defmodule Day8 do
  def part1 do
    File.read!("lib/day8/input.txt")
    |> parse_input()
    |> split_into_layers(25, 6)
    |> min_zeros()
    |> ones_times_twos()

    # "123456789012"
    # |> parse_input()
    # |> split_into_layers(3, 2)
    # |> min_zeros()
    # |> ones_times_twos()
  end

  def part2 do
    File.read!("lib/day8/input.txt")
    |> parse_input()
    |> split_into_layers(25, 6)
    |> combine_layers()
    |> Enum.map(fn
      0 -> ?\s
      1 -> ?X
    end)
    |> Enum.chunk_every(25)
    |> Enum.each(&IO.puts/1)

    # "0222112222120000"
    # |> parse_input()
    # |> split_into_layers(2, 2)
    # |> combine_layers()
  end

  def parse_input(str) do
    str
    |> String.trim()
    |> String.to_charlist()
    |> Enum.map(fn digit -> digit - ?0 end)
  end

  def split_into_layers(input, layer_width, layer_height) do
    Enum.chunk_every(input, layer_width * layer_height)
  end

  def min_zeros(layers) do
    layers
    |> Enum.min_by(fn layer ->
      Enum.count(layer, &(&1 == 0))
    end)
  end

  def ones_times_twos(layer) do
    ones = Enum.count(layer, &(&1 == 1))
    twos = Enum.count(layer, &(&1 == 2))
    ones * twos
  end

  def combine_layers(layers) do
    Enum.zip(layers)
    |> Enum.map(&combine_pixel/1)
  end

  def combine_pixel(pixel) do
    0..(tuple_size(pixel) - 1)
    |> Enum.map(fn index -> elem(pixel, index) end)
    |> Enum.reduce(2, fn
      val, 2 -> val
      _, it -> it
    end)
  end
end