transfer_and_hold(
		_reason: &Self::Reason,
		_source: &AccountId,
		_dest: &AccountId,
		_transferred: Self::Balance,
	) {
	}
}

/// Trait for slashing a fungible asset which can be place on hold.
pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> {
	/// Reduce the balance of some funds on hold in an account.
	///
	/// The resulting imbalance is the first item of the tuple returned.
	///
	/// As much funds that are on hold up to `amount` will be deducted as possible. If this is less
	/// than `amount`, then a non-zero second item will be returned.
	fn slash(
		reason: &Self::Reason,
		who: &AccountId,
		amount: Self::Balance,
	) -> (Credit<AccountId, Self>, Self::Balance) {
		let decrease = Self::decrease_balance_on_hold(reason, who, amount, BestEffort)
			.unwrap_or(Default::default());
		let credit =
			Imbalance::<Self::Balance, Self::OnDropCredit, Self::OnDropDebt>::new(decrease);
		Self::done_slash(reason, who, decrease);
		(credit, amount.saturating_sub(decrease))
	}

	fn done_slash(_reason: &Self::Reason, _who: &AccountId, _amount: Self::Balance) {}
}