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