import * as rq from 'request-promise-native'

const DEFAULT_DELAY = 1000 / 3 // 1/3 of a second
const LOST_HISTORY_ERROR = 1

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms))

export default function poll(bot, delay: number = DEFAULT_DELAY) {
  return bot.api('groups.getLongPollServer', { group_id: bot.options.group_id })
    .then(res => {
      return request(`${res.server}?act=a_check&key=${res.key}` +
        `&wait=25&version=1&ts=${res.ts}`, delay)
    })
    .catch(error => {
      bot.emit('poll-error', error)

      // restart on error
      return poll(bot, delay)
    })

  function request(url, delay: number) {
    return rq(url, { json: true })
      .then(res => {
        if (!res || !res.ts || (res.failed && res.failed !== LOST_HISTORY_ERROR))
          throw new Error('response of the Long Poll server isn\'t valid ' +
            `(${JSON.stringify(res)})`)

        if (res.failed && res.failed === LOST_HISTORY_ERROR)
          bot.emit('poll-error', new Error('event history went out of date or was partially lost'))

        url = url.replace(/ts=.*/, `ts=${res.ts}`) // set new timestamp

        if (!res.failed && res.updates && res.updates.length > 0) {
          for (let update of res.updates) {
            if (update.type === 'message_new') bot.emit('update', update)
          }
        }

        if (bot._stop) return null
        return delay !== 0
          ? sleep(delay).then(() => request(url, delay))
          : request(url, delay)
      })
  }
}