defmodule Solver.Day6 do
  def marker([_h | tail] = line, distinct, counter) do
    line
    |> Enum.take(distinct)
    |> MapSet.new()
    |> MapSet.size()
    |> Kernel.then(fn amount ->
      case amount do
        ^distinct -> counter
        _ -> marker(tail, distinct, counter + 1)
      end
    end)
  end

  def start(msg, distinct) do
    String.graphemes(msg) |> marker(distinct, distinct) |> IO.puts()
  end
end

case File.read("input") do
  {:ok, body} ->
    Solver.Day6.start(body, 4)
    Solver.Day6.start(body, 14)

  {:error, reason} ->
    IO.puts(reason)
end