src/main/java/org/apache/commons/collections4/collection/CompositeCollection.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4.collection;

import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.function.Predicate;
import java.util.stream.Stream;

import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.iterators.EmptyIterator;
import org.apache.commons.collections4.iterators.IteratorChain;
import org.apache.commons.collections4.list.UnmodifiableList;

/**
 * Decorates a collection of other collections to provide a single unified view.
 * <p>
 * Changes made to this collection will actually be made on the decorated collection.
 * Add and remove operations require the use of a pluggable strategy. If no
 * strategy is provided then add and remove are unsupported.
 * </p>
 *
 * @param <E> The type of the elements in the collection
 * @since 3.0
 */
public class CompositeCollection<E> implements Collection<E>, Serializable {

    /**
     * Pluggable strategy to handle changes to the composite.
     *
     * @param <E> The element being held in the collection
     */
    public interface CollectionMutator<E> extends Serializable {

        /**
         * Called when an object is to be added to the composite.
         *
         * @param composite  the CompositeCollection being changed.
         * @param collections  all of the Collection instances in this CompositeCollection.
         * @param obj  the object being added.
         * @return true if the collection is changed.
         * @throws UnsupportedOperationException if add is unsupported.
         * @throws ClassCastException if the object cannot be added due to its type.
         * @throws NullPointerException if the object cannot be added because its null.
         * @throws IllegalArgumentException if the object cannot be added.
         */
        boolean add(CompositeCollection<E> composite, List<Collection<E>> collections, E obj);

        /**
         * Called when a collection is to be added to the composite.
         *
         * @param composite  the CompositeCollection being changed.
         * @param collections  all of the Collection instances in this CompositeCollection.
         * @param coll  the collection being added.
         * @return true if the collection is changed.
         * @throws UnsupportedOperationException if add is unsupported.
         * @throws ClassCastException if the object cannot be added due to its type.
         * @throws NullPointerException if the object cannot be added because its null.
         * @throws IllegalArgumentException if the object cannot be added.
         */
        boolean addAll(CompositeCollection<E> composite,
                              List<Collection<E>> collections,
                              Collection<? extends E> coll);

        /**
         * Called when an object is to be removed to the composite.
         *
         * @param composite  the CompositeCollection being changed.
         * @param collections  all of the Collection instances in this CompositeCollection.
         * @param obj  the object being removed.
         * @return true if the collection is changed.
         * @throws UnsupportedOperationException if removed is unsupported.
         * @throws ClassCastException if the object cannot be removed due to its type.
         * @throws NullPointerException if the object cannot be removed because its null.
         * @throws IllegalArgumentException if the object cannot be removed.
         */
        boolean remove(CompositeCollection<E> composite,
                              List<Collection<E>> collections,
                              Object obj);

    }

    /** Serialization version. */
    private static final long serialVersionUID = 8417515734108306801L;

    /** CollectionMutator to handle changes to the collection. */
    private CollectionMutator<E> mutator;

    /** Collections in the composite. */
    private final List<Collection<E>> all = new ArrayList<>();

    /**
     * Constructs an empty CompositeCollection.
     */
    public CompositeCollection() {
    }

    /**
     * Constructs a Composite Collection with one collection.
     *
     * @param compositeCollection  the Collection to be appended to the composite.
     */
    public CompositeCollection(final Collection<E> compositeCollection) {
        addComposited(compositeCollection);
    }

    /**
     * Constructs a Composite Collection with an array of collections.
     *
     * @param compositeCollections  the collections to composite.
     */
    public CompositeCollection(final Collection<E>... compositeCollections) {
        addComposited(compositeCollections);
    }

    /**
     * Constructs a Composite Collection with two collections.
     *
     * @param compositeCollection1  the Collection to be appended to the composite.
     * @param compositeCollection2  the Collection to be appended to the composite.
     */
    public CompositeCollection(final Collection<E> compositeCollection1,
                               final Collection<E> compositeCollection2) {
        addComposited(compositeCollection1, compositeCollection2);
    }

    /**
     * Adds an object to the collection, throwing UnsupportedOperationException
     * unless a CollectionMutator strategy is specified.
     *
     * @param obj  the object to add.
     * @return {@code true} if the collection was modified.
     * @throws UnsupportedOperationException if CollectionMutator hasn't been set.
     * @throws UnsupportedOperationException if add is unsupported.
     * @throws ClassCastException if the object cannot be added due to its type.
     * @throws NullPointerException if the object cannot be added because its null.
     * @throws IllegalArgumentException if the object cannot be added.
     */
    @Override
    public boolean add(final E obj) {
        if (mutator == null) {
            throw new UnsupportedOperationException(
                "add() is not supported on CompositeCollection without a CollectionMutator strategy");
        }
        return mutator.add(this, all, obj);
    }

    /**
     * Adds a collection of elements to this collection, throwing
     * UnsupportedOperationException unless a CollectionMutator strategy is specified.
     *
     * @param coll  the collection to add.
     * @return true if the collection was modified.
     * @throws UnsupportedOperationException if CollectionMutator hasn't been set.
     * @throws UnsupportedOperationException if add is unsupported.
     * @throws ClassCastException if the object cannot be added due to its type.
     * @throws NullPointerException if the object cannot be added because its null.
     * @throws IllegalArgumentException if the object cannot be added.
     */
    @Override
    public boolean addAll(final Collection<? extends E> coll) {
        if (mutator == null) {
            throw new UnsupportedOperationException(
                "addAll() is not supported on CompositeCollection without a CollectionMutator strategy");
        }
        return mutator.addAll(this, all, coll);
    }

    /**
     * Add these Collections to the list of collections in this composite
     *
     * @param compositeCollection  the Collection to be appended to the composite.
     */
    public void addComposited(final Collection<E> compositeCollection) {
        if (compositeCollection != null) {
            all.add(compositeCollection);
        }
    }

    /**
     * Add these Collections to the list of collections in this composite
     *
     * @param compositeCollections  the Collections to be appended to the composite.
     */
    public void addComposited(final Collection<E>... compositeCollections) {
        Stream.of(compositeCollections).filter(Objects::nonNull).forEach(all::add);
    }

    /**
     * Add these Collections to the list of collections in this composite
     *
     * @param compositeCollection1  the Collection to be appended to the composite.
     * @param compositeCollection2  the Collection to be appended to the composite.
     */
    public void addComposited(final Collection<E> compositeCollection1,
                              final Collection<E> compositeCollection2) {
        if (compositeCollection1 != null) {
            all.add(compositeCollection1);
        }
        if (compositeCollection2 != null) {
            all.add(compositeCollection2);
        }
    }

    /**
     * Removes all of the elements from this collection.
     * <p>
     * This implementation calls {@code clear()} on each collection.
     * </p>
     *
     * @throws UnsupportedOperationException if clear is unsupported.
     */
    @Override
    public void clear() {
        all.forEach(Collection::clear);
    }

    /**
     * Checks whether this composite collection contains the object.
     * <p>
     * This implementation calls {@code contains()} on each collection.
     * </p>
     *
     * @param obj  the object to search for.
     * @return true if obj is contained in any of the contained collections.
     */
    @Override
    public boolean contains(final Object obj) {
        return all.stream().anyMatch(c -> c.contains(obj));
    }

    /**
     * Checks whether this composite contains all the elements in the specified collection.
     * <p>
     * This implementation calls {@code contains()} for each element in the
     * specified collection.
     * </p>
     *
     * @param coll  the collection to check for.
     * @return true if all elements contained.
     */
    @Override
    public boolean containsAll(final Collection<?> coll) {
        return coll != null && coll.stream().allMatch(this::contains);
    }

    /**
     * Gets the collections being decorated.
     *
     * @return Unmodifiable list of all collections in this composite.
     */
    public List<Collection<E>> getCollections() {
        return UnmodifiableList.unmodifiableList(all);
    }

    /**
     * Gets the collection mutator to be used for this CompositeCollection.
     *
     * @return CollectionMutator&lt;E&gt;
     */
    protected CollectionMutator<E> getMutator() {
        return mutator;
    }

    /**
     * Checks whether this composite collection is empty.
     * <p>
     * This implementation calls {@code isEmpty()} on each collection.
     * </p>
     *
     * @return true if all of the contained collections are empty
     */
    @Override
    public boolean isEmpty() {
        return all.stream().allMatch(Collection::isEmpty);
    }

    /**
     * Gets an iterator over all the collections in this composite.
     * <p>
     * This implementation uses an {@code IteratorChain}.
     * </p>
     *
     * @return an {@code IteratorChain} instance which supports
     *  {@code remove()}. Iteration occurs over contained collections in
     *  the order they were added, but this behavior should not be relied upon.
     * @see IteratorChain
     */
    @Override
    public Iterator<E> iterator() {
        if (all.isEmpty()) {
            return EmptyIterator.<E>emptyIterator();
        }
        final IteratorChain<E> chain = new IteratorChain<>();
        all.forEach(item -> chain.addIterator(item.iterator()));
        return chain;
    }

    /**
     * Removes an object from the collection, throwing UnsupportedOperationException
     * unless a CollectionMutator strategy is specified.
     *
     * @param obj  the object being removed.
     * @return true if the collection is changed.
     * @throws UnsupportedOperationException if removed is unsupported.
     * @throws ClassCastException if the object cannot be removed due to its type.
     * @throws NullPointerException if the object cannot be removed because its null.
     * @throws IllegalArgumentException if the object cannot be removed.
     */
    @Override
    public boolean remove(final Object obj) {
        if (mutator == null) {
            throw new UnsupportedOperationException("remove() is not supported on CompositeCollection without a CollectionMutator strategy");
        }
        return mutator.remove(this, all, obj);
    }

    /**
     * Removes the elements in the specified collection from this composite collection.
     * <p>
     * This implementation calls {@code removeAll} on each collection.
     * </p>
     *
     * @param coll  the collection to remove.
     * @return true if the collection was modified.
     * @throws UnsupportedOperationException if removeAll is unsupported.
     */
    @Override
    public boolean removeAll(final Collection<?> coll) {
        if (CollectionUtils.isEmpty(coll)) {
            return false;
        }
        boolean changed = false;
        for (final Collection<E> item : all) {
            changed |= item.removeAll(coll);
        }
        return changed;
    }

    /**
     * Removes a collection from the those being decorated in this composite.
     *
     * @param coll  collection to be removed.
     */
    public void removeComposited(final Collection<E> coll) {
        all.remove(coll);
    }

    /**
     * Removes all of the elements of this collection that satisfy the given predicate from this composite collection.
     * <p>
     * This implementation calls {@code removeIf} on each collection.
     * </p>
     *
     * @param filter  a predicate which returns true for elements to be removed.
     * @return true if the collection was modified.
     * @throws UnsupportedOperationException if removeIf is unsupported.
     * @since 4.4
     */
    @Override
    public boolean removeIf(final Predicate<? super E> filter) {
        if (Objects.isNull(filter)) {
            return false;
        }
        boolean changed = false;
        for (final Collection<E> item : all) {
            changed |= item.removeIf(filter);
        }
        return changed;
    }

    /**
     * Retains all the elements in the specified collection in this composite collection,
     * removing all others.
     * <p>
     * This implementation calls {@code retainAll()} on each collection.
     * </p>
     *
     * @param coll  the collection to remove.
     * @return true if the collection was modified.
     * @throws UnsupportedOperationException if retainAll is unsupported.
     */
    @Override
    public boolean retainAll(final Collection<?> coll) {
        boolean changed = false;
        if (coll != null) {
            for (final Collection<E> item : all) {
                changed |= item.retainAll(coll);
            }
        }
        return changed;
    }

    /**
     * Specify a CollectionMutator strategy instance to handle changes.
     *
     * @param mutator  the mutator to use
     */
    public void setMutator(final CollectionMutator<E> mutator) {
        this.mutator = mutator;
    }

    /**
     * Gets the size of this composite collection.
     * <p>
     * This implementation calls {@code size()} on each collection.
     * </p>
     *
     * @return total number of elements in all contained containers, or
     *         {@code Integer.MAX_VALUE} if the total exceeds it.
     */
    @Override
    public int size() {
        long size = 0;
        for (final Collection<E> item : all) {
            size += item.size();
        }
        return (int) Math.min(size, Integer.MAX_VALUE);
    }

    /**
     * Returns an array containing all of the elements in this composite.
     *
     * @return an object array of all the elements in the collection.
     */
    @Override
    public Object[] toArray() {
        final Object[] result = new Object[size()];
        int i = 0;
        for (final Iterator<E> it = iterator(); it.hasNext(); i++) {
            result[i] = it.next();
        }
        return result;
    }

    /**
     * Returns an object array, populating the supplied array if possible.
     * See {@code Collection} interface for full details.
     *
     * @param <T>  the type of the elements in the collection.
     * @param array  the array to use, populating if possible.
     * @return an array of all the elements in the collection.
     */
    @Override
    @SuppressWarnings("unchecked")
    public <T> T[] toArray(final T[] array) {
        final int size = size();
        Object[] result = null;
        if (array.length >= size) {
            result = array;
        } else {
            result = (Object[]) Array.newInstance(array.getClass().getComponentType(), size);
        }

        int offset = 0;
        for (final Collection<E> item : all) {
            for (final E e : item) {
                result[offset++] = e;
            }
        }
        if (result.length > size) {
            result[size] = null;
        }
        return (T[]) result;
    }

    /**
     * Returns a new collection containing all of the elements.
     *
     * @return A new ArrayList containing all of the elements in this composite.
     *         The new collection is <em>not</em> backed by this composite.
     */
    public Collection<E> toCollection() {
        return new ArrayList<>(this);
    }

}