from urllib.parse import SplitResult, urlsplit, urlunsplit


def normalize_trailing_slash(path_or_url: str, *, trailing: bool = True) -> str:
    """Normalize the path component while preserving query and fragment."""
    if not path_or_url:
        return "/" if trailing else ""

    parts = urlsplit(path_or_url)
    path = parts.path or "/"
    if trailing:
        normalized_path = path if path.endswith("/") else f"{path}/"
    elif path == "/":
        normalized_path = "/"
    else:
        normalized_path = path.rstrip("/")

    if parts.scheme or parts.netloc:
        return urlunsplit(
            SplitResult(parts.scheme, parts.netloc, normalized_path, parts.query, parts.fragment)
        )
    suffix = ""
    if parts.query:
        suffix += f"?{parts.query}"
    if parts.fragment:
        suffix += f"#{parts.fragment}"
    return f"{normalized_path}{suffix}"