// import java.util.PriorityQueue; must be somewhere above this

/** Simulation framework
 *  @author Douglas W. Jones
 *  @version 2019-03-08
 */
class Simulation {

    // this interface is so we can schedule events with lambda expressions
    public interface Action {
	void trigger( float time );
    }

    // Events are scheduled on the event set
    private static class Event {
	final float time; // the simulated time of the event
	final Action act; // the action to trigger at that time

	Event( float t, Action a ) {
	    time = t;
	    act = a;
	}
    }

    // 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
     *  @param t the time at which the event should occur
     *  @param a the Action that should occur at that time
     *  A typical call will look like this
     *  Simulation.schedule( someTime, (float t)->codeToRunAt( t ) );
     *  That is, the Action will be constructed by a lambda expression
     */
    public static void schedule( float t, Action a ) {
	eventSet.add( new Event( t, a ) );
    }

    /** run a simulation
     *  Call this after scheduling at least one event.
     *  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.act.trigger( e.time );
	}
    }
}