Promotion Text Kata

Why this Kata?

The Promotion Text Kata offers an hour-long hands-on practice on readable and maintainable programming. When practicing alone, it improves a developer's craft. When practicing as a team, it educates and aligns the team on a standard set of best practices and coding styles.

Users' goal is to improve the readability of the PromotionTextDecorator class without breaking its functionalities.

This Kata does not aim to improve OOP and design pattern skills.

While heavily rewritten, it's inspired by an example (HtmlUtil.java) in Chapter 3 of the book "Clean Code: A Handbook of Agile Software Craftsmanship" by Robert C. Martin.

How to use this Kata

• Read the requirements (the next section) and implementation of the requirements in before-refactor/ (the folder name may differ slightly by language)
• Rewrite the implementation in a more readable and maintainable way
• Your rewrite should pass all the unit tests provided in tests/ (the folder name may differ slightly by language)
• While unit tests are provided, during the refactor, it's recommended to write your unit tests
• Please don't modify the provided unit tests
• Please don't modify the signature of PromotionTextDecorator.decorate(product), i.e. # of arguments, their types as well as the return type
• Since this Kata doesn't aim to improve OOP and design pattern skills, there is no need to turn PromotionTextDecorator into smaller classes

PromotionTextDecorator Requirements

Given a product, PromotionTextDecorator.decorate should generate a promotion description:

• Every product has these properties:
  • promoted: boolean, whether the product is being promoted
  • oldCentPrice: integer, the original price of the product in cents
  • centPrice: integer, the current price of the product in cents
  • hideDiscount: boolean, whether to hide discount text in description
  • freeShipping: boolean, whether the product is eligible for free shipping
  • description: string, original description of the product
  • promotionText: string, promotion description generated
• Set promotionText to description if the product is not being promoted
• Set promotionText to description with some additional texts. The rules of additional texts are:
  • If the product is discounted (centPrice < oldCentPrice) and its hideDiscount is false, add the text "Don't miss the deal, $X off!" to the beginning and the end of promotionText, where X is (oldCentPrice - centPrice)/100
  • If the product is eligible for free shipping, add the text "Free shipping!" to the beginning and the end of promotionText, after and before discount texts if those exist
  • Use \n as newline character
• Return the generated promotionText

Examples:

const product = {
  promoted: true,
  hideDiscount: false,
  oldCentPrice: 10000,
  centPrice: 9000,
  freeShipping: true,
  description: "Pre-owned vase",
  promotionText: "Some old text",
};

becomes

const product = {
  promoted: true,
  hideDiscount: false,
  oldCentPrice: 10000,
  centPrice: 9000,
  freeShipping: true,
  description: 'Pre-owned vase',
  promotionText: 'Don't miss the deal, $X off!\nFree shipping!\nPre-owned vase\nFree shipping!\nDon't miss the deal, $X off!',
}

Please see the unit tests for more details.

Solution

There is a solution provided in after-refactor/. It is one of the many ways to improve the code. It follows the practices mentioned in the Clean Code book, to name a few:

• Keep functions small
• Reduce nested if and while statements
• One function should do one thing: statements within a function should all be at the same level of abstraction
• Use descriptive names
• Fewer function arguments
• DRY (Don't repeat yourself)
• Concepts that are closely related should be kept vertically close to each other
• Explain yourself in readable code instead of comments