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/* Copyright (C) 2013-2019 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.util.automata.cover;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Iterator;
import java.util.Queue;
import javax.annotation.ParametersAreNonnullByDefault;
import com.google.common.collect.AbstractIterator;
import net.automatalib.automata.DeterministicAutomaton;
import net.automatalib.commons.util.mappings.MutableMapping;
import net.automatalib.words.Word;
/**
* An iterator for the state cover of an automaton. Words are computed lazily (i.e. only when request by {@link
* #next()}.
*
* Supports incremental computation, i.e. given a set of cover traces, only sequences for states not covered by these
* traces are returned.
*
* @param
* automaton state type
* @param
* input symbol type
*
* @author frohme
* @see Covers#stateCover(DeterministicAutomaton, Collection, Collection)
*/
@ParametersAreNonnullByDefault
class IncrementalStateCoverIterator extends AbstractIterator> {
private final DeterministicAutomaton automaton;
private final Collection inputs;
private final Collection> oldCover;
private final MutableMapping> reach;
private final Queue> bfsQueue;
private Iterator inputIterator;
private Record curr;
IncrementalStateCoverIterator(DeterministicAutomaton automaton,
Collection inputs,
Collection> oldCover) {
this.automaton = automaton;
this.inputs = inputs;
this.oldCover = oldCover;
this.reach = automaton.createStaticStateMapping();
this.bfsQueue = new ArrayDeque<>();
}
@Override
protected Word computeNext() {
// first invocation
if (inputIterator == null) {
boolean hasEpsilon = initialize();
curr = bfsQueue.poll();
inputIterator = inputs.iterator();
if (!hasEpsilon) {
return Word.epsilon();
}
}
while (curr != null) {
S state = curr.state;
Word as = curr.accessSequence;
while (inputIterator.hasNext()) {
final I in = inputIterator.next();
final S succ = automaton.getSuccessor(state, in);
if (succ == null) {
continue;
}
if (reach.get(succ) == null) {
Word succAs = as.append(in);
Record succRec = new Record<>(succ, succAs);
reach.put(succ, succRec);
bfsQueue.add(succRec);
return succAs;
}
}
curr = bfsQueue.poll();
inputIterator = inputs.iterator();
}
return endOfData();
}
private boolean initialize() {
Covers.buildReachFromStateCover(reach, bfsQueue, automaton, oldCover, Record::new);
final S init = automaton.getInitialState();
if (reach.get(init) == null) {
// apparently the initial state was not yet covered
Record rec = new Record<>(init, Word.epsilon());
reach.put(init, rec);
bfsQueue.add(rec);
return false;
}
return true;
}
}