xbdd.webapp.resource.feature.DBObjectComparator.java Source code

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Here is the source code for xbdd.webapp.resource.feature.DBObjectComparator.java

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/**
 * Copyright (C) 2015 Orion Health (Orchestral Development Ltd)
 *
 * 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 xbdd.webapp.resource.feature;

import java.util.Collection;
import java.util.Comparator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

import org.apache.commons.lang.StringUtils;

import com.google.common.base.Function;
import com.google.common.collect.Collections2;
import com.mongodb.DBObject;

/**
 * Matcher that compares two DBObjects by the number of times they match a set of regular expressions
 */
public class DBObjectComparator implements Comparator<DBObject> {

    final private ConcurrentMap<DBObject, Integer> cachedCounts = new ConcurrentHashMap<>();

    private Pattern pattern;

    /**
     * Construct a {@link Comparator} with the given set of expressions
     * 
     * @param searchExpressions a list of regular expressions
     * @throws PatternSyntaxException if any of the expressions are not valid regex
     */
    public DBObjectComparator(final Collection<String> searchExpressions) {
        final String regex = StringUtils
                .join(Collections2.transform(searchExpressions, new Function<String, String>() {
                    @Override
                    public String apply(final String input) {
                        return "(" + input + ")";
                    }
                }), "|");
        this.pattern = Pattern.compile(regex);
    }

    @Override
    public int compare(final DBObject obj1, final DBObject obj2) {
        final int obj1Count = getCount(obj1);
        final int obj2Count = getCount(obj2);

        return obj2Count - obj1Count;
    }

    private int getCount(final DBObject obj) {
        int count;
        if (obj == null) {
            count = 0;
        } else if (this.cachedCounts.containsKey(obj)) {
            count = this.cachedCounts.get(obj);
        } else {
            count = countMatches(this.pattern.matcher(obj.toString()));
            this.cachedCounts.put(obj, count);
        }
        return count;
    }

    private int countMatches(final Matcher matcher) {
        int accumulator = 0;
        while (matcher.find()) {
            accumulator++;
        }
        return accumulator;
    }
}