f: simplify arithmetic

Author: arik-so

lightning/src/routing/router.rs

@@ -493,23 +493,14 @@ pub struct Path {
 impl Path {
 	/// Gets the fees for a given path, excluding any excess paid to the recipient.
 	pub fn fee_msat(&self) -> u64 {
-		let route_fee = self.hops.split_last()
-			.map_or(0, |(_, path_prefix)| path_prefix.iter().map(|hop| hop.fee_msat).sum());
-		let trampoline_fee = self.trampoline_hops.iter().map(|hop| hop.fee_msat).sum::<u64>();
-		match &self.blinded_tail {
-			Some(_) => {
-				if self.trampoline_hops.is_empty() {
-					route_fee + trampoline_fee + self.hops.last().map_or(0, |hop| hop.fee_msat)
-				} else {
-					// exclude last RouteHop because its value is the outgoing amount to the
-					// Trampoline entry point
-					route_fee + trampoline_fee
-				}
-			},
-			None => {
-				// Do not count last hop of each path since that's the full value of the payment
-				route_fee + trampoline_fee
-			}
+		let unblinded_hop_fee_iterator = self.hops.iter().rev().map(|hop| hop.fee_msat)
+			.chain(self.trampoline_hops.iter().map(|hop| hop.fee_msat));
+
+		if self.blinded_tail.is_none() || !self.trampoline_hops.is_empty() {
+			// If we don't have a blinded tail or if we have Trampoline hops, we skip the last RouteHop's fee
+			unblinded_hop_fee_iterator.skip(1).sum()
+		} else {
+			unblinded_hop_fee_iterator.sum()
 		}
 	}