utils: backport replace_root

otaclient/_utils/__init__.py

@@ -14,6 +14,7 @@
 
 
 from __future__ import annotations
+import os
 from math import ceil
 from pathlib import Path
 from typing import Any, Callable, Optional, TypeVar
@@ -66,3 +67,21 @@ def get_file_size(
     swapfile_fpath = Path(swapfile_fpath)
     if swapfile_fpath.is_file():
         return ceil(swapfile_fpath.stat().st_size / _multiplier[units])
+
+
+def replace_root(path: str | Path, old_root: str | Path, new_root: str | Path) -> str:
+    """Replace a <path> relative to <old_root> to <new_root>.
+
+    For example, if path="/abc", old_root="/", new_root="/new_root",
+    then we will have "/new_root/abc".
+    """
+    # normalize all the input args
+    path = os.path.normpath(path)
+    old_root = os.path.normpath(old_root)
+    new_root = os.path.normpath(new_root)
+
+    if not (old_root.startswith("/") and new_root.startswith("/")):
+        raise ValueError(f"{old_root=} and/or {new_root=} is not valid root")
+    if os.path.commonpath([path, old_root]) != old_root:
+        raise ValueError(f"{old_root=} is not the root of {path=}")
+    return os.path.join(new_root, os.path.relpath(path, old_root))