Copyright (c) 2010, 2016 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2010, 2016 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.osgi.internal.serviceregistry;

import java.util.*;

public class ShrinkableValueCollectionMap<K, V> extends AbstractMap<K, Collection<V>> implements Map<K, Collection<V>> {
	final Map<? extends K, ? extends Set<? extends Map.Entry<?, ? extends V>>> map;
	Map<Object, Collection<V>> values;

	public ShrinkableValueCollectionMap(Map<? extends K, ? extends Set<? extends Map.Entry<?, ? extends V>>> m) {
		if (m == null) {
			throw new NullPointerException();
		}
		map = m;
		values = null;
	}

	@Override
	public void clear() {
		map.clear();
		if (values != null) {
			values.clear();
		}
	}

	@Override
	public boolean containsKey(Object key) {
		return map.containsKey(key);
	}

	@Override
	public boolean containsValue(Object value) {
		/* Since values are collections and the collection has identity equality,
		 * there is no way any value could be contained in this map unless that
		 * value has already been gotten from this map.
		 */
		if (values == null) {
			return false;
		}
		return values.containsValue(value);
	}

	@Override
	public Set<Map.Entry<K, Collection<V>>> entrySet() {
		return new EntrySet();
	}

	@Override
	public Collection<V> get(Object key) {
		Collection<V> value = null;
		if (values != null) {
			value = values.get(key);
		}
		if (value == null) {
			Set<? extends Map.Entry<?, ? extends V>> entrySet = map.get(key);
			if (entrySet == null) {
				return null;
			}
			value = new ShrinkableEntrySetValueCollection<>(entrySet);
			if (values == null) {
				values = new HashMap<>(map.size());
			}
			values.put(key, value);
		}
		return value;
	}

	@Override
	public boolean isEmpty() {
		return map.isEmpty();
	}

	@Override
	public Collection<V> remove(Object key) {
		Set<? extends Map.Entry<?, ? extends V>> entrySet = map.remove(key);
		Collection<V> value = null;
		if (values != null) {
			value = values.remove(key);
		}
		if ((value == null) && (entrySet != null)) {
			value = new ShrinkableEntrySetValueCollection<>(entrySet);
		}
		return value;
	}

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

	
Set class used for entry sets.
/**
	 * Set class used for entry sets.
	 */
	private final class EntrySet extends AbstractSet<Map.Entry<K, Collection<V>>> {
		EntrySet() {
			super();
		}

		@Override
		public Iterator<Map.Entry<K, Collection<V>>> iterator() {
			return new EntryIterator();
		}

		@Override
		public int size() {
			return ShrinkableValueCollectionMap.this.size();
		}
	}

	
Iterator class used for entry sets.
/** 
	 * Iterator class used for entry sets.
	 */
	private final class EntryIterator implements Iterator<Map.Entry<K, Collection<V>>> {
		private final Iterator<? extends K> iter;
		private K last;

		EntryIterator() {
			iter = map.keySet().iterator();
		}

		@Override
		public boolean hasNext() {
			return iter.hasNext();
		}

		@Override
		public Map.Entry<K, Collection<V>> next() {
			last = iter.next();
			return new Entry(last);
		}

		@Override
		public void remove() {
			iter.remove();
			if (values != null) {
				values.remove(last);
			}
		}
	}

	
This class represents the entry in this map.
/**
	 * This class represents the entry in this map.
	 */
	private final class Entry implements Map.Entry<K, Collection<V>> {
		private final K key;
		private Collection<V> value;

		Entry(final K k) {
			key = k;
		}

		@Override
		public K getKey() {
			return key;
		}

		@Override
		public Collection<V> getValue() {
			if (value == null) {
				value = ShrinkableValueCollectionMap.this.get(key);
			}
			return value;
		}

		@Override
		public Collection<V> setValue(Collection<V> value) {
			throw new UnsupportedOperationException(); // entries cannot be modified.
		}

		@Override
		public String toString() {
			return getKey() + "=" + getValue(); //$NON-NLS-1$
		}

		@Override
		public int hashCode() {
			return hash(getKey()) ^ hash(getValue());
		}

		@Override
		public boolean equals(Object obj) {
			if (obj == this) {
				return true;
			}
			if (!(obj instanceof Map.Entry)) {
				return false;
			}
			Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
			return equality(getKey(), other.getKey()) && equality(getValue(), other.getValue());
		}
	}

	static int hash(Object one) {
		return (one == null) ? 0 : one.hashCode();
	}

	static boolean equality(Object one, Object two) {
		return (one == null) ? (two == null) : one.equals(two);
	}
}