using System;

public class Program

{

    public static void Main()

    {

        Program program = new Program();

        program.CalculateProRataRefundAmount();

    }

    public void CalculateProRataRefundAmount()

    {

        // --------------- CHANGE BELOW PARAMS AS PER THE NEEDS ---------------- //

        DateTime CoverStartDate = Convert.ToDateTime("2021-08-10 00:00:00.000"); // CoverStartDate

        DateTime CancellationDate = Convert.ToDateTime("2022-02-12 23:59:59.000"); // CancellationDate

        decimal RetailPrice = Convert.ToDecimal(539.00);

        int DurationTerm = 15;      

        var refundAmount = 0.00M;

        // --------------- CHANGE ABOVE PARAMS AS PER THE NEEDS ---------------- //

        Program program = new Program();

        int ConsumerMonthElapsed = program.GetConsumerMonthsElapsed(CoverStartDate, CancellationDate);

        if (DurationTerm > 0 && ConsumerMonthElapsed > 0)

        {

            refundAmount = decimal.Round(RetailPrice * GetProRataDeduction(DurationTerm, ConsumerMonthElapsed), 2);

        }

        Console.WriteLine("Cover Start Date: " + CoverStartDate);

        Console.WriteLine("Cancellation Date: " + CancellationDate);

        Console.WriteLine("Retail Price: " + RetailPrice);

        Console.WriteLine("Duration in Months: " + DurationTerm);

        Console.WriteLine("Consumer Months Elapsed: " + ConsumerMonthElapsed);

        Console.WriteLine();

        Console.WriteLine();

        Console.WriteLine("Calculated Refund Amount: " + refundAmount);

    }

    public int GetConsumerMonthsElapsed(DateTime coverStartDate, DateTime CancellationDate)

    {

            int consumerMonthsElapsed = 0;

​

            DateTime coverStartDateTimeForLoop = coverStartDate;

            for (int month = 0; month <= (coverStartDate.Month - CancellationDate.Month); month++)

            {

                if (coverStartDateTimeForLoop <= CancellationDate)

                {

                    consumerMonthsElapsed++;

                    coverStartDateTimeForLoop = coverStartDate.AddMonths(month + 1);

                }

            }

​

            return consumerMonthsElapsed;

    }

​

    private decimal GetProRataDeduction(int durationMonths, int elapsedMonths)

    {

        return 1 - ((decimal)elapsedMonths / durationMonths);

    }

}