/// <summary>
/// Calculates the principal portion of a specific payment on a loan.
/// </summary>
/// <param name="rate">The periodic interest rate (applied every period). This must be greater than or equal to zero.</param>
/// <param name="numberOfPeriods">The total number of periods.</param>
/// <param name="currentBalance">The current balance of the loan. This must be greater than or equal to zero and not contain fractional pennies.</param>
/// <param name="period">The period for which to calculate the principal portion. This must be in the range <c>[1,<paramref name="numberOfPeriods"/>]</c> and defaults to <c>1</c>.</param>
/// <param name="futureBalance">The future balance of the loan. This must be greater than or equal to zero and not contain fractional pennies.</param>
/// <param name="payAtBeginningOfPeriod">Set to <c>true</c> to indicate payments are made at the beginning of the period; by default, payments are made at the end of the period.</param>
/// <returns>The principal portion of the specific payment.</returns>
/// <exception cref="InvalidOperationException">The principal portion of the payment could not be calculated.</exception>
public static decimal PrincipalPayment(decimal rate, uint numberOfPeriods, decimal currentBalance, int period = 1, decimal futureBalance = decimal.Zero, bool payAtBeginningOfPeriod = false)
{
Contract.Requires <ArgumentOutOfRangeException>(rate >= 0, "Rate may not be less than zero.");
VerifyMoneyArgument(currentBalance, "currentBalance");
VerifyMoneyArgument(futureBalance, "futureBalance");
var result = -Exact.PrincipalPayment(rate, numberOfPeriods, currentBalance, period, futureBalance, payAtBeginningOfPeriod);
if (result < decimal.Zero)
{
var e = new InvalidOperationException("The principal portion of the payment could not be calculated.");
e.Data["rate"] = rate;
e.Data["numberOfPeriods"] = numberOfPeriods;
e.Data["currentBalance"] = currentBalance;
e.Data["period"] = period;
e.Data["futureBalance"] = futureBalance;
e.Data["payAtBeginningOfPeriod"] = payAtBeginningOfPeriod;
e.Data["result"] = result;
throw e;
}
try
{
return(checked (Math.Ceiling(result * 100) / 100));
}
catch (OverflowException ex)
{
var e = new InvalidOperationException("The principal portion of the payment could not be calculated.", ex);
e.Data["rate"] = rate;
e.Data["numberOfPeriods"] = numberOfPeriods;
e.Data["currentBalance"] = currentBalance;
e.Data["period"] = period;
e.Data["futureBalance"] = futureBalance;
e.Data["payAtBeginningOfPeriod"] = payAtBeginningOfPeriod;
e.Data["result"] = result;
throw e;
}
}
