Remove BigDecimal from HighPrecisionMoney.fromPreciseAmount

util/src/main/scala/Money.scala

@@ -4,7 +4,6 @@ import language.implicitConversions
 import java.math.MathContext
 import java.text.NumberFormat
 import java.util.{Currency, Locale}
-
 import cats.Monoid
 import cats.data.ValidatedNel
 import cats.syntax.validated._
@@ -351,8 +350,7 @@ case class HighPrecisionMoney private (
 
   val `type`: String = TypeName
 
-  lazy val amount: BigDecimal =
-    (BigDecimal(preciseAmount) * factor(fractionDigits)).setScale(fractionDigits)
+  lazy val amount: BigDecimal = preciseAmountToAmount(preciseAmount, fractionDigits)
 
   def withFractionDigits(fd: Int)(implicit mode: RoundingMode): HighPrecisionMoney = {
     val scaledAmount = amount.setScale(fd, mode)
@@ -474,6 +472,8 @@ case class HighPrecisionMoney private (
 }
 
 object HighPrecisionMoney {
+  import MoneyRounding._
+
   object ImplicitsDecimal {
     final implicit class HighPrecisionMoneyNotation(val amount: BigDecimal) extends AnyVal {
       def EUR: HighPrecisionMoney = HighPrecisionMoney.EUR(amount)
@@ -566,6 +566,9 @@ object HighPrecisionMoney {
   private def amountToPreciseAmount(amount: BigDecimal, fractionDigits: Int): Long =
     (amount * Money.cachedCentPower(fractionDigits)).toLong
 
+  def preciseAmountToAmount(preciseAmount: Long, fractionDigits: Int): BigDecimal =
+    (BigDecimal(preciseAmount) * factor(fractionDigits)).setScale(fractionDigits)
+
   def fromDecimalAmount(amount: BigDecimal, fractionDigits: Int, currency: Currency)(implicit
       mode: RoundingMode): HighPrecisionMoney = {
     val scaledAmount = amount.setScale(fractionDigits, mode)
@@ -606,12 +609,9 @@ object HighPrecisionMoney {
       centAmount: Option[Long]): ValidatedNel[String, HighPrecisionMoney] =
     for {
       fd <- validateFractionDigits(fractionDigits, currency)
-      amount = BigDecimal(preciseAmount) * factor(fd)
-      scaledAmount = amount.setScale(fd, BigDecimal.RoundingMode.UNNECESSARY)
-      ca <- validateCentAmount(scaledAmount, centAmount, currency)
+      ca <- validateCentAmount(preciseAmount, fractionDigits, centAmount, currency)
       // TODO: revisit this part! the rounding mode might be dynamic and configured elsewhere
-      actualCentAmount = ca.getOrElse(
-        roundToCents(scaledAmount, currency)(BigDecimal.RoundingMode.HALF_EVEN))
+      actualCentAmount = ca.getOrElse(roundHalfEven(preciseAmount, fractionDigits, currency))
     } yield HighPrecisionMoney(preciseAmount, fd, actualCentAmount, currency)
 
   private def validateFractionDigits(
@@ -625,13 +625,14 @@ object HighPrecisionMoney {
       fractionDigits.validNel
 
   private def validateCentAmount(
-      amount: BigDecimal,
+      preciseAmount: Long,
+      fractionDigits: Int,
       centAmount: Option[Long],
       currency: Currency): ValidatedNel[String, Option[Long]] =
     centAmount match {
       case Some(actual) =>
-        val min = roundToCents(amount, currency)(RoundingMode.FLOOR)
-        val max = roundToCents(amount, currency)(RoundingMode.CEILING)
+        val min = roundFloor(preciseAmount, fractionDigits, currency)
+        val max = roundCeiling(preciseAmount, fractionDigits, currency)
 
         if (actual < min || actual > max)
           s"centAmount must be correctly rounded preciseAmount (a number between $min and $max).".invalidNel

util/src/main/scala/MoneyRounding.scala

@@ -0,0 +1,84 @@
+package io.sphere.util
+
+import java.util.Currency
+import scala.annotation.tailrec
+
+/** This object contains rounding algorithms for the Money classes. So far we used BigDecimal for
+  * this purpose, but BigDecimal is slower and consumes more memory than this approach.
+  */
+object MoneyRounding {
+
+  private def pow10(n: Int): Long = Math.pow(10, n).toLong
+
+  /** @return
+    *   Floor rounded (preciseAmount, fractionDigits) to the cent value of the given currency
+    */
+  def roundFloor(preciseAmount: Long, fractionDigits: Int, currency: Currency): Long =
+    if (preciseAmount < 0L) {
+      val power = pow10(fractionDigits - currency.getDefaultFractionDigits)
+      val floor = preciseAmount / power
+      val remainder = preciseAmount % power
+      if (remainder == 0L) floor else floor - 1L
+    } else
+      preciseAmount / pow10(fractionDigits - currency.getDefaultFractionDigits)
+
+  /** @return
+    *   Ceiling rounded (preciseAmount, fractionDigits) to the cent value of the given currency
+    */
+  def roundCeiling(preciseAmount: Long, fractionDigits: Int, currency: Currency): Long =
+    if (preciseAmount < 0L)
+      preciseAmount / pow10(fractionDigits - currency.getDefaultFractionDigits)
+    else {
+      val power = pow10(fractionDigits - currency.getDefaultFractionDigits)
+      val floor = preciseAmount / power
+      val remainder = preciseAmount % power
+      if (remainder == 0L) floor else floor + 1L
+    }
+
+  private def getFractionDigits(
+      fractionWithoutLeadingZeros: Long,
+      fractionDigits: Int): List[Int] = {
+    @tailrec
+    def loop(remainder: Long, acc: List[Int]): List[Int] = {
+      val lastDigit = (remainder % 10L).toInt
+      val newRemainder = remainder / 10L
+      val newAcc = lastDigit :: acc
+      if (newRemainder == 0L) newAcc
+      else loop(newRemainder, newAcc)
+    }
+    val digits = loop(fractionWithoutLeadingZeros, List.empty)
+
+    if (digits.length < fractionDigits) List.fill(fractionDigits - digits.length)(0) ::: digits
+    else digits
+  }
+
+  /** @return
+    *   half even rounded (preciseAmount, fractionDigits) to the cent value of the given currency
+    */
+  def roundHalfEven(preciseAmount: Long, fractionDigits: Int, currency: Currency): Long = {
+    val centFractionDigits = fractionDigits - currency.getDefaultFractionDigits
+    val power = pow10(centFractionDigits)
+    val integer = preciseAmount / power
+    val fraction = preciseAmount % power
+
+    // Eg: 3 for 123.456
+    val leastSignificantDigitOfInt = integer % 10L
+
+    val fractionDigitsList = getFractionDigits(fraction, centFractionDigits)
+
+    // Eg: 4 for 123.456
+    val mostSignificantDigitOfFraction :: rest = fractionDigitsList
+
+    if (mostSignificantDigitOfFraction == 5 && rest.forall(_ == 0))
+      if (leastSignificantDigitOfInt % 2L == 0L) integer else integer + 1L
+    else if (mostSignificantDigitOfFraction >= 5)
+      integer + 1L
+    else if (mostSignificantDigitOfFraction == -5 && rest.forall(_ == 0))
+      if (leastSignificantDigitOfInt % 2L == 0L) integer else integer - 1L
+    else if (mostSignificantDigitOfFraction <= -5)
+      integer - 1L
+    else
+      integer
+  }
+
+}

util/src/test/scala/DomainObjectsGen.scala

@@ -18,7 +18,8 @@ object DomainObjectsGen {
 
   val highPrecisionMoney: Gen[HighPrecisionMoney] = for {
     money <- money
-  } yield HighPrecisionMoney.fromMoney(money, money.currency.getDefaultFractionDigits)
+    fractionDigits <- Gen.oneOf(money.currency.getDefaultFractionDigits to 10)
+  } yield HighPrecisionMoney.fromMoney(money, fractionDigits)
 
   val baseMoney: Gen[BaseMoney] = Gen.oneOf(money, highPrecisionMoney)
 

util/src/test/scala/MoneyRoundingSpec.scala

@@ -0,0 +1,78 @@
+package io.sphere.util
+
+import org.scalatest.funspec.AnyFunSpec
+import org.scalatest.matchers.must.Matchers
+import org.scalatest.prop.TableDrivenPropertyChecks
+import org.scalatest.prop.TableDrivenPropertyChecks.Table
+import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
+
+import java.util.Currency
+import scala.math.BigDecimal.RoundingMode
+
+class MoneyRoundingSpec extends AnyFunSpec with Matchers with ScalaCheckDrivenPropertyChecks {
+  val Euro: Currency = Currency.getInstance("EUR")
+  val ZWL: Currency = Currency.getInstance("ZWL")
+  val JPY: Currency = Currency.getInstance("JPY")
+
+  describe("Money Rounding") {
+    it("roundFloor should behave similarly to BigDecimal rounding") {
+      ScalaCheckDrivenPropertyChecks.forAll(DomainObjectsGen.highPrecisionMoney) { h =>
+        val bdRes = HighPrecisionMoney.roundToCents(h.amount, h.currency)(RoundingMode.FLOOR)
+        val longRes =
+          MoneyRounding.roundFloor(h.preciseAmount, h.fractionDigits, h.currency)
+        bdRes must be(longRes)
+      }
+    }
+
+    it("roundCeiling should behave similarly to BigDecimal rounding") {
+      ScalaCheckDrivenPropertyChecks.forAll(DomainObjectsGen.highPrecisionMoney) { h =>
+        val bdRes = HighPrecisionMoney.roundToCents(h.amount, h.currency)(RoundingMode.CEILING)
+        val longRes =
+          MoneyRounding.roundCeiling(h.preciseAmount, h.fractionDigits, h.currency)
+        bdRes must be(longRes)
+      }
+    }
+
+    it("roundHalfEven should behave similarly to BigDecimal rounding") {
+      // I used random generated values later, but I needed these very specific values too to check the
+      // edge cases of the half even rounding
+      val data = Table(
+        ("preciseAmount", "fraction", "currency"),
+        (1119L, 3, Euro),
+        (1111L, 3, Euro),
+        (1115L, 3, Euro),
+        (1125L, 3, Euro),
+        (112500L, 5, Euro),
+        (11250001L, 7, Euro),
+        (11000004L, 7, Euro),
+        (11249999L, 7, Euro),
+        (-1119L, 3, Euro),
+        (-1111L, 3, Euro),
+        (-1115L, 3, Euro),
+        (-1125L, 3, Euro),
+        (-112500L, 5, Euro),
+        (5721482481806080960L, 6, ZWL),
+        (123L, 0, JPY)
+      )
+
+      TableDrivenPropertyChecks.forAll(data) { (preciseAmount, fd, cur) =>
+        val amount = HighPrecisionMoney.preciseAmountToAmount(preciseAmount, fd)
+        val bdRes = HighPrecisionMoney.roundToCents(amount, cur)(RoundingMode.HALF_EVEN)
+
+        val longRes =
+          MoneyRounding.roundHalfEven(preciseAmount, fd, cur)
+
+        bdRes must be(longRes)
+      }
+
+      ScalaCheckDrivenPropertyChecks.forAll(DomainObjectsGen.highPrecisionMoney) { h =>
+        val bdRes = HighPrecisionMoney.roundToCents(h.amount, h.currency)(RoundingMode.HALF_EVEN)
+
+        val longRes =
+          MoneyRounding.roundHalfEven(h.preciseAmount, h.fractionDigits, h.currency)
+
+        bdRes must be(longRes)
+      }
+    }
+  }
+}