trigger with logic?

Hey all, I have been working on a HL2 MOD project for a while and am responsible for triggers of a puzzle device. I've already followed some tutorials about triggering a rotating door while getting close or through a button. Now, my short-term goal is to trigger a door's open only when multiple levers(triggers) been pulled up in order or in a pattern. (ex. lever 1 and 3 are up, 2 is down) I am thinking that should I do it in Hammer or through coding? Any idea of where I should get started or giving direction of research is extremely appreciated.

I think it would be easier to do a string of logic entities than code it.

I can imagine that using the input/output system of the button entity can achieve such goal.

You must give very exact clues to the player on the order of these triggers though. Having the player do it by trial and error would be exceedingly frustrating.