Expense Report Refactoring C++ Kata

Overview

This kata complements Clean Code: SOLID, Ep. 10 - Open-Closed Principle.

In this exercise, you'll practice refactoring code to adhere to the Open-Closed Principle (OCP). You'll be working with an expense report system that tracks different types of expenses and prints a final report.

Instructions

Exercise 1

The ExpenseReport class in the expense_report.h file generates an expense report. It iterates over a list of expenses, printing out a line for each expense and totaling up the amounts.

The current implementation, however, is complex and hard to understand, and it's not easy to modify or extend its behavior. It's your task to refactor this code to make it cleaner and more maintainable, while ensuring that it still correctly calculates and prints the report.

Make sure the program still behaves the same way after your refactoring. There's a unit test suite in place that checks that on a very rudimentary level by just looking at the output of the program.

Exercise 2

When you're done with refactoring, test the quality of your refactoring by implementing two additional scenarios:

1. Extend our system to handle two more types of expenses.

   1. Transportation. Surcharge: 5% of the expense amount.
   2. Supplies. Surcharge: No surcharge.

2. Add dynamic surcharge based on day of week.

   • For dinners on weekends, the surcharge is 15% of the expense amount.
   • For breakfasts on weekends, the surcharge is 10% of the expense amount.
   • On weekdays, the surcharges remain the same as before (10% for dinner and 5% for breakfast).

   You may need to add a date field to the Expense class to support this requirement. The date should be the date when the expense occurred.

   Note

   You can use the std::tm type in C++ to work with dates, and you can determine if a date is a weekend by using the following function:

   #include <ctime>
   #include <iomanip>
   #include <iostream>
   #include <string>
   
   bool is_weekend(const std::string& date_str)
   {
       std::tm date{};
       std::istringstream ss(date_str);
       ss >> std::get_time(&date, "%Y-%m-%d");
       std::mktime(&date);
   
       int day_of_week = date.tm_wday;
       // Check if it's Saturday (6) or Sunday (0)
       return day_of_week == 6 || day_of_week == 0;
   }
   
   int main()
   {
       std::string date_str = "2023-06-17";  // this is a Saturday
       std::cout << is_weekend(date_str) << std::endl;  // this should print: 1
       return 0;
   }

Usage

You can import this project into Replit, and it will handle all dependencies automatically.

Prerequisites

• CMake 3.19+
• Ninja
• GTest

Build

make build

Run main

make run

Run tests

make test