const crypto = require('crypto')
const { HttpError } = require('./http')

let tokenCache = null

function wxConfigured() {
  return !!(process.env.WX_APPID && process.env.WX_SECRET)
}

async function code2session(code, deviceId) {
  if (!wxConfigured()) {
    const seed = deviceId || 'guest'
    return {
      openid: `demo_${crypto.createHash('sha1').update(seed).digest('hex').slice(0, 16)}`,
      demo: true
    }
  }

  const url = new URL('https://api.weixin.qq.com/sns/jscode2session')
  url.search = new URLSearchParams({
    appid: process.env.WX_APPID,
    secret: process.env.WX_SECRET,
    js_code: code,
    grant_type: 'authorization_code'
  }).toString()

  let session
  try {
    const res = await fetch(url, { signal: AbortSignal.timeout(8000) })
    session = await res.json()
  } catch (error) {
    throw new HttpError(502, '微信登录服务不可用')
  }
  if (!session.openid) throw new HttpError(400, session.errmsg || '微信登录失败')
  return { openid: session.openid, demo: false }
}

async function getAccessToken() {
  if (!wxConfigured()) throw new HttpError(400, '未配置 WX_APPID / WX_SECRET，无法发送订阅消息')
  if (tokenCache && tokenCache.expiresAt > Date.now() + 60_000) return tokenCache.token

  const url = new URL('https://api.weixin.qq.com/cgi-bin/token')
  url.search = new URLSearchParams({
    grant_type: 'client_credential',
    appid: process.env.WX_APPID,
    secret: process.env.WX_SECRET
  }).toString()

  const res = await fetch(url, { signal: AbortSignal.timeout(8000) })
  const body = await res.json()
  if (!body.access_token) throw new HttpError(502, body.errmsg || '获取微信 access_token 失败')
  tokenCache = {
    token: body.access_token,
    expiresAt: Date.now() + (Number(body.expires_in) || 7200) * 1000
  }
  return tokenCache.token
}

function clip(value, max) {
  const text = value == null ? '' : String(value)
  return text.length > max ? text.slice(0, max) : text
}

// Default field mapping for a typical “活动提醒” template (thing / time / thing).
function buildRemindData(activity) {
  return {
    thing1: { value: clip(activity.title || '卓米会活动', 20) },
    time2: { value: clip(activity.startAt || '待定', 20) },
    thing3: { value: clip(activity.address || '详见活动页', 20) }
  }
}

async function sendSubscribeMessage({ openid, templateId, page, data }) {
  const token = await getAccessToken()
  const res = await fetch(
    `https://api.weixin.qq.com/cgi-bin/message/subscribe/send?access_token=${encodeURIComponent(token)}`,
    {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        touser: openid,
        template_id: templateId,
        page: page || '',
        data,
        miniprogram_state: process.env.WX_MINI_STATE || 'formal'
      }),
      signal: AbortSignal.timeout(8000)
    }
  )
  const body = await res.json()
  return { ok: body.errcode === 0, errcode: body.errcode, errmsg: body.errmsg || '' }
}

module.exports = {
  wxConfigured,
  code2session,
  getAccessToken,
  buildRemindData,
  sendSubscribeMessage
}