Strategy Pattern

// ─── EXAMPLE 1 ──────────────────────────────────────────────────────────────
// WHAT WE ARE IMPLEMENTING:
// A check-out cart selecting pricing deductions (flat, percentage, or
// seasonal discounts) at checkout.
//
// WHERE THE STRATEGY FITS IN:
// DiscountStrategy is the Strategy interface. FlatDiscount and
// PercentageDiscount represent Concrete Strategies. CheckoutCart is the
// Context.
// ────────────────────────────────────────────────────────────────────────────
// --- Strategy interface ---
interface PricingStrategy {
    double calculatePrice(double basePrice, int hours);
}

// --- Concrete strategies ---
class HourlyPricing implements PricingStrategy {
    public double calculatePrice(double basePrice, int hours) {
        return basePrice * hours;
    }
}

class DailyPricing implements PricingStrategy {
    public double calculatePrice(double basePrice, int hours) {
        int days = (int) Math.ceil(hours / 24.0);
        return basePrice * days * 0.8;  // 20% discount
    }
}

class WeekendSurchargePricing implements PricingStrategy {
    private final double surchargeFactor = 1.5;
    public double calculatePrice(double basePrice, int hours) {
        return basePrice * hours * surchargeFactor;
    }
}

// --- Context (uses strategy) ---
class ParkingFeeCalculator {
    private final PricingStrategy strategy;

    public ParkingFeeCalculator(PricingStrategy strategy) {
        this.strategy = strategy;
    }

    public double calculate(double basePrice, int hours) {
        return strategy.calculatePrice(basePrice, hours);
    }
}

public class Main {
    public static void main(String[] args) {
        // Pick strategy at runtime
        ParkingFeeCalculator weekday = new ParkingFeeCalculator(new HourlyPricing());
        ParkingFeeCalculator weekend = new ParkingFeeCalculator(new WeekendSurchargePricing());

        System.out.println("Weekday 5h: " + weekday.calculate(10, 5));   // 50.0
        System.out.println("Weekend 5h: " + weekend.calculate(10, 5));   // 75.0
        System.out.println("Daily 30h: " + new ParkingFeeCalculator(new DailyPricing()).calculate(10, 30)); // 240.0
    }
}