public double Handle(CalculateTrolleyQuery query)
{
TrolleyGuard.AgainstDuplicatePurchasedQuantities(query);
var(appliedSpecials, remainingPurchasedQuantities) = SubstituteQuantitiesWithSpecials(query.Specials, query.Quantities);
return(CalculateTotalPrice(query.Products, appliedSpecials, remainingPurchasedQuantities));
}
public static void AgainstDuplicatePurchasedQuantities(CalculateTrolleyQuery query)
{
if (query.Quantities.GroupBy(quantity => quantity.Name).Any(grouping => grouping.Count() > 1))
{
throw new ArgumentException("Duplicate purchased product name not allowed");
}
}