def flatten_update_data(data: dict, parent_key="") -> dict:
    """Convert nested dict to MongoDB dot notation."""
    items = {}
    for k, v in data.items():
        new_key = f"{parent_key}.{k}" if parent_key else k
        if isinstance(v, dict):
            items.update(flatten_update_data(v, new_key))
        else:
            items[new_key] = v
    return items


def generate_default_password() -> str:
    """
    Generate a random secure password for new employees.
    Format: 6 random digits (e.g., 847293)
    """
    import secrets
    return ''.join([str(secrets.randbelow(10)) for _ in range(6)])