modify flexible-fee module to charge KSM only in the situation of ins…

pallets/flexible-fee/src/fee_dealer.rs

@@ -37,41 +37,63 @@ pub trait FeeDealer<AccountId, Balance> {
 pub struct FixedCurrencyFeeRate<T: Config>(PhantomData<T>);
 
 impl<T: Config> FeeDealer<T::AccountId, PalletBalanceOf<T>> for FixedCurrencyFeeRate<T> {
-	/// Make sure there are enough BNC to be deducted if the user has assets in other form of tokens
+	/// Make sure there is enough BNC to be deducted if the user has assets in other form of tokens
 	/// rather than BNC.
 	fn ensure_can_charge_fee(
 		who: &T::AccountId,
 		fee: PalletBalanceOf<T>,
-		_reason: WithdrawReasons,
+		reason: WithdrawReasons,
 	) -> DispatchResult {
-		let fee_currency_id: CurrencyId = T::AlternativeFeeCurrencyId::get();
-		let (fee_currency_base, native_currency_base): (u32, u32) =
-			T::AltFeeCurrencyExchangeRate::get();
-
-		let fee_currency_balance = T::MultiCurrency::free_balance(fee_currency_id, who);
-
-		let consume_fee_currency_amount =
-			fee.saturating_mul(fee_currency_base.into()) / native_currency_base.into();
-		ensure!(
-			consume_fee_currency_amount <=
-				PalletBalanceOf::<T>::unique_saturated_from(fee_currency_balance.into()),
-			Error::<T>::NotEnoughBalance
-		);
-
-		// deduct fee currency and increase native currency amount
-		// This withdraw operation allows death. So it will succeed given the remaining amount less
-		// than the existential deposit.
-		T::MultiCurrency::withdraw(
-			fee_currency_id,
-			who,
-			T::Balance::from(consume_fee_currency_amount),
-		)?;
-		T::MultiCurrency::deposit(T::NativeCurrencyId::get(), who, T::Balance::from(fee))?;
-
-		crate::Pallet::<T>::deposit_event(Event::FixedRateFeeExchanged(
-			fee_currency_id,
-			consume_fee_currency_amount,
-		));
+		// First, check if the user has enough BNC balance to be deducted.assert_eq!
+		let existential_deposit = <<T as Config>::Currency as Currency<
+			<T as frame_system::Config>::AccountId,
+		>>::minimum_balance();
+		// check native balance if is enough
+		let native_is_enough = <<T as Config>::Currency as Currency<
+			<T as frame_system::Config>::AccountId,
+		>>::free_balance(who)
+		.checked_sub(&(fee + existential_deposit.into()))
+		.map_or(false, |new_free_balance| {
+			<<T as Config>::Currency as Currency<
+										<T as frame_system::Config>::AccountId,
+									>>::ensure_can_withdraw(
+										who, fee, reason, new_free_balance
+									)
+									.is_ok()
+		});
+
+		if !native_is_enough {
+			// If the user doesn't has enough BNC, then we will use KSM as the fee currency.
+			let fee_currency_id: CurrencyId = T::AlternativeFeeCurrencyId::get();
+			let (fee_currency_base, native_currency_base): (u32, u32) =
+				T::AltFeeCurrencyExchangeRate::get();
+
+			let fee_currency_balance = T::MultiCurrency::free_balance(fee_currency_id, who);
+
+			let consume_fee_currency_amount =
+				fee.saturating_mul(fee_currency_base.into()) / native_currency_base.into();
+			ensure!(
+				consume_fee_currency_amount <=
+					PalletBalanceOf::<T>::unique_saturated_from(fee_currency_balance.into()),
+				Error::<T>::NotEnoughBalance
+			);
+
+			// deduct fee currency and increase native currency amount
+			// This withdraw operation allows death. So it will succeed given the remaining amount
+			// less than the existential deposit.
+			T::MultiCurrency::withdraw(
+				fee_currency_id,
+				who,
+				T::Balance::from(consume_fee_currency_amount),
+			)?;
+			T::MultiCurrency::deposit(T::NativeCurrencyId::get(), who, T::Balance::from(fee))?;
+
+			crate::Pallet::<T>::deposit_event(Event::FixedRateFeeExchanged(
+				fee_currency_id,
+				consume_fee_currency_amount,
+			));
+		}
+
 		Ok(())
 	}
 }

pallets/flexible-fee/src/tests.rs

@@ -355,6 +355,7 @@ fn ensure_can_charge_fee_v2_should_work() {
 // #[ignore = "This should be used with mock config type FeeDealer = FixedCurrencyFeeRate."]
 fn withdraw_fee_should_work_v2() {
 	new_test_ext().execute_with(|| {
+		assert_ok!(Currencies::deposit(CurrencyId::Native(TokenSymbol::ASG), &CHARLIE, 108));
 		assert_ok!(Currencies::deposit(CurrencyId::Token(TokenSymbol::KSM), &CHARLIE, 2));
 
 		// prepare call variable
@@ -368,14 +369,15 @@ fn withdraw_fee_should_work_v2() {
 		let xt = TestXt::new(call.clone(), Some((0u64, extra)));
 		let info = xt.get_dispatch_info();
 
-		// println!("info: {:?}", info);
-
-		assert_eq!(<Test as crate::Config>::Currency::free_balance(&CHARLIE), 0);
+		// In the first time, we can charge transaction fee by native token.
+		assert_ok!(FlexibleFee::withdraw_fee(&CHARLIE, &call, &info, 107, 8));
+		assert_eq!(<Test as crate::Config>::Currency::free_balance(&CHARLIE), 1);
 
-		// 99 inclusion fee and a tip of 8
+		// In the second time, we charge transaction fee by KSM.
+		// 99 inclusion fee + a tip of 8
 		assert_ok!(FlexibleFee::withdraw_fee(&CHARLIE, &call, &info, 107, 8));
 
-		assert_eq!(<Test as crate::Config>::Currency::free_balance(&CHARLIE), 0);
+		assert_eq!(<Test as crate::Config>::Currency::free_balance(&CHARLIE), 1);
 	});
 }
 

runtime/asgard/src/lib.rs

@@ -632,7 +632,7 @@ impl pallet_tips::Config for Runtime {
 
 impl pallet_transaction_payment::Config for Runtime {
 	type FeeMultiplierUpdate = ();
-	type OnChargeTransaction = pallet_transaction_payment::CurrencyAdapter<Balances, ()>;
+	type OnChargeTransaction = FlexibleFee;
 	type TransactionByteFee = TransactionByteFee;
 	type WeightToFee = IdentityFee<Balance>;
 }

runtime/dev/src/lib.rs

@@ -633,7 +633,7 @@ impl pallet_tips::Config for Runtime {
 
 impl pallet_transaction_payment::Config for Runtime {
 	type FeeMultiplierUpdate = ();
-	type OnChargeTransaction = pallet_transaction_payment::CurrencyAdapter<Balances, ()>;
+	type OnChargeTransaction = FlexibleFee;
 	type TransactionByteFee = TransactionByteFee;
 	type WeightToFee = IdentityFee<Balance>;
 }