fix: review

lib/commission-math.js

@@ -0,0 +1,41 @@
+const BN = require('./bn')
+const configManager = require('./new-config-manager')
+const coinUtils = require('./coin-utils')
+
+function truncateCrypto (cryptoAtoms, cryptoCode) {
+  const DECIMAL_PLACES = 3
+  if (cryptoAtoms.eq(0)) return cryptoAtoms
+
+  const scale = 5 // TODO: change this to coins.displayScale when coins have that attribute
+  const scaleFactor = BN(10).pow(scale)
+
+  return BN(cryptoAtoms).truncated().div(scaleFactor)
+    .round(DECIMAL_PLACES).times(scaleFactor)
+}
+
+function fiatToCrypto (tx, rec, deviceId, config) {
+  const usableFiat = rec.fiat - rec.cashInFee
+
+  const commissions = configManager.getCommissions(tx.cryptoCode, deviceId, config)
+  const tickerRate = BN(tx.rawTickerPrice)
+  const discount = getDiscountRate(tx.discount, commissions[tx.direction])
+  const rate = tickerRate.mul(discount).round(5)
+  const unitScale = coinUtils.getCryptoCurrency(tx.cryptoCode).unitScale
+  const unitScaleFactor = BN(10).pow(unitScale)
+
+  return truncateCrypto(BN(usableFiat).div(rate.div(unitScaleFactor)), tx.cryptoCode)
+}
+
+function getDiscountRate (discount, commission) {
+  const bnDiscount = discount ? BN(discount) : BN(0)
+  const bnCommission = BN(commission)
+  const percentageDiscount = BN(1).sub(bnDiscount.div(100))
+  const percentageCommission = bnCommission.div(100)
+  return BN(1).add(percentageDiscount.mul(percentageCommission))
+}
+
+module.exports = {
+  truncateCrypto,
+  fiatToCrypto,
+  getDiscountRate
+}