using System;

​

/**

 1. The Context

    A loan has many programs. Loan programs are created based on market needs, government regulations, and many other aspects.

​

 2. The Problem

    We need to accomodate the creation of many loand programs that we work with in our codes

    so we can easily add a new loan program in the future with the ease of maintanance yet flexible. However,

    there are so many different requirements and not all loan programs are offered the same way.

 3. The Solution

    Create a Strategy to encapsulate what varies among the loan programs to handle the various requirement.

*/

public class LoanProgram

{

    public static void Main()

    {

        // Getting properties of a Conventional loan.

        double downPayment = 50000;

        double appraisedValue = 250000.00;

        double loanAmount = appraisedValue - downPayment;

        Conventional conventional = new Conventional("Conventional");

        conventional.setDownPayment(downPayment);

        conventional.LoanAmount = loanAmount;

        conventional.AppraisedValue = appraisedValue;

        Console.WriteLine("LTV is: {0}", conventional.calculateLTV());

        Console.WriteLine("{0} Mortgage Insurance is {1}", conventional.program, conventional.calculateMortgageInsurance());

        // Getting properties of an FHA loan.

        downPayment = 7500.00;

        appraisedValue = 250000.00;

        loanAmount = appraisedValue - downPayment;

        FHA fha = new FHA("FHA");

        fha.setDownPayment(downPayment);

        fha.LoanAmount = loanAmount;

        fha.AppraisedValue = appraisedValue;

        Console.WriteLine("LTV is: {0}", fha.calculateLTV());

        Console.WriteLine("{0} Mortgage Insurance is {1}", fha.program, fha.calculateMortgageInsurance());

    }

    interface IRequireDownPaymentBehavior

    {

        void setDownPayment(double downPayment);

        double calculateMortgageInsurance();

    }

    public abstract class Loan

    {

        public string program;

        private double loanAmount;

        private double appraisedValue;

        public Loan(string program)

        {

            this.program = program;

        }

        public double LoanAmount { get; set; }

        public double AppraisedValue { get; set; }

        public double calculateLTV()

        {

            return (LoanAmount / AppraisedValue) * 100;

        }

    }

    public class Conventional : Loan, IRequireDownPaymentBehavior

    {   

        private double downPayment;

        const double requiredMortgageInsuranceConventional = 1.5;

        public Conventional(string program) : base(program)

        {

        }

        public void setDownPayment(double downPayment) {

            this.downPayment = downPayment;

        }

        public double calculateMortgageInsurance()

        {

            double mortgageInsurancePercentage;

            if (calculateLTV() > 80) {

                mortgageInsurancePercentage = requiredMortgageInsuranceConventional;

            } else {

                mortgageInsurancePercentage = 0;

            }

            return (mortgageInsurancePercentage * ((1 / 100.00) * LoanAmount));

        }

    }

    public class FHA : Loan, IRequireDownPaymentBehavior

    {

        private double downPayment;

        const double requiredMortgageInsuranceFHA = 1.0;

        public FHA(string program) : base(program)

        {

        }

        public void setDownPayment(double downPayment) {

            this.downPayment = downPayment;

        }

        public double calculateMortgageInsurance()

        {

            return (requiredMortgageInsuranceFHA * ((1 / 100.00) * LoanAmount));

        }

    }

    /**

     * VA loan can be guaranteed with no down payment and doesn't require a mortgage insurance.

     */

    public class VA : Loan

    {

        public VA(string program) : base(program)

        {

        }

    }

}