public class HomeController : Controller
    {
        private readonly ILogger _logger;

        public HomeController(ILogger logger)
        {
            _logger = logger;
        }

        public IActionResult Index()
        {
            return View();
        }

        public IActionResult Code()
        {
            return View();
        }

        public IActionResult App()
        {
            // Create an instance of the model
            Loan loan = new();

            // Set the default loan amount
            loan.Payment = 0.0m;
            loan.TotalInterest = 0.0m;
            loan.TotalCost = 0.0m;
            loan.Rate = 3.5m;
            loan.Amount = 150000m;
            loan.Term = 30;

            return View(loan);
        }

        [HttpPost]
        [AutoValidateAntiforgeryToken]
        public IActionResult App(Loan loan)
        {
            // Calculate the loan and get the payments
            var loanHelper = new LoanHelper();

            Loan newLoan = loanHelper.GetPayments(loan);

            return View(newLoan);
        }

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
        }
    }
                    
                    

HomeController

Sets up the initial state of App, Index, and Code views. The overloading App function calls on LoanHelper to update the App view.

    public class LoanHelper
    {
        public Loan GetPayments(Loan loan)
        {
            // Calculate monthly payment
            loan.Payment = CalcPayment(loan.Amount, loan.Rate, loan.Term);

            // Create loop from 1 to the term
            var balance = loan.Amount;
            var totalInterest = 0.0m;
            var monthlyInterest = 0.0m;
            var monthlyPrincipal = 0.0m;
            var monthlyRate = CalcMonthlyRate(loan.Rate);
            var monthsInTerm = CalcMonthsInAnnualTerm(loan.Term);

            // Calculate a payment schedule
            // Loop over each month until reaching the term of the loan
            for (int month = 1; month <= monthsInTerm; month++)
            {
                monthlyInterest = CalcMonthlyInterest(balance, monthlyRate);
                totalInterest += monthlyInterest;
                monthlyPrincipal = loan.Payment - monthlyInterest;
                balance -= monthlyPrincipal;

                LoanPayment loanPayment = new();

                loanPayment.Month = month;
                loanPayment.Payment = loan.Payment;
                loanPayment.MonthlyPrincipal = monthlyPrincipal;
                loanPayment.MonthlyInterest = monthlyInterest;
                loanPayment.TotalInterest = totalInterest;
                loanPayment.Balance = balance;

                // Push payments in the loan
                // Push the object into the loan model
                loan.Payments.Add(loanPayment);
            }

            loan.TotalInterest = totalInterest;
            loan.TotalCost = loan.Amount + totalInterest;

            // Return the loan to the view
            return loan;
        }

        private decimal CalcPayment(decimal amount, decimal rate, int term)
        {
            var monthlyRate = CalcMonthlyRate(rate);
            var rateD = Convert.ToDouble(monthlyRate);
            var amountD = Convert.ToDouble(amount);

            var paymentD = (amountD * rateD) / (1 - Math.Pow(1 + rateD, -term * 12));

            return Convert.ToDecimal(paymentD);
        }

        private decimal CalcMonthlyRate(decimal rate)
        {
            return rate / 1200;
        }

        private decimal CalcMonthlyInterest(decimal balance, decimal monthlyRate)
        {
            return balance * monthlyRate;
        }

        private int CalcMonthsInAnnualTerm(int term)
        {
            return term * 12;
        }
    }
                    
                    

LoanHelper

GetPayment function

Calls on private functions to calculate the monthly payment of a given loan amount, term, and rate.

For each month, it returns the following:

• Monthly payment
• Monthly principal
• Monthly interest
• Total interest
• Remaining balance

Private functions

Local functions that calculate the following:

• Months in an annual payment period
• Monthly interest
• Monthly payment

    public class Loan
    {
        public decimal Amount { get; set; }

        public decimal Rate { get; set; }

        public int Term { get; set; }

        public decimal Payment { get; set; }

        public decimal TotalInterest { get; set; }

        public decimal TotalCost { get; set; }

        public List Payments { get; set; } = new List();


    }
                    
                    

Loan

Constructs the structure of a loan.

    public class LoanPayment
    {
        public int Month { get; set; }
        public decimal Payment { get; set; }
        public decimal MonthlyPrincipal { get; set; }
        public decimal MonthlyInterest { get; set; }
        public decimal TotalInterest { get; set; }
        public decimal Balance {get; set; }
    }
                    
                    

LoanPayment

Constructs the structure of a loan payment.