while (@lines) { 
  $line = shift(@lines);
  ($time, $id, $code) = parse($line);
  $hash{$id}{want} ||= 'open';
  next unless ($hash{$id}{want} eq $code);

  if ($code eq 'open') {
    $hash{$id}{open} = $time;
    $hash{$id}{want} = 'hold';
  } else { 
    $hash{$id}{total} += $time - $hash{$id}{open};
    $hash{$id}{want} = 'open';
    delete $hash{$id}{open};
  }
}