1 files changed, 61 insertions, 0 deletions
diff --git a/object/storer/packed/delta_cache.go b/object/storer/packed/delta_cache.go
new file mode 100644
index 00000000..3bf3a035
--- /dev/null
+++ b/object/storer/packed/delta_cache.go
@@ -0,0 +1,61 @@
+package packed
+
+import (
+	"codeberg.org/lindenii/furgit/internal/lru"
+	objecttype "codeberg.org/lindenii/furgit/object/type"
+)
+
+const defaultDeltaCacheMaxBytes = 32 << 20
+
+// deltaBaseKey identifies one base object by pack location.
+type deltaBaseKey struct {
+	packName string
+	offset   uint64
+}
+
+// deltaBaseValue stores one cached base object body.
+type deltaBaseValue struct {
+	ty      objecttype.Type
+	content []byte
+}
+
+// deltaCache wraps a weighted LRU for resolved delta bases.
+type deltaCache struct {
+	lru *lru.Cache[deltaBaseKey, deltaBaseValue]
+}
+
+// newDeltaCache creates a delta base cache with a byte budget.
+func newDeltaCache(maxBytes int64) *deltaCache {
+	return &deltaCache{
+		lru: lru.New(
+			maxBytes,
+			func(_ deltaBaseKey, value deltaBaseValue) int64 {
+				return int64(len(value.content))
+			},
+			nil,
+		),
+	}
+}
+
+// get returns a cloned cached base object value.
+func (cache *deltaCache) get(key deltaBaseKey) (objecttype.Type, []byte, bool) {
+	value, ok := cache.lru.Get(key)
+	if !ok {
+		return objecttype.TypeInvalid, nil, false
+	}
+
+	return value.ty, append([]byte(nil), value.content...), true
+}
+
+// add stores a cloned base object value.
+func (cache *deltaCache) add(key deltaBaseKey, ty objecttype.Type, content []byte) {
+	cache.lru.Add(key, deltaBaseValue{
+		ty:      ty,
+		content: append([]byte(nil), content...),
+	})
+}
+
+// clear removes all cached entries.
+func (cache *deltaCache) clear() {
+	cache.lru.Clear()
+}