defmodule Aoc2023.Day11 do
  use Aoc2023

  def parse(input) do
    coords =
      input
      |> lines
      |> Enum.map(pipe(String.to_charlist() |> Enum.map(&(&1 == ?#))))
      |> Enum.with_index()
      |> Enum.flat_map(fn {row, y} ->
        row
        |> Enum.with_index()
        |> Enum.filter(pipe(elem(0)))
        |> Enum.map(fn {_, x} -> {y, x} end)
      end)

    ys = coords |> Enum.map(pipe(elem(0))) |> MapSet.new()
    empty_rows = MapSet.difference(MapSet.new(0..(ys |> Enum.max())), ys)
    xs = coords |> Enum.map(pipe(elem(1))) |> MapSet.new()
    empty_cols = MapSet.difference(MapSet.new(0..(xs |> Enum.max())), xs)
    fn expansion ->
      coords_ =
        coords
        |> Enum.map(fn {y, x} ->
          {y + Enum.count(empty_rows, &(&1 < y)) * (expansion - 1),
           x + Enum.count(empty_cols, &(&1 < x)) * (expansion - 1)}
        end)

      coords_
      |> Enum.with_index()
      |> Enum.flat_map(fn {c, i} -> coords_ |> Enum.drop(i + 1) |> Enum.map(&{c, &1}) end)
      |> Enum.map(&dist/1)
      |> Enum.sum()
    end
  end

  defp dist({{y1, x1}, {y2, x2}}) do
    abs(x1 - x2) + abs(y1 - y2)
  end

  def part1(input) do
    input.(2)
  end

  def part2(input) do
    input.(1_000_000)
  end
end