Improve code quality

I've written this in a hurry for a client on Fiverr, incrementally adding features he asked for. The code is a bit of a mess now. I should add tests and refactor things.

The issue does not name files, tests, or a specific behavior to preserve; it only says the code is messy and needs tests and refactoring. Start by asking the maintainer to identify a small target area and expected test coverage. Done would require an agreed scope, tests for that area, and a refactor that preserves existing behavior.

Written by the indexing model from the issue text.