Acme Widget Co – Basket Proof of Concept

This is a proof of concept implementation of Acme Widget Co’s sales basket system.
It models a product catalog, delivery charge rules, and promotional offers in a clean, extensible, and testable way.

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Design Goals

• Separation of Concerns

  • Basket orchestrates items, totals, and applies rules.
  • Catalog defines products and prices.
  • DeliveryRule and OfferRule subclasses encapsulate pricing logic.

• Dependency Injection

  • Basket accepts a catalog, delivery rule, and list of offers at initialization.
  • Makes swapping or testing rules easy.

• Strategy Pattern

  • Delivery rules and offers implement an apply method.
  • New business rules can be added without modifying Basket.

• Extensibility

  • Add new offers or delivery schemes by subclassing OfferRule or DeliveryRule.
  • Existing code does not need modification.

• Testability

  • Unit tests for rules.
  • Integration tests verify total calculations with offers and delivery.

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Implementation

Core Classes

• Basket – main entry point, tracks items and calculates totals.
• Catalog – defines available products and their prices.
• DeliveryRule (abstract) – base for delivery charge strategies.
• DeliveryStandard – implements Acme’s delivery charges.
• OfferRule (abstract) – base for promotional strategies.
• OfferRedWidgetHalfPrice – implements “buy one Red Widget, get the second half price”.

Products Catalog

Code	Name	Price
R01	Red Widget	$32.95
G01	Green Widget	$24.95
B01	Blue Widget	$7.95

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Example Usage

require_relative "config/initializer"

basket = Basket.new(
  catalog: Catalog::PRODUCTS,
  delivery_rule: DeliveryStandard.new,
  offers: [OfferRedWidgetHalfPrice.new]
)

basket.add("B01")
basket.add("G01")
puts basket.total # => 37.85