defmodule Day3 do
  def init_state(part) do
    %{sum: 0, part: part}
  end

  defp find_duplicates(line) do
    line
    |> String.to_charlist()
    |> Enum.chunk_every(Integer.floor_div(String.length(line), 2))
    |> Enum.map(&MapSet.new/1)
    |> then(fn [a, b] -> MapSet.intersection(a, b) end)
    |> MapSet.to_list()
  end

  defp to_priority(c) do
    if is_nil(c) do
      0
    else
      if c < 97 do
        c - 38
      else
        c - 96
      end
    end
  end

  def execute(line, state) do
    increment_sum = fn s -> Map.update(state, :sum, 0, &(&1 + s)) end

    trimmed = line |> String.trim()

    unless String.length(trimmed) == 0 do
      trimmed
      |> find_duplicates()
      |> Enum.map(&to_priority(&1))
      |> Enum.reduce(&(&1 + &2))
      |> increment_sum.()
    else
      state
    end
  end

  def get_answer(state) do
    state.sum
  end
end