Create RefValue container

ugit/data.py

@@ -3,6 +3,8 @@ from pathlib import Path, PurePath
 import hashlib
 import os
 
+from collections import namedtuple
+
 GIT_DIR = ".ugit"
 
 
@@ -11,11 +13,15 @@ def init():
     Path.mkdir(f"{GIT_DIR}/objects")
 
 
-def update_ref(ref, oid):
+RefValue = namedtuple("RefValue", ["symbolic", "value"])
+
+
+def update_ref(ref, value):
+    assert not value.symbolic
     ref_path = f"{GIT_DIR}/{ref}"
     Path.mkdir(ref_path, exist_ok=True)
     with open(ref_path, "w") as f:
-        f.write(oid)
+        f.write(value.value)
 
 
 def get_ref(ref):
@@ -28,7 +34,7 @@ def get_ref(ref):
     if value and value.startswith("ref:"):
         return get_ref(value.split(":", 1)[1].strip())
 
-    return value
+    return RefValue(symbolic=False, value=value)
 
 
 def iter_refs():