Rotating Shift Schedule-Auto Populate

Hello,

I've often used forums in the past and contributed to many forums along the way where I had expertise. I was hoping that someone would help me out. I did a quick search and found some useful information but nothing exactly what I am looking for.

I'm not a real advanced Excel user so please bear with me. I work a rotating shift schedule. There are 4 separate shifts, each shift is composed of at least 4 people (some shifts have an extra person due to training).

The shift itself is fairly simple. It consists of rotating 12 hour shifts, 14 days on a month and 14 days off. The shift repeats every 4 weeks. I will graphically attempt to explain how the shift flows:
SchedMap.PNG


The shift template I have created automatically populates the calendar for the given year. On Sheet 1 (information sheet) you input the Weekday of Jan 1 for the year. For example, if you input Wednesday as January 1st the rest of the calendar will auto-populate. Of course, this doesn't account for leap years but I can create a custom one just for the leap year and it should be no problem.

The people will also auto-populate from sheet 1. The hard part I am seeking help with involves inputting the specific shift for each group of people (four shifts A, B, C, and D). I created what I call a "shift map" on sheet 2. I've investigated using Vlookup but where I get stuck is whenever the first day of the year the shift in question is off.

What I'm looking for is for a way that I can populate the first day of the month (starting with January) and have the rest of the sheet auto populate for the whole year. Right now I have each month as a separate sheet but this is not necessary, they can all be on one giant sheet if that helps.

Currently I'm hand entering each shift for each day of the year. As you can see, this is pretty laborious and prone to errors. The finished version of the shift schedule looks like this:
Shift Schedule example Jan2018.PNG

How can I use a function to auto-populate the shift for the rest of the year given that the start of the rotation is known?

I've attached the excel file below.
Thanks for your help.