/*
 * 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
 * limitations under the License.
 */
package org.apache.commons.beanutils;

import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

A customized implementation of java.util.HashMap designed
to operate in a multithreaded environment where the large majority of
method calls are read-only, instead of structural changes.  When operating
in "fast" mode, read calls are non-synchronized and write calls perform the
following steps:

Clone the existing collection
Perform the modification on the clone
Replace the existing collection with the (modified) clone

When first created, objects of this class default to "slow" mode, where
all accesses of any type are synchronized but no cloning takes place.  This
is appropriate for initially populating the collection, followed by a switch
to "fast" mode (by calling setFast(true)) after initialization
is complete.
NOTE: If you are creating and accessing a
HashMap only within a single thread, you should use
java.util.HashMap directly (with no synchronization), for
maximum performance.
NOTE: This class is not cross-platform.
Using it may cause unexpected failures on some architectures.
It suffers from the same problems as the double-checked locking idiom.
In particular, the instruction that clones the internal collection and the
instruction that sets the internal reference to the clone can be executed
or perceived out-of-order.  This means that any read operation might fail
unexpectedly, as it may be reading the state of the internal collection
before the internal collection is fully formed.
For more information on the double-checked locking idiom, see the

Double-Checked Locking Idiom Is Broken Declaration.
Since:
Commons Collections 1.0
Version:
$Id$/**
 * <p>A customized implementation of <code>java.util.HashMap</code> designed
 * to operate in a multithreaded environment where the large majority of
 * method calls are read-only, instead of structural changes.  When operating
 * in "fast" mode, read calls are non-synchronized and write calls perform the
 * following steps:</p>
 * <ul>
 * <li>Clone the existing collection
 * <li>Perform the modification on the clone
 * <li>Replace the existing collection with the (modified) clone
 * </ul>
 * <p>When first created, objects of this class default to "slow" mode, where
 * all accesses of any type are synchronized but no cloning takes place.  This
 * is appropriate for initially populating the collection, followed by a switch
 * to "fast" mode (by calling <code>setFast(true)</code>) after initialization
 * is complete.</p>
 *
 * <p><strong>NOTE</strong>: If you are creating and accessing a
 * <code>HashMap</code> only within a single thread, you should use
 * <code>java.util.HashMap</code> directly (with no synchronization), for
 * maximum performance.</p>
 *
 * <p><strong>NOTE</strong>: <i>This class is not cross-platform.
 * Using it may cause unexpected failures on some architectures.</i>
 * It suffers from the same problems as the double-checked locking idiom.
 * In particular, the instruction that clones the internal collection and the
 * instruction that sets the internal reference to the clone can be executed
 * or perceived out-of-order.  This means that any read operation might fail
 * unexpectedly, as it may be reading the state of the internal collection
 * before the internal collection is fully formed.
 * For more information on the double-checked locking idiom, see the
 * <a href="http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html">
 * Double-Checked Locking Idiom Is Broken Declaration</a>.</p>
 *
 * @since Commons Collections 1.0
 * @version $Id$
 */
class WeakFastHashMap<K, V> extends HashMap<K, V> {

    
The underlying map we are managing.
/**
     * The underlying map we are managing.
     */
    private Map<K, V> map = null;

    
Are we currently operating in "fast" mode?
/**
     * Are we currently operating in "fast" mode?
     */
    private boolean fast = false;

    // Constructors
    // ----------------------------------------------------------------------

    
Construct an empty map.
/**
     * Construct an empty map.
     */
    public WeakFastHashMap() {
        super();
        this.map = createMap();
    }

    
Construct an empty map with the specified capacity.
Params:
capacity –  the initial capacity of the empty map/**
     * Construct an empty map with the specified capacity.
     *
     * @param capacity  the initial capacity of the empty map
     */
    public WeakFastHashMap(final int capacity) {
        super();
        this.map = createMap(capacity);
    }

    
Construct an empty map with the specified capacity and load factor.
Params:
capacity –  the initial capacity of the empty map
factor –  the load factor of the new map/**
     * Construct an empty map with the specified capacity and load factor.
     *
     * @param capacity  the initial capacity of the empty map
     * @param factor  the load factor of the new map
     */
    public WeakFastHashMap(final int capacity, final float factor) {
        super();
        this.map = createMap(capacity, factor);
    }

    
Construct a new map with the same mappings as the specified map.
Params:
map –  the map whose mappings are to be copied/**
     * Construct a new map with the same mappings as the specified map.
     *
     * @param map  the map whose mappings are to be copied
     */
    public WeakFastHashMap(final Map<? extends K, ? extends V> map) {
        super();
        this.map = createMap(map);
    }


    // Property access
    // ----------------------------------------------------------------------

    
 Returns true if this map is operating in fast mode.
 @return true if this map is operating in fast mode
/**
     *  Returns true if this map is operating in fast mode.
     *
     *  @return true if this map is operating in fast mode
     */
    public boolean getFast() {
        return (this.fast);
    }

    
 Sets whether this map is operating in fast mode.
 @param fast true if this map should operate in fast mode
/**
     *  Sets whether this map is operating in fast mode.
     *
     *  @param fast true if this map should operate in fast mode
     */
    public void setFast(final boolean fast) {
        this.fast = fast;
    }


    // Map access
    // ----------------------------------------------------------------------
    // These methods can forward straight to the wrapped Map in 'fast' mode.
    // (because they are query methods)

    
Return the value to which this map maps the specified key.  Returns
null if the map contains no mapping for this key, or if
there is a mapping with a value of null.  Use the
containsKey() method to disambiguate these cases.
Params:
key –  the key whose value is to be returned
Returns:
the value mapped to that key, or null/**
     * Return the value to which this map maps the specified key.  Returns
     * <code>null</code> if the map contains no mapping for this key, or if
     * there is a mapping with a value of <code>null</code>.  Use the
     * <code>containsKey()</code> method to disambiguate these cases.
     *
     * @param key  the key whose value is to be returned
     * @return the value mapped to that key, or null
     */
    @Override
    public V get(final Object key) {
        if (fast) {
            return (map.get(key));
        } else {
            synchronized (map) {
                return (map.get(key));
            }
        }
    }

    
Return the number of key-value mappings in this map.
Returns:
the current size of the map/**
     * Return the number of key-value mappings in this map.
     *
     * @return the current size of the map
     */
    @Override
    public int size() {
        if (fast) {
            return (map.size());
        } else {
            synchronized (map) {
                return (map.size());
            }
        }
    }

    
Return true if this map contains no mappings.
Returns:
is the map currently empty/**
     * Return <code>true</code> if this map contains no mappings.
     *
     * @return is the map currently empty
     */
    @Override
    public boolean isEmpty() {
        if (fast) {
            return (map.isEmpty());
        } else {
            synchronized (map) {
                return (map.isEmpty());
            }
        }
    }

    
Return true if this map contains a mapping for the
specified key.
Params:
key –  the key to be searched for
Returns:
true if the map contains the key/**
     * Return <code>true</code> if this map contains a mapping for the
     * specified key.
     *
     * @param key  the key to be searched for
     * @return true if the map contains the key
     */
    @Override
    public boolean containsKey(final Object key) {
        if (fast) {
            return (map.containsKey(key));
        } else {
            synchronized (map) {
                return (map.containsKey(key));
            }
        }
    }

    
Return true if this map contains one or more keys mapping
to the specified value.
Params:
value –  the value to be searched for
Returns:
true if the map contains the value/**
     * Return <code>true</code> if this map contains one or more keys mapping
     * to the specified value.
     *
     * @param value  the value to be searched for
     * @return true if the map contains the value
     */
    @Override
    public boolean containsValue(final Object value) {
        if (fast) {
            return (map.containsValue(value));
        } else {
            synchronized (map) {
                return (map.containsValue(value));
            }
        }
    }

    // Map modification
    // ----------------------------------------------------------------------
    // These methods perform special behaviour in 'fast' mode.
    // The map is cloned, updated and then assigned back.
    // See the comments at the top as to why this won't always work.

    
Associate the specified value with the specified key in this map.
If the map previously contained a mapping for this key, the old
value is replaced and returned.
Params:
key –  the key with which the value is to be associated
value –  the value to be associated with this key
Returns:
the value previously mapped to the key, or null/**
     * Associate the specified value with the specified key in this map.
     * If the map previously contained a mapping for this key, the old
     * value is replaced and returned.
     *
     * @param key  the key with which the value is to be associated
     * @param value  the value to be associated with this key
     * @return the value previously mapped to the key, or null
     */
    @Override
    public V put(final K key, final V value) {
        if (fast) {
            synchronized (this) {
                final Map<K, V> temp = cloneMap(map);
                final V result = temp.put(key, value);
                map = temp;
                return (result);
            }
        } else {
            synchronized (map) {
                return (map.put(key, value));
            }
        }
    }

    
Copy all of the mappings from the specified map to this one, replacing
any mappings with the same keys.
Params:
in –  the map whose mappings are to be copied/**
     * Copy all of the mappings from the specified map to this one, replacing
     * any mappings with the same keys.
     *
     * @param in  the map whose mappings are to be copied
     */
    @Override
    public void putAll(final Map<? extends K, ? extends V> in) {
        if (fast) {
            synchronized (this) {
                final Map<K, V> temp =  cloneMap(map);
                temp.putAll(in);
                map = temp;
            }
        } else {
            synchronized (map) {
                map.putAll(in);
            }
        }
    }

    
Remove any mapping for this key, and return any previously
mapped value.
Params:
key –  the key whose mapping is to be removed
Returns:
the value removed, or null/**
     * Remove any mapping for this key, and return any previously
     * mapped value.
     *
     * @param key  the key whose mapping is to be removed
     * @return the value removed, or null
     */
    @Override
    public V remove(final Object key) {
        if (fast) {
            synchronized (this) {
                final Map<K, V> temp = cloneMap(map);
                final V result = temp.remove(key);
                map = temp;
                return (result);
            }
        } else {
            synchronized (map) {
                return (map.remove(key));
            }
        }
    }

    
Remove all mappings from this map.
/**
     * Remove all mappings from this map.
     */
    @Override
    public void clear() {
        if (fast) {
            synchronized (this) {
                map = createMap();
            }
        } else {
            synchronized (map) {
                map.clear();
            }
        }
    }

    // Basic object methods
    // ----------------------------------------------------------------------

    
Compare the specified object with this list for equality.  This
implementation uses exactly the code that is used to define the
list equals function in the documentation for the
Map.equals method.
Params:
o –  the object to be compared to this list
Returns:
true if the two maps are equal/**
     * Compare the specified object with this list for equality.  This
     * implementation uses exactly the code that is used to define the
     * list equals function in the documentation for the
     * <code>Map.equals</code> method.
     *
     * @param o  the object to be compared to this list
     * @return true if the two maps are equal
     */
    @Override
    public boolean equals(final Object o) {
        // Simple tests that require no synchronization
        if (o == this) {
            return (true);
        } else if (!(o instanceof Map)) {
            return (false);
        }
        final Map<?, ?> mo = (Map<?, ?>) o;

        // Compare the two maps for equality
        if (fast) {
            if (mo.size() != map.size()) {
                return (false);
            }
            for (final Map.Entry<K, V> e : map.entrySet()) {
                final K key = e.getKey();
                final V value = e.getValue();
                if (value == null) {
                    if (!(mo.get(key) == null && mo.containsKey(key))) {
                        return (false);
                    }
                } else {
                    if (!value.equals(mo.get(key))) {
                        return (false);
                    }
                }
            }
            return (true);

        } else {
            synchronized (map) {
                if (mo.size() != map.size()) {
                    return (false);
                }
                for (final Map.Entry<K, V> e : map.entrySet()) {
                    final K key = e.getKey();
                    final V value = e.getValue();
                    if (value == null) {
                        if (!(mo.get(key) == null && mo.containsKey(key))) {
                            return (false);
                        }
                    } else {
                        if (!value.equals(mo.get(key))) {
                            return (false);
                        }
                    }
                }
                return (true);
            }
        }
    }

    
Return the hash code value for this map.  This implementation uses
exactly the code that is used to define the list hash function in the
documentation for the Map.hashCode method.
Returns:
suitable integer hash code/**
     * Return the hash code value for this map.  This implementation uses
     * exactly the code that is used to define the list hash function in the
     * documentation for the <code>Map.hashCode</code> method.
     *
     * @return suitable integer hash code
     */
    @Override
    public int hashCode() {
        if (fast) {
            int h = 0;
            for (final Map.Entry<K, V> e : map.entrySet()) {
                h += e.hashCode();
            }
            return (h);
        } else {
            synchronized (map) {
                int h = 0;
                for (final Map.Entry<K, V> e : map.entrySet()) {
                    h += e.hashCode();
                }
                return (h);
            }
        }
    }

    
Return a shallow copy of this FastHashMap instance.
The keys and values themselves are not copied.
Returns:
a clone of this map/**
     * Return a shallow copy of this <code>FastHashMap</code> instance.
     * The keys and values themselves are not copied.
     *
     * @return a clone of this map
     */
    @Override
    public Object clone() {
        WeakFastHashMap<K, V> results = null;
        if (fast) {
            results = new WeakFastHashMap<K, V>(map);
        } else {
            synchronized (map) {
                results = new WeakFastHashMap<K, V>(map);
            }
        }
        results.setFast(getFast());
        return (results);
    }

    // Map views
    // ----------------------------------------------------------------------

    
Return a collection view of the mappings contained in this map.  Each
element in the returned collection is a Map.Entry.
Returns:
the set of map Map entries/**
     * Return a collection view of the mappings contained in this map.  Each
     * element in the returned collection is a <code>Map.Entry</code>.
     * @return the set of map Map entries
     */
    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        return new EntrySet();
    }

    
Return a set view of the keys contained in this map.
Returns:
the set of the Map's keys/**
     * Return a set view of the keys contained in this map.
     * @return the set of the Map's keys
     */
    @Override
    public Set<K> keySet() {
        return new KeySet();
    }

    
Return a collection view of the values contained in this map.
Returns:
the set of the Map's values/**
     * Return a collection view of the values contained in this map.
     * @return the set of the Map's values
     */
    @Override
    public Collection<V> values() {
        return new Values();
    }

    // Abstractions on Map creations (for subclasses such as WeakFastHashMap)
    // ----------------------------------------------------------------------

    protected Map<K, V> createMap() {
        return new WeakHashMap<K, V>();
    }

    protected Map<K, V> createMap(final int capacity) {
        return new WeakHashMap<K, V>(capacity);
    }

    protected Map<K, V> createMap(final int capacity, final float factor) {
        return new WeakHashMap<K, V>(capacity, factor);
    }

    protected Map<K, V> createMap(final Map<? extends K, ? extends V> map) {
        return new WeakHashMap<K, V>(map);
    }

    protected Map<K, V> cloneMap(final Map<? extends K, ? extends V> map) {
        return createMap(map);
    }

    // Map view inner classes
    // ----------------------------------------------------------------------

    
Abstract collection implementation shared by keySet(), values() and entrySet().
Type parameters:
<E> – the element type/**
     * Abstract collection implementation shared by keySet(), values() and entrySet().
     *
     * @param <E> the element type
     */
    private abstract class CollectionView<E> implements Collection<E> {

        public CollectionView() {
        }

        protected abstract Collection<E> get(Map<K, V> map);
        protected abstract E iteratorNext(Map.Entry<K, V> entry);


        public void clear() {
            if (fast) {
                synchronized (WeakFastHashMap.this) {
                    map = createMap();
                }
            } else {
                synchronized (map) {
                    get(map).clear();
                }
            }
        }

        public boolean remove(final Object o) {
            if (fast) {
                synchronized (WeakFastHashMap.this) {
                    final Map<K, V> temp = cloneMap(map);
                    final boolean r = get(temp).remove(o);
                    map = temp;
                    return r;
                }
            } else {
                synchronized (map) {
                    return get(map).remove(o);
                }
            }
        }

        public boolean removeAll(final Collection<?> o) {
            if (fast) {
                synchronized (WeakFastHashMap.this) {
                    final Map<K, V> temp = cloneMap(map);
                    final boolean r = get(temp).removeAll(o);
                    map = temp;
                    return r;
                }
            } else {
                synchronized (map) {
                    return get(map).removeAll(o);
                }
            }
        }

        public boolean retainAll(final Collection<?> o) {
            if (fast) {
                synchronized (WeakFastHashMap.this) {
                    final Map<K, V> temp = cloneMap(map);
                    final boolean r = get(temp).retainAll(o);
                    map = temp;
                    return r;
                }
            } else {
                synchronized (map) {
                    return get(map).retainAll(o);
                }
            }
        }

        public int size() {
            if (fast) {
                return get(map).size();
            } else {
                synchronized (map) {
                    return get(map).size();
                }
            }
        }


        public boolean isEmpty() {
            if (fast) {
                return get(map).isEmpty();
            } else {
                synchronized (map) {
                    return get(map).isEmpty();
                }
            }
        }

        public boolean contains(final Object o) {
            if (fast) {
                return get(map).contains(o);
            } else {
                synchronized (map) {
                    return get(map).contains(o);
                }
            }
        }

        public boolean containsAll(final Collection<?> o) {
            if (fast) {
                return get(map).containsAll(o);
            } else {
                synchronized (map) {
                    return get(map).containsAll(o);
                }
            }
        }

        public <T> T[] toArray(final T[] o) {
            if (fast) {
                return get(map).toArray(o);
            } else {
                synchronized (map) {
                    return get(map).toArray(o);
                }
            }
        }

        public Object[] toArray() {
            if (fast) {
                return get(map).toArray();
            } else {
                synchronized (map) {
                    return get(map).toArray();
                }
            }
        }


        @Override
        public boolean equals(final Object o) {
            if (o == this) {
                return true;
            }
            if (fast) {
                return get(map).equals(o);
            } else {
                synchronized (map) {
                    return get(map).equals(o);
                }
            }
        }

        @Override
        public int hashCode() {
            if (fast) {
                return get(map).hashCode();
            } else {
                synchronized (map) {
                    return get(map).hashCode();
                }
            }
        }

        public boolean add(final E o) {
            throw new UnsupportedOperationException();
        }

        public boolean addAll(final Collection<? extends E> c) {
            throw new UnsupportedOperationException();
        }

        public Iterator<E> iterator() {
            return new CollectionViewIterator();
        }

        private class CollectionViewIterator implements Iterator<E> {

            private Map<K, V> expected;
            private Map.Entry<K, V> lastReturned = null;
            private final Iterator<Map.Entry<K, V>> iterator;

            public CollectionViewIterator() {
                this.expected = map;
                this.iterator = expected.entrySet().iterator();
            }

            public boolean hasNext() {
                if (expected != map) {
                    throw new ConcurrentModificationException();
                }
                return iterator.hasNext();
            }

            public E next() {
                if (expected != map) {
                    throw new ConcurrentModificationException();
                }
                lastReturned = iterator.next();
                return iteratorNext(lastReturned);
            }

            public void remove() {
                if (lastReturned == null) {
                    throw new IllegalStateException();
                }
                if (fast) {
                    synchronized (WeakFastHashMap.this) {
                        if (expected != map) {
                            throw new ConcurrentModificationException();
                        }
                        WeakFastHashMap.this.remove(lastReturned.getKey());
                        lastReturned = null;
                        expected = map;
                    }
                } else {
                    iterator.remove();
                    lastReturned = null;
                }
            }
        }
    }

    
Set implementation over the keys of the FastHashMap
/**
     * Set implementation over the keys of the FastHashMap
     */
    private class KeySet extends CollectionView<K> implements Set<K> {

        @Override
        protected Collection<K> get(final Map<K, V> map) {
            return map.keySet();
        }

        @Override
        protected K iteratorNext(final Map.Entry<K, V> entry) {
            return entry.getKey();
        }

    }

    
Collection implementation over the values of the FastHashMap
/**
     * Collection implementation over the values of the FastHashMap
     */
    private class Values extends CollectionView<V> {

        @Override
        protected Collection<V> get(final Map<K, V> map) {
            return map.values();
        }

        @Override
        protected V iteratorNext(final Map.Entry<K, V> entry) {
            return entry.getValue();
        }
    }

    
Set implementation over the entries of the FastHashMap
/**
     * Set implementation over the entries of the FastHashMap
     */
    private class EntrySet extends CollectionView<Map.Entry<K, V>> implements Set<Map.Entry<K, V>> {

        @Override
        protected Collection<Map.Entry<K, V>> get(final Map<K, V> map) {
            return map.entrySet();
        }

        @Override
        protected Map.Entry<K, V> iteratorNext(final Map.Entry<K, V> entry) {
            return entry;
        }

    }

}