Expense report refactoring kata in C++

Practice the Open-Closed Principle by refactoring an expense report without changing its behavior. Setup is complete when all four starter tests pass.

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.

Tip

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;
}

Prerequisites

Required:

• Git
• A compiler with C++17 support. Choose one:
  • GCC 10+ on Linux
  • LLVM Clang 14+ on Linux
  • Apple Clang 17+ on macOS
  • MSVC 2022 on Windows
• CMake 3.24 or later

Optional:

• GNU Make, for shorter commands. Every required task also has direct CMake and CTest commands. Make may be unavailable on Windows.

You do not need to install GoogleTest separately. CMake finds an installed copy or downloads the pinned release when needed.

Set up the kata

1. Clone the repository:

   git clone https://github.com/Coding-Cuddles/expense-report-refactoring-cpp-kata.git

2. Enter the repository directory:

   cd expense-report-refactoring-cpp-kata

3. Run the starter tests. Use Make when it is installed:

   make test

   Otherwise, use CMake and CTest directly:

   cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
   cmake --build build --config Debug
   ctest --test-dir build --build-config Debug --output-on-failure

The first run may download and build GoogleTest. CTest should report 100% tests passed.

If a command reports a missing compiler or CMake, install that prerequisite and run the setup commands again.

Setup is complete when CTest reports 100% tests passed.

Work on the kata

1. Refactor expense_report.h while preserving the behavior covered by test_expense_report.cpp.

2. Run the tests after each change. Use Make when it is installed:

   make test

   Otherwise, use CMake and CTest directly:

   cmake --build build --config Debug
   ctest --test-dir build --build-config Debug --output-on-failure

   Continue when CTest reports 100% tests passed.

Make command reference

Make is optional. Run make or make help to list these commands in the terminal.

Command	Result
make all	Build and run the test suite
make help	Show the Make command reference
make build	Configure and build without running tests
make test	Build and run the test suite
make format	Format tracked C++ and header files
make format-check	Check formatting without changing files
make clean	Remove generated build artifacts