public double TaxFor(double grossSalary)
{
var lowerTaxBand = new TaxBand(5000.0, 0.1, null);
var middleTaxBand = new TaxBand(20000.0, 0.2, lowerTaxBand);
var upperTaxBand = new TaxBand(40000.0, 0.4, middleTaxBand);
return(upperTaxBand.TaxFor(grossSalary));
}
private double TaxForLowerBands(double grossSalary)
{
return(lowerTaxBand?.TaxFor(GrossToTaxAtLowerBand(grossSalary)) ?? 0);
}