defmodule Two do
  def calculate(file) do
    file
    |> File.read!()
    |> String.split("\n")
    |> Stream.reject(&(&1 == ""))
    |> Stream.reject(&is_nil/1)
    |> Stream.map(&String.to_integer/1)
    |> Stream.cycle()
    |> Enum.reduce_while({0, MapSet.new()}, fn i, {current_frequency, seen} ->
      new_frequency = current_frequency + i

      if MapSet.member?(seen, new_frequency) do
        {:halt, new_frequency}
      else
        {:cont, {new_frequency, MapSet.put(seen, new_frequency)}}
      end
    end)
  end
end