package de.yasc.example.petrinet;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import java.util.stream.Collectors;

public final class Petrinet {

    private static final class Place {

        int tokens;

        boolean empty() {
            return tokens <= 0;
        }

        void dec() {
            assert tokens > 0;
            tokens--;
        }

        void inc() {
            tokens++;
        }
    }

    private static final class Transition {

        final List<Place> preset;
        final List<Place> postset;

        public Transition(List<Place> preset, List<Place> postset) {
            this.preset = preset;
            this.postset = postset;
        }

        boolean enabled() {
            return preset.stream().noneMatch(Place::empty);
        }

        void fire() {
            preset.forEach(Place::dec);
            postset.forEach(Place::inc);
        }
    }

    final private Random prng = new Random();
    final private Place[] places;
    final private List<Transition> transitions;

    public Petrinet(int places) {
        this.places = new Place[places];
        for (int i = 0 ; i < places ; i++)
            this.places[i] = new Place();
        transitions = new ArrayList<>();
    }

    public void addTransistion(Integer[] preset, Integer[] postset) {
        transitions.add(new Transition(
                Arrays.stream(preset).map((i) -> places[i]).collect(Collectors.toList()),
                Arrays.stream(postset).map((i) -> places[i]).collect(Collectors.toList())
        ));
    }
    
    public void addMarking(Integer ... marking) {
        Arrays.stream(marking).forEach((i) -> places[i].inc());
    }
    
    public boolean step() {
        var enabledTransitions = transitions.stream().filter(Transition::enabled).collect(Collectors.toList());
        if (enabledTransitions.isEmpty()) {
            return false;
        } else {
            enabledTransitions.get(prng.nextInt(enabledTransitions.size())).fire();
            return true;
        }
    }
    
    public int step(int k) {
        int i = 0;
        while (i < k) {
            if (!step())
                return i;
            ++i;
        }
        return i;
    }
    
    public Integer[] getMarking() {
        final var marking = new ArrayList<Integer>();
        for (int p = 0 ; p < places.length ; p++) {
            marking.addAll(Collections.nCopies(places[p].tokens, p));
        }
        return marking.toArray(new Integer[0]);
    }
}