Spell Resistance

Anyone figured out a system which resist some of the damage?

I could probably figure this out by myself but It would be alot of trigger, if someone already made this maybe you can tell me how you did.

A unit has different resistance types (fire,nature,ice,air)
Some spells are based by only one of those elements, some are based of 2 or 3.
If the unit has for example 30 fire resistance and the caster casts an fire spell its:

(Fire) 30/100 = 0,3 x damage of spell

And if the spell is based on fire and air and the units has 30 fire res. and 20 air res.
It would be:
(Fire) 30/100 = 0,3
(Air) 20/100 = 0,2 + 0,3 x damage of spell
(Probably has to change this last one)

IT would be easy if we had a GetEventDamageType() event response.

Changing damage gotten is not anything difficult actually, I 've done that with pasive manashield and with Amplify Damage.

Another way would be making all the spells enhanced with triggers, and to use things like the caster system's damage option for damage factor on abilities

Well in the map Im making, the spell damage is actually made in triggers.
I could figure out how to do this system but it would be alot of big triggers.
I just wonder if anyone could show me an example of this made in small triggers.
(I cant use JASS or GUI)