All AI in TriadCity is Event-Driven. Actually, Pretty Much Everything in TriadCity is Event-Driven.

All NPC behaviors in TriadCity are event-driven. Not just NPC AI, but all change everywhere in the virtual world, from the motion of subway trains to room descriptions morphing at night to the growth of fruit on trees. Here's a quick sketch of some TC event basics.

In TriadCity every action is encapsulated in an Event object. This is straightforward in OO Land. Take for example player-generated actions. Player Commands are expressed in the server code as Strategy Pattern objects encapsulating the necessary algorithm. Each Command will generate one or more Events as its outcome(s). The Steal command generates a ThiefEvent, which it parameterizes differently depending on success or failure. Commands instantiate the appropriate Event type at the appropriate moment within their algorithms, handing off the new Event instance to the current Room, which propagates it wherever it needs to go.

Here's the structure:

public Interface Event {
        long getID();
        long getEventType();
        long getVisibility();
        String getSourceID();
        String getTargetID();
        String getRoomID();
        String getMessageForSource();
        String getMessageForTarget();
        String getMessageForRoom();
        ....
}

The Steal command populates ThiefEvent with the information shown above and a ton more. The eventType will vary depending whether the Steal succeeds or fails; the assigned visibility will be computed depending on the Thief's Skill level and multiple variables. The messageForSource will be: "You steal the silver coins from the drunken Texan", or "You fail to steal the silver coins from the well-dressed man, and are detected." Appropriate messages are computed for the target and for bystanders in the Room. When ready, the ThiefEvent is passed to the Room, which in turn passes it to everybody and everything currently present.

What happens next?

Up to world authors.

One form of NPC behavior is triggered when Events are received. The Behavior instance tests the Event against its triggering conditions. Am I supposed to fire when the Event is a ThiefEvent and its getEventType() == STEAL_FAILS_EVENT_TYPE and the NPC I'm assigned to is the Event.getTarget()? Or in English, did someone just try to steal from me and fail? If the world author has assigned the TriggeredAttackBehavior to an NPC and given it those trigger conditions, then the victim will attack the Thief when those conditions are met. This is a form of rule-based AI, expressed in OO patterns.

Who'll see what happened? Depends on their SeeSkill and other attributes. If observers are skilled enough, they may be able to watch Thieves stealing from victims. The victim won't see it happen, but observers with high enough SeeSkill might. One of many many forms of character subjectivity in TriadCity.

OO allows TriggeredBehaviors to be niftily flexible. Behaviors can be triggered if they receive any MovementEvent, or only if the MovementEvent.getEventType() == BOW_EVENT_TYPE. So: any movement in your Room and you'll jump to your feet on guard. But, you'll only Bow if someone Bows to you first.

All Behaviors are Event-triggered, even ones which appear random, for instance pigeons moving around the Gray Plaza. Although their movement Behavior is indeed semi-random, it's triggered by a worldwide pulse called the DoBehaviorsEvent, which is propagated everywhere in the game world once per second by an Executor running a background Thread. Every Behavior tests that DoBehaviorsEvent: do I ignore it, or randomly do something, or do something not randomly? TimeEvents trigger actions such as closing shops and going home, and so on.

Events are integral to Player subjectivity. One form this takes is that Player objects include a Consciousness Strategy object via composition. That Consciousness object acts as a filter on the Events passed through it. It has the ability to modify or ignore the Event.getMessageForXYZ() methods it encounters, or generate entirely new ones. This is one of the ways we can make you see things which maybe aren't even "there".

Events in TriadCity are like the chemical "messages" flying around your brain, telling you when to breathe and fire your heart muscle and decide to go online to play games.