monorepo/LCU.WebApps.Indirect.ReserveManagementSystem/Api/ReserveManagementSystemApi/Helpers/LoanCalculationHelper.cs

using ReserveManagementSystemLib.Models;

namespace ReserveManagementSystemApi.Helpers
{
    public class LoanCalculationHelper 
    {
        private decimal _daysInterest;
        private LoanReserve loanReserve = new LoanReserve();

        public LoanCalculationHelper()
        {

        }
        public LoanReserve CalculateBuyDown(CalculationConfig cc)
        {
            // Case - Buy down Below Threshold where difference in rates is less than or equal to 0.25 percent
            if (cc.BuydownRateDifference() <= cc.NoReserveThreshold()) //we already know it's positive
            {
                loanReserve.ReserveAmount = 0;
                loanReserve.ReserveTypeMessage = "No Reserve";
                loanReserve.FlatFeePaid = false;
                return loanReserve;
            }

            // Case - This is a regular Buy Down
            _daysInterest = cc.BuydownRateDifference() / 100 * cc.DaysToFirstPmt() * cc.LoanData().LoanAmount / 
                            365 * (decimal)Math.Pow(1 + (double)cc.LoanData().ContractRate / 100, (double)cc.LoanData().Term / 12);

            loanReserve.ReserveAmount = -(cc.BuyFinanceCharge - cc.ContractFinanceCharge + _daysInterest);
            loanReserve.ReserveTypeMessage = "Buy Down Reserve";
            loanReserve.FlatFeePaid = false;
            return loanReserve;
        }

        public LoanReserve CalculateNoMarkup(CalculationConfig cc)
        {
            // Case - Contract rate is equal to the Buy rate
            _daysInterest = cc.StdRate() * cc.DaysToFirstPmt() * cc.LoanData().LoanAmount / 
                            365 * (decimal)Math.Pow(1 + (double)cc.LoanData().ContractRate / 100, (double)cc.LoanData().Term / 12);

            loanReserve.ReserveAmount = (cc.ContractFinanceCharge - cc.BuyFinanceCharge + _daysInterest);
            loanReserve.ReserveTypeMessage = "No Reserve";
            loanReserve.FlatFeePaid = false;
            return loanReserve;
        }

        public LoanReserve CalculateStandardMarkup(CalculationConfig cc)
        {
            // Case - Contract rate is greater than Buy rate                      
            _daysInterest = (1 - cc.ReserveDiscount()/100) * cc.StdRate() / 100 * cc.DaysToFirstPmt() * cc.LoanData().LoanAmount /  
                            365 * (decimal)Math.Pow(1 + (double)cc.LoanData().ContractRate / 100, (double)cc.LoanData().Term / 12);

            loanReserve.ReserveAmount = ((1 - cc.ReserveDiscount() / 100) * (cc.ContractFinanceCharge - cc.BuyFinanceCharge) + _daysInterest);

            if ((double)cc.StdRate() <= 2.5)
            {
                loanReserve.ReserveTypeMessage = "Standard Reserve";
            }
            else
            {
                loanReserve.ReserveTypeMessage = "Standard Reserve - Exceeds Max Markup";
            }
            return loanReserve;
        }

        public LoanReserve AssignFlatFee(LoanReserve loanReserve, CalculationConfig cc)
        {
            loanReserve.FlatFeePaid = false;
            if (loanReserve.ReserveAmount < (cc.FlatFeePercent() / 100 * cc._loanData.LoanAmount * (1 - cc.ReserveDiscount() / 100)))
            {
                loanReserve.ReserveAmount = (cc.FlatFeePercent() / 100 * cc._loanData.LoanAmount * (1 - cc.ReserveDiscount() / 100));
                loanReserve.ReserveTypeMessage = "Flat Fee Reserve";
                loanReserve.FlatFeePaid = true;
            }

            return loanReserve;
        }

        public decimal FinanceCharge(int term, decimal loanAmount, decimal rate)
        {
            if (rate == 0) { return 0; }
            double paymentRate = (double)rate / (double)1200;
            decimal rateFactor = (decimal)Math.Pow((1 + paymentRate), (double)term);
            return (loanAmount * term * rate / 1200 * rateFactor) / (rateFactor - 1) - loanAmount;
        }     

        internal DateTime GetLastChargebackDate(DateTime loanDate, DateTime firstPmtDate, int numOfChargebackPayments, Int16? numOfChargebackDays)
        {
            // in rare cases that date from loan date is most recent, check table values and compare between loan date vs. first payment date
            int result = DateTime.Compare(loanDate.AddDays((Double)numOfChargebackDays), firstPmtDate.AddMonths(numOfChargebackPayments - 1));
            if (result > 0)
            { 
                return loanDate.AddDays((Double)numOfChargebackDays); //Loan Date is most recent
            }
            return firstPmtDate.AddMonths(numOfChargebackPayments - 1); 
        }

        internal decimal CalculateChargeback(decimal reserve, int term, int remainingMonths)
        {
            return reserve * MonthFactor(remainingMonths) / MonthFactor(term);
        }

        private decimal MonthFactor(int numberOfMonths)
        {
            return numberOfMonths * (numberOfMonths + 1) / 2;
        }

        public int GetRemainingMonths(Loan loanData)
        {
            if (loanData.PaidLoanDate >= loanData.FinalPmtDate)
                return 0;

            var monthsOccurred = (loanData.PaidLoanDate.Value - loanData.FirstPmtDate).TotalDays / (365) * 12 + 1;

            var remainingMonths = (int)(loanData.Term - Math.Round((decimal)monthsOccurred, 0));
            return remainingMonths;
        }

    }
}