import logging
from dataclasses import dataclass

import httpx

try:
    from app.settings import settings
except ModuleNotFoundError:
    from settings import settings


logger = logging.getLogger("app.wechat_login")

INVALID_CODE_ERRCODES = {40029, 40163}
MISCONFIGURED_APP_ERRCODES = {40013, 40125}


@dataclass(frozen=True)
class WechatCodeSession:
    openid: str
    session_key: str
    unionid: str | None = None


class WechatAuthError(Exception):
    def __init__(self, detail: str, *, status_code: int, errcode: int | None = None):
        super().__init__(detail)
        self.status_code = status_code
        self.errcode = errcode


class WechatAuthService:
    def __init__(self, client: httpx.Client | None = None):
        self._client = client

    def exchange_code(self, code: str) -> WechatCodeSession:
        if not settings.wechat_app_id or not settings.wechat_app_secret:
            raise WechatAuthError("wechat login is not configured", status_code=503)

        response = self._request_code2session(code)
        data = self._parse_response_json(response)

        errcode = self._parse_errcode(data.get("errcode"))
        if errcode not in (None, 0):
            errmsg = data.get("errmsg")
            logger.warning(
                "wechat code2session rejected login code",
                extra={
                    "event": "wechat_code2session_rejected",
                    "errcode": errcode,
                    "errmsg": errmsg,
                },
            )
            raise self._map_exchange_error(errcode)

        openid = data.get("openid")
        session_key = data.get("session_key")
        unionid = data.get("unionid")

        if not isinstance(openid, str) or not openid:
            raise WechatAuthError("wechat login response missing openid", status_code=502)
        if not isinstance(session_key, str) or not session_key:
            raise WechatAuthError("wechat login response missing session_key", status_code=502)
        if not isinstance(unionid, str) or not unionid:
            unionid = None

        return WechatCodeSession(openid=openid, session_key=session_key, unionid=unionid)

    def _request_code2session(self, code: str) -> httpx.Response:
        params = {
            "appid": settings.wechat_app_id,
            "secret": settings.wechat_app_secret,
            "js_code": code,
            "grant_type": "authorization_code",
        }

        client = self._client
        owns_client = client is None
        if client is None:
            client = httpx.Client(
                base_url=settings.wechat_api_base_url.rstrip("/"),
                timeout=settings.wechat_http_timeout_seconds,
            )

        try:
            response = client.get("/sns/jscode2session", params=params)
            response.raise_for_status()
            return response
        except httpx.HTTPError as exc:
            logger.warning(
                "wechat code2session request failed",
                extra={"event": "wechat_code2session_request_failed"},
            )
            raise WechatAuthError("wechat login service unavailable", status_code=502) from exc
        finally:
            if owns_client:
                client.close()

    def _parse_response_json(self, response: httpx.Response) -> dict:
        try:
            data = response.json()
        except ValueError as exc:
            raise WechatAuthError("invalid response from wechat login service", status_code=502) from exc
        if not isinstance(data, dict):
            raise WechatAuthError("invalid response from wechat login service", status_code=502)
        return data

    def _parse_errcode(self, value: object) -> int | None:
        if value is None:
            return None
        try:
            return int(value)
        except (TypeError, ValueError):
            return None

    def _map_exchange_error(self, errcode: int) -> WechatAuthError:
        if errcode in INVALID_CODE_ERRCODES:
            return WechatAuthError("invalid or expired wechat login code", status_code=401, errcode=errcode)
        if errcode in MISCONFIGURED_APP_ERRCODES:
            return WechatAuthError("wechat login is not configured correctly", status_code=503, errcode=errcode)
        return WechatAuthError("wechat login service unavailable", status_code=502, errcode=errcode)


def get_wechat_auth_service() -> WechatAuthService:
    return WechatAuthService()