Advent of Code 2016 - Day 8

Mix.install([
  {:kino, "~> 0.10.0"}
])

Input

raw_input = Kino.Input.textarea("Paste Input:")

input_lines = raw_input |> Kino.Input.read() |> String.split("\n")

defmodule InputParse do
  import String, only: [to_integer: 1]

  def to_dims(d) do
    String.split(d, "x")
    |> Enum.map(&to_integer/1)
    |> List.to_tuple()
  end

  def parse(data), do: Enum.map(data, &parse_line(String.split(&1, " ")))

  def parse_line(["rect", d]), do: {:rect, to_dims(d)}
  def parse_line([_, _, "y=" <> y, _, by]), do: {:row, to_integer(y), to_integer(by)}
  def parse_line([_, _, "x=" <> x, _, by]), do: {:column, to_integer(x), to_integer(by)}
end

defmodule Grid do
  @on "█"
  @off "."
  @width 50
  @height 6

  def new() do
    for w <- 0..(@width - 1), h <- 0..(@height - 1), into: %{} do
      {{w, h}, @off}
    end
  end

  def operation(grid, {:rect, {w, h}}) do
    for x <- 0..(w - 1), y <- 0..(h - 1), reduce: grid do
      acc -> %{acc | {x, y} => @on}
    end
  end

  def operation(grid, {:row, at, by}) do
    grid
    |> line_by_row(at)
    |> Map.new(fn {{x, y}, _} ->
      {{rem(x + by, @width), y}, grid[{x, y}]}
    end)
    |> then(&amp;Map.merge(grid, &amp;1))
  end

  def operation(grid, {:column, at, by}) do
    grid
    |> line_by_column(at)
    |> Map.new(fn {{x, y}, _} ->
      {{x, rem(y + by, @height)}, grid[{x, y}]}
    end)
    |> then(&amp;Map.merge(grid, &amp;1))
  end

  def display(grid) do
    for h <- 0..(@height - 1) do
      for w <- 0..(@width - 1) do
        IO.write(grid[{w, h}])
      end

      IO.puts("")
    end

    IO.puts("")

    :ok
  end

  defp line_by(grid, n, xy), do: Map.filter(grid, fn {k, _} -> elem(k, xy) == n end)
  defp line_by_column(grid, at), do: line_by(grid, at, 0)
  defp line_by_row(grid, at), do: line_by(grid, at, 1)

  def run(input) do
    process =
      input
      |> InputParse.parse()
      |> Enum.reduce(Grid.new(), fn op, acc ->
        Grid.operation(acc, op)
      end)

    {Enum.count(process, fn {_, v} -> v == @on end), display(after_lit)}
  end
end

Grid.run(input_lines)