Add CSV mapping rule and Undo last rename feature

Made-with: Cursor

engine/pipeline.py

@@ -1,12 +1,16 @@
 """
 Apply a list of rules to a list of filenames; produce preview and perform renames.
+Undo: save a log after renames; undo reverses renames from that log.
 """
+import json
 import os
 from pathlib import Path
 from typing import List, Optional
 
 from .rules import Rule
 
+UNDO_FILENAME = ".bulk-renamer-undo.json"
+
 
 def _split_name(name: str) -> tuple[str, str]:
     if "." in name and not name.startswith("."):
@@ -26,7 +30,7 @@ def apply_pipeline(
     for r in rules:
         if not r.enabled:
             continue
-        stem, ext = r.apply(stem, ext, index, total)
+        stem, ext = r.apply(stem, ext, index, total, original_name=name)
     return stem + ext
 
 
@@ -104,3 +108,55 @@ def perform_renames(
                 pass
 
     return results
+
+
+def undo_log_path(base_dir: str) -> Path:
+    return Path(base_dir) / UNDO_FILENAME
+
+
+def save_undo_log(base_dir: str, renames: List[tuple[str, str]]) -> None:
+    """Save (old_name, new_name) list so undo can reverse it. Overwrites any existing log for this folder."""
+    path = undo_log_path(base_dir)
+    data = {"renames": renames}
+    try:
+        path.write_text(json.dumps(data, indent=0), encoding="utf-8")
+    except OSError:
+        pass
+
+
+def load_undo_log(base_dir: str) -> Optional[List[tuple[str, str]]]:
+    """Load the last rename log for this folder. Returns list of (old_name, new_name) or None."""
+    path = undo_log_path(base_dir)
+    if not path.is_file():
+        return None
+    try:
+        data = json.loads(path.read_text(encoding="utf-8"))
+        return data.get("renames")
+    except (OSError, json.JSONDecodeError, TypeError):
+        return None
+
+
+def remove_undo_log(base_dir: str) -> None:
+    """Remove the undo log file for this folder."""
+    path = undo_log_path(base_dir)
+    try:
+        path.unlink()
+    except OSError:
+        pass
+
+
+def perform_undo(base_dir: str) -> List[tuple[str, str, Optional[str]]]:
+    """
+    Undo the last rename in base_dir using the saved log.
+    Returns same format as perform_renames. Does not remove the log on failure.
+    """
+    renames = load_undo_log(base_dir)
+    if not renames:
+        return []
+    # Reverse: rename current (new) back to original (old). Order must be reversed for chains.
+    undo_list = [(new_name, old_name) for (old_name, new_name) in renames]
+    undo_list.reverse()
+    results = perform_renames(base_dir, undo_list, dry_run=False)
+    if not any(r[2] for r in results):
+        remove_undo_log(base_dir)
+    return results