Find files from ref dir that are not present in target dir

compare_dirs.ex

defmodule CompareDirs do

  def compare(ref, target) do
    ref_list = md5_dir(ref)
    target_list = md5_dir(target)

    Enum.reduce(ref_list, [], fn({path, hash}, acc) ->
      case Enum.find(target_list, fn({_t_path, t_hash}) -> t_hash == hash end) do
        true -> acc
        _    -> acc ++ [path]
      end
    end)
  end

  def md5_dir(path) do
    ls_r(path)
    |> Enum.map(fn x -> {x, md5_file(x)} end)
  end

  def ls_r(path \\ ".") do
    cond do
      File.regular?(path) -> [path]
      File.dir?(path) ->
        File.ls!(path)
        |> Enum.map(&Path.join(path, &1))
        |> Enum.map(&ls_r/1)
        |> Enum.concat
      true -> []
    end
  end

  def md5_file(path) do
    File.stream!(path,[],2048)
    |> Enum.reduce(:crypto.hash_init(:md5), fn(line, acc) -> :crypto.hash_update(acc,line) end)
    |> :crypto.hash_final
    |> Base.encode16
  end

end