From 8e7b1e0f553eece98b8899abb4b4efacb75cbf71 Mon Sep 17 00:00:00 2001
From: elnosh <elnosh@pm.me>
Date: Tue, 30 Sep 2025 10:33:35 -0400
Subject: [PATCH] ln-resource-mgr: increase opportunity cost gradually

---
 ln-resource-mgr/src/htlc_manager.rs     |  6 +++++-
 ln-resource-mgr/src/outgoing_channel.rs | 20 ++++++++++++++------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/ln-resource-mgr/src/htlc_manager.rs b/ln-resource-mgr/src/htlc_manager.rs
index 0c0a00aa..50bfe6c5 100644
--- a/ln-resource-mgr/src/htlc_manager.rs
+++ b/ln-resource-mgr/src/htlc_manager.rs
@@ -32,7 +32,11 @@ impl ReputationParams {
     /// Calculates the opportunity_cost of a htlc being held on our channel - allowing one [`reputation_period`]'s
     /// grace period, then charging for every subsequent period.
     pub(super) fn opportunity_cost(&self, fee_msat: u64, hold_time: Duration) -> u64 {
-        (hold_time.as_secs() / self.resolution_period.as_secs()).saturating_mul(fee_msat)
+        (0_f64.max(
+            (hold_time.as_secs_f64() - self.resolution_period.as_secs_f64())
+                / self.resolution_period.as_secs_f64(),
+        ) * (fee_msat as f64))
+            .round() as u64
     }
 
     /// Calculates the worst case reputation damage of a htlc, assuming it'll be held for its full expiry_delta.
diff --git a/ln-resource-mgr/src/outgoing_channel.rs b/ln-resource-mgr/src/outgoing_channel.rs
index 1f5faa77..0df9a146 100644
--- a/ln-resource-mgr/src/outgoing_channel.rs
+++ b/ln-resource-mgr/src/outgoing_channel.rs
@@ -137,12 +137,13 @@ mod tests {
         // Less than resolution_period has zero cost.
         assert_eq!(params.opportunity_cost(100, Duration::from_secs(10)), 0);
 
-        // Equal to resolution_period or within one period is equal to fee.
-        assert_eq!(params.opportunity_cost(100, Duration::from_secs(60)), 100);
-        assert_eq!(params.opportunity_cost(100, Duration::from_secs(65)), 100);
+        // Above resolution period it is gradually incremented.
+        assert_eq!(params.opportunity_cost(100, Duration::from_secs(61)), 2);
+        assert_eq!(params.opportunity_cost(100, Duration::from_secs(90)), 50);
+        assert_eq!(params.opportunity_cost(100, Duration::from_secs(120)), 100);
 
         // Multiple periods above resolution_period charges multiples of fee.
-        assert_eq!(params.opportunity_cost(100, Duration::from_secs(600)), 1000);
+        assert_eq!(params.opportunity_cost(100, Duration::from_secs(600)), 900);
     }
 
     #[test]
@@ -164,7 +165,14 @@ mod tests {
                 slow_resolve,
                 AccountableSignal::Accountable,
                 true,
-                Ok(-2000),
+                Ok(-1000),
+            ),
+            (
+                1000,
+                Duration::from_secs(90),
+                AccountableSignal::Accountable,
+                true,
+                Ok(500),
             ),
             (
                 1000,
@@ -178,7 +186,7 @@ mod tests {
                 slow_resolve,
                 AccountableSignal::Accountable,
                 false,
-                Ok(-3000),
+                Ok(-2000),
             ),
             (
                 1000,