Shift Rotation schedule pattern filled automatic yearly

HI there experts,

I used a worksheet for managing a year shift-rotation schedule for four shifts (A, B, C and D) with 4 days working pattern through 12 hr per day for a shift (DAY and NIGHT shifts) and the other two shifts on REST and REST ON CALL. I created a formula to fill the calendar each month by matching day with date formula (i.e: 1 Jan 2017 is Sunday) then i have to fill the working shift manually in each day for the whole year with a pattern AAAADDDDBBBBCCCC.
The question is: I need a formula or a macro to fill this automatically when i enter the year by stating for example which shift has ended the last year or any other ideas to accomplish that.

I am trying to attach a worksheet