internal/mru: Add

1 files changed, 31 insertions, 0 deletions

diff --git a/internal/mru/sync.go b/internal/mru/sync.go
new file mode 100644
index 00000000..69fc3446
--- /dev/null
+++ b/internal/mru/sync.go
@@ -0,0 +1,31 @@
+package mru
+
+// Sync reconciles the order's membership to present.
+//
+// Surviving keys keep their relative recency order,
+// absent keys are dropped,
+// and newly present keys are appended after the survivors.
+func (order *Order[K]) Sync(present map[K]struct{}) {
+	order.mu.Lock()
+	defer order.mu.Unlock()
+
+	keys := order.Keys()
+
+	next := make([]K, 0, len(present))
+	seen := make(map[K]struct{}, len(present))
+
+	for _, key := range keys {
+		if _, ok := present[key]; ok {
+			next = append(next, key)
+			seen[key] = struct{}{}
+		}
+	}
+
+	for key := range present {
+		if _, ok := seen[key]; !ok {
+			next = append(next, key)
+		}
+	}
+
+	order.snapshot.Store(&next)
+}