feat(main.py): implement undo functionality for grading actions

main.py

@@ -76,6 +76,9 @@ class MediaGrader:
         self.window_width = 800
         self.window_height = 600
 
+        # Undo functionality
+        self.undo_history = []  # List of (source_path, destination_path, original_index) tuples
+
     def find_media_files(self) -> List[Path]:
         """Find all media files recursively in the directory"""
         media_files = []
@@ -365,6 +368,9 @@ class MediaGrader:
             shutil.move(str(current_file), str(destination))
             print(f"Moved {current_file.name} to grade {grade}")
 
+            # Track this move for undo functionality
+            self.undo_history.append((str(destination), str(current_file), self.current_index))
+
             self.media_files.pop(self.current_index)
 
             if self.current_index >= len(self.media_files):
@@ -379,6 +385,40 @@ class MediaGrader:
 
         return True
 
+    def undo_last_action(self):
+        """Undo the last grading action by moving file back and restoring to media list"""
+        if not self.undo_history:
+            print("No actions to undo!")
+            return False
+            
+        # Get the last action
+        moved_file_path, original_file_path, original_index = self.undo_history.pop()
+        
+        try:
+            # Move the file back to its original location
+            shutil.move(moved_file_path, original_file_path)
+            
+            # Add the file back to the media list at its original position
+            original_file = Path(original_file_path)
+            
+            # Insert the file back at the appropriate position
+            if original_index <= len(self.media_files):
+                self.media_files.insert(original_index, original_file)
+            else:
+                self.media_files.append(original_file)
+            
+            # Navigate to the restored file
+            self.current_index = original_index
+            
+            print(f"Undone: Moved {original_file.name} back from grade folder")
+            return True
+            
+        except Exception as e:
+            print(f"Error undoing action: {e}")
+            # If undo failed, put the action back in history
+            self.undo_history.append((moved_file_path, original_file_path, original_index))
+            return False
+
     def run(self):
         """Main grading loop"""
         self.media_files = self.find_media_files()
@@ -396,6 +436,7 @@ class MediaGrader:
         print("  1-5: Grade and move file")
         print("  N: Next file")
         print("  P: Previous file")
+        print("  U: Undo last grading action")
         print("  Q/ESC: Quit")
 
         cv2.namedWindow("Media Grader", cv2.WINDOW_NORMAL)
@@ -446,6 +487,10 @@ class MediaGrader:
                 elif key == ord("p"):
                     self.current_index = max(0, self.current_index - 1)
                     break
+                elif key == ord("u"):
+                    if self.undo_last_action():
+                        # File was restored, reload it
+                        break
                 elif key in [ord("1"), ord("2"), ord("3"), ord("4"), ord("5")]:
                     grade = int(chr(key))
                     if not self.grade_media(grade):