How do I do a Cast stance to spell cast combo transition?

So I have a casting state, which is initiated by key press. This causes the the character to prepare of casting a chosen spell. I also have a punch action. This makes him attack. But I would like so when he is in casting state, and punch is activated, for him to begin and offensive cast. Not sure how to do this, Any help would be much loved. The end goal is that the character will wait upon casting state for another press to determine whether the the spell is offensive, defensive, or other then will proceed to carry out cast. So, If i hold shift to get ready to cast, then left click, he shoots fireball. But if i press R he will cast heal. But only if i am holding shift.