{
  my $iterator;
  sub _file_iterator {
    my @files = @_;
    my $f = sub {
      shift @files;
    };
    return $f;
  }

  sub get_next_file {
    my $s = shift;

    if (!$s->{_selected_file}) {
      my @files = @_ ? @_ : $s->get_files;
      $iterator = _file_iterator(@files) if !$iterator;
    }
    my $next_file = $iterator->();
    $s->{_selected_file} = $next_file;
    $iterator = '' if !$next_file;
    return $next_file;
  }
}