func solveForPayment(
amount currency.Amount, rate float64, length int) currency.Amount {
amountF := amount.Float64()
if rate == 0.0 {
return amount.FromFloat64(amountF / float64(length))
}
result := amount.FromFloat64(amountF * rate * (1.0 + 1.0/(math.Pow((1.0+rate), float64(length))-1.0)))
resultI := result.Int64()
if resultI <= 0 {
resultI = 1
}
interestOnly := amount.FromFloat64(amountF * rate).Int64()
if resultI <= interestOnly {
resultI = interestOnly + 1
}
return result.FromInt64(resultI)
}
