move base bridge fee computations to primitives

system-parachains/asset-hubs/asset-hub-kusama/src/xcm_config.rs

@@ -722,18 +722,9 @@ pub mod bridging {
 	parameter_types! {
 		/// Base price of every byte of the Kusama -> Polkadot message. Can be adjusted via
 		/// governance `set_storage` call.
-		///
-		/// Default value is our estimation of the:
-		///
-		/// 1) an approximate cost of XCM execution (`ExportMessage` and surroundings) at Kusama bridge Hub;
-		///
-		/// 2) the approximate cost of Kusama -> Polkadot message delivery transaction on Polkadot Bridge Hub,
-		///    converted into KSMs using 1:5 conversion rate;
-		///
-		/// 3) the approximate cost of Kusama -> Polkadot message confirmation transaction on Kusama Bridge Hub.
-		pub storage XcmBridgeHubRouterBaseFee: Balance = bp_bridge_hub_kusama::BridgeHubKusamaBaseXcmFeeInKsms::get()
-				.saturating_add(bp_bridge_hub_polkadot::BridgeHubPolkadotBaseDeliveryFeeInDots::get().saturating_mul(30))
-				.saturating_add(bp_bridge_hub_kusama::BridgeHubKusamaBaseConfirmationFeeInKsms::get());
+		pub storage XcmBridgeHubRouterBaseFee: Balance = bp_bridge_hub_kusama::estimate_kusama_to_polkadot_message_fee(
+			bp_bridge_hub_polkadot::BridgeHubPolkadotBaseDeliveryFeeInDots::get()
+		);
 		/// Price of every byte of the Kusama -> Polkadot message. Can be adjusted via
 		/// governance `set_storage` call.
 		pub storage XcmBridgeHubRouterByteFee: Balance = TransactionByteFee::get();

system-parachains/asset-hubs/asset-hub-polkadot/src/xcm_config.rs

@@ -614,18 +614,9 @@ pub mod bridging {
 	parameter_types! {
 		/// Base price of every byte of the Polkadot -> Kusama message. Can be adjusted via
 		/// governance `set_storage` call.
-		///
-		/// Default value is our estimation of the:
-		///
-		/// 1) an approximate cost of XCM execution (`ExportMessage` and surroundings) at Polkadot bridge hub;
-		///
-		/// 2) the approximate cost of Polkadot -> Kusama message delivery transaction on Kusama Bridge Hub,
-		///    converted into DOTs using 5:1 conversion rate;
-		///
-		/// 3) the approximate cost of Polkadot -> Kusama message confirmation transaction on Polkadot Bridge Hub.
-		pub storage XcmBridgeHubRouterBaseFee: Balance = bp_bridge_hub_polkadot::BridgeHubPolkadotBaseXcmFeeInDots::get()
-				.saturating_add(bp_bridge_hub_kusama::BridgeHubKusamaBaseDeliveryFeeInKsms::get().saturating_div(30))
-				.saturating_add(bp_bridge_hub_polkadot::BridgeHubPolkadotBaseConfirmationFeeInDots::get());
+		pub storage XcmBridgeHubRouterBaseFee: Balance = bp_bridge_hub_polkadot::estimate_polkadot_to_kusama_message_fee(
+			bp_bridge_hub_kusama::BridgeHubKusamaBaseDeliveryFeeInKsms::get()
+		);
 		/// Price of every byte of the Polkadot -> Kusama message. Can be adjusted via
 		/// governance `set_storage` call.
 		pub storage XcmBridgeHubRouterByteFee: Balance = TransactionByteFee::get();

system-parachains/bridge-hubs/bridge-hub-kusama/primitives/Cargo.toml

@@ -9,6 +9,10 @@ license.workspace = true
 
 [dependencies]
 
+# Local
+kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false}
+polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false}
+
 # Bridge Dependencies
 bp-bridge-hub-cumulus = { default-features = false , version = "0.4.0" }
 bp-runtime = { default-features = false , version = "0.4.0" }
@@ -27,6 +31,8 @@ std = [
 	"bp-messages/std",
 	"bp-runtime/std",
 	"frame-support/std",
+	"kusama-runtime-constants/std",
+	"polkadot-runtime-constants/std",
 	"sp-api/std",
 	"sp-runtime/std",
 	"sp-std/std",

system-parachains/bridge-hubs/bridge-hub-kusama/primitives/src/lib.rs

@@ -30,7 +30,7 @@ use frame_support::{
 	dispatch::DispatchClass,
 	sp_runtime::{MultiAddress, MultiSigner},
 };
-use sp_runtime::RuntimeDebug;
+use sp_runtime::{FixedPointNumber, FixedU128, RuntimeDebug, Saturating};
 
 /// BridgeHubKusama parachain.
 #[derive(RuntimeDebug)]
@@ -99,3 +99,52 @@ frame_support::parameter_types! {
 	/// (initially was calculated by test `BridgeHubKusama::can_calculate_fee_for_complex_message_confirmation_transaction` + `33%`)
 	pub const BridgeHubKusamaBaseConfirmationFeeInKsms: u128 = 61_600_495_508;
 }
+
+/// Compute the total estimated fee that needs to be paid in KSMs by the sender when sending
+/// message from Kusama Bridge Hub to Polkadot Bridge Hub.
+pub fn estimate_kusama_to_polkadot_message_fee(
+	bridge_hub_polkadot_base_delivery_fee_in_udots: Balance,
+) -> Balance {
+	// Sender must pay:
+	//
+	// 1) an approximate cost of XCM execution (`ExportMessage` and surroundings) at Kusama bridge Hub;
+	//
+	// 2) the approximate cost of Kusama -> Polkadot message delivery transaction on Polkadot Bridge Hub,
+	//    converted into KSMs using 1:5 conversion rate;
+	//
+	// 3) the approximate cost of Kusama -> Polkadot message confirmation transaction on Kusama Bridge Hub.
+	BridgeHubKusamaBaseXcmFeeInKsms::get()
+		.saturating_add(convert_from_udot_to_uksm(bridge_hub_polkadot_base_delivery_fee_in_udots))
+		.saturating_add(BridgeHubKusamaBaseConfirmationFeeInKsms::get())
+}
+
+/// Convert from uDOTs to uKSMs.
+fn convert_from_udot_to_uksm(price_in_udot: Balance) -> Balance {
+	// assuming exchange rate is 5 DOTs for 1 KSM
+	let ksm_to_dot_economic_rate = FixedU128::from_rational(1, 5);
+	// tokens have different nominals and we need to take that into account
+	let nominal_ratio = FixedU128::from_rational(
+		kusama_runtime_constants::currency::UNITS,
+		polkadot_runtime_constants::currency::UNITS,
+	);
+
+	ksm_to_dot_economic_rate
+		.saturating_mul(nominal_ratio)
+		.saturating_mul(FixedU128::saturating_from_integer(price_in_udot))
+		.into_inner() / FixedU128::DIV
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn convert_from_udot_to_uksm_works() {
+		let price_in_udot = 77 * polkadot_runtime_constants::currency::UNITS;
+		let same_price_in_uksm = convert_from_udot_to_uksm(price_in_udot);
+
+		let price_in_dot = FixedU128::from_rational(price_in_udot, polkadot_runtime_constants::currency::UNITS);
+		let price_in_ksm = FixedU128::from_rational(same_price_in_uksm, kusama_runtime_constants::currency::UNITS);
+		assert_eq!(price_in_dot / FixedU128::saturating_from_integer(5), price_in_ksm);
+	}
+}

system-parachains/bridge-hubs/bridge-hub-polkadot/primitives/Cargo.toml

@@ -9,6 +9,10 @@ license.workspace = true
 
 [dependencies]
 
+# Local
+kusama-runtime-constants = { path = "../../../../relay/kusama/constants", default-features = false}
+polkadot-runtime-constants = { path = "../../../../relay/polkadot/constants", default-features = false}
+
 # Bridge Dependencies
 bp-bridge-hub-cumulus = { default-features = false , version = "0.4.0" }
 bp-runtime = { default-features = false , version = "0.4.0" }
@@ -27,6 +31,8 @@ std = [
 	"bp-messages/std",
 	"bp-runtime/std",
 	"frame-support/std",
+	"kusama-runtime-constants/std",
+	"polkadot-runtime-constants/std",
 	"sp-api/std",
 	"sp-runtime/std",
 	"sp-std/std",

system-parachains/bridge-hubs/bridge-hub-polkadot/primitives/src/lib.rs

@@ -25,7 +25,7 @@ use bp_runtime::{
 	decl_bridge_finality_runtime_apis, decl_bridge_messages_runtime_apis, Chain, Parachain,
 };
 use frame_support::dispatch::DispatchClass;
-use sp_runtime::RuntimeDebug;
+use sp_runtime::{FixedPointNumber, FixedU128, RuntimeDebug, Saturating};
 
 /// BridgeHubPolkadot parachain.
 #[derive(RuntimeDebug)]
@@ -78,13 +78,62 @@ frame_support::parameter_types! {
 	/// The XCM fee that is paid for executing XCM program (with `ExportMessage` instruction) at the Polkadot
 	/// BridgeHub.
 	/// (initially was calculated by test `BridgeHubPolkadot::can_calculate_weight_for_paid_export_message_with_reserve_transfer` + `33%`)
-	pub const BridgeHubPolkadotBaseXcmFeeInDots: u128 = 4_858_960_000;
+	pub const BridgeHubPolkadotBaseXcmFeeInDots: Balance = 4_858_960_000;
 
 	/// Transaction fee that is paid at the Polkadot BridgeHub for delivering single inbound message.
 	/// (initially was calculated by test `BridgeHubPolkadot::can_calculate_fee_for_complex_message_delivery_transaction` + `33%`)
-	pub const BridgeHubPolkadotBaseDeliveryFeeInDots: u128 = 19_251_966_280;
+	pub const BridgeHubPolkadotBaseDeliveryFeeInDots: Balance = 19_251_966_280;
 
 	/// Transaction fee that is paid at the Polkadot BridgeHub for delivering single outbound message confirmation.
 	/// (initially was calculated by test `BridgeHubPolkadot::can_calculate_fee_for_complex_message_confirmation_transaction` + `33%`)
-	pub const BridgeHubPolkadotBaseConfirmationFeeInDots: u128 = 18_480_166_280;
+	pub const BridgeHubPolkadotBaseConfirmationFeeInDots: Balance = 18_480_166_280;
+}
+
+/// Compute the total estimated fee that needs to be paid in DOTs by the sender when sending
+/// message from Polkadot Bridge Hub to Kusama Bridge Hub.
+pub fn estimate_polkadot_to_kusama_message_fee(
+	bridge_hub_kusama_base_delivery_fee_in_uksms: Balance,
+) -> Balance {
+	// Sender must pay:
+	//
+	// 1) an approximate cost of XCM execution (`ExportMessage` and surroundings) at Polkadot bridge Hub;
+	//
+	// 2) the approximate cost of Polkadot -> Kusama message delivery transaction on Kusama Bridge Hub,
+	//    converted into KSMs using 1:5 conversion rate;
+	//
+	// 3) the approximate cost of Polkadot -> Kusama message confirmation transaction on Polkadot Bridge Hub.
+	BridgeHubPolkadotBaseXcmFeeInDots::get()
+		.saturating_add(convert_from_uksm_to_udot(bridge_hub_kusama_base_delivery_fee_in_uksms))
+		.saturating_add(BridgeHubPolkadotBaseConfirmationFeeInDots::get())
+}
+
+/// Convert from uKSMs to uDOTs.
+fn convert_from_uksm_to_udot(price_in_uksm: Balance) -> Balance {
+	// assuming exchange rate is 5 DOTs for 1 KSM
+	let dot_to_ksm_economic_rate = FixedU128::from_rational(5, 1);
+	// tokens have different nominals and we need to take that into account
+	let nominal_ratio = FixedU128::from_rational(
+		polkadot_runtime_constants::currency::UNITS,
+		kusama_runtime_constants::currency::UNITS,
+	);
+
+	dot_to_ksm_economic_rate
+		.saturating_mul(nominal_ratio)
+		.saturating_mul(FixedU128::saturating_from_integer(price_in_uksm))
+		.into_inner() / FixedU128::DIV
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn convert_from_uksm_to_udot_works() {
+		let price_in_uksm = 77 * kusama_runtime_constants::currency::UNITS;
+		let same_price_in_udot = convert_from_uksm_to_udot(price_in_uksm);
+
+		let price_in_ksm = FixedU128::from_rational(price_in_uksm, kusama_runtime_constants::currency::UNITS);
+		let price_in_dot = FixedU128::from_rational(same_price_in_udot, polkadot_runtime_constants::currency::UNITS);
+		assert_eq!(price_in_dot / FixedU128::saturating_from_integer(5), price_in_ksm);
+	}
 }