1 files changed, 50 insertions, 0 deletions
diff --git a/internal/peel/peel.go b/internal/peel/peel.go
new file mode 100644
index 00000000..a3e84b8d
--- /dev/null
+++ b/internal/peel/peel.go
@@ -0,0 +1,50 @@
+// Package peel peels Git object references through annotated tags.
+package peel
+
+import (
+	stderrors "errors"
+
+	giterrors "codeberg.org/lindenii/furgit/errors"
+	"codeberg.org/lindenii/furgit/object"
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objectstore"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// ToCommit peels annotated tags transitively until a commit is reached.
+func ToCommit(store objectstore.Store, id objectid.ObjectID) (objectid.ObjectID, error) {
+	for {
+		ty, _, err := store.ReadHeader(id)
+		if err != nil {
+			if stderrors.Is(err, objectstore.ErrObjectNotFound) {
+				return objectid.ObjectID{}, &giterrors.ObjectMissingError{OID: id}
+			}
+
+			return objectid.ObjectID{}, err
+		}
+
+		if ty != objecttype.TypeTag {
+			if ty != objecttype.TypeCommit {
+				return objectid.ObjectID{}, &giterrors.ObjectTypeError{OID: id, Got: ty, Want: objecttype.TypeCommit}
+			}
+
+			return id, nil
+		}
+
+		_, content, err := store.ReadBytesContent(id)
+		if err != nil {
+			if stderrors.Is(err, objectstore.ErrObjectNotFound) {
+				return objectid.ObjectID{}, &giterrors.ObjectMissingError{OID: id}
+			}
+
+			return objectid.ObjectID{}, err
+		}
+
+		tag, err := object.ParseTag(content, id.Algorithm())
+		if err != nil {
+			return objectid.ObjectID{}, err
+		}
+
+		id = tag.Target
+	}
+}