something like
Code:
/run for i=1,40 do local B=UnitBuff("target",i); if B then print(i.."="..B) end end
can be done to print out the name of all the buff on the target. The bad part is blizzard has pretty much removed all functionality, from the macro side of the house, to do anything useful with this information. In short you can not cast anything based on ingame logic controls, or tests. You can however write or use an existing addon that can modify a button on the fly that will provide this functionality. Check out something like SmartBuff on the addon site of your chosing.