Test for current AC power status

Hello All...
Is there a way to test for the current status of AC power?  I need a rule to test whether or not AC is currently active before the rule is executed.  For example:
 
Whenever sunset
AND AC Power is OK
THEN do something
 
It is important that the task does not execute when AC is down even though the Elk is running on battery backup. 
 
Thanks for your help.

whenever sunset
  and ac failure trouble exists
 
As an 'and' clause, it doesn't look like you can't check for AC is OK.
 
Of course by saying 'whenever sunset' its not going to do much good if the AC fails between sunset and sunrise as it won't be detected.  That rule is only executed once a day at sunset, and that may be your intent.
 
Creative use of rules and pseudo outputs as flags may get you what you want.