from google.genai import types


def thinking_config(level: str | None) -> types.ThinkingConfig | None:
    """Use a supported reasoning level, or omit it for the model default."""
    if level is None:
        return None
    if level not in {"minimal", "low", "medium", "high"}:
        raise ValueError(
            f"Invalid Gemini thinking level {level!r}; "
            'expected "minimal", "low", "medium", "high", or None'
        )
    return types.ThinkingConfig(thinking_level=level)