public LoanResponseDetailsDto CalculateLoan(LoanRequestDetailsDto loanRequestDetails)
{
var response = new LoanResponseDetailsDto();
response.MonthlyPayment = _loanService.CalculateMonthlyPayment(loanRequestDetails);
response.AdministrationFee = _loanService.CalculateAdministrationFee(loanRequestDetails);
response.TotalInterestPaid = _loanService.CalculateTotalInterestPaid(
response.MonthlyPayment,
loanRequestDetails.LoanDuration,
loanRequestDetails.LoanAmount);
response.APR = _loanService.CalculateAPR(loanRequestDetails);
return(response);
}
public double CalculateAPR(LoanRequestDetailsDto loanRequest)
{
var totalAccruedAmount = loanRequest.LoanAmount * (1 + loanRequest.LoanDuration * loanRequest.InterestRate / 100);
var interestAccrued = totalAccruedAmount - loanRequest.LoanAmount;
var administrationFee = CalculateAdministrationFee(loanRequest);
double apr = 0;
if (loanRequest.LoanAmount != 0 || loanRequest.LoanDuration != 0)
{
apr = 100 * ((administrationFee + interestAccrued) / loanRequest.LoanAmount) / loanRequest.LoanDuration;
}
return(apr);
}
public void CalculateAPR_CalculatesCorrectValue()
{
var service = GetService();
var loanRequest = new LoanRequestDetailsDto()
{
LoanAmount = 2000,
LoanDuration = 2,
AdministrationAmount = 200,
AdministrationFixed = 100,
InterestRate = 5
};
var result = service.CalculateAPR(loanRequest);
Assert.AreEqual(10, Math.Round(result, 2));
}
public void CalculateMonthlyPayment_CalculatesCorrectValue()
{
var service = GetService();
var loanRequest = new LoanRequestDetailsDto()
{
LoanAmount = 500000,
LoanDuration = 10,
AdministrationAmount = 10000,
AdministrationFixed = 1,
InterestRate = 5
};
var result = service.CalculateMonthlyPayment(loanRequest);
Assert.AreEqual(5303.28, Math.Round(result, 2));
}
public double CalculateMonthlyPayment(LoanRequestDetailsDto loanRequest)
{
var months = loanRequest.LoanDuration * 12;
var rate = (loanRequest.InterestRate / 100) / 12;
var discountFactor = months;
if (rate != 0)
{
var discountFactorNumerator = Math.Pow(1 + rate, months) - 1;
var discountFactorDenominator = rate * Math.Pow(1 + rate, months);
discountFactor = discountFactorNumerator / discountFactorDenominator;
}
return(discountFactor == 0
? 0
: loanRequest.LoanAmount / discountFactor);
}
public double CalculateAdministrationFee(LoanRequestDetailsDto loanRequest)
{
return(Math.Min(
loanRequest.LoanAmount * loanRequest.AdministrationFixed / 100,
loanRequest.AdministrationAmount));
}