private static double calculateAccruedInterest(double lastBalance, double totalInterest, DateTime startingDate, DateTime endingDate, DateTime lastWithdrawlDate, InterestType interestType)
{
// If there are no wothdraws, set the last withdrawl to starting date
if (lastWithdrawlDate == DateTime.MinValue)
{
lastWithdrawlDate = startingDate;
}
// Calculate number of days since last withdrawl to the starting transaction date
int daysSinceLastWithdrawl = startingDate.Subtract(lastWithdrawlDate).Days;
// If there are no withdralws in the last 10 days, use 5% rate
if (daysSinceLastWithdrawl > 10)
{
return(InterestCalculator.calculateAccruedInterest(lastBalance, totalInterest, 5, startingDate, endingDate, interestType));
}
// If the span is more, we need to use different rates based on withdrawl date (like amount based rate slabs)
DateTime nextInterestRateUpgradeDate = lastWithdrawlDate.AddDays(10);
if (nextInterestRateUpgradeDate < endingDate)
{
// use 0.1% rate until 10-day withdrawl rule breaks, and use 5% after that date
double interest = InterestCalculator.calculateAccruedInterest(lastBalance, totalInterest, 0.1, startingDate, nextInterestRateUpgradeDate, interestType);
return(interest + InterestCalculator.calculateAccruedInterest(lastBalance, totalInterest + interest, 5, nextInterestRateUpgradeDate, endingDate, interestType));
}
else
{
// Use 0.1% rate if there are no withdrawls in the past 10 days
return(InterestCalculator.calculateAccruedInterest(lastBalance, totalInterest, 0.1, startingDate, endingDate, interestType));
}
}
/// <summary>
/// Caculates interest earned in the checking account
/// </summary>
/// <returns>amount</returns>
public override double InterestEarned()
{
lock (TransactionLock)
{
// Use 0.1% rate accrued daily
return(InterestCalculator.calculateAccruedInterest(Transactions, 0.1, DateTime.Now, InterestType.COMPOUNDED_DAILY));
}
}
private static double calculateAccruedInterest(double lastBalance, double totalInterest, DateTime startingDate, DateTime endingDate, InterestType interestType)
{
// If the balance is less than $1000, use 0.1% rate
if (lastBalance <= 1000)
{
return(InterestCalculator.calculateAccruedInterest(lastBalance, totalInterest, 0.1, startingDate, endingDate, interestType));
}
// Otherwise, apply 0.1% on $1000, and 0.2% on balance over $1000
double interest = InterestCalculator.calculateAccruedInterest(1000, totalInterest, 0.1, startingDate, endingDate, interestType);
return(interest + InterestCalculator.calculateAccruedInterest((lastBalance - 1000), (totalInterest + interest), 0.2, startingDate, endingDate, interestType));
}