8.exs

defmodule Tree do
  def parse(str) when is_bitstring(str) do
    str |> String.split() |> Enum.map(&String.to_integer/1)
  end

  def nodes_metadata(list)

  def nodes_metadata([]) do
    {[], []}
  end

  def nodes_metadata([0 | [m | t]]) do
    {Enum.take(t, m), Enum.drop(t, m)}
  end

  def nodes_metadata([c | [m | t]]) do
    {cm, nt} =
      Enum.reduce(1..c, {[], t}, fn _, acc ->
        {cm, nt} = nodes_metadata(acc |> elem(1))

        {
          List.flatten(acc |> elem(0), cm),
          nt
        }
      end)

    {metadata, left} = nodes_metadata([0 | [m | nt]])

    {
      List.flatten(metadata, cm),
      left
    }
  end

  def nodes_value(list)

  def nodes_value([]) do
    {0, []}
  end

  def nodes_value([0 | [m | t]]) do
    {Enum.sum(Enum.take(t, m)), Enum.drop(t, m)}
  end

  def nodes_value([c | [m | t]]) do
    {cm, nt} =
      Enum.reduce(1..c, {[], t}, fn _, acc ->
        {cm, nt} = nodes_value(acc |> elem(1))

        {
          List.flatten(elem(acc, 0), [cm]),
          nt
        }
      end)

    {metadata, left} = nodes_metadata([0 | [m | nt]])
    values = Enum.map(metadata, fn index -> Enum.at(cm, index - 1) || 0 end)

    {
      Enum.sum(values),
      left
    }
  end
end

nodes =
  File.read("8.txt")
  |> elem(1)
  |> Tree.parse()

nodes
|> Tree.nodes_metadata()
|> elem(0)
|> Enum.sum()
|> IO.inspect(charlists: :as_lists)

nodes |> Tree.nodes_value() |> elem(0) |> IO.inspect(charlists: :as_lists)