/* Copyright (C) 2013-2018 TU Dortmund
 * This file is part of AutomataLib, http://www.automatalib.net/.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.automatalib.automata.base.fast;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import net.automatalib.automata.GrowableAlphabetAutomaton;
import net.automatalib.automata.ShrinkableAutomaton;
import net.automatalib.automata.UniversalFiniteAlphabetAutomaton;
import net.automatalib.automata.base.StateIDDynamicMapping;
import net.automatalib.automata.concepts.StateIDs;
import net.automatalib.automata.helpers.StateIDStaticMapping;
import net.automatalib.commons.util.mappings.MutableMapping;
import net.automatalib.commons.util.nid.DynamicList;
import net.automatalib.commons.util.nid.IDChangeNotifier;
import net.automatalib.words.Alphabet;
import net.automatalib.words.impl.Alphabets;

public abstract class AbstractFastMutableNondet<S extends AbstractFastNondetState<T>, I, T, SP, TP>
        implements ShrinkableAutomaton<S, I, T, SP, TP>,
                   UniversalFiniteAlphabetAutomaton<S, I, T, SP, TP>,
                   StateIDs<S>,
                   GrowableAlphabetAutomaton<I> {

    private final DynamicList<S> states = new DynamicList<>();
    private final IDChangeNotifier<S> tracker = new IDChangeNotifier<>();

    private final Set<S> initialStates = new HashSet<>();

    protected Alphabet<I> inputAlphabet;

    public AbstractFastMutableNondet(Alphabet<I> inputAlphabet) {
        this.inputAlphabet = inputAlphabet;
    }

    @Override
    public int getStateId(S state) {
        return state.getId();
    }

    @Override
    public S getState(int id) {
        return states.get(id);
    }

    @Override
    public Set<S> getInitialStates() {
        return initialStates;
    }

    @Override
    public <V> MutableMapping<S, V> createDynamicStateMapping() {
        StateIDDynamicMapping<S, V> mapping = new StateIDDynamicMapping<>(this);
        tracker.addListener(mapping, true);
        return mapping;
    }

    @Override
    public Collection<T> getTransitions(S state, I input) {
        int inputIdx = inputAlphabet.getSymbolIndex(input);
        return state.getTransitions(inputIdx);
    }

    @Override
    public void clear() {
        states.clear();
        initialStates.clear();
    }

    @Override
    public S addState(SP property) {
        S newState = createState(property);
        states.add(newState);
        return newState;
    }

    @Override
    public void setInitial(S state, boolean initial) {
        if (initial) {
            initialStates.add(state);
        } else {
            initialStates.remove(state);
        }
    }

    @Override
    public void setTransitions(S state, I input, Collection<? extends T> transitions) {
        int inputIdx = inputAlphabet.getSymbolIndex(input);
        state.setTransitions(inputIdx, transitions);
    }

    @Override
    public void removeAllTransitions(S state) {
        state.clearTransitions();
    }

    protected abstract S createState(SP property);

    @Override
    public void removeState(S state, S replacement) {
        ShrinkableAutomaton.unlinkState(this, state, replacement, inputAlphabet);
        states.remove(state);
        if (initialStates.remove(state)) {
            initialStates.add(state);
        }
    }

    @Override
    public Alphabet<I> getInputAlphabet() {
        return inputAlphabet;
    }

    @Override
    public void addAlphabetSymbol(I symbol) {
        if (this.inputAlphabet.containsSymbol(symbol)) {
            return;
        }

        this.inputAlphabet = Alphabets.withNewSymbol(this.inputAlphabet, symbol);
        final int newAlphabetSize = this.inputAlphabet.size();

        for (final S s : this.getStates()) {
            s.ensureInputCapacity(newAlphabetSize);
        }
    }

    @Override
    public Collection<S> getStates() {
        return states;
    }

    @Override
    public <V> MutableMapping<S, V> createStaticStateMapping() {
        return new StateIDStaticMapping<>(this, size());
    }

    @Override
    public StateIDs<S> stateIDs() {
        return this;
    }

}

@@ -730,24 +730,54 @@
 Collection;%0A
+import java.util.Collections;%0A
 import java.
@@ -2719,38 +2719,60 @@
 input);%0A        
-return
+final Collection%3CT%3E result =
  state.getTransi
@@ -2788,16 +2788,81 @@
 utIdx);%0A
+        return result == null ? Collections.emptySet() : result;%0A
     %7D%0A%0A 

fix NPE on partial NFAs