enum Shipping: Error {
    case outOfRange(String)
}

protocol ShippingStrategy {
    func calculateShippingCost(
        packageWeightInKilograms: Float,
        packageDimensionsInInches: CGPoint,
        destination: String) throws -> Int
}

class WorldWideShippingStrategy: ShippingStrategy {

    func calculateShippingCost(
        packageWeightInKilograms: Float,
        packageDimensionsInInches: CGPoint,
        destination: String) throws -> Int {
        guard packageWeightInKilograms > 0.0 else {
            throw Shipping.outOfRange("package weight must be positive and non-zero")
        }

        guard packageDimensionsInInches.x > 0.0 || packageDimensionsInInches.y > 0.0 else {
            throw Shipping.outOfRange("Package dimensions must be positive and nonzero")
        }

        guard destination != null else {
            throw Shipping.outOfRange("Destination must be provided")
        }

        // calculate shipping cost
        let shippingCost = 50

        guard shippingCost > 0 else {
            throw Shipping.outOfRange("The calculated shipping cost is out of range")
        }

        return shippingCost
    }

}