defmodule Pdf.RefTable do
  @moduledoc false
  def to_iolist(objects, offset \\ 0) do
    {objects_iolist, offset} = objects_to_iolist(objects, offset)

    {[
       "xref\n",
       "0",
       " ",
       to_string(length(objects) + 1),
       "\n",
       first_reference(),
       objects_iolist
     ], offset}
  end

  defp first_reference, do: "0000000000 65535 f \n"

  defp objects_to_iolist(list, offset, acc \\ [])
  defp objects_to_iolist([], offset, acc), do: {Enum.reverse(acc), offset}

  defp objects_to_iolist([object | tail], offset, acc) do
    size = object |> Pdf.Export.to_iolist() |> :binary.list_to_bin() |> byte_size()
    iolist = object_to_ref(object, offset)
    offset = offset + size
    objects_to_iolist(tail, offset, [iolist | acc])
  end

  defp object_to_ref(object, offset) do
    [
      String.pad_leading(to_string(offset), 10, "0"),
      " ",
      String.pad_leading(object.generation, 5, "0"),
      " n \n"
    ]
  end
end