View Source Advent of Code Utils

Input fetching and boilerplate generation for Advent of Code.

The goal of this project is to eliminate most of the manual labor involved with working on the yearly Advent of Code challenges.

As a sample, this is the workflow you'd use when working on the challenge of the first of December 2020:

$ mix aoc
* Creating: lib/2020/1.ex
* Creating: input/2020_1.txt
* Creating: input/2020_1_example.txt
Today's challenge can be found at:

Afterwards, lib/2020/1.ex will look as follows:

import AOC

aoc 2020, 1 do
  def p1(input) do

  def p2(input) do

While solving your challenge, you can use the AOC.IEx.p1e/1 and AOC.IEx.p2e/1 helpers in iex to test your solution so far with the example input. Once ready, you can use AOC.IEx.p1i/1 and AOC.IEx.p2i/1 to run your solution on your puzzle input.

The project also optionally supports automatically recompiling your mix project when using the aforementioned helpers, timing your solutions, and boilerplate generation for unit testing your solution modules. It also supports working on puzzles from previous days or years. Check out the docs or the cheatsheet for more information.

Setup & Use

  • Add advent_of_code_utils to your list of dependencies in mix.exs:

    def deps do
        {:advent_of_code_utils, "~> 4.0"}
  • Configure your Advent of Code project in config/config.exs:

    • Store your session cookie. You can find this by inspecting your cookies after logging in to the advent of code website.

      config :advent_of_code_utils, session: "<your cookie>"
    • (Optional) Set auto_compile? to true if you want the various AOC.IEx.p* helpers to recompile your project:

      config :advent_of_code_utils, auto_compile?: true
    • (Optional) Set time_calls? to true if you want the various AOC.IEx.p* helpers to show the runtime of calling a solution.

      config :advent_of_code_utils, time_calls?: true
    • (Optional) Set gen_tests? to true if you want mix aoc.gen to generate unit test code.

      config :advent_of_code_utils, gen_tests?: true
    • (Optional) Configure iex to display charlists as lists. This will prevent lists like [99, 97, 116] to show up as 'cat':

      config :iex, inspect: [charlists: :as_lists]
    • If you follow these steps, your config/config.exs should look as follows:

      import Config
      config :advent_of_code_utils,
        auto_compile?: true,
        time_calls?: true,
        gen_tests?: true,
        session: "<your session cookie>"
      config :iex,
        inspect: [charlists: :as_lists]
  • (Optional) Add import AOC.IEx to your .iex.exs file. This allows you to use the utilities defined in AOC.IEx without specifying the module name.

  • (Optional) Add input/ to your .gitignore file if you use git.

Now that you are set up, you can use mix aoc to work on today's challenge. The day and year of a challenge can be passed in various ways, so this project can still be used when working on older challenges.

If you only want to use this application to fetch the input of a challenge without generating any code, you can skip most of the optional steps above and use mix aoc.get instead of mix aoc.

Example Input

Besides fetching input, mix aoc.get and mix aoc will also fetch example input for the given day. This is done by reading the first code example on the challenge webpage, which is generally that day's example input.

Since this method is not 100% reliable, you may you wish to disable this behaviour. This can be done by passing the --no-example flag to mix aoc or mix aoc.get or by setting fetch_example? to false in your config.exs file.

Time Zones

By default, this project uses your system time (as determined by NaiveDateTime.local_now/0), to determine the current "day". Said otherwise, if your computer says it is currently the 8th of December, mix aoc.get, AOC.IEx.p1/2, and other functions which reason about time will assume it is the 8th day of December. This can be problematic if you live in a time zone which does not align well with the publication time of the AOC puzzles (midnight US Eastern Standard Time).

This problem can be solved by setting the time_zone option of advent_of_code_utils. When this option is set to :aoc, the project will determine the current day based on EST, the time zone of the advent of code servers. When it is said to :local (the default), your system time will be used. Alternatively, a valid time zone string can be supplied, in which case the project will determine the current day based on the provided time zone.

# Use the aoc timezone instead of local time
config :advent_of_code_utils, time_zone: :aoc


This project grew from a collection of utilities I wrote for myself when working on advent of code. I polished these utilities, but it is possible some bugs are still present. If you run into any issue, feel free to create an issue on GitHub.

AoC Automation Guidelines

This tool follows the automation guidelines on the /r/adventofcode community wiki. The following information is intended to specify how we follow these guidelines:

  • All code that communicates with the AoC servers is located in lib/mix/tasks/aoc.get.ex.
  • This tool only communicates with the AoC servers at the request of the user (i.e. when they use mix aoc.get or mix aoc).
  • Fetched inputs are stored locally and are never retrieved again unless the user deletes the retrieved file manually (do_if_file_does_not_exist/2).
  • The User-Agent header is set in fetch/2 and contains my personal contact information and a reference to this repository.