// Simulation.java

import java.util.PriorityQueue;

/** Simulation framework
 *  @author Douglas W. Jones
 *  @version 2019-04-12
 */
public class Simulation {

    /** Users create subclasses of Event for each scheduled action
     */
    public abstract class Event {
	/** The time at which the event will happen */
	public float time;

	// the action to be taken when the even occurs
	abstract void trigger();
    }

    // the central organizing data structure of the simulation
    private static final PriorityQueue <Event> eventSet
	= new PriorityQueue <Event> (
	    ( Event e1, Event e2 ) -> Float.compare( e1.time, e2.time )
    );

    /** schedule a new event
     *  <P>The minimal call will look like this:
     *  <P><TT>Simulation.schedule( e );</TT>
     *  <P>More typically, a call will use an anonymous subclass like this:
     *  <P><TT>Simulation.schedule( new Simulation.event() {
     *  <BR>&nbsp; time = ...
     *  <BR>&nbsp; void trigger() { ... }
     *  <BR>} );</TT>
     *  @param e the event to schedule
     */
    public static void schedule( Event e ) {
	eventSet.add( e );
    }

    /** run a simulation
     *  Call this after scheduling at least one event.
     *  <P>The simulation will run until either there are no more events or
     *  some event terminates the program.
     *  From this point on, a typical simulation program will be event driven
     *  with the ordering of computations determined by chronological ordering
     *  of scheduled events.
     */
    public static void run() {
	while (!eventSet.isEmpty()) {
	    Event e = eventSet.remove();
	    e.trigger();
	}
    }
}