v12.0.0 - initial commit

packages/server/lib/forex.js

@@ -0,0 +1,84 @@
+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(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(err => {
+    const erroredService = API_QUEUE.shift()
+    API_QUEUE.push(erroredService)
+    if (retries >= MAX_ROTATIONS)
+      throw new Error(
+        `FOREX API error from ${erroredService.name} ${err?.message}`,
+      )
+
+    return getRate(++retries, fiatCode, defaultFiatMarket)
+  })
+}
+
+module.exports = { getFiatRates, getRate }