defmodule AOC.Day3 do
  use AOC.Day, day: 3

  def parse_input(lines), do: lines

  def part1(input) do
    input
    |> Enum.map(fn line ->
      comp_size = line |> String.length() |> div(2)
      {comp1, comp2} = line |> String.to_charlist() |> Enum.split(comp_size)
      comp1 = MapSet.new(comp1)
      comp2 = MapSet.new(comp2)

      MapSet.intersection(comp1, comp2)
      |> MapSet.to_list()
      |> hd()
      |> get_priority()
    end)
    |> Enum.sum()
  end

  def part2(input) do
    input
    |> Enum.chunk_every(3)
    |> Enum.map(fn group ->
      group
      |> Enum.map(&String.to_charlist/1)
      |> Enum.map(&MapSet.new/1)
      |> Enum.reduce(&MapSet.intersection/2)
      |> MapSet.to_list()
      |> hd()
      |> get_priority()
    end)
    |> Enum.sum()
  end

  def get_priority(char) when char >= ?a, do: char - 96
  def get_priority(char), do: char - 38
end