defmodule Day1 do
  def part1 do
    File.read!("lib/day1/input.txt")
    |> String.split("\n")
    |> Enum.reject(&(&1 == ""))
    |> Enum.map(fn line ->
      {module, _} = Integer.parse(line)
      fuel_for(module)
    end)
    |> Enum.sum()
  end

  def part2 do
    File.read!("lib/day1/input.txt")
    |> String.split("\n")
    |> Enum.reject(&(&1 == ""))
    |> Enum.map(fn line ->
      {module, _} = Integer.parse(line)
      total_fuel(module)
    end)
    |> Enum.sum()
  end

  def total_fuel(mass \\ part1())
  def total_fuel(mass) when mass <= 0, do: mass

  def total_fuel(mass) do
    fuel_mass = fuel_for(mass)
    fuel_mass + total_fuel(fuel_mass)
  end

  def fuel_for(mass) do
    max(Integer.floor_div(mass, 3) - 2, 0)
  end
end