const axios = require('axios')

const APPID = process.env.WX_APPID
const APPSECRET = process.env.WX_APPSECRET

// access_token 内存缓存（微信全局唯一，2 小时有效）
let _token = { value: null, expireAt: 0 }

async function getAccessToken() {
  const now = Date.now()
  // 提前 5 分钟刷新，避免临界过期
  if (_token.value && _token.expireAt - now > 5 * 60 * 1000) {
    return _token.value
  }

  const url = `https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=${APPID}&secret=${APPSECRET}`
  const { data } = await axios.get(url, { timeout: 8000 })
  if (!data.access_token) {
    throw new Error(`获取 access_token 失败: ${JSON.stringify(data)}`)
  }
  _token = {
    value: data.access_token,
    expireAt: now + (data.expires_in - 300) * 1000
  }
  return _token.value
}

// code2session：拿 openid（小程序登录）
async function code2session(code) {
  const url = `https://api.weixin.qq.com/sns/jscode2session?appid=${APPID}&secret=${APPSECRET}&js_code=${code}&grant_type=authorization_code`
  const { data } = await axios.get(url, { timeout: 8000 })
  if (data.errcode) {
    throw new Error(`code2session 失败: ${JSON.stringify(data)}`)
  }
  return { openid: data.openid, unionid: data.unionid || null, session_key: data.session_key }
}

// 发送订阅消息
async function sendSubscribeMessage({ touser, page, data, templateId, miniprogramState = 'formal' }) {
  const token = await getAccessToken()
  const url = `https://api.weixin.qq.com/cgi-bin/message/subscribe/send?access_token=${token}`
  const body = {
    touser,
    template_id: templateId,
    page,
    miniprogram_state: miniprogramState,
    lang: 'zh_CN',
    data
  }
  const { data: res } = await axios.post(url, body, { timeout: 8000 })
  if (res.errcode !== 0) {
    throw new Error(`发送订阅消息失败: ${JSON.stringify(res)}`)
  }
  return res
}

module.exports = { getAccessToken, code2session, sendSubscribeMessage }