import { fetch } from 'undici';

const JSCODE2SESSION_URL = 'https://api.weixin.qq.com/sns/jscode2session';

export function loadWechatMiniappConfig(env = process.env) {
  const appId =
    env.H5_WECHAT_MINIAPP_APP_ID?.trim() ??
    env.H5_WECHAT_APP_ID?.trim() ??
    '';
  const appSecret =
    env.H5_WECHAT_MINIAPP_APP_SECRET?.trim() ??
    env.H5_WECHAT_APP_SECRET?.trim() ??
    '';
  return {
    enabled: Boolean(appId && appSecret),
    appId,
    appSecret,
  };
}

export async function exchangeMiniProgramCode(
  { appId, appSecret, code, fetchImpl = fetch } = {},
) {
  const jsCode = String(code ?? '').trim();
  if (!appId || !appSecret) {
    throw Object.assign(new Error('小程序登录未配置 AppID/AppSecret'), {
      code: 'wechat_miniapp_not_configured',
    });
  }
  if (!jsCode) {
    throw Object.assign(new Error('缺少微信登录 code'), { code: 'invalid_code' });
  }

  const url = new URL(JSCODE2SESSION_URL);
  url.searchParams.set('appid', appId);
  url.searchParams.set('secret', appSecret);
  url.searchParams.set('js_code', jsCode);
  url.searchParams.set('grant_type', 'authorization_code');

  const response = await fetchImpl(url);
  const payload = await response.json().catch(() => ({}));
  if (!response.ok) {
    throw Object.assign(new Error('微信登录服务暂不可用'), {
      code: 'wechat_miniapp_http_failed',
      status: response.status,
    });
  }
  if (payload.errcode) {
    throw Object.assign(new Error(payload.errmsg || '微信 code 无效或已过期'), {
      code: 'wechat_miniapp_code_failed',
      errcode: payload.errcode,
    });
  }
  const openid = String(payload.openid ?? '').trim();
  if (!openid) {
    throw Object.assign(new Error('微信未返回 openid'), { code: 'wechat_miniapp_openid_missing' });
  }
  return {
    openid,
    sessionKey: payload.session_key ?? null,
    unionid: payload.unionid ? String(payload.unionid).trim() : null,
  };
}