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 *      http://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.List;
021import java.util.Objects;
022import java.util.concurrent.atomic.AtomicReference;
023import java.util.function.BiPredicate;
024import java.util.function.Predicate;
025
026/**
027 * Produces Bloom filters from a collection (for example, {@link LayeredBloomFilter}).
028 *
029 * @since 4.5.0-M2
030 */
031@FunctionalInterface
032public interface BloomFilterExtractor {
033
034    /**
035     * Creates a BloomFilterExtractor from an array of Bloom filters.
036     *
037     * <ul>
038     * <li>The asBloomFilterArray() method returns a copy of the original array with references to the original filters.</li>
039     * <li>The forEachBloomFilterPair() method uses references to the original filters.</li>
040     * </ul>
041     * <p>
042     * <em>All modifications to the Bloom filters are reflected in the original filters</em>
043     * </p>
044     *
045     * @param <T>     The BloomFilter type.
046     * @param filters The filters to be returned by the extractor.
047     * @return THe BloomFilterExtractor containing the filters.
048     */
049    static <T extends BloomFilter<T>> BloomFilterExtractor fromBloomFilterArray(final BloomFilter<?>... filters) {
050        Objects.requireNonNull(filters, "filters");
051        return new BloomFilterExtractor() {
052
053            /**
054             * This implementation returns a copy the original array, the contained Bloom filters are references to the originals, any modifications to them are
055             * reflected in the original filters.
056             */
057            @Override
058            public BloomFilter[] asBloomFilterArray() {
059                return filters.clone();
060            }
061
062            /**
063             * This implementation uses references to the original filters. Any modifications to the filters are reflected in the originals.
064             */
065            @Override
066            public boolean processBloomFilterPair(final BloomFilterExtractor other, final BiPredicate<BloomFilter, BloomFilter> func) {
067                final CountingPredicate<BloomFilter> p = new CountingPredicate<>(filters, func);
068                return other.processBloomFilters(p) && p.processRemaining();
069            }
070
071            @Override
072            public boolean processBloomFilters(final Predicate<BloomFilter> predicate) {
073                for (final BloomFilter filter : filters) {
074                    if (!predicate.test(filter)) {
075                        return false;
076                    }
077                }
078                return true;
079            }
080        };
081    }
082
083    /**
084     * Return an array of the Bloom filters in the collection.
085     * <p>
086     * <em>Implementations should specify if the array contains deep copies, immutable instances, or references to the filters in the collection.</em>
087     * </p>
088     * <p>
089     * The default method returns a deep copy of the enclosed filters.
090     * </p>
091     *
092     * @return An array of Bloom filters.
093     */
094    default BloomFilter[] asBloomFilterArray() {
095        final List<BloomFilter> filters = new ArrayList<>();
096        processBloomFilters(f -> filters.add(f.copy()));
097        return filters.toArray(new BloomFilter[0]);
098    }
099
100    /**
101     * 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.
102     *
103     * @return the merged bloom filter, never null.
104     * @throws NullPointerException if this call did not process any filters.
105     */
106    default BloomFilter flatten() {
107        final AtomicReference<BloomFilter> ref = new AtomicReference<>();
108        processBloomFilters(x -> {
109            if (ref.get() == null) {
110                ref.set(new SimpleBloomFilter(x.getShape()));
111            }
112            return ref.get().merge(x);
113        });
114        return Objects.requireNonNull(ref.get(), "No filters.");
115    }
116
117    /**
118     * 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.
119     * If either {@code this} extractor or {@code other} extractor has fewer BloomFilters the method will provide {@code null} for all excess calls to the
120     * {@code func}.
121     *
122     * <p>
123     * <em>This implementation returns references to the Bloom filter. Other implementations should specify if the array contains deep copies, immutable
124     * instances, or references to the filters in the collection.</em>
125     * </p>
126     *
127     * @param other The other BloomFilterExtractor that provides the y values in the (x,y) pair.
128     * @param func  The function to apply.
129     * @return {@code true} if the {@code func} returned {@code true} for every pair, {@code false} otherwise.
130     */
131    default boolean processBloomFilterPair(final BloomFilterExtractor other, final BiPredicate<BloomFilter, BloomFilter> func) {
132        final CountingPredicate<BloomFilter> p = new CountingPredicate<>(asBloomFilterArray(), func);
133        return other.processBloomFilters(p) && p.processRemaining();
134    }
135
136    /**
137     * Executes a Bloom filter Predicate on each Bloom filter in the collection. The ordering of the Bloom filters is not specified by this interface.
138     *
139     * @param bloomFilterPredicate the predicate to evaluate each Bloom filter with.
140     * @return {@code false} when the first filter fails the predicate test. Returns {@code true} if all filters pass the test.
141     */
142    boolean processBloomFilters(Predicate<BloomFilter> bloomFilterPredicate);
143}