Day5

Mix.install([
  {:req, "~> 0.3.0"}
])

Input

# thanks to https://twitter.com/ryoung786/status/1598415749638397962?s=20&t=TLW9UlzqB9uOYhPjuGQuSQ

day = 5
aoc_session = System.fetch_env!("LB_AOC_SESSION_COOKIE")
input_url = "https://adventofcode.com/2022/day/#{day}/input"

input = Req.get!(input_url, headers: [cookie: "session=#{aoc_session}"]).body

input =
  input
  |> String.split("\n")
  |> Enum.chunk_by(&(&1 == ""))
  |> Enum.reject(&(&1 == [""]))

Main module

defmodule Day5 do
  def run(input, mode \\ :simple) do
    stacks = parse_stacks(input)
    moves = parse_moves(input)

    stacks
    |> apply_moves(moves, mode)
    |> Enum.map(fn {_, [head | _]} -> head end)
    |> Enum.join()
  end

  defp apply_moves(stacks, moves, mode) do
    Enum.reduce(moves, stacks, fn [count, from, to], stacks ->
      from_stack = Map.get(stacks, from)
      moving_values = Enum.take(from_stack, count)
      from_stack = Enum.drop(from_stack, count)

      stacks
      |> push_on_stack(to, moving_values(moving_values, mode))
      |> Map.put(from, from_stack)
    end)
  end

  defp moving_values(moving_values, :simple), do: Enum.reverse(moving_values)
  defp moving_values(moving_values, _), do: moving_values

  defp parse_moves([_, moves]) do
    Enum.map(moves, fn move ->
      [count, from, to] = String.split(move, ["move ", " from ", " to "], trim: true)

      [String.to_integer(count), from, to]
    end)
  end

  defp parse_stacks([stacks, _]) do
    [_ | stacks] =
      stacks
      |> Enum.reverse()
      |> Enum.map(fn s ->
        s
        |> String.codepoints()
        |> Enum.chunk_every(4)
        |> Enum.map(&Enum.join/1)
      end)

    stacks
    |> Enum.reduce(%{}, fn values, stacks ->
      values_with_index =
        Enum.with_index(values, fn v, index ->
          v = String.replace(v, ["[", "]", " "], "")
          ["#{index + 1}", v]
        end)

      Enum.reduce(values_with_index, stacks, fn [index, value], stacks ->
        push_on_stack(stacks, index, [value])
      end)
    end)
  end

  defp push_on_stack(stacks, _index, [""]), do: stacks

  defp push_on_stack(stacks, index, value),
    do: Map.put(stacks, index, value ++ Map.get(stacks, index, []))
end

Part 1

Day5.run(input)

Part 2

Day5.run(input, :bulk)