Advent of Ruby

A CLI app for doing Advent of Code in Ruby

• Building on an existing gem
• Technical challenges
• Reconnecting with my inner Ruby learner

I’ve been working on Advent of Ruby, a CLI tool for doing Advent of Code in Ruby. Besides the usual features of such tools, it can also show other people’s solutions.

I heard about Advent of Code years ago, but I never had the guts to try it out because I knew I’d give up in the first week. December is stressful enough without 25 days of increasingly difficult code puzzles, where I would inevitably measure my self-worth by how pathetically soon I bail out. (Yeah, I should probably talk to my therapist about that.)

Then it dawned on me that I can ignore the new puzzles in December and simply work on past years’ puzzles at my own leisurely pace at any time of year.

So I solved a few old puzzles and found it enjoyable. Except… there was a lot of juggling files and browser tabs: downloading each puzzle’s input file, creating files for my solution and automated tests, submitting my solution, and looking up other people’s solutions on GitHub and Reddit.

I thought, “I spend a lot of time on this task. I should write a program automating it!”

Building on an existing gem

There are several Advent of Code utility gems out there already. I decided to build on AoC-rb because it’s simple and already does some of what I want with its two core commands:

• aoc bootstrap YEAR DAY downloads the input file, using your session cookie for adventofcode.com that you’ve pasted into .env. Also creates a solution file and a spec file.
• aoc run YEAR DAY runs your solution and shows the resulting answer.

I added two new commands, commit for committing new/modified solutions to Git, and progress for showing overall progress across years.

But mostly I expanded the existing bootstrap and run commands:

• bootstrap additionally creates Markdown files with the puzzle’s instructions and other people’s solutions from Reddit and GitHub.
• run additionally runs specs and can submit your solution to adventofcode.com.
• For both commands, the year and day arguments may be omitted, and will be inferred based on Git history and untracked files.
• For run, the puzzle part can be inferred too, based on whether the instructions file has been re-downloaded to include Part 2 instructions after solving Part 1.

Because of how arguments are inferred like this, the workflow can be as simple as arb bootstrap → arb run repeatedly → arb commit → repeat for the next puzzle. See it in action in the demo video.

Technical challenges

I did a few new things in this project:

• Capturing RSpec output while also printing it was interesting, especially because writing specs for the run command (which, among other things, runs the user’s specs for a puzzle) meant running RSpec from within RSpec 🤪
• Pre-downloading all Advent of Code solutions in Ruby from Reddit and GitHub led to my largest commits ever at over 100k lines.
  • Actually the huge commits were due to VCR cassettes for specs for the secret CLI app within this gem that I built to download Ruby solutions, but which could be used for any language.
• Writing end-to-end specs for a CLI app that has a lot of side effects (creating files, printing output, etc.) was a new experience for me. My other gem Reading has zero side effects because all it does is parse a CSV reading log and return the data. The difference shows in the tests: Reading has 441 tests that run in 0.1 seconds, whereas Advent of Ruby has 32 tests that run in 10 seconds. I could have spent time rearchitecting the gem to make it more unit-testable and not write end-to-end tests for everything, but as I wrote in a commit message, I am just a man and I want to finish this thing before the birth of my second child.

Reconnecting with my inner Ruby learner

I had fun building this gem. It took me back to when I was learning Ruby by doing exercises on Exercism. In fact, Exercism inspired this gem: I wanted to recapture the joy of using a cohesive UI to solve a programming puzzle and then scroll through other people’s Ruby solutions, often having my mind blown by an elegant approach that I never would have thought of.

Also, I know that solving all past Advent of Code will take anywhere from a few years to the rest of my life, but at least now I have more motivation in the fact that I need to make the time that I spent working on this gem worthwhile—though, according to xkcd, the odds are not good.