/*
 * 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.collections4.map;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Map;

/**
 * A {@code Map} implementation that matches keys and values based
 * on {@code ==} not {@code equals()}.
 * <p>
 * <strong>This map will violate the detail of various Map and map view contracts.</strong>
 * As a general rule, don't compare this map to other maps. In particular, you can't
 * use decorators like {@link ListOrderedMap} on it, which silently assume that these
 * contracts are fulfilled.
 * <p>
 * <strong>Note that IdentityMap is not synchronized and is not thread-safe.</strong>
 * If you wish to use this map from multiple threads concurrently, you must use
 * appropriate synchronization. The simplest approach is to wrap this map
 * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
 * exceptions when accessed by concurrent threads without synchronization.
 * <p>
 * From 4.0, this class is replaced by java.util.IdentityHashMap but kept as a
 * test-class because it is still used by the ReferenceIdentityMapTest.
 *
 * @param <K> the type of the keys in this map
 * @param <V> the type of the values in this map
 * @since 3.0
 */
public class IdentityMap<K, V>
        extends AbstractHashedMap<K, V> implements Serializable, Cloneable {

    /** Serialisation version */
    private static final long serialVersionUID = 2028493495224302329L;

    /**
     * Constructs a new empty map with default size and load factor.
     */
    public IdentityMap() {
        super(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_THRESHOLD);
    }

    /**
     * Constructs a new, empty map with the specified initial capacity.
     *
     * @param initialCapacity  the initial capacity
     * @throws IllegalArgumentException if the initial capacity is negative
     */
    public IdentityMap(final int initialCapacity) {
        super(initialCapacity);
    }

    /**
     * Constructs a new, empty map with the specified initial capacity and
     * load factor.
     *
     * @param initialCapacity  the initial capacity
     * @param loadFactor  the load factor
     * @throws IllegalArgumentException if the initial capacity is negative
     * @throws IllegalArgumentException if the load factor is less than zero
     */
    public IdentityMap(final int initialCapacity, final float loadFactor) {
        super(initialCapacity, loadFactor);
    }

    /**
     * Constructor copying elements from another map.
     *
     * @param map  the map to copy
     * @throws NullPointerException if the map is null
     */
    public IdentityMap(final Map<K, V> map) {
        super(map);
    }

    /**
     * Gets the hash code for the key specified.
     * This implementation uses the identity hash code.
     *
     * @param key  the key to get a hash code for
     * @return the hash code
     */
    @Override
    protected int hash(final Object key) {
        return System.identityHashCode(key);
    }

    /**
     * Compares two keys for equals.
     * This implementation uses {@code ==}.
     *
     * @param key1  the first key to compare
     * @param key2  the second key to compare
     * @return true if equal by identity
     */
    @Override
    protected boolean isEqualKey(final Object key1, final Object key2) {
        return key1 == key2;
    }

    /**
     * Compares two values for equals.
     * This implementation uses {@code ==}.
     *
     * @param value1  the first value to compare
     * @param value2  the second value to compare
     * @return true if equal by identity
     */
    @Override
    protected boolean isEqualValue(final Object value1, final Object value2) {
        return value1 == value2;
    }

    /**
     * Creates an entry to store the data.
     * This implementation creates an IdentityEntry instance.
     *
     * @param next  the next entry in sequence
     * @param hashCode  the hash code to use
     * @param key  the key to store
     * @param value  the value to store
     * @return the newly created entry
     */
    @Override
    protected IdentityEntry<K, V> createEntry(final HashEntry<K, V> next, final int hashCode,
                                              final K key, final V value) {
        return new IdentityEntry<>(next, hashCode, key, value);
    }

    /**
     * HashEntry
     */
    protected static class IdentityEntry<K, V> extends HashEntry<K, V> {

        protected IdentityEntry(final HashEntry<K, V> next, final int hashCode, final K key, final V value) {
            super(next, hashCode, key, value);
        }

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

        @Override
        public int hashCode() {
            return System.identityHashCode(getKey()) ^
                   System.identityHashCode(getValue());
        }
    }

    /**
     * Clones the map without cloning the keys or values.
     *
     * @return a shallow clone
     */
    @Override
    public IdentityMap<K, V> clone() {
        return (IdentityMap<K, V>) super.clone();
    }

    /**
     * Write the map out using a custom routine.
     */
    private void writeObject(final ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        doWriteObject(out);
    }

    /**
     * Read the map in using a custom routine.
     */
    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        doReadObject(in);
    }

}
