aoc2017_day13.ex

defmodule Day13 do
  def part1(), do:
    scanners() |> severities(0) |> Enum.sum()

  def part2(), do:
    0
    |> Stream.iterate(&(&1+1))
    |> Stream.transform(scanners(), &{[severities(&2, &1)], &2})
    |> Stream.take_while(&(not Enum.empty?(&1)))
    |> Enum.count()

  def scanners(), do:
    "input.txt"
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(fn row -> row |> String.split(": ") |> Enum.map(&String.to_integer/1) end)
    |> Enum.map(fn [pos, depth] -> %{pos: pos, depth: depth, interval: 2 * (depth - 1)} end)

  def severities(scanners, start_time), do:
    scanners
    |> Stream.filter(&(rem(start_time + &1.pos, &1.interval) == 0))
    |> Stream.map(&(&1.depth * &1.pos))
end

Day13.part1() |> IO.inspect
Day13.part2() |> IO.inspect