net.conquiris.lucene.search.ExplicitComparator.java Source code

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Here is the source code for net.conquiris.lucene.search.ExplicitComparator.java

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/*
 * Copyright (C) the original author or authors.
 *
 * 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 net.conquiris.lucene.search;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Comparator;
import java.util.Set;

import javax.annotation.Nullable;

import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import com.google.common.primitives.Ints;

/**
 * Comparator with an explicit order provided by a collection of values. Values not in the
 * collection are assigned the last position.
 * @author Andres Rodriguez
 */
final class ExplicitComparator<T> implements Comparator<T> {
    /** Rank map. */
    private final ImmutableMap<T, Integer> rankMap;
    /** Rank for values not in the map. */
    private final int otherRank;

    static <T> ExplicitComparator<T> of(Iterable<? extends T> values) {
        return new ExplicitComparator<T>(values);
    }

    /**
    * Constructor.
    * @param values Values in sort order. Duplicates and {@code nulls} are filtered out.
    */
    private ExplicitComparator(Iterable<? extends T> values) {
        checkNotNull(values);
        ImmutableMap.Builder<T, Integer> builder = ImmutableMap.builder();
        Set<T> visited = Sets.newHashSet();
        int rank = 0;
        for (T value : Iterables.filter(values, Predicates.notNull())) {
            if (visited.add(value)) {
                builder.put(value, rank);
                rank++;
            }
        }
        this.rankMap = builder.build();
        this.otherRank = rank + 1;
    }

    private int rank(@Nullable T value) {
        Integer rank = rankMap.get(value);
        if (rank != null) {
            return rank.intValue();
        }
        return otherRank;
    }

    /*
     * (non-Javadoc)
     * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
     */
    @Override
    public int compare(T o1, T o2) {
        return Ints.compare(rank(o1), rank(o2));
    }
}