"""会话管理 API (阶段 3 接入 LangGraph checkpoint + SQLite)."""
from __future__ import annotations

import json
import logging
import uuid

from fastapi import APIRouter, HTTPException
from langchain_core.messages import HumanMessage, AIMessage

from app.agents.graph import get_compiled_graph
from app.agents.state import messages_to_lc
from app.models import db

logger = logging.getLogger(__name__)
router = APIRouter(prefix="/sessions", tags=["sessions"])


@router.get("")
async def list_sessions(limit: int = 50) -> dict:
    sessions = db.session_list(limit=limit)
    return {"sessions": sessions, "total": len(sessions)}


@router.get("/{session_id}")
async def get_session(session_id: str) -> dict:
    """返回会话 + 消息历史."""
    session = db.session_get(session_id)
    if session is None:
        # 可能还没消息, 但 LangGraph checkpoint 里有. 试一下
        pass
    messages = db.message_list_by_session(session_id)
    return {
        "session": session or {"id": session_id, "title": None, "message_count": 0},
        "messages": messages,
    }


@router.delete("/{session_id}")
async def delete_session(session_id: str) -> dict:
    """删除会话. SQLite + LangGraph checkpoint 一并清."""
    db.session_delete(session_id)
    # LangGraph checkpoint 删: 用其内部 API
    try:
        graph = await get_compiled_graph()
        checkpointer = graph.checkpointer  # AsyncSqliteSaver
        if hasattr(checkpointer, "adelete_thread"):
            await checkpointer.adelete_thread(session_id)
    except Exception as e:  # noqa: BLE001
        logger.warning("LangGraph checkpoint delete failed for %s: %s", session_id, e)
    return {"session_id": session_id, "deleted": True}


@router.post("")
async def create_session(title: str | None = None) -> dict:
    """新建会话. 返回 session_id, 供后续 chat 使用."""
    session_id = uuid.uuid4().hex
    db.session_upsert(session_id, title=title)
    return {"session_id": session_id, "title": title}