"""微信服务号事件回调模块。

接收微信服务号推送的事件消息（关注/取消关注等），
将关注者的 openid 存入 pending_service_binding 表，
等待用户在小程序中输入手机号完成绑定。

需要在微信服务号后台配置：
- 服务器地址 URL: https://dda.gaowenbu.cn/api/wechat/callback
- Token: 与 .env 中 WECHAT_SA_TOKEN 一致
"""

import hashlib
import logging
import xml.etree.ElementTree as ET

from fastapi import APIRouter, Query, Request, Response
from sqlalchemy import select
from sqlalchemy.orm import Session

from backend.app.core.config import get_settings
from backend.app.db import SessionLocal
from backend.app.models.system import User, PendingServiceBinding

logger = logging.getLogger(__name__)

router = APIRouter(tags=["wechat-callback"])


def _check_signature(signature: str, timestamp: str, nonce: str, token: str) -> bool:
    """验证微信签名。"""
    items = sorted([token, timestamp, nonce])
    s = "".join(items).encode("utf-8")
    return hashlib.sha1(s).hexdigest() == signature


def _parse_xml_message(xml_str: str) -> dict:
    """解析微信推送的 XML 消息。"""
    result = {}
    try:
        root = ET.fromstring(xml_str)
        for child in root:
            result[child.tag] = child.text or ""
    except ET.ParseError:
        pass
    return result


@router.get("/api/wechat/callback")
def verify_callback(
    signature: str = Query(...),
    timestamp: str = Query(...),
    nonce: str = Query(...),
    echostr: str = Query(...),
):
    """微信服务器验证接口（GET 请求）。"""
    settings = get_settings()
    if _check_signature(signature, timestamp, nonce, settings.wechat_sa_token):
        return Response(content=echostr, media_type="text/plain")
    return Response(content="invalid", media_type="text/plain", status_code=403)


@router.post("/api/wechat/callback")
async def handle_callback(request: Request):
    """微信事件推送接口（POST 请求）。"""
    xml_str = (await request.body()).decode("utf-8")
    msg = _parse_xml_message(xml_str)

    msg_type = msg.get("MsgType", "")
    event = msg.get("Event", "").lower()
    from_user = msg.get("FromUserName", "")

    if msg_type == "event" and event in ("subscribe", "unsubscribe"):
        session = SessionLocal()
        try:
            if event == "subscribe":
                _handle_subscribe(session, from_user)
            elif event == "unsubscribe":
                _handle_unsubscribe(session, from_user)
            session.commit()
        except Exception:
            session.rollback()
            logger.exception("处理服务号事件失败: event=%s, openid=%s", event, from_user)
        finally:
            session.close()

    return Response(content="success", media_type="text/plain")


def _handle_subscribe(session: Session, openid: str) -> None:
    """处理关注事件：存入 pending_service_binding 表。"""
    existing = session.execute(
        select(PendingServiceBinding).where(PendingServiceBinding.service_open_id == openid)
    ).scalar_one_or_none()

    if existing:
        existing.bound = False
        session.add(existing)
        logger.info("服务号重新关注: openid=%s, 更新 pending binding", openid)
    else:
        binding = PendingServiceBinding(service_open_id=openid, bound=False)
        session.add(binding)
        logger.info("服务号新关注: openid=%s, 创建 pending binding", openid)


def _handle_unsubscribe(session: Session, openid: str) -> None:
    """处理取消关注事件：清空用户 service_open_id，删除 pending binding。"""
    user = session.execute(
        select(User).where(User.service_open_id == openid)
    ).scalar_one_or_none()
    if user is not None:
        user.service_open_id = None
        session.add(user)
        logger.info("用户 %s (id=%s) 取消关注服务号", user.real_name, user.id)

    pending = session.execute(
        select(PendingServiceBinding).where(PendingServiceBinding.service_open_id == openid)
    ).scalar_one_or_none()
    if pending:
        session.delete(pending)