il.ac.bgu.cs.bp.bpjs.eventselection.SimpleEventSelectionStrategy Maven / Gradle / Ivy

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package il.ac.bgu.cs.bp.bpjs.eventselection;

import il.ac.bgu.cs.bp.bpjs.bprogram.runtimeengine.BSyncStatement;
import il.ac.bgu.cs.bp.bpjs.events.BEvent;
import il.ac.bgu.cs.bp.bpjs.eventsets.ComposableEventSet;
import il.ac.bgu.cs.bp.bpjs.eventsets.EventSet;
import il.ac.bgu.cs.bp.bpjs.eventsets.Events;
import java.util.ArrayList;
import static java.util.Collections.emptySet;
import static java.util.Collections.singleton;
import java.util.List;
import java.util.Optional;
import java.util.Random;
import java.util.Set;
import java.util.stream.Collectors;
import static java.util.stream.Collectors.toSet;
import org.mozilla.javascript.Context;

/**
 * An event selection strategy that:
 * 
 * Randomly selects an internal event that's requested and not blocked.

 * 
If no such event is available, selects the first external event that's not blocked
 * If no such event is available, returns an empty result.
 * 
 * 
 * Under this strategy, if the selected event is internal, and has {@code equal} events queued externally,
 * these events are not removed.
 * 
 * @author michael
 */
public class SimpleEventSelectionStrategy implements EventSelectionStrategy {
    
    private final Random rnd;
    private final long seed;
    
    public SimpleEventSelectionStrategy( long seed ) {
        rnd = new Random(seed);
        this.seed = seed;
    }
    
    public SimpleEventSelectionStrategy() {
        rnd = new Random();
        seed = rnd.nextLong();
        rnd.setSeed(seed);
    }
    
    
    @Override
    public Set selectableEvents(Set statements, List externalEvents) {
        if ( statements.isEmpty() ) {
            // Corner case, not sure this is even possible.
            return externalEvents.isEmpty() ? emptySet() : singleton(externalEvents.get(0));
        }
        
        EventSet blocked = ComposableEventSet.anyOf(statements.stream()
                .filter( stmt -> stmt!=null )
                .map(BSyncStatement::getBlock )
                .filter(r -> r != Events.emptySet )
                .collect( Collectors.toSet() ) );
        
        Set requested = statements.stream()
                .filter( stmt -> stmt!=null )
                .flatMap( stmt -> stmt.getRequest().stream() )
                .collect( Collectors.toSet() );
        
        // Let's see what internal events are requested and not blocked (if any).
        try {
            Context.enter();
            Set requestedAndNotBlocked = requested.stream()
                    .filter( req -> !blocked.contains(req) )
                    .collect( toSet() );

            return requestedAndNotBlocked.isEmpty() ?
                    externalEvents.stream().filter( e->!blocked.contains(e) ) // No internal events requested, defer to externals.
                                  .findFirst().map( e->singleton(e) ).orElse(emptySet())
                    : requestedAndNotBlocked;
        } finally {
            Context.exit();
        }
    }

    @Override
    public Optional select(Set statements, List externalEvents, Set selectableEvents) {
        if ( selectableEvents.isEmpty() ) {
            return Optional.empty();
        }
        
        BEvent chosen = new ArrayList<>(selectableEvents).get(rnd.nextInt(selectableEvents.size()));
        
        Set requested = statements.stream()
                .filter( stmt -> stmt!=null )
                .flatMap( stmt -> stmt.getRequest().stream() )
                .collect( Collectors.toSet() );
        
        if (requested.contains(chosen)) {
            return Optional.of(new EventSelectionResult(chosen));
        } else {
            // that was an internal event, need to find the first index 
            return Optional.of(new EventSelectionResult(chosen, singleton(externalEvents.indexOf(chosen))));
        }
    }
    
    public long getSeed() {
        return seed;
    }
}