1 files changed, 126 insertions, 0 deletions
diff --git a/object/store/packed/idx_lookup_candidates.go b/object/store/packed/idx_lookup_candidates.go
new file mode 100644
index 00000000..a2de262a
--- /dev/null
+++ b/object/store/packed/idx_lookup_candidates.go
@@ -0,0 +1,126 @@
+package packed
+
+import (
+	"fmt"
+	"os"
+	"slices"
+	"strings"
+)
+
+// packCandidate describes one discovered pack/index pair.
+type packCandidate struct {
+	// packName is the .pack basename.
+	packName string
+	// idxName is the .idx basename.
+	idxName string
+	// mtime is the pack file modification time for initial ordering.
+	mtime int64
+}
+
+type candidateSnapshot struct {
+	candidates      []packCandidate
+	candidateByPack map[string]packCandidate
+}
+
+// Refresh rescans objects/pack and atomically installs a fresh candidate list
+// for future lookups.
+//
+// Refresh does not invalidate existing readers. Cached pack/index mappings,
+// including ones for previously visible candidates, may be retained until
+// Close.
+func (store *Store) Refresh() error {
+	store.refreshMu.Lock()
+	defer store.refreshMu.Unlock()
+
+	candidates, err := store.discoverCandidates()
+	if err != nil {
+		return err
+	}
+
+	candidateByPack := make(map[string]packCandidate, len(candidates))
+	for _, candidate := range candidates {
+		candidateByPack[candidate.packName] = candidate
+	}
+
+	store.reconcileMRU(candidates)
+
+	store.candidates.Store(&candidateSnapshot{
+		candidates:      candidates,
+		candidateByPack: candidateByPack,
+	})
+
+	return nil
+}
+
+func (store *Store) ensureCandidates() (*candidateSnapshot, error) {
+	snapshot := store.candidates.Load()
+	if snapshot != nil {
+		return snapshot, nil
+	}
+
+	err := store.Refresh()
+	if err != nil {
+		return nil, err
+	}
+
+	return store.candidates.Load(), nil
+}
+
+// discoverCandidates scans the objects/pack root and returns sorted pack/index
+// pairs.
+func (store *Store) discoverCandidates() ([]packCandidate, error) {
+	dir, err := store.root.Open(".")
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+
+		return nil, err
+	}
+
+	defer func() { _ = dir.Close() }()
+
+	entries, err := dir.ReadDir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	candidates := make([]packCandidate, 0, len(entries))
+	for _, entry := range entries {
+		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".idx") {
+			continue
+		}
+
+		idxName := entry.Name()
+		packName := strings.TrimSuffix(idxName, ".idx") + ".pack"
+
+		packInfo, err := store.root.Stat(packName)
+		if err != nil {
+			if os.IsNotExist(err) {
+				return nil, fmt.Errorf("objectstore/packed: missing pack file for index %q", idxName)
+			}
+
+			return nil, err
+		}
+
+		candidates = append(candidates, packCandidate{
+			packName: packName,
+			idxName:  idxName,
+			mtime:    packInfo.ModTime().UnixNano(),
+		})
+	}
+
+	slices.SortFunc(candidates, func(a, b packCandidate) int {
+		if a.mtime != b.mtime {
+			if a.mtime > b.mtime {
+				return -1
+			}
+
+			return 1
+		}
+
+		return strings.Compare(a.packName, b.packName)
+	})
+
+	return candidates, nil
+}