SearchHTMLExcerpt

/**
 * This file Copyright (c) 2015 Magnolia International
 * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
 *
 *
 * This file is dual-licensed under both the Magnolia
 * Network Agreement and the GNU General Public License.
 * You may elect to use one or the other of these licenses.
 *
 * This file is distributed in the hope that it will be
 * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
 * implied warranty of MERCHANTABILITY or FITNESS FOR A
 * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
 * Redistribution, except as permitted by whichever of the GPL
 * or MNA you select, is prohibited.
 *
 * 1. For the GPL license (GPL), you can redistribute and/or
 * modify this file under the terms of the GNU General
 * Public License, Version 3, as published by the Free Software
 * Foundation.  You should have received a copy of the GNU
 * General Public License, Version 3 along with this program;
 * if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * 2. For the Magnolia Network Agreement (MNA), this file
 * and the accompanying materials are made available under the
 * terms of the MNA which accompanies this distribution, and
 * is available at http://www.magnolia-cms.com/mna.html
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package info.magnolia.jackrabbit.lucene;

import java.io.IOException;
import java.util.Set;

import org.apache.jackrabbit.core.query.lucene.AbstractExcerpt;
import org.apache.jackrabbit.core.query.lucene.DefaultHighlighter;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermPositionVector;

/**
 * Provides an HTML excerpt highlighting the searched term. By default it will strip all HTML tags and jcr identifiers which might have been indexed.
 * Suppose you were searching for "foo" and the text found containing it is something like
 *
 * <pre>
 * &lt;p&gt;This is an "excerpt" &lt;em&gt;highlighting&lt;/em&gt; the word foo deadbeef-face-babe-cafe-babecafebabe...
 * </pre>
 *
 * it produces a result like the following which can then be used e.g. in a search result page.
 *
 * <pre>
 * &lt;div class="excerpt"&gt;
 *  &lt;span class="excerpt-fragment"&gt;This is an excerpt highlighting the word &lt;strong&gt;foo&lt;/strong&gt;...&lt;/span&gt;
 * &lt;div&gt;
 *
 * </pre>
 */
public class SearchHTMLExcerpt extends AbstractExcerpt {

    private static final String UUID_REGEX = "(jcr:)?[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12}";

    private final NoXMLEscapeHighlighter highlighter = new NoXMLEscapeHighlighter();

    @Override
    protected String createExcerpt(TermPositionVector tpv, String text, int maxFragments, int maxFragmentSize) throws IOException {

        String excerpt = highlighter.doHighlight(tpv, getQueryTerms(), text,
                "<div class=\"excerpt\">", "</div>", "<span class=\"excerpt-fragment\">", "</span>", "<strong>", "</strong>",
                maxFragments, maxFragmentSize / 2);

        // need to strip ids after the highlighting else the latter, for some reason, doesn't match query terms correctly.
        return excerpt.replaceAll(UUID_REGEX, "");
    }

    /**
     * Unlike {@link DefaultHighlighter} this one does not XML escape its string input.
     * The XML escaping done by DefaultHighlighter escapes HTML tags and quotes (") with HTML entities, e.g &lt;p&gt; becomes &amplt;p&ampgt;
     * which is ugly to see e.g. in a search result page.
     */
    private class NoXMLEscapeHighlighter extends DefaultHighlighter {
        /**
         * @return raw input
         */
        @Override
        public String escape(String input) {
            return input;
        }

        /**
         * We need to override this and call it explicitly as otherwise our {@link #escape(String)} method would never be called,
         * see {@link DefaultHighlighter#highlight(TermPositionVector, Set, String, String, String, String, String, String, String, int, int)} line #109.
         */
        @Override
        protected String doHighlight(TermPositionVector tvec, Set<Term[]> queryTerms, String text, String excerptStart, String excerptEnd, String fragmentStart, String fragmentEnd, String hlStart, String hlEnd, int maxFragments, int surround) throws IOException {
            return super.doHighlight(tvec, queryTerms, text, excerptStart, excerptEnd, fragmentStart, fragmentEnd, hlStart, hlEnd, maxFragments, surround);
        }
    }
}