defmodule Print do

  def start(file, width, height) do
    pid = spawn(fn -> init(file, width, height) end)
    {:ok, pid}
  end

  def init(file, width, height) do
    {:ok, fd} = File.open(file, [:write])
    IO.puts(fd, "P6")
    IO.puts(fd, "#generated by ppm.ex")
    IO.puts(fd, "#{width} #{height}")
    IO.puts(fd, "255")
    rows(height, 1, width, fd)
    IO.puts("Image #{file} printed!")
    File.close(fd)
  end

  defp rows(0, _, _, _fd), do: :ok
  defp rows(h, n, w, fd) do
    receive do
      :go ->
	### the server has sent a row to a client
        :ok
    end

    receive do
      {:row, ^n, row} ->
        chars = row(row)
        IO.write(fd, chars)
        rows(h - 1, n + 1, w, fd)
    after
      1000 ->
        black =
          List.foldr(Enum.to_list(1..w), [], fn _, a ->
            [0, 0, 0 | a]
          end)

        IO.write(fd, black)
        rows(h - 1, n + 1, w, fd)
    end
  end

  defp row(row) do
    List.foldr(row, [], fn {:rgb, r, g, b}, a ->
      [r, g, b | a]
    end)
  end

end