public static decimal CalculatePrice(this ParcelSpecification spec, ParcelInput input)
        {
            var basePrice = spec.Price;

            var weightSurcharge = 0;

            if (input.Weight > spec.MaxWeight)
            {
                weightSurcharge = (input.Weight - spec.MaxWeight) * spec.WeightSurcharge;
            }

            return(basePrice + weightSurcharge);
        }
        public static bool WouldFit(this ParcelSpecification parcelType, ParcelInput input)
        {
            if (input.X >= parcelType.MaxDimension)
            {
                return(false);
            }
            if (input.Y >= parcelType.MaxDimension)
            {
                return(false);
            }
            if (input.Z >= parcelType.MaxDimension)
            {
                return(false);
            }

            return(true);
        }