1 files changed, 29 insertions, 0 deletions
diff --git a/format/commitgraph/read/lookup.go b/format/commitgraph/read/lookup.go
new file mode 100644
index 00000000..5f1b08f6
--- /dev/null
+++ b/format/commitgraph/read/lookup.go
@@ -0,0 +1,29 @@
+package read
+
+import (
+	"codeberg.org/lindenii/furgit/internal/intconv"
+	objectid "codeberg.org/lindenii/furgit/object/id"
+)
+
+// Lookup resolves one object ID to one graph position.
+func (reader *Reader) Lookup(oid objectid.ObjectID) (Position, error) {
+	if oid.Algorithm() != reader.algo {
+		return Position{}, &NotFoundError{OID: oid}
+	}
+
+	for layerIdx := len(reader.layers) - 1; layerIdx >= 0; layerIdx-- {
+		layer := &reader.layers[layerIdx]
+
+		found, ok := layerLookup(layer, oid)
+		if ok {
+			idxU32, err := intconv.IntToUint32(layerIdx)
+			if err != nil {
+				return Position{}, err
+			}
+
+			return Position{Graph: idxU32, Index: found}, nil
+		}
+	}
+
+	return Position{}, &NotFoundError{OID: oid}
+}