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
// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! Adapters to work with `frame_support::traits::Currency` through XCM.

use super::MintLocation;
use frame_support::traits::{ExistenceRequirement::AllowDeath, Get, WithdrawReasons};
use sp_runtime::traits::CheckedSub;
use sp_std::{marker::PhantomData, result};
use xcm::latest::{Error as XcmError, MultiAsset, MultiLocation, Result, XcmContext};
use xcm_executor::{
	traits::{ConvertLocation, MatchesFungible, TransactAsset},
	Assets,
};

/// Asset transaction errors.
enum Error {
	/// The given asset is not handled. (According to [`XcmError::AssetNotFound`])
	AssetNotHandled,
	/// `MultiLocation` to `AccountId` conversion failed.
	AccountIdConversionFailed,
}

impl From<Error> for XcmError {
	fn from(e: Error) -> Self {
		use XcmError::FailedToTransactAsset;
		match e {
			Error::AssetNotHandled => XcmError::AssetNotFound,
			Error::AccountIdConversionFailed => FailedToTransactAsset("AccountIdConversionFailed"),
		}
	}
}

/// Simple adapter to use a currency as asset transactor. This type can be used as `type
/// AssetTransactor` in `xcm::Config`.
///
/// # Example
/// ```
/// use parity_scale_codec::Decode;
/// use frame_support::{parameter_types, PalletId};
/// use sp_runtime::traits::{AccountIdConversion, TrailingZeroInput};
/// use xcm::latest::prelude::*;
/// use xcm_builder::{ParentIsPreset, CurrencyAdapter, IsConcrete};
///
/// /// Our chain's account id.
/// type AccountId = sp_runtime::AccountId32;
///
/// /// Our relay chain's location.
/// parameter_types! {
///     pub RelayChain: MultiLocation = Parent.into();
///     pub CheckingAccount: AccountId = PalletId(*b"checking").into_account_truncating();
/// }
///
/// /// Some items that implement `ConvertLocation<AccountId>`. Can be more, but for now we just assume we accept
/// /// messages from the parent (relay chain).
/// pub type LocationConverter = (ParentIsPreset<AccountId>);
///
/// /// Just a dummy implementation of `Currency`. Normally this would be `Balances`.
/// pub type CurrencyImpl = ();
///
/// /// Final currency adapter. This can be used in `xcm::Config` to specify how asset related transactions happen.
/// pub type AssetTransactor = CurrencyAdapter<
///     // Use this `Currency` impl instance:
///     CurrencyImpl,
///     // The matcher: use the currency when the asset is a concrete asset in our relay chain.
///     IsConcrete<RelayChain>,
///     // The local converter: default account of the parent relay chain.
///     LocationConverter,
///     // Our chain's account ID type.
///     AccountId,
///     // The checking account. Can be any deterministic inaccessible account.
///     CheckingAccount,
/// >;
/// ```
pub struct CurrencyAdapter<Currency, Matcher, AccountIdConverter, AccountId, CheckedAccount>(
	PhantomData<(Currency, Matcher, AccountIdConverter, AccountId, CheckedAccount)>,
);

impl<
		Currency: frame_support::traits::Currency<AccountId>,
		Matcher: MatchesFungible<Currency::Balance>,
		AccountIdConverter: ConvertLocation<AccountId>,
		AccountId: Clone, // can't get away without it since Currency is generic over it.
		CheckedAccount: Get<Option<(AccountId, MintLocation)>>,
	> CurrencyAdapter<Currency, Matcher, AccountIdConverter, AccountId, CheckedAccount>
{
	fn can_accrue_checked(_checked_account: AccountId, _amount: Currency::Balance) -> Result {
		Ok(())
	}
	fn can_reduce_checked(checked_account: AccountId, amount: Currency::Balance) -> Result {
		let new_balance = Currency::free_balance(&checked_account)
			.checked_sub(&amount)
			.ok_or(XcmError::NotWithdrawable)?;
		Currency::ensure_can_withdraw(
			&checked_account,
			amount,
			WithdrawReasons::TRANSFER,
			new_balance,
		)
		.map_err(|_| XcmError::NotWithdrawable)
	}
	fn accrue_checked(checked_account: AccountId, amount: Currency::Balance) {
		Currency::deposit_creating(&checked_account, amount);
		Currency::deactivate(amount);
	}
	fn reduce_checked(checked_account: AccountId, amount: Currency::Balance) {
		let ok =
			Currency::withdraw(&checked_account, amount, WithdrawReasons::TRANSFER, AllowDeath)
				.is_ok();
		if ok {
			Currency::reactivate(amount);
		} else {
			frame_support::defensive!(
				"`can_check_in` must have returned `true` immediately prior; qed"
			);
		}
	}
}

impl<
		Currency: frame_support::traits::Currency<AccountId>,
		Matcher: MatchesFungible<Currency::Balance>,
		AccountIdConverter: ConvertLocation<AccountId>,
		AccountId: Clone, // can't get away without it since Currency is generic over it.
		CheckedAccount: Get<Option<(AccountId, MintLocation)>>,
	> TransactAsset
	for CurrencyAdapter<Currency, Matcher, AccountIdConverter, AccountId, CheckedAccount>
{
	fn can_check_in(_origin: &MultiLocation, what: &MultiAsset, _context: &XcmContext) -> Result {
		log::trace!(target: "xcm::currency_adapter", "can_check_in origin: {:?}, what: {:?}", _origin, what);
		// Check we handle this asset.
		let amount: Currency::Balance =
			Matcher::matches_fungible(what).ok_or(Error::AssetNotHandled)?;
		match CheckedAccount::get() {
			Some((checked_account, MintLocation::Local)) =>
				Self::can_reduce_checked(checked_account, amount),
			Some((checked_account, MintLocation::NonLocal)) =>
				Self::can_accrue_checked(checked_account, amount),
			None => Ok(()),
		}
	}

	fn check_in(_origin: &MultiLocation, what: &MultiAsset, _context: &XcmContext) {
		log::trace!(target: "xcm::currency_adapter", "check_in origin: {:?}, what: {:?}", _origin, what);
		if let Some(amount) = Matcher::matches_fungible(what) {
			match CheckedAccount::get() {
				Some((checked_account, MintLocation::Local)) =>
					Self::reduce_checked(checked_account, amount),
				Some((checked_account, MintLocation::NonLocal)) =>
					Self::accrue_checked(checked_account, amount),
				None => (),
			}
		}
	}

	fn can_check_out(_dest: &MultiLocation, what: &MultiAsset, _context: &XcmContext) -> Result {
		log::trace!(target: "xcm::currency_adapter", "check_out dest: {:?}, what: {:?}", _dest, what);
		let amount = Matcher::matches_fungible(what).ok_or(Error::AssetNotHandled)?;
		match CheckedAccount::get() {
			Some((checked_account, MintLocation::Local)) =>
				Self::can_accrue_checked(checked_account, amount),
			Some((checked_account, MintLocation::NonLocal)) =>
				Self::can_reduce_checked(checked_account, amount),
			None => Ok(()),
		}
	}

	fn check_out(_dest: &MultiLocation, what: &MultiAsset, _context: &XcmContext) {
		log::trace!(target: "xcm::currency_adapter", "check_out dest: {:?}, what: {:?}", _dest, what);
		if let Some(amount) = Matcher::matches_fungible(what) {
			match CheckedAccount::get() {
				Some((checked_account, MintLocation::Local)) =>
					Self::accrue_checked(checked_account, amount),
				Some((checked_account, MintLocation::NonLocal)) =>
					Self::reduce_checked(checked_account, amount),
				None => (),
			}
		}
	}

	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, _context: &XcmContext) -> Result {
		log::trace!(target: "xcm::currency_adapter", "deposit_asset what: {:?}, who: {:?}", what, who);
		// Check we handle this asset.
		let amount = Matcher::matches_fungible(&what).ok_or(Error::AssetNotHandled)?;
		let who =
			AccountIdConverter::convert_location(who).ok_or(Error::AccountIdConversionFailed)?;
		let _imbalance = Currency::deposit_creating(&who, amount);
		Ok(())
	}

	fn withdraw_asset(
		what: &MultiAsset,
		who: &MultiLocation,
		_maybe_context: Option<&XcmContext>,
	) -> result::Result<Assets, XcmError> {
		log::trace!(target: "xcm::currency_adapter", "withdraw_asset what: {:?}, who: {:?}", what, who);
		// Check we handle this asset.
		let amount = Matcher::matches_fungible(what).ok_or(Error::AssetNotHandled)?;
		let who =
			AccountIdConverter::convert_location(who).ok_or(Error::AccountIdConversionFailed)?;
		Currency::withdraw(&who, amount, WithdrawReasons::TRANSFER, AllowDeath)
			.map_err(|e| XcmError::FailedToTransactAsset(e.into()))?;
		Ok(what.clone().into())
	}

	fn internal_transfer_asset(
		asset: &MultiAsset,
		from: &MultiLocation,
		to: &MultiLocation,
		_context: &XcmContext,
	) -> result::Result<Assets, XcmError> {
		log::trace!(target: "xcm::currency_adapter", "internal_transfer_asset asset: {:?}, from: {:?}, to: {:?}", asset, from, to);
		let amount = Matcher::matches_fungible(asset).ok_or(Error::AssetNotHandled)?;
		let from =
			AccountIdConverter::convert_location(from).ok_or(Error::AccountIdConversionFailed)?;
		let to =
			AccountIdConverter::convert_location(to).ok_or(Error::AccountIdConversionFailed)?;
		Currency::transfer(&from, &to, amount, AllowDeath)
			.map_err(|e| XcmError::FailedToTransactAsset(e.into()))?;
		Ok(asset.clone().into())
	}
}