const _ = require('lodash/fp')
const axios = require('axios')
const mem = require('mem')

const BN = require('./bn')
const T = require('./time')

const MAX_ROTATIONS = 5

const _getFiatRates = () =>
  axios.get('https://bitpay.com/api/rates').then(response => response.data)

const getFiatRates = mem(_getFiatRates, {
  maxAge: 6 * T.hours,
  cacheKey: () => '',
})

const API_QUEUE = [
  {
    api: getBitPayFxRate,
    name: 'bitpay',
    fiatCodeProperty: 'code',
    rateProperty: 'rate',
  },
]

function getBitPayFxRate(
  fiatCode,
  defaultFiatMarket,
  fiatCodeProperty,
  rateProperty,
) {
  return getFiatRates().then(({ data: fxRates }) => {
    const defaultFiatRate = findCurrencyRates(
      fxRates,
      defaultFiatMarket,
      fiatCodeProperty,
      rateProperty,
    )
    const fxRate = findCurrencyRates(
      fxRates,
      fiatCode,
      fiatCodeProperty,
      rateProperty,
    ).div(defaultFiatRate)
    return {
      fxRate,
    }
  })
}

function findCurrencyRates(fxRates, fiatCode, fiatCodeProperty, rateProperty) {
  const rates = _.find(_.matchesProperty(fiatCodeProperty, fiatCode), fxRates)
  if (!rates || !rates[rateProperty])
    throw new Error(`Unsupported currency: ${fiatCode}`)
  return new BN(rates[rateProperty].toString())
}

const getRate = (retries = 1, fiatCode, defaultFiatMarket) => {
  const selected = _.first(API_QUEUE).name
  const activeAPI = _.first(API_QUEUE).api
  const fiatCodeProperty = _.first(API_QUEUE).fiatCodeProperty
  const rateProperty = _.first(API_QUEUE).rateProperty

  if (!activeAPI) throw new Error(`FOREX api ${selected} does not exist.`)

  return activeAPI(
    fiatCode,
    defaultFiatMarket,
    fiatCodeProperty,
    rateProperty,
  ).catch(() => {
    // Switch service
    const erroredService = API_QUEUE.shift()
    API_QUEUE.push(erroredService)
    if (retries >= MAX_ROTATIONS)
      throw new Error(`FOREX API error from ${erroredService.name}`)

    return getRate(++retries, fiatCode)
  })
}

module.exports = { getFiatRates, getRate }