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The Adobe Experience Manager SDK
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/*
 * Copyright 1997-2008 Day Management AG
 * Barfuesserplatz 6, 4001 Basel, Switzerland
 * All Rights Reserved.
 *
 * This software is the confidential and proprietary information of
 * Day Management AG, ("Confidential Information"). You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Day.
 */
package com.day.cq.search.eval;

import java.util.Comparator;

import javax.jcr.query.Row;

import com.day.cq.search.Predicate;
import com.day.cq.search.facets.FacetExtractor;

/**
 * AbstractPredicateEvaluator is a base implementation for
 * predicate evaluators. Predicate evaluator implementations are encouraged
 * to extend from this abstract base class to minimize migration efforts when
 * new changes are added to the {@link PredicateEvaluator} API.
 *
 * This implementation basically does "nothing":
 * 

 *   returns no xpath expression
 *   does not filter
 *   (implementations have to implement at least one of the two above)
 *   provides no order by properties or order comparator
 *   provides no facet extractor
 *   automatically covers newer interface methods by implementing them using the old methods
 * 
 * 
 * @since 5.2
 */
public abstract class AbstractPredicateEvaluator implements PredicateEvaluator {

    /**
     * Default implementation that always returns null, ie. adds
     * nothing to the XPath query. Subclasses can choose whether they want to
     * implement this method or use the
     * {@link #includes(Predicate, Row, EvaluationContext)} method for advanced
     * filtering (or both).
     */
    public String getXPathExpression(Predicate predicate, EvaluationContext context) {
        // default implementation for subclasses that only implement includes()
        return null;
    }

    /**
     * Default implementation that always returns null.
     */
    public String[] getOrderByProperties(Predicate predicate, EvaluationContext context) {
        return null;
    }

    /**
     * Returns the inverted boolean value of the deprecated
     * {@link #isFiltering(Predicate, EvaluationContext)} method (ie. if not
     * overridden, true).
     */
    public boolean canXpath(Predicate predicate, EvaluationContext context) {
        // capabilities were previously defined solely by isFiltering()
        return !isFiltering(predicate, context);
    }

    /**
     * Returns the same as the deprecated
     * {@link #isFiltering(Predicate, EvaluationContext)} method (ie. if not
     * overridden, false).
     */
    public boolean canFilter(Predicate predicate, EvaluationContext context) {
        // capabilities were previously defined solely by isFiltering()
        return isFiltering(predicate, context);
    }

    /**
     * Default implementation that always returns false, because
     * the {@link #includes(Predicate, Row, EvaluationContext)} also always
     * returns true in this implementation and hence does no
     * filtering at all.
     */
    @Deprecated
    public boolean isFiltering(Predicate predicate, EvaluationContext context) {
        return false;
    }
    
    /**
     * Default implementation that always returns true, ie. it does
     * not "touch" the result set at all.
     */
    public boolean includes(Predicate predicate, Row row, EvaluationContext context) {
        return true;
    }

    /**
     * Default implementation that always returns null.
     */
    public Comparator getOrderByComparator(Predicate predicate, EvaluationContext context) {
        return null;
    }
    
    /**
     * Default implementation that always returns null, ie. no
     * facets will be extracted for the predicate.
     */
    public FacetExtractor getFacetExtractor(Predicate predicate, EvaluationContext context) {
        return null;
    }

}