Day 13

Mix.install([
  {:kino, "~> 0.6.2"}
])

Input

input = Kino.Input.textarea("In put here:")

[points, instructions] =
  input
  |> Kino.Input.read()
  |> String.split("\n\n", trim: true)

folds =
  instructions
  |> String.split("\n", trim: true)
  |> Enum.map(&(String.slice(&1, 11..-1) |> String.split("=")))
  |> Enum.map(fn [a, b] -> {String.to_atom(a), String.to_integer(b)} end)

coords =
  points
  |> String.split("\n")
  |> Enum.map(fn x ->
    [x, y] = String.split(x, ",", trim: true)
    {String.to_integer(x), String.to_integer(y)}
  end)

defmodule Paper do
  def fold(paper, {:x, loc}) do
    Enum.map(paper, fn
      {x, y} when x > loc ->
        {2 * loc - x, y}

      {x, y} ->
        {x, y}
    end)
    |> Enum.uniq()
  end

  def fold(paper, {:y, loc}) do
    Enum.map(paper, fn
      {x, y} when y > loc ->
        {x, 2 * loc - y}

      {x, y} ->
        {x, y}
    end)
    |> Enum.uniq()
  end

  def print(paper, fold \\ %{}) do
    IO.puts("============")
    xs = paper |> Enum.map(&elem(&1, 0))
    ys = paper |> Enum.map(&elem(&1, 1))

    for y <- 0..Enum.max(ys) do
      [
        Integer.to_charlist(y),
        ' '
        | for x <- 0..Enum.max(xs) do
            cond do
              fold[:y] == y -> '--'
              fold[:x] == x -> '||'
              {x, y} in paper -> '##'
              true -> '  '
            end
          end
      ]
      |> Enum.concat()
      |> IO.puts()
    end

    IO.puts("============")
  end
end

Part 1

[first | rest] = folds

fold = IO.inspect([first] |> Enum.into(%{}))
IO.inspect(fold[:x])

coords |> Paper.fold(first) |> Enum.count()

fold[:x] == 655

Part 2

Enum.reduce(folds, coords, fn fold, acc ->
  Paper.fold(acc, fold) |> tap(&Paper.print(&1, [fold] |> Enum.into(%{})))
end)
|> Paper.print()