/*
 * 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
 *
 *      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
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package org.apache.commons.collections4.bidimap;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Objects;
import java.util.function.Predicate;

import org.apache.commons.collections4.BidiMap;
import org.apache.commons.collections4.MapIterator;
import org.apache.commons.collections4.ResettableIterator;
import org.apache.commons.collections4.collection.AbstractCollectionDecorator;
import org.apache.commons.collections4.iterators.AbstractIteratorDecorator;
import org.apache.commons.collections4.keyvalue.AbstractMapEntryDecorator;

Abstract BidiMap implemented using two maps. 
 An implementation can be written simply by implementing the createBidiMap(Map, Map, BidiMap) method. 
Type parameters:
<K> – the type of the keys in the map
<V> – the type of the values in the map
See Also:
DualHashBidiMap
DualTreeBidiMap
Since:
3.0/**
 * Abstract {@link BidiMap} implemented using two maps.
 * <p>
 * An implementation can be written simply by implementing the
 * {@link #createBidiMap(Map, Map, BidiMap)} method.
 * </p>
 *
 * @param <K> the type of the keys in the map
 * @param <V> the type of the values in the map
 *
 * @see DualHashBidiMap
 * @see DualTreeBidiMap
 * @since 3.0
 */
public abstract class AbstractDualBidiMap<K, V> implements BidiMap<K, V> {

    
Normal delegate map.
/**
     * Normal delegate map.
     */
    transient Map<K, V> normalMap;

    
Reverse delegate map.
/**
     * Reverse delegate map.
     */
    transient Map<V, K> reverseMap;

    
Inverse view of this map.
/**
     * Inverse view of this map.
     */
    transient BidiMap<V, K> inverseBidiMap = null;

    
View of the keys.
/**
     * View of the keys.
     */
    transient Set<K> keySet = null;

    
View of the values.
/**
     * View of the values.
     */
    transient Set<V> values = null;

    
View of the entries.
/**
     * View of the entries.
     */
    transient Set<Map.Entry<K, V>> entrySet = null;

    
Creates an empty map, initialised by createMap.
 This constructor remains in place for deserialization. All other usage is deprecated in favour of AbstractDualBidiMap(Map, Map). /**
     * Creates an empty map, initialised by <code>createMap</code>.
     * <p>
     * This constructor remains in place for deserialization.
     * All other usage is deprecated in favour of
     * {@link #AbstractDualBidiMap(Map, Map)}.
     */
    protected AbstractDualBidiMap() {
        super();
    }

    
Creates an empty map using the two maps specified as storage.

The two maps must be a matching pair, normal and reverse.
They will typically both be empty.

Neither map is validated, so nulls may be passed in.
If you choose to do this then the subclass constructor must populate
the maps[] instance variable itself.
Params:
normalMap –  the normal direction map
reverseMap –  the reverse direction map
Since:
3.1/**
     * Creates an empty map using the two maps specified as storage.
     * <p>
     * The two maps must be a matching pair, normal and reverse.
     * They will typically both be empty.
     * <p>
     * Neither map is validated, so nulls may be passed in.
     * If you choose to do this then the subclass constructor must populate
     * the <code>maps[]</code> instance variable itself.
     *
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @since 3.1
     */
    protected AbstractDualBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap) {
        super();
        this.normalMap = normalMap;
        this.reverseMap = reverseMap;
    }

    
Constructs a map that decorates the specified maps,
used by the subclass createBidiMap implementation.
Params:
normalMap –  the normal direction map
reverseMap –  the reverse direction map
inverseBidiMap –  the inverse BidiMap/**
     * Constructs a map that decorates the specified maps,
     * used by the subclass <code>createBidiMap</code> implementation.
     *
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @param inverseBidiMap  the inverse BidiMap
     */
    protected AbstractDualBidiMap(final Map<K, V> normalMap, final Map<V, K> reverseMap,
                                  final BidiMap<V, K> inverseBidiMap) {
        super();
        this.normalMap = normalMap;
        this.reverseMap = reverseMap;
        this.inverseBidiMap = inverseBidiMap;
    }

    
Creates a new instance of the subclass.
Params:
normalMap –  the normal direction map
reverseMap –  the reverse direction map
inverseMap –  this map, which is the inverse in the new map
Returns:
the inverse map/**
     * Creates a new instance of the subclass.
     *
     * @param normalMap  the normal direction map
     * @param reverseMap  the reverse direction map
     * @param inverseMap  this map, which is the inverse in the new map
     * @return the inverse map
     */
    protected abstract BidiMap<V, K> createBidiMap(Map<V, K> normalMap, Map<K, V> reverseMap, BidiMap<K, V> inverseMap);

    // Map delegation
    //-----------------------------------------------------------------------

    @Override
    public V get(final Object key) {
        return normalMap.get(key);
    }

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

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

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

    @Override
    public boolean equals(final Object obj) {
        return normalMap.equals(obj);
    }

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

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

    // BidiMap changes
    //-----------------------------------------------------------------------

    @Override
    public V put(final K key, final V value) {
        if (normalMap.containsKey(key)) {
            reverseMap.remove(normalMap.get(key));
        }
        if (reverseMap.containsKey(value)) {
            normalMap.remove(reverseMap.get(value));
        }
        final V obj = normalMap.put(key, value);
        reverseMap.put(value, key);
        return obj;
    }

    @Override
    public void putAll(final Map<? extends K, ? extends V> map) {
        for (final Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
            put(entry.getKey(), entry.getValue());
        }
    }

    @Override
    public V remove(final Object key) {
        V value = null;
        if (normalMap.containsKey(key)) {
            value = normalMap.remove(key);
            reverseMap.remove(value);
        }
        return value;
    }

    @Override
    public void clear() {
        normalMap.clear();
        reverseMap.clear();
    }

    @Override
    public boolean containsValue(final Object value) {
        return reverseMap.containsKey(value);
    }

    // BidiMap
    //-----------------------------------------------------------------------
    
Obtains a MapIterator over the map.
The iterator implements ResetableMapIterator.
This implementation relies on the entrySet iterator.

The setValue() methods only allow a new value to be set.
If the value being set is already in the map, an IllegalArgumentException
is thrown (as setValue cannot change the size of the map).
Returns:
a map iterator/**
     * Obtains a <code>MapIterator</code> over the map.
     * The iterator implements <code>ResetableMapIterator</code>.
     * This implementation relies on the entrySet iterator.
     * <p>
     * The setValue() methods only allow a new value to be set.
     * If the value being set is already in the map, an IllegalArgumentException
     * is thrown (as setValue cannot change the size of the map).
     *
     * @return a map iterator
     */
    @Override
    public MapIterator<K, V> mapIterator() {
        return new BidiMapIterator<>(this);
    }

    @Override
    public K getKey(final Object value) {
        return reverseMap.get(value);
    }

    @Override
    public K removeValue(final Object value) {
        K key = null;
        if (reverseMap.containsKey(value)) {
            key = reverseMap.remove(value);
            normalMap.remove(key);
        }
        return key;
    }

    @Override
    public BidiMap<V, K> inverseBidiMap() {
        if (inverseBidiMap == null) {
            inverseBidiMap = createBidiMap(reverseMap, normalMap, this);
        }
        return inverseBidiMap;
    }

    // Map views
    //-----------------------------------------------------------------------
    
Gets a keySet view of the map.
Changes made on the view are reflected in the map.
The set supports remove and clear but not add.
Returns:
the keySet view/**
     * Gets a keySet view of the map.
     * Changes made on the view are reflected in the map.
     * The set supports remove and clear but not add.
     *
     * @return the keySet view
     */
    @Override
    public Set<K> keySet() {
        if (keySet == null) {
            keySet = new KeySet<>(this);
        }
        return keySet;
    }

    
Creates a key set iterator.
Subclasses can override this to return iterators with different properties.
Params:
iterator –  the iterator to decorate
Returns:
the keySet iterator/**
     * Creates a key set iterator.
     * Subclasses can override this to return iterators with different properties.
     *
     * @param iterator  the iterator to decorate
     * @return the keySet iterator
     */
    protected Iterator<K> createKeySetIterator(final Iterator<K> iterator) {
        return new KeySetIterator<>(iterator, this);
    }

    
Gets a values view of the map.
Changes made on the view are reflected in the map.
The set supports remove and clear but not add.
Returns:
the values view/**
     * Gets a values view of the map.
     * Changes made on the view are reflected in the map.
     * The set supports remove and clear but not add.
     *
     * @return the values view
     */
    @Override
    public Set<V> values() {
        if (values == null) {
            values = new Values<>(this);
        }
        return values;
    }

    
Creates a values iterator.
Subclasses can override this to return iterators with different properties.
Params:
iterator –  the iterator to decorate
Returns:
the values iterator/**
     * Creates a values iterator.
     * Subclasses can override this to return iterators with different properties.
     *
     * @param iterator  the iterator to decorate
     * @return the values iterator
     */
    protected Iterator<V> createValuesIterator(final Iterator<V> iterator) {
        return new ValuesIterator<>(iterator, this);
    }

    
Gets an entrySet view of the map.
Changes made on the set are reflected in the map.
The set supports remove and clear but not add.

The Map Entry setValue() method only allow a new value to be set.
If the value being set is already in the map, an IllegalArgumentException
is thrown (as setValue cannot change the size of the map).
Returns:
the entrySet view/**
     * Gets an entrySet view of the map.
     * Changes made on the set are reflected in the map.
     * The set supports remove and clear but not add.
     * <p>
     * The Map Entry setValue() method only allow a new value to be set.
     * If the value being set is already in the map, an IllegalArgumentException
     * is thrown (as setValue cannot change the size of the map).
     *
     * @return the entrySet view
     */
    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        if (entrySet == null) {
            entrySet = new EntrySet<>(this);
        }
        return entrySet;
    }

    
Creates an entry set iterator.
Subclasses can override this to return iterators with different properties.
Params:
iterator –  the iterator to decorate
Returns:
the entrySet iterator/**
     * Creates an entry set iterator.
     * Subclasses can override this to return iterators with different properties.
     *
     * @param iterator  the iterator to decorate
     * @return the entrySet iterator
     */
    protected Iterator<Map.Entry<K, V>> createEntrySetIterator(final Iterator<Map.Entry<K, V>> iterator) {
        return new EntrySetIterator<>(iterator, this);
    }

    //-----------------------------------------------------------------------
    
Inner class View.
/**
     * Inner class View.
     */
    protected static abstract class View<K, V, E> extends AbstractCollectionDecorator<E> {

        
Generated serial version ID. /** Generated serial version ID. */
        private static final long serialVersionUID = 4621510560119690639L;

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<K, V> parent;

        
Constructs a new view of the BidiMap.
Params:
coll –  the collection view being decorated
parent –  the parent BidiMap/**
         * Constructs a new view of the BidiMap.
         *
         * @param coll  the collection view being decorated
         * @param parent  the parent BidiMap
         */
        protected View(final Collection<E> coll, final AbstractDualBidiMap<K, V> parent) {
            super(coll);
            this.parent = parent;
        }

        @Override
        public boolean equals(final Object object) {
            return object == this || decorated().equals(object);
        }

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

        
Since:
4.4/**
         * @since 4.4
         */
        @Override
        public boolean removeIf(Predicate<? super E> filter) {
            if (parent.isEmpty() || Objects.isNull(filter)) {
                return false;
            }
            boolean modified = false;
            final Iterator<?> it = iterator();
            while (it.hasNext()) {
                @SuppressWarnings("unchecked")
                final E e = (E) it.next();
                if (filter.test(e)) {
                    it.remove();
                    modified = true;
                }
            }
            return modified;
        }

        @Override
        public boolean removeAll(final Collection<?> coll) {
            if (parent.isEmpty() || coll.isEmpty()) {
                return false;
            }
            boolean modified = false;
            final Iterator<?> it = coll.iterator();
            while (it.hasNext()) {
                modified |= remove(it.next());
            }
            return modified;
        }

        
{@inheritDoc}

This implementation iterates over the elements of this bidi map, checking each element in
turn to see if it's contained in coll. If it's not contained, it's removed
from this bidi map. As a consequence, it is advised to use a collection type for
coll that provides a fast (e.g. O(1)) implementation of Collection.contains(Object). /**
         * {@inheritDoc}
         * <p>
         * This implementation iterates over the elements of this bidi map, checking each element in
         * turn to see if it's contained in <code>coll</code>. If it's not contained, it's removed
         * from this bidi map. As a consequence, it is advised to use a collection type for
         * <code>coll</code> that provides a fast (e.g. O(1)) implementation of
         * {@link Collection#contains(Object)}.
         */
        @Override
        public boolean retainAll(final Collection<?> coll) {
            if (parent.isEmpty()) {
                return false;
            }
            if (coll.isEmpty()) {
                parent.clear();
                return true;
            }
            boolean modified = false;
            final Iterator<E> it = iterator();
            while (it.hasNext()) {
                if (coll.contains(it.next()) == false) {
                    it.remove();
                    modified = true;
                }
            }
            return modified;
        }

        @Override
        public void clear() {
            parent.clear();
        }
    }

    //-----------------------------------------------------------------------
    
Inner class KeySet.
/**
     * Inner class KeySet.
     */
    protected static class KeySet<K> extends View<K, Object, K> implements Set<K> {

        
Serialization version /** Serialization version */
        private static final long serialVersionUID = -7107935777385040694L;

        
Constructs a new view of the BidiMap.
Params:
parent –  the parent BidiMap/**
         * Constructs a new view of the BidiMap.
         *
         * @param parent  the parent BidiMap
         */
        @SuppressWarnings("unchecked")
        protected KeySet(final AbstractDualBidiMap<K, ?> parent) {
            super(parent.normalMap.keySet(), (AbstractDualBidiMap<K, Object>) parent);
        }

        @Override
        public Iterator<K> iterator() {
            return parent.createKeySetIterator(super.iterator());
        }

        @Override
        public boolean contains(final Object key) {
            return parent.normalMap.containsKey(key);
        }

        @Override
        public boolean remove(final Object key) {
            if (parent.normalMap.containsKey(key)) {
                final Object value = parent.normalMap.remove(key);
                parent.reverseMap.remove(value);
                return true;
            }
            return false;
        }
    }

    
Inner class KeySetIterator.
/**
     * Inner class KeySetIterator.
     */
    protected static class KeySetIterator<K> extends AbstractIteratorDecorator<K> {

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<K, ?> parent;

        
The last returned key /** The last returned key */
        protected K lastKey = null;

        
Whether remove is allowed at present /** Whether remove is allowed at present */
        protected boolean canRemove = false;

        
Constructor.
Params:
iterator –  the iterator to decorate
parent –  the parent map/**
         * Constructor.
         * @param iterator  the iterator to decorate
         * @param parent  the parent map
         */
        protected KeySetIterator(final Iterator<K> iterator, final AbstractDualBidiMap<K, ?> parent) {
            super(iterator);
            this.parent = parent;
        }

        @Override
        public K next() {
            lastKey = super.next();
            canRemove = true;
            return lastKey;
        }

        @Override
        public void remove() {
            if (canRemove == false) {
                throw new IllegalStateException("Iterator remove() can only be called once after next()");
            }
            final Object value = parent.normalMap.get(lastKey);
            super.remove();
            parent.reverseMap.remove(value);
            lastKey = null;
            canRemove = false;
        }
    }

    //-----------------------------------------------------------------------
    
Inner class Values.
/**
     * Inner class Values.
     */
    protected static class Values<V> extends View<Object, V, V> implements Set<V> {

        
Serialization version /** Serialization version */
        private static final long serialVersionUID = 4023777119829639864L;

        
Constructs a new view of the BidiMap.
Params:
parent –  the parent BidiMap/**
         * Constructs a new view of the BidiMap.
         *
         * @param parent  the parent BidiMap
         */
        @SuppressWarnings("unchecked")
        protected Values(final AbstractDualBidiMap<?, V> parent) {
            super(parent.normalMap.values(), (AbstractDualBidiMap<Object, V>) parent);
        }

        @Override
        public Iterator<V> iterator() {
            return parent.createValuesIterator(super.iterator());
        }

        @Override
        public boolean contains(final Object value) {
            return parent.reverseMap.containsKey(value);
        }

        @Override
        public boolean remove(final Object value) {
            if (parent.reverseMap.containsKey(value)) {
                final Object key = parent.reverseMap.remove(value);
                parent.normalMap.remove(key);
                return true;
            }
            return false;
        }
    }

    
Inner class ValuesIterator.
/**
     * Inner class ValuesIterator.
     */
    protected static class ValuesIterator<V> extends AbstractIteratorDecorator<V> {

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<Object, V> parent;

        
The last returned value /** The last returned value */
        protected V lastValue = null;

        
Whether remove is allowed at present /** Whether remove is allowed at present */
        protected boolean canRemove = false;

        
Constructor.
Params:
iterator –  the iterator to decorate
parent –  the parent map/**
         * Constructor.
         * @param iterator  the iterator to decorate
         * @param parent  the parent map
         */
        @SuppressWarnings("unchecked")
        protected ValuesIterator(final Iterator<V> iterator, final AbstractDualBidiMap<?, V> parent) {
            super(iterator);
            this.parent = (AbstractDualBidiMap<Object, V>) parent;
        }

        @Override
        public V next() {
            lastValue = super.next();
            canRemove = true;
            return lastValue;
        }

        @Override
        public void remove() {
            if (canRemove == false) {
                throw new IllegalStateException("Iterator remove() can only be called once after next()");
            }
            super.remove(); // removes from maps[0]
            parent.reverseMap.remove(lastValue);
            lastValue = null;
            canRemove = false;
        }
    }

    //-----------------------------------------------------------------------
    
Inner class EntrySet.
/**
     * Inner class EntrySet.
     */
    protected static class EntrySet<K, V> extends View<K, V, Map.Entry<K, V>> implements Set<Map.Entry<K, V>> {

        
Serialization version /** Serialization version */
        private static final long serialVersionUID = 4040410962603292348L;

        
Constructs a new view of the BidiMap.
Params:
parent –  the parent BidiMap/**
         * Constructs a new view of the BidiMap.
         *
         * @param parent  the parent BidiMap
         */
        protected EntrySet(final AbstractDualBidiMap<K, V> parent) {
            super(parent.normalMap.entrySet(), parent);
        }

        @Override
        public Iterator<Map.Entry<K, V>> iterator() {
            return parent.createEntrySetIterator(super.iterator());
        }

        @Override
        public boolean remove(final Object obj) {
            if (obj instanceof Map.Entry == false) {
                return false;
            }
            final Map.Entry<?, ?> entry = (Map.Entry<?, ?>) obj;
            final Object key = entry.getKey();
            if (parent.containsKey(key)) {
                final V value = parent.normalMap.get(key);
                if (value == null ? entry.getValue() == null : value.equals(entry.getValue())) {
                    parent.normalMap.remove(key);
                    parent.reverseMap.remove(value);
                    return true;
                }
            }
            return false;
        }
    }

    
Inner class EntrySetIterator.
/**
     * Inner class EntrySetIterator.
     */
    protected static class EntrySetIterator<K, V> extends AbstractIteratorDecorator<Map.Entry<K, V>> {

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<K, V> parent;

        
The last returned entry /** The last returned entry */
        protected Map.Entry<K, V> last = null;

        
Whether remove is allowed at present /** Whether remove is allowed at present */
        protected boolean canRemove = false;

        
Constructor.
Params:
iterator –  the iterator to decorate
parent –  the parent map/**
         * Constructor.
         * @param iterator  the iterator to decorate
         * @param parent  the parent map
         */
        protected EntrySetIterator(final Iterator<Map.Entry<K, V>> iterator, final AbstractDualBidiMap<K, V> parent) {
            super(iterator);
            this.parent = parent;
        }

        @Override
        public Map.Entry<K, V> next() {
            last = new MapEntry<>(super.next(), parent);
            canRemove = true;
            return last;
        }

        @Override
        public void remove() {
            if (canRemove == false) {
                throw new IllegalStateException("Iterator remove() can only be called once after next()");
            }
            // store value as remove may change the entry in the decorator (eg.TreeMap)
            final Object value = last.getValue();
            super.remove();
            parent.reverseMap.remove(value);
            last = null;
            canRemove = false;
        }
    }

    
Inner class MapEntry.
/**
     * Inner class MapEntry.
     */
    protected static class MapEntry<K, V> extends AbstractMapEntryDecorator<K, V> {

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<K, V> parent;

        
Constructor.
Params:
entry –  the entry to decorate
parent –  the parent map/**
         * Constructor.
         * @param entry  the entry to decorate
         * @param parent  the parent map
         */
        protected MapEntry(final Map.Entry<K, V> entry, final AbstractDualBidiMap<K, V> parent) {
            super(entry);
            this.parent = parent;
        }

        @Override
        public V setValue(final V value) {
            final K key = MapEntry.this.getKey();
            if (parent.reverseMap.containsKey(value) &&
                parent.reverseMap.get(value) != key) {
                throw new IllegalArgumentException(
                        "Cannot use setValue() when the object being set is already in the map");
            }
            parent.put(key, value);
            return super.setValue(value);
        }
    }

    
Inner class MapIterator.
/**
     * Inner class MapIterator.
     */
    protected static class BidiMapIterator<K, V> implements MapIterator<K, V>, ResettableIterator<K> {

        
The parent map /** The parent map */
        protected final AbstractDualBidiMap<K, V> parent;

        
The iterator being wrapped /** The iterator being wrapped */
        protected Iterator<Map.Entry<K, V>> iterator;

        
The last returned entry /** The last returned entry */
        protected Map.Entry<K, V> last = null;

        
Whether remove is allowed at present /** Whether remove is allowed at present */
        protected boolean canRemove = false;

        
Constructor.
Params:
parent –  the parent map/**
         * Constructor.
         * @param parent  the parent map
         */
        protected BidiMapIterator(final AbstractDualBidiMap<K, V> parent) {
            super();
            this.parent = parent;
            this.iterator = parent.normalMap.entrySet().iterator();
        }

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

        @Override
        public K next() {
            last = iterator.next();
            canRemove = true;
            return last.getKey();
        }

        @Override
        public void remove() {
            if (canRemove == false) {
                throw new IllegalStateException("Iterator remove() can only be called once after next()");
            }
            // store value as remove may change the entry in the decorator (eg.TreeMap)
            final V value = last.getValue();
            iterator.remove();
            parent.reverseMap.remove(value);
            last = null;
            canRemove = false;
        }

        @Override
        public K getKey() {
            if (last == null) {
                throw new IllegalStateException(
                        "Iterator getKey() can only be called after next() and before remove()");
            }
            return last.getKey();
        }

        @Override
        public V getValue() {
            if (last == null) {
                throw new IllegalStateException(
                        "Iterator getValue() can only be called after next() and before remove()");
            }
            return last.getValue();
        }

        @Override
        public V setValue(final V value) {
            if (last == null) {
                throw new IllegalStateException(
                        "Iterator setValue() can only be called after next() and before remove()");
            }
            if (parent.reverseMap.containsKey(value) &&
                parent.reverseMap.get(value) != last.getKey()) {
                throw new IllegalArgumentException(
                        "Cannot use setValue() when the object being set is already in the map");
            }
            return parent.put(last.getKey(), value);
        }

        @Override
        public void reset() {
            iterator = parent.normalMap.entrySet().iterator();
            last = null;
            canRemove = false;
        }

        @Override
        public String toString() {
            if (last != null) {
                return "MapIterator[" + getKey() + "=" + getValue() + "]";
            }
            return "MapIterator[]";
        }
    }

}