Create the tag ref

how_to/Change_22.md

@@ -0,0 +1,28 @@
+- tag: Create the tag ref
+
+After we've implemented refs in the previous change, it's time to create a ref
+when the user creates a tag.
+
+`create_tag` now calls update_ref with the tag name to actually create the tag.
+
+For namespacing purposes, we'll put all tags under *refs/tags/*. That is, if the
+user creates *my-cool-commit* tag, we'll create *refs/tags/my-cool-commit* ref
+to point to the desired OID.
+
+Then we'll update *data.py* to handle this "namespaced" ref. Since we can't have
+a / in the file name, we'll create directories for it. Now if a ref
+*refs/tags/sometag* is created, it will be placed under *.ugit/refs/tags* in a
+file named *sometag*.
+
+To verify that this code works, you can run:
+```
+$ ugit tag test
+```
+
+And make sure that the tag points to HEAD:
+```
+$ cat .ugit/refs/tags/test
+$ cat .ugit/HEAD
+```
+
+The last two commands should give the same output.

ugit/base.py

@@ -96,6 +96,8 @@ def commit(message):
 
     return oid
 
+def create_tag(name, oid):
+    data.update_ref(f"refs/tags/{name}", oid)
 
 def checkout(oid):
     commit = get_commit(oid)

ugit/data.py

@@ -11,13 +11,16 @@ def init():
 
 
 def update_ref(ref, oid):
-    with open(f"{GIT_DIR}/{ref}", "w") as f:
+    ref_path = f"{GIT_DIR}/{ref}"
+    Path.mkdir(ref_path, exist_ok=True)
+    with open(ref_path, "w") as f:
         f.write(oid)
 
 
 def get_ref(ref):
-    if Path.is_file(f"{GIT_DIR}/{ref}"):
-        with open(f"{GIT_DIR}/HEAD") as f:
+    ref_path = f"{GIT_DIR}/{ref}"
+    if Path.is_file(ref_path):
+        with open(ref_path) as f:
             return f.read().strip()