How to automatically manage backup files (with retention)

I would like to automate my backup-management workflow for certain applications, but I couldn't find out how to do this on Mac OSX 10.10:

Lets say an application creates its backup files into a directory with several subdirectories by date. Those subdirs then contain the important backup files:

backup_dir 15_01_13 backup_data.dat backup_data2.dat

    15_01_14 
           backup_data.dat 
           backup_data2.dat 

    15_01_15 
           backup_data.dat 
           backup_data2.dat 
 

Lightroom for example does this.

How can I automatically manage these backups if I want to delete every directory/file older than 1 week, but only if I have 2 complete backups left? I recently purchased Hazel, but it seems that the subdirectories are a problem regarding the additional check clause "if at least 2 backups are left".

Can this be done by a combination of AppleScript and Hazel or the like?

Thanks for every help!