Design a Wishlist and Cart System with Discounts

Problem

Design an OOP model for Myntra's wishlist, cart, and checkout system with a flexible discount/coupon engine.

Requirements

• addToWishlist(userId, productId) / moveToCart(userId, productId)
• applyDiscount(cartId, couponCode) → validates and applies
• getCartTotal(cartId) — returns itemised + discounted total
• checkout(cartId, paymentMethod) → reserves inventory and creates order
• Multiple discount types: flat, percentage, BOGO, minimum cart value

Key classes

Wishlist, Cart, CartItem, DiscountRule, DiscountEngine, Order

Patterns

• Strategy for different discount types
• Decorator for stacking multiple discounts
• Template Method for checkout flow steps

Extension

Add "save for later" — moves item from cart to a saved list without deleting.