text: 'use strict'
  
  const DEV = process.env.NODE_ENV === 'dev'
  const DEBUG = /\bhafas-client\b/.test(process.env.DEBUG || '')
  
  const {randomBytes} = require('crypto')
  const createHash = require('create-hash')
  const captureStackTrace = DEV ? require('capture-stack-trace') : () => {}
  const {stringify} = require('qs')
  const ProxyAgent = require('https-proxy-agent')
  const Promise = require('pinkie-promise')
  const {fetch} = require('fetch-ponyfill')({Promise})
  const {addErrorInfo} = require('./errors')
  
  const proxyAddress = process.env.HTTPS_PROXY || process.env.HTTP_PROXY || null
  const proxyAgent = proxyAddress ? new ProxyAgent(proxyAddress) : null
  
  const id = randomBytes(6).toString('hex')
  const randomizeUserAgent = (userAgent) => {
  	const i = Math.round(Math.random() * userAgent.length)
  	return userAgent.slice(0, i) + id + userAgent.slice(i)
  }
  
  const md5 = input => createHash('md5').update(input).digest()
  
  const request = (ctx, userAgent, reqData) => {
  	const {profile, opt} = ctx
  
  	const body = profile.transformReqBody(ctx, {
  		// todo: is it `eng` actually?
  		// RSAG has `deu` instead of `de`
  		lang: opt.language || 'en',
  		svcReqL: [reqData]
  	})
  	if (DEBUG) console.error(JSON.stringify(body))
  
  	const req = profile.transformReq(ctx, {
  		agent: proxyAgent,
  		method: 'post',
  		// todo: CORS? referrer policy?
  		body: JSON.stringify(body),
  		headers: {
  			'Content-Type': 'application/json',
  			'Accept-Encoding': 'gzip, br, deflate',
  			'Accept': 'application/json',
  			'user-agent': randomizeUserAgent(userAgent)
  		},
  		redirect: 'follow',
  		query: {}
  	})
  
  	if (profile.addChecksum || profile.addMicMac) {
  		if (!Buffer.isBuffer(profile.salt)) {
  			throw new TypeError('profile.salt must be a Buffer.')
  		}
  		if (profile.addChecksum) {
  			const checksum = md5(Buffer.concat([
  				Buffer.from(req.body, 'utf8'),
  				profile.salt
  			]))
  			req.query.checksum = checksum.toString('hex')
  		}
  		if (profile.addMicMac) {
  			const mic = md5(Buffer.from(req.body, 'utf8'))
  			req.query.mic = mic.toString('hex')
  
  			const micAsHex = Buffer.from(mic.toString('hex'), 'utf8')
  			const mac = md5(Buffer.concat([micAsHex, profile.salt]))
  			req.query.mac = mac.toString('hex')
  		}
  	}
  
  	const url = profile.endpoint + '?' + stringify(req.query)
  
  	// Async stack traces are not supported everywhere yet, so we create our own.
  	const err = new Error()
  	err.isHafasError = true // todo: rename to `isHafasClientError`
  	err.request = req.body // todo: commit as bugfix
  	err.url = url
  	captureStackTrace(err)
  
  	return fetch(url, req)
  	.then((res) => {
  		err.statusCode = res.status
  		if (!res.ok) {
  			err.message = res.statusText
  			throw err
  		}
  		return res.json()
  	})
  	.then((b) => {
  		if (DEBUG) console.error(JSON.stringify(b))
  
  		if (b.err && b.err !== 'OK') {
  			addErrorInfo(err, b.err, b.errTxt, b.id)
  			throw err
  		}
  		if (!b.svcResL || !b.svcResL[0]) {
  			err.message = 'invalid response'
  			throw err
  		}
  		if (b.svcResL[0].err !== 'OK') {
  			addErrorInfo(err, b.svcResL[0].err, b.svcResL[0].errTxt, b.id)
  			throw err
  		}
  
  		const res = b.svcResL[0].res
  		return {
  			res,
  			common: profile.parseCommon({...ctx, res})
  		}
  	})
  }
  
  module.exports = request
  