"A" shift vs "B" shift work days into calendar

[RonNCmale]

Attached is a calendar that two shifts work "A" and "B" shift. There is a pattern to the work schedule when A is working B is off and vise versa. The pattern goes first week AA BB AAA; Second week BB AA BBB and then it starts over; Third Week AA BB AAA; forth week BB AA BBB. Is their a simple code that can insert the shift scheduled to work without having to manually do it.

Thanks in Advance.
Note: I started it manually to give an idea of the pattern.