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/* Copyright (C) 2013-2020 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.api.oracle;

import java.util.Collection;
import java.util.Objects;

import de.learnlib.api.SUL;
import de.learnlib.api.query.DefaultQuery;
import net.automatalib.automata.concepts.Output;
import net.automatalib.automata.fsa.DFA;
import net.automatalib.automata.transducers.MealyMachine;
import net.automatalib.words.Word;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Decides whether the intersection of the language of a given hypothesis and some other language (e.g. from a {@link
 * SUL} is empty. If the intersection is not empty it provides a counterexample, such that it is a word in the
 * intersection. More precisely an emptiness oracle decides whether L(H) ∩ L(SUL) = ∅.
 *
 * @param 
 *         the automaton type
 * @param 
 *         the input type
 * @param 
 *         the output type
 *
 * @author Jeroen Meijer
 */
public interface EmptinessOracle, I, D> {

    default boolean isCounterExample(Output hypothesis, Iterable input, D output) {
        return Objects.equals(hypothesis.computeOutput(input), output);
    }

    @Nullable DefaultQuery findCounterExample(A hypothesis, Collection inputs);

    interface DFAEmptinessOracle extends EmptinessOracle, I, Boolean> {}

    interface MealyEmptinessOracle extends EmptinessOracle, I, Word> {}
}