Standardisation 3

copienator/filesystem.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import shutil
+import uuid
+from contextlib import contextmanager
+from pathlib import Path
+
+
+def _remove_path(path: Path) -> None:
+    if path.is_symlink() or path.is_file():
+        path.unlink()
+    elif path.exists():
+        shutil.rmtree(path)
+
+
+@contextmanager
+def staged_directory(destination: str | Path):
+    """Build a directory beside its destination and replace on success."""
+    target = Path(destination)
+    target.parent.mkdir(parents=True, exist_ok=True)
+    token = uuid.uuid4().hex
+    staging = target.with_name(f".{target.name}.{token}.tmp")
+    backup = target.with_name(f".{target.name}.{token}.backup")
+    staging.mkdir()
+    committed = False
+    try:
+        yield staging
+        if target.exists():
+            target.replace(backup)
+        try:
+            staging.replace(target)
+            committed = True
+        except Exception:
+            if backup.exists() and not target.exists():
+                backup.replace(target)
+            raise
+        if backup.exists():
+            _remove_path(backup)
+    finally:
+        if staging.exists():
+            _remove_path(staging)
+        if not committed and backup.exists() and not target.exists():
+            backup.replace(target)