defmodule Day4 do
  def part1 do
    158_126..624_574
    |> Enum.reduce(0, fn n, acc ->
      if test1(n) do
        IO.inspect(n)
        acc + 1
      else
        acc
      end
    end)
  end

  def part2 do
    158_126..624_574
    |> Enum.reduce(0, fn n, acc ->
      if test2(n) do
        IO.inspect(n)
        acc + 1
      else
        acc
      end
    end)
  end

  def test1(n) do
    cl = Integer.to_charlist(n)
    chunks = chunk_by_digits(cl)

    chunks == Enum.sort(chunks) && Enum.any?(chunks, &(length(&1) >= 2))
  end

  def test2(n) do
    cl = Integer.to_charlist(n)
    chunks = chunk_by_digits(cl)

    chunks == Enum.sort(chunks) && Enum.any?(chunks, &(length(&1) == 2))
  end

  def chunk_by_digits(cl, current_chunk \\ [], chunks \\ [])

  def chunk_by_digits([a, b | rest], current_chunk, chunks) do
    rest = [b | rest]

    if a == b do
      chunk_by_digits(rest, [a | current_chunk], chunks)
    else
      chunk_by_digits(rest, [], [Enum.reverse([a | current_chunk]) | chunks])
    end
  end

  def chunk_by_digits([a | []], current_chunk, chunks) do
    Enum.reverse([Enum.reverse([a | current_chunk]) | chunks])
  end
end