public List <PeriodDataModel> CalculateSchedule(AmortCalcModel model)
{
var terms = model.TermInMonths;
var unpaidPrincipalBalance = model.PrincipalLoanAmount;
var interestRate = model.AnnualInterestRate;
var monthlyIntRate = ((interestRate / 100) / 12);
var schedule = new List <PeriodDataModel>
{
new PeriodDataModel()
{
EndOfPeriodBalance = unpaidPrincipalBalance
}
};
for (int i = 1; i <= terms; i++)
{
var lastPeriod = schedule[i - 1];
var interestPaid = lastPeriod.EndOfPeriodBalance * monthlyIntRate;
var power = (double)Math.Pow(1.0 + (double)monthlyIntRate, terms - i + 1);
var principalPaid = (lastPeriod.EndOfPeriodBalance * monthlyIntRate * power / (power - 1)) - interestPaid;
var endBalance = lastPeriod.EndOfPeriodBalance - principalPaid;
schedule.Add(new PeriodDataModel()
{
Period = i,
EndOfPeriodBalance = Math.Round(endBalance, 2),
InterestPaid = Math.Round(interestPaid, 2),
PrincipalPaid = Math.Round(principalPaid, 2)
});
}
return(schedule);
}
public double CalculateSingleInstalment(AmortCalcModel model)
{
var calculatedPrincipalLoanAmount = model.PrincipalLoanAmount - model.Deposit;
var interestRate = (model.AnnualInterestRate / 100) / 12;
var power = Math.Pow((1 + interestRate), model.TermInMonths);
var instalment = calculatedPrincipalLoanAmount * power * interestRate / (power - 1);
return(Math.Round(instalment, 2));
}
public void CalculateSchedule_valid_inputs_should_return_schedule()
{
// Arrange
IAmortCalcService classUnderTest = new AmortCalcService();
var amortCalcModel = new AmortCalcModel()
{
AnnualInterestRate = 5.44,
TermInMonths = 3,
PaymentFrequency = PaymentFrequencyTypes.Monthly,
Deposit = 0,
PrincipalLoanAmount = 5000
};
var expected = new List <PeriodDataModel>()
{
new PeriodDataModel()
{
EndOfPeriodBalance = 5000,
InterestPaid = 0,
Period = 0,
PrincipalPaid = 0
},
new PeriodDataModel()
{
EndOfPeriodBalance = 3340.87,
InterestPaid = 22.67,
Period = 1,
PrincipalPaid = 1659.13
},
new PeriodDataModel()
{
EndOfPeriodBalance = 1674.21,
InterestPaid = 15.15,
Period = 2,
PrincipalPaid = 1666.66
},
new PeriodDataModel()
{
EndOfPeriodBalance = 0,
InterestPaid = 7.59,
Period = 3,
PrincipalPaid = 1674.21
}
};
// Act
var actual = classUnderTest.CalculateSchedule(amortCalcModel);
// Assert
actual.Should().BeEquivalentTo(expected);
}
public void CalculateSingleInstalment_valid_inputs_should_return_instalment(double expected, double deposit)
{
// Arrange
IAmortCalcService classUnderTest = new AmortCalcService();
var amortCalcModel = new AmortCalcModel()
{
AnnualInterestRate = 5.44,
TermInMonths = 360,
PaymentFrequency = PaymentFrequencyTypes.Monthly,
Deposit = deposit,
PrincipalLoanAmount = 820000
};
// Act
var actual = classUnderTest.CalculateSingleInstalment(amortCalcModel);
// Assert
Assert.AreEqual(expected, actual);
}
