private decimal CalculateExtraPayments(MortgageInformation mortgage, int i)
{
var extraPayment = 0m;
if (mortgage.ExtraPayments != null && mortgage.ExtraPayments.ExtraPaymentInterval > 0 && mortgage.ExtraPayments.ExtraPaymentAmount > 0)
{
if (i % mortgage.ExtraPayments.ExtraPaymentInterval == 0)
{
extraPayment = mortgage.ExtraPayments.ExtraPaymentAmount;
}
}
return extraPayment;
}
private decimal CalculateInterestDue(MortgageInformation mortgageInformation, decimal intrestRate, decimal currentBalance)
{
var cp = (decimal)mortgageInformation.CompoundPeriod;
var value = 1 + intrestRate / cp;
var pf = (decimal)mortgageInformation.PaymentFrequency;
var power = cp / pf;
var result = (Math.Pow((double)value, (double)power) - 1) * (double)currentBalance;
return (decimal)((Math.Round(result, 2)));
}
public IList<PaymentScheduleItem> GeneratePaymentSchedule(MortgageInformation mortgageInformation)
{
var result = new List<PaymentScheduleItem>();
if (mortgageInformation == null || mortgageInformation.Term < 1 || mortgageInformation.LoanAmount <= 0)
{
return result;
}
var currentPaymentDate = mortgageInformation.FirstPaymentDate;
var numOfPayments = NumberOfMonthlyPayments(mortgageInformation.PaymentFrequency, mortgageInformation.Term);
var calculatedCurrentBalance = mortgageInformation.LoanAmount;
var calculatedPreviousRate = mortgageInformation.AnnualInterestRate;
var calculatedPreviousPaymentDue = 0m;
var cmltvTaxReturned = 0m;
for (int i = 1; i <= numOfPayments && calculatedCurrentBalance > 0; i++)
{
var item = new PaymentScheduleItem();
item.PaymentNumber = i;
item.IntrestRate = CalculateInterestRate(mortgageInformation, i, calculatedPreviousRate);
item.PaymentDate = CalculatePaymentDate(mortgageInformation, i, currentPaymentDate);
item.IntrestDue = CalculateInterestDue(mortgageInformation, item.IntrestRate, calculatedCurrentBalance);
item.PaymentDue = CalculatePaymentDue(mortgageInformation, i, item.IntrestRate, item.IntrestDue, calculatedCurrentBalance, calculatedPreviousRate, calculatedPreviousPaymentDue);
item.ExtraPayments = CalculateExtraPayments(mortgageInformation, i);
item.PrincipalPaid = CalculatePrincipalPaid(item.PaymentDue, item.IntrestDue, item.ExtraPayments);
item.Balance = CalculateCurrentBalance(calculatedCurrentBalance, item.PrincipalPaid);
item.TaxReturned = CalculateTaxReturned(mortgageInformation.TaxBracket, item.IntrestDue);
result.Add(item);
currentPaymentDate = item.PaymentDate;
cmltvTaxReturned += item.TaxReturned;
item.CmltvTaxReturned = cmltvTaxReturned;
calculatedPreviousRate = item.IntrestRate;
calculatedPreviousPaymentDue = item.PaymentDue;
calculatedCurrentBalance = item.Balance;
}
return result;
}
private decimal CalculateInterestRate(MortgageInformation mortgageInformation, int i, decimal calculatedPreviousRate)
{
if (mortgageInformation.RateType == MortgageEnums.RateType.Variable && i > 1)
{
var rate = calculatedPreviousRate;
if (mortgageInformation.PeriodsBetweenAdjustments != 0 && i >= (int)mortgageInformation.PaymentFrequency * mortgageInformation.YearsRateRemainsFixed)
{
if (mortgageInformation.PeriodsBetweenAdjustments == 0 || (i - 1) % mortgageInformation.PeriodsBetweenAdjustments == 0)
{
rate = Math.Max(mortgageInformation.IntrestRateMin,
calculatedPreviousRate +
mortgageInformation.EstimatedAdjustment);
}
return Math.Min(mortgageInformation.IntrestRateCap, rate);
}
}
return mortgageInformation.AnnualInterestRate;
}
private decimal CalculatePaymentDue(MortgageInformation mortgageInformation, int i, decimal intrestRate, decimal intrestDue, decimal currentBalance, decimal calculatedPreviousRate, decimal calculatedPreviousPaymentDue)
{
decimal paymentDue;
var cp = (decimal)mortgageInformation.CompoundPeriod;
var pf = (decimal)mortgageInformation.PaymentFrequency;
var fullBalancePlusIntrest = currentBalance + intrestDue;
var nper = mortgageInformation.Term * pf;
if (i == nper)
{
paymentDue = currentBalance + intrestDue;
}
else
{
if (intrestRate == calculatedPreviousRate && i > 1)
{
paymentDue = calculatedPreviousPaymentDue;
}
//TODO handle Acc Bi-Weekly
//TODO handle Acc Weekly
else
{
var value = 1 + intrestRate / cp;
var power = cp / pf;
var result = (Math.Pow((double)value, (double)power) - 1);
var pmt = -Financial.Pmt(result, (double)nper - i + 1, (double)currentBalance);
paymentDue = (decimal)Math.Round(pmt, 2);
}
}
return Math.Min(fullBalancePlusIntrest, paymentDue);
}
private DateTime CalculatePaymentDate(MortgageInformation mortgageInformation, int i, DateTime currentPaymentDate)
{
switch (mortgageInformation.PaymentFrequency)
{
case MortgageEnums.PaymentFrequency.Monthly:
return i == 1 ? currentPaymentDate : currentPaymentDate.AddMonths(1);
case MortgageEnums.PaymentFrequency.SemiMonthly://TODO
case MortgageEnums.PaymentFrequency.BiWeekly://TODO
case MortgageEnums.PaymentFrequency.Weekly://TODO
default:
return currentPaymentDate.AddMonths(i);
}
}
private MortgageInformation BuildMortgageInformation(MortgageRequest mortgageRequest)
{
RateInformation rateInfo = BuildRateInfo(mortgageRequest);
PaymentInformation payInfo = BuildPaymentInfo(mortgageRequest);
ExtraPayments extraPayments = BuildExtraPayments(mortgageRequest);
var mortgageInfo = new MortgageInformation(rateInfo, payInfo, extraPayments)
{
LoanAmount = mortgageRequest.LoanAmount,
AnnualInterestRate = mortgageRequest.AnnualInterestRate,
Term = mortgageRequest.Term,
CompoundPeriod = mortgageRequest.CompoundPeriod,
PaymentFrequency = mortgageRequest.PaymentFrequency,
TaxBracket = mortgageRequest.TaxBracket
};
return mortgageInfo;
}
