Check date in mapping

Hello,

I'm looking for mapping date function

If the month as of now minus 1 the function transfer all the date If the month is not now minus 1 the function send "wrong month".

For example:

If I send today to the function 2007.004 I receive "wrong month"

If I send today to the function 2007.007 I receive 2007.007

Regards

Elad