Please Assist. Enemy Artificial Intelligence. ( A.I. )

Alright So I tried to find tutorials on the web about this but the people that made the tutorials were making them for extremely basic and simple AI. I am looking for an ai system that implements LOS (Line of Sight) and Aggro. I want an enemy to be say 10 meters away and then the LOS kicks in and he chases me and if close enough initializes combat. Secondly I want the AI to change target based on damage dealt and healing dealt. If the damage dealer is doing more damage than the tank is taunting. then the damage dealer gets the aggro. I'll do all the work and research and even follow tutorials all I ask is if anyone knows of how to do this then give me a quick idea on how to. Or send me a link to a tutorial. Thanks!