/* This file is part of the OWL API.
 * The contents of this file are subject to the LGPL License, Version 3.0.
 * Copyright 2014, 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.
 * 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 static org.semanticweb.owlapi.util.OWLAPIPreconditions.checkNotNull;

import java.util.List;

import javax.annotation.Nullable;

import org.semanticweb.owlapi.model.AddAxiom;
import org.semanticweb.owlapi.model.OWLAxiomChange;
import org.semanticweb.owlapi.model.OWLAxiomVisitor;
import org.semanticweb.owlapi.model.OWLOntology;
import org.semanticweb.owlapi.model.OWLOntologyChange;
import org.semanticweb.owlapi.model.OWLOntologyChangeVisitor;
import org.semanticweb.owlapi.model.RemoveAxiom;

/**
 * Provides a convenient method to filter add/remove axiom changes based on the type of axiom that
 * is being added or removed from an ontology.<br>
 * The general pattern of use is to simply create an instance of the {@code OWLOntologyChangeFilter}
 * and override the appropriate visit methods corresponding to the types of axioms that are of
 * interest. Each visit corresponds to a single change and the {@code isAdd} or {@code isRemove}
 * methods can be used to determine if the axiom corresponding to the change is being added or
 * removed from an ontology - the ontology can be obtained via the {@code getOntology} method.<br>
 * Example: Suppose we are interested in changes that alter the domain of an object property. We
 * receive a list of changes, {@code ontChanges}, from an ontology change listener. We can use the
 * {@code OWLOntologyChangeFilter} to filter out the changes that alter the domain of an object
 * property in the following way:<br>
 *
 * <pre>
 * OWLOntologyChangeFilter filter = new OWLOntologyChangeFilter() {
 * <br>
 *      // Override the object property domain visit method
 *      public void visit(OWLObjectPropertyDomainAxiom axiom) {
 *          // Determine if the axiom is being added or removed
 *          if(isAdd()) {
 *              // Get hold of the ontology that the change applied to
 *              OWLOntology ont = getOntology();
 *              // Do something here
 *          }
 *      }
 * }
 * // Process the list of changes
 * filter.processChanges(ontChanges);
 * </pre>
 *
 * @author Matthew Horridge, The University Of Manchester, Bio-Health Informatics Group
 * @since 2.0.0
 */
public class OWLOntologyChangeFilter implements OWLAxiomVisitor, OWLOntologyChangeVisitor {

    protected boolean add;
    @Nullable
    protected OWLOntology ontology;

    /**
     * @param changes changes to process
     */
    public void processChanges(List<? extends OWLOntologyChange> changes) {
        checkNotNull(changes, "changes cannot be null");
        changes.forEach(c -> c.accept(this));
    }

    protected void processChange(OWLAxiomChange change) {
        checkNotNull(change, "change cannot be null");
        ontology = change.getOntology();
        change.getAxiom().accept(this);
        ontology = null;
    }

    /**
     * @return Determines if the current change caused an axiom to be added to an ontology.
     */
    protected boolean isAdd() {
        return add;
    }

    /**
     * @return Determines if the current change caused an axiom to be removed from an ontology.
     */
    protected boolean isRemove() {
        return !add;
    }

    /**
     * Gets the ontology which the current change being visited was applied to.
     *
     * @return The ontology or {@code null} if the filter is not in a change visit cycle. When
     * called from within a {@code visit} method, the return value is guarenteed not to be {@code
     * null}.
     */
    @Nullable
    protected OWLOntology getOntology() {
        return ontology;
    }

    @Override
    public void visit(AddAxiom change) {
        add = true;
        processChange(change);
    }

    @Override
    public void visit(RemoveAxiom change) {
        add = false;
        processChange(change);
    }
}