Design a shopping cart with coupons and tax

Q: Design a shopping cart with coupons and tax

Evaluates object-oriented design, domain modeling, encapsulation/immutability, and extensible pricing/discount strategies within the Software Engineering Fundamentals domain at a component-level/class-interface design abstraction.

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Question

Design an object-oriented shopping cart module for an e-commerce system.

Requirements:

A cart can add items and update item quantities .
The cart supports checkout . After checkout, the cart becomes immutable (no further changes to items/quantities/coupons).
The cart can apply coupons . There may be multiple coupon types, for example:
- Percentage off (e.g., 20% off)
- BOGO (Buy-One-Get-One) style discounts
The cart must compute tax based on a state tax rate .
The prompt is intentionally vague: explain what clarifying questions you would ask, then propose a clean class/interface design and describe how totals are calculated.

Deliverables:

Key classes and responsibilities (e.g., Cart, LineItem, Product, Pricing/Discount/Tax components).
Core methods and data structures.
How you prevent modification after checkout.
How you model different coupon types and make it easy to add new ones.

Design a shopping cart with coupons and tax

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