class WelcomePolicy:
    DEFAULT_WELCOME_MESSAGE = (
        "\u4f60\u597d\uff01\u6211\u662f AI \u52a9\u624b\uff0c\u6709\u4ec0\u4e48\u53ef\u4ee5\u5e2e\u4f60\u7684\uff1f"
    )

    def __init__(self):
        self._welcomed_users: set[str] = set()
        self._message_template: str | None = None

    def configure(self, message_template: str | None = None) -> None:
        if message_template:
            self._message_template = message_template

    def mark_welcomed(self, internal_user_id: str) -> bool:
        if internal_user_id in self._welcomed_users:
            return False
        self._welcomed_users.add(internal_user_id)
        return True

    def get_welcome_message(self) -> str:
        if self._message_template:
            return self._message_template
        return self.DEFAULT_WELCOME_MESSAGE