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/*
 * This file is part of the OWL API.
 *
 * The contents of this file are subject to the LGPL License, Version 3.0.
 *
 * Copyright (C) 2011, The University of Manchester
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see http://www.gnu.org/licenses/.
 *
 *
 * Alternatively, the contents of this file may be used under the terms of the Apache License, Version 2.0
 * in which case, the provisions of the Apache License Version 2.0 are applicable instead of those above.
 *
 * Copyright 2011, University of Manchester
 *
 * 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 org.semanticweb.owlapi.util;

import org.semanticweb.owlapi.model.OWLDataFactory;
import org.semanticweb.owlapi.model.OWLDataProperty;
import org.semanticweb.owlapi.model.OWLObjectInverseOf;
import org.semanticweb.owlapi.model.OWLObjectProperty;
import org.semanticweb.owlapi.model.OWLObjectPropertyExpression;
import org.semanticweb.owlapi.model.OWLPropertyExpressionVisitor;

/** Author: Matthew Horridge

 * The University Of Manchester

 * Information Management Group

 * Date: 06-Jun-2008

 * 

 * This utility class can be used to obtain an object property expression in its
 * simplest form. Let P be an object property name and PE a property expression,
 * then the simplification is inductively defined as: simp(P) = P simp(inv(P)) =
 * inv(P) simp(inv(inv(PE)) = simp(PE) */
public class ObjectPropertySimplifier {
    private final OWLDataFactory dataFactory;
    private final Simplifier simplifier;

    /** @param dataFactory
     *            datafactory to use */
    public ObjectPropertySimplifier(OWLDataFactory dataFactory) {
        this.dataFactory = dataFactory;
        simplifier = new Simplifier();
    }


    /** Gets an object property expression in its simplest form.
     * 
     * @param prop
     *            The object property expression to be simplified.
     * @return The simplest form of the object property expression. */
    public OWLObjectPropertyExpression getSimplified(OWLObjectPropertyExpression prop) {
        simplifier.reset();
        prop.accept(simplifier);
        if (simplifier.isInverse()) {
            return dataFactory.getOWLObjectInverseOf(simplifier.getProperty());
        } else {
            return simplifier.getProperty();
        }
    }

    private static class Simplifier implements OWLPropertyExpressionVisitor {
        private OWLObjectProperty property;
        private int depth;

        public Simplifier() {}

        public void reset() {
            depth = 0;
            property = null;
        }

        public OWLObjectProperty getProperty() {
            return property;
        }

        public boolean isInverse() {
            return depth % 2 != 0;
        }

        @Override
        public void visit(OWLObjectProperty p) {
            property = p;
        }

        @Override
        public void visit(OWLObjectInverseOf p) {
            depth++;
            p.getInverse().accept(this);
        }

        @Override
        public void visit(OWLDataProperty p) {}
    }
}