private Money getTotalInterestOnLoan(
      final MonetaryCurrency currency,
      final List<LoanRepaymentScheduleInstallment> repaymentScheduleInstallments) {

    Money cumulativeInterest = Money.zero(currency);

    for (LoanRepaymentScheduleInstallment scheduledRepayment : repaymentScheduleInstallments) {
      cumulativeInterest = cumulativeInterest.plus(scheduledRepayment.getInterest(currency));
    }

    return cumulativeInterest;
  }
  @Override
  public Money calculate(
      final LocalDate actualDisbursementDate,
      final LocalDate paidInFullDate,
      final Money loanPrincipal,
      final BigDecimal interestRatePerAnnum,
      final List<LoanRepaymentScheduleInstallment> repaymentScheduleInstallments,
      final List<LoanTransaction> loanRepayments) {

    MonetaryCurrency currency = loanPrincipal.getCurrency();

    Money totalOriginalInterest = getTotalInterestOnLoan(currency, repaymentScheduleInstallments);

    BigDecimal dailyEquivalentPeriodicInterestRate =
        interestRatePerAnnum.divide(BigDecimal.valueOf(36500), 9, RoundingMode.HALF_EVEN);

    Money totalRecalculatedPrincipalPaid = Money.zero(loanPrincipal.getCurrency());
    Money totalRecalculatedInterestPaid = Money.zero(loanPrincipal.getCurrency());
    LocalDate lastBalanceDate = actualDisbursementDate;
    Money outstandingBalance = loanPrincipal;
    for (LoanTransaction loanRepayment : loanRepayments) {

      int daysAtBalance =
          Days.daysBetween(lastBalanceDate, loanRepayment.getTransactionDate()).getDays();

      BigDecimal periodInterestRateForPaymentPeriod =
          dailyEquivalentPeriodicInterestRate.multiply(BigDecimal.valueOf(daysAtBalance));
      BigDecimal interestDueOnPaymentDateAmount =
          outstandingBalance.getAmount().multiply(periodInterestRateForPaymentPeriod);

      Money interestDueOnPaymentDate =
          Money.of(loanPrincipal.getCurrency(), interestDueOnPaymentDateAmount);
      Money principalDueOnPaymentDate =
          loanRepayment.getAmount(currency).minus(interestDueOnPaymentDate);

      totalRecalculatedPrincipalPaid =
          totalRecalculatedPrincipalPaid.plus(principalDueOnPaymentDate);
      totalRecalculatedInterestPaid = totalRecalculatedInterestPaid.plus(interestDueOnPaymentDate);

      logger.warn(
          "Installment: "
              + lastBalanceDate
              + " - "
              + loanRepayment.getTransactionDate()
              + " principal: "
              + principalDueOnPaymentDate
              + "interest: "
              + interestDueOnPaymentDate
              + " total: "
              + loanRepayment.getAmount());

      lastBalanceDate = loanRepayment.getTransactionDate();
      outstandingBalance = outstandingBalance.minus(principalDueOnPaymentDate);
    }

    // finally
    // add up total paid to date - work out interest due on that

    int daysAtBalance = Days.daysBetween(lastBalanceDate, paidInFullDate).getDays();

    BigDecimal periodInterestRateForPaymentPeriod =
        dailyEquivalentPeriodicInterestRate.multiply(BigDecimal.valueOf(daysAtBalance));
    BigDecimal interestDueOnPaymentDateAmount =
        outstandingBalance.getAmount().multiply(periodInterestRateForPaymentPeriod);

    Money interestDueOnPaymentDate =
        Money.of(loanPrincipal.getCurrency(), interestDueOnPaymentDateAmount);

    Money principalDueOnPaymentDate = outstandingBalance;

    Money netOutstandingOnPaidInFullDate = principalDueOnPaymentDate.plus(interestDueOnPaymentDate);

    totalRecalculatedPrincipalPaid = totalRecalculatedPrincipalPaid.plus(principalDueOnPaymentDate);
    totalRecalculatedInterestPaid = totalRecalculatedInterestPaid.plus(interestDueOnPaymentDate);

    logger.warn(
        "Installment: "
            + lastBalanceDate
            + " - "
            + paidInFullDate
            + " principal: "
            + principalDueOnPaymentDate
            + "interest: "
            + interestDueOnPaymentDate
            + " total: "
            + netOutstandingOnPaidInFullDate);

    lastBalanceDate = paidInFullDate;
    outstandingBalance = outstandingBalance.minus(principalDueOnPaymentDate);

    Money rebate = Money.zero(loanPrincipal.getCurrency());

    // Interest can be greater for following reasons:
    // 1. calculated interest may be slightly ahead based on daily
    // equivalent
    // method of calculating interest compared to original method.

    // 2. payments were under expected amount or after expected date
    // resulting in larger outstanding balance being used to calculate
    // interest
    // at each repayment point in time.
    if (totalRecalculatedInterestPaid.isLessThan(totalOriginalInterest)
        && totalRecalculatedInterestPaid.isGreaterThanZero()) {
      rebate = totalOriginalInterest.minus(totalRecalculatedInterestPaid);
    }

    return rebate;
  }