Trigger Help - A Spell

[Damien8]

The GUI doesn't seem to be capable of running the spell I'm trying to make and I'm unfamiliar with JASS. Please help?

The spell has two levels. At level 1 it lasts 20 seconds. At level 2 is lasts 30.

While active, whenever the caster takes damage he deals that much damage to every enemy within a range of 600 of him.

How do I make this happen, whether in the GUI or in JASS?

 

[terradont]

Well, there is a unit takes damage event, but it must be added through another trigger, and this leaks. I'm not sure how to fix this leak.
Whenever a unit learns the spell, add the event (unit takes damage) to your main trigger. There, pick all units around the (damaged unit) and order (damaged unit) to deal (damage dealt) to (picked unit)