private void CalculateValue()
{
var result = _voucherValidator.Validate(Products, Vouchers);
ErrorMessages = result.invalidVouchers?.OfType <InvalidVoucherDecorator>()?.Select(invalid => invalid.Message).ToList(); // show messages
TotalValue = _valueCalculator.CalculateValue(Products, result.validVouchers);
}
public void CalculateValue(IValueCalculator calculator, int basisPoints)
{
ValueDelta = calculator.CalculateValue(this, basisPoints);
}