Blog

Mert Özen's blog posts on software development, backend, frontend, and DevOps.

Series

.NET Core Web API 36 Angular 31 JavaScript Basics 19 JavaScript Intermediate 18 JavaScript Advanced 16 TypeScript Basics 14 TypeScript Intermediate 14 TypeScript Advanced 12 Entity Framework Core 28 Dapper 16 Git & GitHub 29 Web Security (OWASP Top 10) 21 LLM Fundamentals 20 C# Fundamentals 20 Object-Oriented Programming in C# 16 C# Collections and Generics 11 LINQ 17 Asynchronous Programming in C# 17 Advanced C# 14 C# Versions 6 Solution Patterns 22 SOLID and Design Principles 12 Clean Code 13 Design Patterns 23 UML and Modeling 18 Introduction to Software Architecture 9

2 posts found #legacy-code

Newest Oldest Popular

Software Design PART 14

Clean Code in Practice: Cleaning Up a Legacy OrderService Step by Step

The safe way to clean up legacy code is to first pin the current behavior with a small seam and characterization tests, then make every step a separate commit and keep behavior changes in their own fix commits. The post cleans up the 609-line OrderService in 16 commits with green tests at every commit; the highest Cognitive Complexity drops from 92 to 10, and the smells left on purpose are listed with their reasons.

7 Nov 2026 14 min 3

Software Design PART 01

What Is Clean Code? Readability, Cost of Change and the 2025 Second Edition

Clean code is code that works and is also cheap to read and change: in Bookstore's legacy OrderService the same cart yields four different totals because of the Turkish I trap, a drifted copy of the pricing logic and DateTime.Now. The 2025 second edition rewrote the book into Code, Design, Architecture and Craftsmanship parts; this series cleans the 609-line file step by step.

7 Nov 2026 16 min 5