"""Generate a short session name from user messages via LLM."""

from navi.llm.base import LLMBackend, Message

_SYSTEM = (
    "You are a session title generator. "
    "Given the user's messages from a conversation, produce ONE short title (3–6 words, no punctuation at the end). "
    "The title must reflect the actual topic. "
    "Respond in the same language as the user's messages. "
    "If the messages contain no clear topic yet (e.g. only greetings, very short or ambiguous text), "
    "reply with exactly: NO_TITLE"
)


async def generate_session_name(
    user_messages: list[str],
    backend: LLMBackend,
    model: str,
) -> str | None:
    """Return a short title or None if content isn't substantial enough."""
    if not user_messages:
        return None

    combined = "\n".join(f"- {m}" for m in user_messages[:10])
    messages = [
        Message(role="system", content=_SYSTEM),
        Message(role="user", content=f"User messages:\n{combined}"),
    ]

    resp = await backend.complete(messages, tools=[], model=model, temperature=0.4)
    text = (resp.content or "").strip()

    if not text or text.upper() == "NO_TITLE" or len(text) > 80:
        return None

    # Strip surrounding quotes if the model added them
    return text.strip('"\'')
