defmodule Aoc2023.Day9 do
  use Aoc2023

  defp prediction(lst) do
    case lst |> Enum.uniq() do
      [val] -> val
      _ -> List.last(lst) + prediction(Enum.zip_with(lst, Enum.drop(lst, 1), &(&2 - &1)))
    end
  end

  def parse(input) do
    input
    |> lines
    |> Enum.map(pipe(String.split() |> Enum.map(&String.to_integer/1)))
  end

  def part1(input) do
    input
    |> Enum.map(&prediction/1)
    |> Enum.sum()
  end

  def part2(input) do
    input
    |> Enum.map(pipe(Enum.reverse() |> prediction))
    |> Enum.sum()
  end
end