    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.bloomfilter;
    018
    019import java.util.ArrayList;
    020import java.util.Arrays;
    021import java.util.List;
    022import java.util.Objects;
    023import java.util.concurrent.atomic.AtomicReference;
    024import java.util.function.BiPredicate;
    025import java.util.function.Predicate;
    026
    027/**
    028 * Produces Bloom filters from a collection (for example, {@link LayeredBloomFilter}).
    029 *
    030 * @since 4.5.0-M2
    031 */
    032@FunctionalInterface
    033public interface BloomFilterExtractor {
    034
    035    /**
    036     * Creates a BloomFilterExtractor from an array of Bloom filters.
    037     *
    038     * <ul>
    039     * <li>The asBloomFilterArray() method returns a copy of the original array with references to the original filters.</li>
    040     * <li>The forEachBloomFilterPair() method uses references to the original filters.</li>
    041     * </ul>
    042     * <p>
    043     * <em>All modifications to the Bloom filters are reflected in the original filters</em>
    044     * </p>
    045     *
    046     * @param <T>     The BloomFilter type.
    047     * @param filters The filters to be returned by the extractor.
    048     * @return THe BloomFilterExtractor containing the filters.
    049     */
    050    static <T extends BloomFilter<T>> BloomFilterExtractor fromBloomFilterArray(final BloomFilter<?>... filters) {
    051        Objects.requireNonNull(filters, "filters");
    052        return new BloomFilterExtractor() {
    053
    054            /**
    055             * This implementation returns a copy the original array, the contained Bloom filters are references to the originals, any modifications to them are
    056             * reflected in the original filters.
    057             */
    058            @Override
    059            public BloomFilter[] asBloomFilterArray() {
    060                return filters.clone();
    061            }
    062
    063            /**
    064             * This implementation uses references to the original filters. Any modifications to the filters are reflected in the originals.
    065             */
    066            @Override
    067            public boolean processBloomFilterPair(final BloomFilterExtractor other, final BiPredicate<BloomFilter, BloomFilter> func) {
    068                final CountingPredicate<BloomFilter> p = new CountingPredicate<>(filters, func);
    069                return other.processBloomFilters(p) && p.processRemaining();
    070            }
    071
    072            @Override
    073            public boolean processBloomFilters(final Predicate<BloomFilter> predicate) {
    074                return Arrays.stream(filters).allMatch(predicate);
    075            }
    076        };
    077    }
    078
    079    /**
    080     * Return an array of the Bloom filters in the collection.
    081     * <p>
    082     * <em>Implementations should specify if the array contains deep copies, immutable instances, or references to the filters in the collection.</em>
    083     * </p>
    084     * <p>
    085     * The default method returns a deep copy of the enclosed filters.
    086     * </p>
    087     *
    088     * @return An array of Bloom filters.
    089     */
    090    default BloomFilter[] asBloomFilterArray() {
    091        final List<BloomFilter> filters = new ArrayList<>();
    092        processBloomFilters(f -> filters.add(f.copy()));
    093        return filters.toArray(new BloomFilter[0]);
    094    }
    095
    096    /**
    097     * Create a standard (non-layered) Bloom filter by merging all of the layers. If the filter is empty this method will return an empty Bloom filter.
    098     *
    099     * @return The merged bloom filter, never null.
    100     * @throws NullPointerException if this call did not process any filters.
    101     */
    102    default BloomFilter flatten() {
    103        final AtomicReference<BloomFilter> ref = new AtomicReference<>();
    104        processBloomFilters(x -> {
    105            if (ref.get() == null) {
    106                ref.set(new SimpleBloomFilter(x.getShape()));
    107            }
    108            return ref.get().merge(x);
    109        });
    110        return Objects.requireNonNull(ref.get(), "No filters.");
    111    }
    112
    113    /**
    114     * Applies the {@code func} to each Bloom filter pair in order. Will apply all of the Bloom filters from the other BloomFilterExtractor to this extractor.
    115     * If either {@code this} extractor or {@code other} extractor has fewer BloomFilters the method will provide {@code null} for all excess calls to the
    116     * {@code func}.
    117     *
    118     * <p>
    119     * <em>This implementation returns references to the Bloom filter. Other implementations should specify if the array contains deep copies, immutable
    120     * instances, or references to the filters in the collection.</em>
    121     * </p>
    122     *
    123     * @param other The other BloomFilterExtractor that provides the y values in the (x, y) pair.
    124     * @param func  The function to apply.
    125     * @return {@code true} if the {@code func} returned {@code true} for every pair, {@code false} otherwise.
    126     */
    127    default boolean processBloomFilterPair(final BloomFilterExtractor other, final BiPredicate<BloomFilter, BloomFilter> func) {
    128        final CountingPredicate<BloomFilter> p = new CountingPredicate<>(asBloomFilterArray(), func);
    129        return other.processBloomFilters(p) && p.processRemaining();
    130    }
    131
    132    /**
    133     * Executes a Bloom filter Predicate on each Bloom filter in the collection. The ordering of the Bloom filters is not specified by this interface.
    134     *
    135     * @param bloomFilterPredicate The predicate to evaluate each Bloom filter with.
    136     * @return {@code false} when the first filter fails the predicate test. Returns {@code true} if all filters pass the test.
    137     */
    138    boolean processBloomFilters(Predicate<BloomFilter> bloomFilterPredicate);
    139}