from __future__ import annotations

import json

from langchain_core.language_models.chat_models import BaseChatModel
from langchain_core.messages import HumanMessage, SystemMessage

from graph.state import AgentState
from prompts.templates import ANSWER_PROMPT


def generate_answer(state: AgentState, model: BaseChatModel) -> dict:
    evidence = json.dumps(state.get("evidence", []), ensure_ascii=False, indent=2)[:30000]
    prompt = ANSWER_PROMPT.format(question=state["question"], evidence=evidence)
    try:
        response = model.invoke([SystemMessage(content=prompt), HumanMessage(content=state["question"])])
        answer = str(response.content).strip()
        return {"draft_answer": answer, "error": ""}
    except Exception as exc:
        return {"draft_answer": "", "error": f"Answer generation failed: {exc}"}