Immune to special attacks.

I have this spell (ulitmate) that should make my hero immune to all attacks and spells other than melee.

How is this done with triggers and/or jass? (need more than a yes or no )

Spell immunity is no problem, there is an ability for that. But ranged attacks, that's different. If you have a classification to spare (such as aincent or sapper) you can give it to the hero and make all ranged attacks unable to target units with that classification. That's the first and simplest thing I could think of.

There is a passive version of defend out there, you can make it give piercing inmunity.

I also think that hardened skin or resistant skin allows to factor damage from ranged attacks

There is no 'simple' way of making a unit immune to all attacks except for melee? (this includes spells and ranges of all kind)?
I mean how is this done?