How I Refactored a Monolithic Code Base Into an Add-In Architecture

Before my first professional job, I would listen to developers talk about what it was like to work on someone else's messy code that consisted of anti-patterns. They would tell horror stories. Then, I took my second assignment as a fresh Dotnet developer, and that horror was exactly what I had been scared of. My new job was to integrate engineering rule sets into an engineering application. The application was already developed and running with a library with three rule sets.