feat(chain): add ChainPosition::confirmations_lower_bound

diff --git a/crates/chain/src/chain_data.rs b/crates/chain/src/chain_data.rs
index 7ec88fba8ff082f18eb68892169f4c51cf7c86de..b03a9682354a3e7d92c8875a6354ee59942c4627 100644 (file)
--- a/crates/chain/src/chain_data.rs
+++ b/crates/chain/src/chain_data.rs
@@ -83,6 +83,21 @@ impl<A: Anchor> ChainPosition<A> {
             ChainPosition::Unconfirmed { .. } => None,
         }
     }
+
+    /// Number of confirmations of this position, given `tip`.
+    ///
+    /// Returns `0` if unconfirmed, or if the confirmation height is above `tip`.
+    pub fn confirmations_lower_bound(&self, tip: u32) -> u32 {
+        let Some(height) = self.confirmation_height_upper_bound() else {
+            return 0;
+        };
+
+        if height > tip {
+            return 0;
+        }
+
+        tip - height + 1
+    }
 }
 
 /// Ordering for `ChainPosition`:
@@ -335,4 +350,29 @@ mod test {
             ]
         );
     }
+
+    #[test]
+    fn test_confirmations_lower_bound() {
+        let confirmed_at = |height: u32| ChainPosition::Confirmed {
+            anchor: ConfirmationBlockTime {
+                confirmation_time: 0,
+                block_id: BlockId {
+                    height,
+                    ..Default::default()
+                },
+            },
+            transitively: None,
+        };
+
+        assert_eq!(confirmed_at(100).confirmations_lower_bound(100), 1);
+        assert_eq!(confirmed_at(99).confirmations_lower_bound(100), 2);
+        assert_eq!(confirmed_at(90).confirmations_lower_bound(100), 11);
+        assert_eq!(confirmed_at(101).confirmations_lower_bound(100), 0);
+
+        let unconfirmed = ChainPosition::<ConfirmationBlockTime>::Unconfirmed {
+            first_seen: Some(1),
+            last_seen: Some(2),
+        };
+        assert_eq!(unconfirmed.confirmations_lower_bound(100), 0);
+    }
 }