You should try a similar task with a recent model (Opus 4.5, GPT 5.2, etc) and see if there are any improvements since your last attempt. I also encourage using a coding agent. It can use test files that you provide, and perform compile-test loops to work out any mistakes.

It sounds like you used an older model, and perhaps copy-pasted code from a chat session. (Just guessing, based on what you described.)