Simple mock backend for a questions/answers app

qasurvey-backend.js

/**
 * Quick test
 *
$ node
> b = require('./qasurvey-backend')
> b.submitAnswer(20, 'Yes').catch(console.error)
> b.submitAnswer(20, 'No').catch(console.error)
> b.submitAnswer(1337, 'Maybe').catch(console.error)
> b.fetchRoom(20).then(r => b.submitAnswer(r.id, 'Yes')).then(console.log).catch(console.error)
*/


const FAILURE_RATE = 0.25
const MIN_RESPONSE_TIME = 120
const MAX_RESPONSE_TIME = 2500
const MIN_OTHER_USERS_WAIT = 5000
const MAX_OTHER_USERS_WAIT = 20000

module.exports = {
  fetchRoom: (roomId) => pretend((resolve, reject) => () => {
    const idx = parseInt(roomId) % Qs.length
    if (Math.random() <= FAILURE_RATE) {
      reject(new Error('RequestFailed'))
    } else {
      const Q = Qs[idx]
      const room = DB[roomId] = DB[roomId] || { id: roomId, question: Q }
      const Qanswers = room.answers || {}
      answers.forEach(a => Qanswers[a] = Qanswers[a] || 0)
      room.answers = Qanswers
      resolve(room)
    }
  }),

  fetchRandomRoom: () => {
    return module.exports.fetchRoom(randint(Qs.length))
  },

  submitAnswer: (roomId, answer) => pretend((resolve, reject) => () => {
    const room = DB[roomId]
    if (!room || answers.indexOf(answer) < 0) {
      console.log(roomId, room, answer, answers)
      reject(new Error('BadRequest'))
    } else {
      room.answers[answer]++
      resolve(room)
    }
  })
}

const randint = max => Math.floor(Math.random() * max)
const pickRando = arr => arr[randint(arr.length)]
const randBetween = (min, max) => min + Math.random() * (max - min)
const pretend = cb => new Promise((resolve, reject) => {
  setTimeout(cb(resolve,reject), randBetween(MIN_RESPONSE_TIME, MAX_RESPONSE_TIME))
})

const Qs = [
  "Do you like space westerns?",
  "Do you think SSI can?",
  "Is the sun bigger than the earth?",
  "Is astrological sign useful to ascertain personality compatibility between people?",
  "Do you enjoy reading science fiction comedy?",
]

const answers = ["Yes", "No"]

const DB = {
  1337: {[answers[0]]: 101, [answers[1]]: 0, whatISthisEVEN: 'lol'}
}

function otherUsersDoStuffToo() {
  DB[pickRando(Object.keys(DB))][pickRando(answers)]++
  setTimeout(otherUsersDoStuffToo, waitBetween(MIN_OTHER_USERS_WAIT, MAX_OTHER_USERS_WAIT))
}