defmodule Aoc2023.Day8 do
  require Integer
  use Aoc2023

  def parse(input) do
    input
    |> String.split("\n\n")
    |> then(fn [directions, map] ->
      {
        directions |> String.to_charlist() |> Enum.map(&%{?L => 0, ?R => 1}[&1]),
        map
        |> lines
        |> Enum.map(&Regex.run(~r/(\w+) = \((\w+), (\w+)\)/, &1, capture: :all_but_first))
        |> Enum.map(fn [src, dst1, dst2] -> {src, {dst1, dst2}} end)
        |> Enum.into(%{})
      }
    end)
  end

  defp run({directions, map}, node, filter) do
    directions
    |> Stream.cycle()
    |> Stream.scan(node, fn dir, pos -> map[pos] |> elem(dir) end)
    |> Enum.find_index(filter)
    |> Kernel.+(1)
  end

  def part1({directions, map}) do
    if map["AAA"], do: run({directions, map}, "AAA", &(&1 == "ZZZ"))
  end

  def part2({directions, map}) do
    map
    |> Enum.map(pipe(elem(0)))
    |> Enum.filter(pipe(String.ends_with?("A")))
    |> Enum.map(&run({directions, map}, &1, pipe(String.ends_with?("Z"))))
    |> lcm
  end
end