[VladVladikoff]

I would love to try this out. I have a horrible legacy project that is written in angular by a really amateur developer, full of huge blocks of copy pasted code that has minor modifications in each block. I’ve tried before to get an LLM to rewrite it to something more sensible, but I have not succeeded, usually it just ends up breaking everything. Is there a guide or some system to follow? What’s the best way to accomplish a task like this?

[jaggederest]

I think one way is to take the existing system in something like a docker container or equivalent, some kind of black box, and write tests against it in pure HTTP calls or using browser automation to record (can drive it with AI). When you've reached a truly massive test suite that covers everything, you delete the container and use the test suite as an oracle for writing a new version (open book, the AI can look at the test suite but not change it).

This is a tactic based on things I have read in "Working Effectively with Legacy Code" by Michael Feathers - he discusses using cut points to build a testing firewall to bring code under test, then gradually expanding the test suite from that beachhead of confirmed interface.

[astrange]

I've been very successful so far using Sonnet 4.6 (1M) as the basic model in Claude Code, plus Codex and gemini-review plugins for second/third opinions. (The last one is somewhat busted and hardcoded old gemini versions, I should patch it up.)

I needed to use Opus 4.7 for one project because it used very recent APIs, and it certainly is smart but it's also very expensive.

[rurban]

Normal engineering practices as thought since the 70ies.

Break the problems up into manageable pieces. Make a plan, have tests to verify the outcome, implement that part. Rinse and repeat. Have integration tests.

[phpnode]

I have an approach that can handle this if you're interested? My email is in my profile.