#2 Open Close Principle [‘O’ in SOLID]

enum DiscountType {
    case seasonal
    case loyalty
    case nodiscount
}

class DiscountCalculator {
    func calculateDiscount(discountType: DiscountType, amount: Double) -> Double {
        switch discountType {
        case .seasonal:
            return amount * 0.1
        case .loyalty:
            return amount * 0.15
        case .nodiscount:
            return 0
//        Including a default case can handle unexpected cases but won't prompt Xcode to show an error or warning if a new DiscountType is added later. This means new cases could be missed without any compile-time notifications.
        default:
            return 0
        }
    }
}

// usage
let discountCalcualtor = DiscountCalculator()
discountCalcualtor.calculateDiscount(discountType: .seasonal, amount: 100)
discountCalcualtor.calculateDiscount(discountType: .loyalty, amount: 100)
discountCalcualtor.calculateDiscount(discountType: .nodiscount, amount: 100)

protocol Discount {
    func apply(amount: Double) -> Double
}

class SeasonalDiscount: Discount {
    func apply(amount: Double) -> Double {
        return amount * 0.1
    }
}

class LoyaltyDiscount: Discount {
    func apply(amount: Double) -> Double {
        return amount * 0.15
    }
}

class DiscountCalculatorOCP {
    private var discounts: [Discount]

    init(discounts: [Discount]) {
        self.discounts = discounts
    }

    func calculateTotalDiscount(amount: Double) -> Double {
        var totalDiscount = 0.0
        for discount in discounts {
            totalDiscount += discount.apply(amount: amount)
        }
        return totalDiscount
    }
}

// usage
let seasonalDiscount = SeasonalDiscount()
let loyaltyDiscount = LoyaltyDiscount()
let discountCalculatorOCP = DiscountCalculatorOCP(discounts: [seasonalDiscount, loyaltyDiscount])
discountCalculatorOCP.calculateTotalDiscount(amount: 100)