from __future__ import annotations

import hashlib
import time
from dataclasses import dataclass
from typing import Any

import httpx
from fastapi import Request

from app.core.config import settings
from app.core.exceptions import AppError


@dataclass(frozen=True)
class AuthenticatedUser:
    """外部认证用户：承载从 Django 用户中心解析出的标准用户信息。"""

    user_id: str
    source: str = "django_user_center"
    username: str | None = None
    display_name: str | None = None
    tenant_id: str | None = None
    role: str | None = None


class ExternalAuthService:
    """外部认证服务：调用 Django `/api/user/users/me/` 并标准化当前登录用户。"""

    _cache: dict[str, tuple[float, AuthenticatedUser]] = {}

    async def authenticate(self, request: Request) -> AuthenticatedUser:
        """用户鉴权：转发前端鉴权凭证到 Django 用户中心，成功后返回标准用户信息。"""
        if not settings.auth_user_me_url:
            raise AppError("AUTH_CONFIG_MISSING", "auth user me url is not configured", 500)

        outbound_headers = self._build_forward_headers(request)
        if not outbound_headers:
            raise AppError("AUTH_CREDENTIAL_REQUIRED", "Authorization or Cookie is required", 401)

        cache_key = self._cache_key(outbound_headers)
        cached = self._read_cache(cache_key)
        if cached:
            return cached

        try:
            async with httpx.AsyncClient(timeout=settings.auth_timeout_seconds, follow_redirects=False) as client:
                response = await client.get(settings.auth_user_me_url, headers=outbound_headers)
        except httpx.TimeoutException as exc:
            raise AppError("AUTH_USER_CENTER_UNAVAILABLE", "auth user center request timeout", 503) from exc
        except httpx.HTTPError as exc:
            raise AppError("AUTH_USER_CENTER_UNAVAILABLE", "auth user center unavailable", 503) from exc

        if response.status_code != 200:
            raise AppError("AUTH_USER_INVALID", "current login user is invalid", 401)

        try:
            payload = response.json()
        except ValueError as exc:
            raise AppError("AUTH_USER_PARSE_FAILED", "auth user center returned invalid json", 502) from exc

        user = self._parse_user(payload)
        self._write_cache(cache_key, user)
        return user

    def _build_forward_headers(self, request: Request) -> dict[str, str]:
        """认证转发：只透传鉴权必要 Header，避免把无关内部头转发给用户中心。"""
        headers: dict[str, str] = {}
        authorization = request.headers.get("Authorization")
        cookie = request.headers.get("Cookie")
        if authorization:
            headers["Authorization"] = authorization
        if cookie:
            headers["Cookie"] = cookie
        if request.headers.get("X-CSRFToken"):
            headers["X-CSRFToken"] = request.headers["X-CSRFToken"]
        return headers

    def _parse_user(self, payload: dict[str, Any]) -> AuthenticatedUser:
        """用户解析：兼容常见 Django 用户接口结构，并提取稳定 user_id。"""
        data = payload.get("data") if isinstance(payload.get("data"), dict) else payload
        user_id = self._first_present(data, ["id", "user_id", "uid", "pk", "uuid"])
        if user_id is None:
            raise AppError("AUTH_USER_PARSE_FAILED", "auth user id is missing", 502)
        username = self._first_present(data, ["username", "account", "mobile", "phone"])
        display_name = self._first_present(data, ["display_name", "name", "nickname", "real_name"])
        role = self._first_present(data, ["role", "user_role"])
        tenant_id = self._first_present(data, ["tenant_id", "org_id", "organization_id"])
        return AuthenticatedUser(
            user_id=str(user_id),
            username=str(username) if username is not None else None,
            display_name=str(display_name) if display_name is not None else None,
            role=str(role) if role is not None else None,
            tenant_id=str(tenant_id) if tenant_id is not None else None,
        )

    @staticmethod
    def _first_present(data: dict[str, Any], keys: list[str]) -> Any:
        """用户解析：按优先级读取第一个非空字段。"""
        for key in keys:
            value = data.get(key)
            if value is not None and value != "":
                return value
        return None

    @staticmethod
    def _cache_key(headers: dict[str, str]) -> str:
        """认证缓存：基于鉴权凭证生成不可逆缓存键，避免保存明文 token。"""
        raw = "|".join(f"{key}:{value}" for key, value in sorted(headers.items()))
        return hashlib.sha256(raw.encode("utf-8")).hexdigest()

    def _read_cache(self, cache_key: str) -> AuthenticatedUser | None:
        """认证缓存：读取进程内短期用户缓存，减少频繁请求 Django 用户中心。"""
        item = self._cache.get(cache_key)
        if not item:
            return None
        expires_at, user = item
        if expires_at <= time.time():
            self._cache.pop(cache_key, None)
            return None
        return user

    def _write_cache(self, cache_key: str, user: AuthenticatedUser) -> None:
        """认证缓存：写入短期用户缓存，缓存只保存标准用户信息，不保存 token 明文。"""
        ttl = max(settings.auth_cache_ttl_seconds, 0)
        if ttl <= 0:
            return
        self._cache[cache_key] = (time.time() + ttl, user)