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This artifact provides the implementation of the L* learning algorithm described in the paper "Learning Regular Sets from Queries and Counterexamples" (https://doi.org/10.1016/0890-5401(87)90052-6) by Dana Angluin including variations and optimizations thereof such as the versions based on "On the Learnability of Infinitary Regular Sets" (https://dx.doi.org/10.1006/inco.1995.1070) by Oded Maler and Amir Pnueli or "Inference of finite automata using homing sequences" (http://dx.doi.org/10.1006/inco.1993.1021) by Ronald L. Rivest and Robert E. Schapire.

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/* Copyright (C) 2013-2018 TU Dortmund
 * This file is part of LearnLib, http://www.learnlib.de/.
 *
 * 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 de.learnlib.algorithms.lstar;

import java.util.Collections;
import java.util.List;

import de.learnlib.algorithms.lstar.ce.ObservationTableCEXHandler;
import de.learnlib.algorithms.lstar.ce.ObservationTableCEXHandlers;
import de.learnlib.algorithms.lstar.closing.ClosingStrategies;
import de.learnlib.algorithms.lstar.closing.ClosingStrategy;
import de.learnlib.api.oracle.MembershipOracle;
import de.learnlib.api.query.DefaultQuery;
import de.learnlib.datastructure.observationtable.Row;
import net.automatalib.automata.GrowableAlphabetAutomaton;
import net.automatalib.automata.MutableDeterministic;
import net.automatalib.words.Alphabet;
import net.automatalib.words.Word;

public abstract class AbstractExtensibleAutomatonLStar & GrowableAlphabetAutomaton>
        extends AbstractAutomatonLStar {

    protected final ObservationTableCEXHandler cexHandler;
    protected final ClosingStrategy closingStrategy;
    protected final List> initialPrefixes;
    protected final List> initialSuffixes;

    protected AbstractExtensibleAutomatonLStar(Alphabet alphabet,
                                               MembershipOracle oracle,
                                               AI internalHyp,
                                               List> initialPrefixes,
                                               List> initialSuffixes,
                                               ObservationTableCEXHandler cexHandler,
                                               ClosingStrategy closingStrategy) {
        super(alphabet, oracle, internalHyp);
        this.initialPrefixes = initialPrefixes;
        this.initialSuffixes = initialSuffixes;
        this.cexHandler = cexHandler;
        this.closingStrategy = closingStrategy;
    }

    @Override
    protected void refineHypothesisInternal(DefaultQuery ceQuery) {
        List>> unclosed = cexHandler.handleCounterexample(ceQuery, table, hypothesisOutput(), oracle);
        completeConsistentTable(unclosed, cexHandler.needsConsistencyCheck());
    }

    @Override
    protected List> initialPrefixes() {
        return initialPrefixes;
    }

    @Override
    protected List> initialSuffixes() {
        return initialSuffixes;
    }

    @Override
    protected List> selectClosingRows(List>> unclosed) {
        return closingStrategy.selectClosingRows(unclosed, table, oracle);
    }

    public static final class BuilderDefaults {

        public static  List> initialPrefixes() {
            return Collections.singletonList(Word.epsilon());
        }

        public static  List> initialSuffixes() {
            return Collections.emptyList();
        }

        public static  ObservationTableCEXHandler cexHandler() {
            return ObservationTableCEXHandlers.CLASSIC_LSTAR;
        }

        public static  ClosingStrategy closingStrategy() {
            return ClosingStrategies.CLOSE_FIRST;
        }

    }

}