WrappedCollection.java

/*
 * JBoss, Home of Professional Open Source
 * Copyright 2010, Red Hat Middleware LLC, and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * Licensed 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
 *
 * http://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.jboss.solder.util.collections;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;

import static org.jboss.solder.util.collections.Preconditions.checkNotNull;

/**
 * Collection decorator that stays in sync with the multimap values for a
 * key. There are two kinds of wrapped collections: full and subcollections.
 * Both have a delegate pointing to the underlying collection class.
 * <p/>
 * <p/>
 * Full collections, identified by a null ancestor field, contain all
 * multimap values for a given key. Its delegate is a value in
 * {@link AbstractMultimap#map} whenever the delegate is non-empty. The
 * {@code refreshIfEmpty}, {@code removeIfEmpty}, and {@code addToMap}
 * methods ensure that the {@code WrappedCollection} and map remain
 * consistent.
 * <p/>
 * <p/>
 * A subcollection, such as a sublist, contains some of the values for a
 * given key. Its ancestor field points to the full wrapped collection with
 * all values for the key. The subcollection {@code refreshIfEmpty}, {@code
 * removeIfEmpty}, and {@code addToMap} methods call the corresponding
 * methods of the full wrapped collection.
 */
class WrappedCollection<K, V> extends AbstractCollection<V> {
    /**
     *
     */
    private final AbstractMultimap<K, V> abstractMultimap;
    final K key;
    Collection<V> delegate;
    final WrappedCollection<K, V> ancestor;
    final Collection<V> ancestorDelegate;

    WrappedCollection(AbstractMultimap<K, V> abstractMultimap, K key, Collection<V> delegate, WrappedCollection<K, V> ancestor) {
        this.abstractMultimap = abstractMultimap;
        this.key = key;
        this.delegate = delegate;
        this.ancestor = ancestor;
        this.ancestorDelegate = (ancestor == null) ? null : ancestor.getDelegate();
    }

    public AbstractMultimap<K, V> getParent() {
        return this.abstractMultimap;
    }

    /**
     * If the delegate collection is empty, but the multimap has values for
     * the key, replace the delegate with the new collection for the key.
     * <p/>
     * <p/>
     * For a subcollection, refresh its ancestor and validate that the
     * ancestor delegate hasn't changed.
     */
    void refreshIfEmpty() {
        if (ancestor != null) {
            ancestor.refreshIfEmpty();
            if (ancestor.getDelegate() != ancestorDelegate) {
                throw new ConcurrentModificationException();
            }
        } else if (delegate.isEmpty()) {
            Collection<V> newDelegate = abstractMultimap.map.get(key);
            if (newDelegate != null) {
                delegate = newDelegate;
            }
        }
    }

    /**
     * If collection is empty, remove it from {@code map}. For subcollections,
     * check whether the ancestor collection is empty.
     */
    void removeIfEmpty() {
        if (ancestor != null) {
            ancestor.removeIfEmpty();
        } else if (delegate.isEmpty()) {
            abstractMultimap.map.remove(key);
        }
    }

    K getKey() {
        return key;
    }

    /**
     * Add the delegate to the map. Other {@code WrappedCollection} methods
     * should call this method after adding elements to a previously empty
     * collection.
     * <p/>
     * <p/>
     * Subcollection add the ancestor's delegate instead.
     */
    void addToMap() {
        if (ancestor != null) {
            ancestor.addToMap();
        } else {
            abstractMultimap.map.put(key, delegate);
        }
    }

    @Override
    public int size() {
        refreshIfEmpty();
        return delegate.size();
    }

    @Override
    public boolean equals(Object object) {
        if (object == this) {
            return true;
        }
        refreshIfEmpty();
        return delegate.equals(object);
    }

    @Override
    public int hashCode() {
        refreshIfEmpty();
        return delegate.hashCode();
    }

    @Override
    public String toString() {
        refreshIfEmpty();
        return delegate.toString();
    }

    Collection<V> getDelegate() {
        return delegate;
    }

    @Override
    public Iterator<V> iterator() {
        refreshIfEmpty();
        return new WrappedIterator(this);
    }


    @Override
    public boolean add(V value) {
        refreshIfEmpty();
        boolean wasEmpty = delegate.isEmpty();
        boolean changed = delegate.add(value);
        if (changed) {
            abstractMultimap.totalSize++;
            if (wasEmpty) {
                addToMap();
            }
        }
        return changed;
    }

    WrappedCollection<K, V> getAncestor() {
        return ancestor;
    }

    // The following methods are provided for better performance.

    @Override
    public boolean addAll(Collection<? extends V> collection) {
        if (collection.isEmpty()) {
            return false;
        }
        int oldSize = size(); // calls refreshIfEmpty
        boolean changed = delegate.addAll(collection);
        if (changed) {
            int newSize = delegate.size();
            abstractMultimap.totalSize += (newSize - oldSize);
            if (oldSize == 0) {
                addToMap();
            }
        }
        return changed;
    }

    @Override
    public boolean contains(Object o) {
        refreshIfEmpty();
        return delegate.contains(o);
    }

    @Override
    public boolean containsAll(Collection<?> c) {
        refreshIfEmpty();
        return delegate.containsAll(c);
    }

    @Override
    public void clear() {
        int oldSize = size(); // calls refreshIfEmpty
        if (oldSize == 0) {
            return;
        }
        delegate.clear();
        abstractMultimap.totalSize -= oldSize;
        removeIfEmpty(); // maybe shouldn't be removed if this is a sublist
    }

    @Override
    public boolean remove(Object o) {
        refreshIfEmpty();
        boolean changed = delegate.remove(o);
        if (changed) {
            abstractMultimap.totalSize--;
            removeIfEmpty();
        }
        return changed;
    }

    @Override
    public boolean removeAll(Collection<?> c) {
        if (c.isEmpty()) {
            return false;
        }
        int oldSize = size(); // calls refreshIfEmpty
        boolean changed = delegate.removeAll(c);
        if (changed) {
            int newSize = delegate.size();
            abstractMultimap.totalSize += (newSize - oldSize);
            removeIfEmpty();
        }
        return changed;
    }

    @Override
    public boolean retainAll(Collection<?> c) {
        checkNotNull(c);
        int oldSize = size(); // calls refreshIfEmpty
        boolean changed = delegate.retainAll(c);
        if (changed) {
            int newSize = delegate.size();
            abstractMultimap.totalSize += (newSize - oldSize);
            removeIfEmpty();
        }
        return changed;
    }
}