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.collection;
018
019import java.util.Collection;
020import java.util.HashMap;
021import java.util.Iterator;
022import java.util.Objects;
023import java.util.function.Predicate;
024
025import org.apache.commons.collections4.MultiMap;
026import org.apache.commons.collections4.Transformer;
027import org.apache.commons.collections4.map.MultiValueMap;
028
029/**
030 * An IndexedCollection is a Map-like view onto a Collection. It accepts a
031 * keyTransformer to define how the keys are converted from the values.
032 * <p>
033 * Modifications made to this decorator modify the index as well as the
034 * decorated {@link Collection}. However, modifications to the underlying
035 * {@link Collection} will not update the index and it will get out of sync.
036 * </p>
037 * <p>
038 * If modification of the decorated {@link Collection} is unavoidable, then a
039 * call to {@link #reindex()} will update the index to the current contents of
040 * the {@link Collection}.
041 * </p>
042 *
043 * @param <K> The type of object in the index.
044 * @param <C> The type of object in the collection.
045 * @since 4.0
046 */
047public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
048
049    // TODO: replace with MultiValuedMap
050
051    /** Serialization version */
052    private static final long serialVersionUID = -5512610452568370038L;
053
054    /**
055     * Creates an {@link IndexedCollection} for a non-unique index.
056     *
057     * @param <K>            the index object type.
058     * @param <C>            the collection type.
059     * @param coll           The decorated {@link Collection}.
060     * @param keyTransformer The {@link Transformer} for generating index keys.
061     * @return The created {@link IndexedCollection}.
062     */
063    public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
064        return new IndexedCollection<>(coll, keyTransformer, MultiValueMap.<K, C>multiValueMap(new HashMap<>()), false);
065    }
066
067    /**
068     * Creates an {@link IndexedCollection} for a unique index.
069     * <p>
070     * If an element is added, which maps to an existing key, an {@link IllegalArgumentException} will be thrown.
071     * </p>
072     *
073     * @param <K>            the index object type.
074     * @param <C>            the collection type.
075     * @param coll           The decorated {@link Collection}.
076     * @param keyTransformer The {@link Transformer} for generating index keys.
077     * @return The created {@link IndexedCollection}.
078     */
079    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
080        return new IndexedCollection<>(coll, keyTransformer, MultiValueMap.<K, C>multiValueMap(new HashMap<>()), true);
081    }
082
083    /** The {@link Transformer} for generating index keys. */
084    private final Transformer<C, K> keyTransformer;
085
086    /** The map of indexes to collected objects. */
087    private final MultiMap<K, C> index;
088
089    /** The uniqueness constraint for the index. */
090    private final boolean uniqueIndex;
091
092    /**
093     * Creates a {@link IndexedCollection}.
094     *
095     * @param coll  decorated {@link Collection}.
096     * @param keyTransformer  {@link Transformer} for generating index keys.
097     * @param map  map to use as index.
098     * @param uniqueIndex  if the index shall enforce uniqueness of index keys.
099     */
100    public IndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer, final MultiMap<K, C> map, final boolean uniqueIndex) {
101        super(coll);
102        this.keyTransformer = keyTransformer;
103        this.index = map;
104        this.uniqueIndex = uniqueIndex;
105        reindex();
106    }
107
108    /**
109     * {@inheritDoc}
110     *
111     * @throws IllegalArgumentException if the object maps to an existing key and the index
112     *   enforces a uniqueness constraint.
113     */
114    @Override
115    public boolean add(final C object) {
116        final K key = toValidKey(object);
117        final boolean added = super.add(object);
118        if (added) {
119            index.put(key, object);
120        }
121        return added;
122    }
123
124    @Override
125    public boolean addAll(final Collection<? extends C> coll) {
126        boolean changed = false;
127        for (final C c: coll) {
128            changed |= add(c);
129        }
130        return changed;
131    }
132
133    /**
134     * Provides checking for adding the index.
135     *
136     * @param object The object to index.
137     * @throws IllegalArgumentException if the object maps to an existing key and the index
138     *   enforces a uniqueness constraint.
139     */
140    private void addToIndex(final C object) {
141        index.put(toValidKey(object), object);
142    }
143
144    @Override
145    public void clear() {
146        super.clear();
147        index.clear();
148    }
149
150    /**
151     * {@inheritDoc}
152     * <p>
153     * Note: uses the index for fast lookup.
154     * </p>
155     */
156    @SuppressWarnings("unchecked")
157    @Override
158    public boolean contains(final Object object) {
159        return index.containsKey(keyTransformer.apply((C) object));
160    }
161
162    /**
163     * {@inheritDoc}
164     * <p>
165     * Note: uses the index for fast lookup.
166     * </p>
167     */
168    @Override
169    public boolean containsAll(final Collection<?> coll) {
170        return coll.stream().allMatch(this::contains);
171    }
172
173    /**
174     * Gets the element associated with the given key.
175     * <p>
176     * In case of a non-unique index, this method will return the first
177     * value associated with the given key. To retrieve all elements associated
178     * with a key, use {@link #values(Object)}.
179     * </p>
180     *
181     * @param key  key to look up.
182     * @return element found.
183     * @see #values(Object)
184     */
185    public C get(final K key) {
186        @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
187        final Collection<C> coll = (Collection<C>) index.get(key);
188        return coll == null ? null : coll.iterator().next();
189    }
190
191    /**
192     * Clears the index and re-indexes the entire decorated {@link Collection}.
193     */
194    public void reindex() {
195        index.clear();
196        decorated().forEach(this::addToIndex);
197    }
198
199    @SuppressWarnings("unchecked")
200    @Override
201    public boolean remove(final Object object) {
202        final boolean removed = super.remove(object);
203        if (removed) {
204            removeFromIndex((C) object);
205        }
206        return removed;
207    }
208
209    @Override
210    public boolean removeAll(final Collection<?> coll) {
211        boolean changed = false;
212        for (final Object o : coll) {
213            changed |= remove(o);
214        }
215        return changed;
216    }
217
218    /**
219     * Removes an object from the index.
220     *
221     * @param object The object to remove.
222     */
223    private void removeFromIndex(final C object) {
224        index.removeMapping(keyTransformer.apply(object), object);
225    }
226
227    /**
228     * @since 4.4
229     */
230    @Override
231    public boolean removeIf(final Predicate<? super C> filter) {
232        if (Objects.isNull(filter)) {
233            return false;
234        }
235        boolean changed = false;
236        final Iterator<C> it = iterator();
237        while (it.hasNext()) {
238            if (filter.test(it.next())) {
239                it.remove();
240                changed = true;
241            }
242        }
243        if (changed) {
244            reindex();
245        }
246        return changed;
247    }
248
249    @Override
250    public boolean retainAll(final Collection<?> coll) {
251        final boolean changed = super.retainAll(coll);
252        if (changed) {
253            reindex();
254        }
255        return changed;
256    }
257
258    private K toValidKey(final C object) {
259        final K key = keyTransformer.apply(object);
260        if (uniqueIndex && index.containsKey(key)) {
261            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
262        }
263        return key;
264    }
265
266    /**
267     * Gets all elements associated with the given key.
268     *
269     * @param key  key to look up.
270     * @return A collection of elements found, or null if {@code contains(key) == false}.
271     */
272    @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection.
273    public Collection<C> values(final K key) {
274        return (Collection<C>) index.get(key);
275    }
276
277}