defmodule Adam7 do
  @doc """
  Merge the extracted seven passes into a corresponding image.
  """
  def merge(passes, {width, height}) do
    Enum.reduce(1..7, empty_image_rows(width, height), fn (pass, image_rows) ->
      Adam7.Pass.merge(pass, {width, height}, Enum.at(passes, pass-1), image_rows)
    end)
    |> :array.to_list
    |> Enum.map(&:array.to_list/1)
  end

  defp empty_image_rows(width, height) do
    :array.new([
      {:size, height},
      {:fixed, true},
      {:default, :array.new([
          {:size, width},
          {:fixed, true}
        ])
      }
    ])
  end
end