Auto attack player with spell

[Leroy]

Okay so i dont want it to purposely attack players but if im attacked i want it to attack back with a spell. I know you can make it so it attacks them with auto retaliate but thats just my weapon, can i make it so it uses an attack spell without me knowing what the players name is?
Any help is appreciated,
thanks!

Edit:
Also, if someone could make a script in macro that auto says !bless everytime i log in (ex: after death).
thanks!