is there a martial art based on an continuous flow of attack?

All arts to some extent acknowledge your opponent will have a window to attack you no matter what your intent is or how attacking minded you are.

That's why xingyiquan covers the center line, always has one hand moving backwards as the other moves forwards (clearing your opponents arms out of the way or dealing with their attack isn't the only reason for this but it is a reason)

Likewise most arts have the intent of destroying your opponent before he can attack you or imposing your will and intent on them to such a degree that you don't care what he does to you.

Xingyiquan is famous for this intent/will but equally other arts have this, Thai fighters are famous for wanting to destroy their opponent impose their will regardless of what is coming back at them for example.

Bak mei has the intent of destroying you imposing their will on you regardless as well