Conditional String Concatenation based on different cell being empty or not

I am trying to fill a cell with a certain concatenated string if a different cell is empty and if that 2nd cell is not empty, then I will use a different concatenated string.

For example:

A1...........................A2.....................A3...............................A4 would be:

Bob.........................01.....................Black Light.....................(Bob 01) Black Light
......................................................A Time to Hunt...............A Time to Hunt


I think I can figure out the concatenation pieces, but not the conditional bits (I'm a Excel novice - or whatever is less than a novice).

TIA