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.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 *
046 * @since 4.0
047 */
048public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
049
050    // TODO: replace with MultiValuedMap
051
052    /** Serialization version */
053    private static final long serialVersionUID = -5512610452568370038L;
054
055    /**
056     * Create an {@link IndexedCollection} for a non-unique index.
057     *
058     * @param <K> the index object type.
059     * @param <C> the collection type.
060     * @param coll the decorated {@link Collection}.
061     * @param keyTransformer the {@link Transformer} for generating index keys.
062     * @return the created {@link IndexedCollection}.
063     */
064    public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll,
065                                                                            final Transformer<C, K> keyTransformer) {
066        return new IndexedCollection<>(coll, keyTransformer,
067                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
068                                           false);
069    }
070
071    /**
072     * Create an {@link IndexedCollection} for a unique index.
073     * <p>
074     * If an element is added, which maps to an existing key, an {@link IllegalArgumentException}
075     * will be thrown.
076     *
077     * @param <K> the index object type.
078     * @param <C> the collection type.
079     * @param coll the decorated {@link Collection}.
080     * @param keyTransformer the {@link Transformer} for generating index keys.
081     * @return the created {@link IndexedCollection}.
082     */
083    public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll,
084                                                                         final Transformer<C, K> keyTransformer) {
085        return new IndexedCollection<>(coll, keyTransformer,
086                                           MultiValueMap.<K, C>multiValueMap(new HashMap<>()),
087                                           true);
088    }
089
090    /** The {@link Transformer} for generating index keys. */
091    private final Transformer<C, K> keyTransformer;
092
093    /** The map of indexes to collected objects. */
094    private final MultiMap<K, C> index;
095
096    /** The uniqueness constraint for the index. */
097    private final boolean uniqueIndex;
098
099    /**
100     * Create a {@link IndexedCollection}.
101     *
102     * @param coll  decorated {@link Collection}
103     * @param keyTransformer  {@link Transformer} for generating index keys
104     * @param map  map to use as index
105     * @param uniqueIndex  if the index shall enforce uniqueness of index keys
106     */
107    public IndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer,
108                             final MultiMap<K, C> map, final boolean uniqueIndex) {
109        super(coll);
110        this.keyTransformer = keyTransformer;
111        this.index = map;
112        this.uniqueIndex = uniqueIndex;
113        reindex();
114    }
115
116    /**
117     * {@inheritDoc}
118     *
119     * @throws IllegalArgumentException if the object maps to an existing key and the index
120     *   enforces a uniqueness constraint
121     */
122    @Override
123    public boolean add(final C object) {
124        final boolean added = super.add(object);
125        if (added) {
126            addToIndex(object);
127        }
128        return added;
129    }
130
131    @Override
132    public boolean addAll(final Collection<? extends C> coll) {
133        boolean changed = false;
134        for (final C c: coll) {
135            changed |= add(c);
136        }
137        return changed;
138    }
139
140    /**
141     * Provides checking for adding the index.
142     *
143     * @param object the object to index
144     * @throws IllegalArgumentException if the object maps to an existing key and the index
145     *   enforces a uniqueness constraint
146     */
147    private void addToIndex(final C object) {
148        final K key = keyTransformer.transform(object);
149        if (uniqueIndex && index.containsKey(key)) {
150            throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
151        }
152        index.put(key, object);
153    }
154
155    @Override
156    public void clear() {
157        super.clear();
158        index.clear();
159    }
160
161    /**
162     * {@inheritDoc}
163     * <p>
164     * Note: uses the index for fast lookup
165     */
166    @SuppressWarnings("unchecked")
167    @Override
168    public boolean contains(final Object object) {
169        return index.containsKey(keyTransformer.transform((C) object));
170    }
171
172    /**
173     * {@inheritDoc}
174     * <p>
175     * Note: uses the index for fast lookup
176     */
177    @Override
178    public boolean containsAll(final Collection<?> coll) {
179        for (final Object o : coll) {
180            if (!contains(o)) {
181                return false;
182            }
183        }
184        return true;
185    }
186
187    /**
188     * Gets the element associated with the given key.
189     * <p>
190     * In case of a non-unique index, this method will return the first
191     * value associated with the given key. To retrieve all elements associated
192     * with a key, use {@link #values(Object)}.
193     *
194     * @param key  key to look up
195     * @return element found
196     * @see #values(Object)
197     */
198    public C get(final K key) {
199        @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
200        final Collection<C> coll = (Collection<C>) index.get(key);
201        return coll == null ? null : coll.iterator().next();
202    }
203
204    /**
205     * Clears the index and re-indexes the entire decorated {@link Collection}.
206     */
207    public void reindex() {
208        index.clear();
209        for (final C c : decorated()) {
210            addToIndex(c);
211        }
212    }
213
214    @SuppressWarnings("unchecked")
215    @Override
216    public boolean remove(final Object object) {
217        final boolean removed = super.remove(object);
218        if (removed) {
219            removeFromIndex((C) object);
220        }
221        return removed;
222    }
223
224    @Override
225    public boolean removeAll(final Collection<?> coll) {
226        boolean changed = false;
227        for (final Object o : coll) {
228            changed |= remove(o);
229        }
230        return changed;
231    }
232
233    /**
234     * Removes an object from the index.
235     *
236     * @param object the object to remove
237     */
238    private void removeFromIndex(final C object) {
239        index.remove(keyTransformer.transform(object));
240    }
241
242    /**
243     * @since 4.4
244     */
245    @Override
246    public boolean removeIf(final Predicate<? super C> filter) {
247        if (Objects.isNull(filter)) {
248            return false;
249        }
250        boolean changed = false;
251        final Iterator<C> it = iterator();
252        while (it.hasNext()) {
253            if (filter.test(it.next())) {
254                it.remove();
255                changed = true;
256            }
257        }
258        if (changed) {
259            reindex();
260        }
261        return changed;
262    }
263
264    @Override
265    public boolean retainAll(final Collection<?> coll) {
266        final boolean changed = super.retainAll(coll);
267        if (changed) {
268            reindex();
269        }
270        return changed;
271    }
272
273    /**
274     * Gets all elements associated with the given key.
275     *
276     * @param key  key to look up
277     * @return a collection of elements found, or null if {@code contains(key) == false}
278     */
279    @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
280    public Collection<C> values(final K key) {
281        return (Collection<C>) index.get(key);
282    }
283
284}