AbstractInputCheckedMapDecorator

/*
 * 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.lang.reflect.Array;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.commons.collections4.iterators.AbstractIteratorDecorator;
import org.apache.commons.collections4.keyvalue.AbstractMapEntryDecorator;
import org.apache.commons.collections4.set.AbstractSetDecorator;

/**
 * An abstract base class that simplifies the task of creating map decorators.
 * <p>
 * The Map API is very difficult to decorate correctly, and involves implementing
 * lots of different classes. This class exists to provide a simpler API.
 * </p>
 * <p>
 * Special hook methods are provided that are called when objects are added to
 * the map. By overriding these methods, the input can be validated or manipulated.
 * In addition to the main map methods, the entrySet is also affected, which is
 * the hardest part of writing map implementations.
 * </p>
 * <p>
 * This class is package-scoped, and may be withdrawn or replaced in future
 * versions of Commons Collections.
 * </p>
 *
 * @since 3.1
 */
abstract class AbstractInputCheckedMapDecorator<K, V>
        extends AbstractMapDecorator<K, V> {

    /**
     * Implementation of an entry set that checks additions via setValue.
     */
    private final class EntrySet extends AbstractSetDecorator<Map.Entry<K, V>> {

        /** Generated serial version ID. */
        private static final long serialVersionUID = 4354731610923110264L;

        /** The parent map */
        private final AbstractInputCheckedMapDecorator<K, V> parent;

        protected EntrySet(final Set<Map.Entry<K, V>> set, final AbstractInputCheckedMapDecorator<K, V> parent) {
            super(set);
            this.parent = parent;
        }

        @Override
        public Iterator<Map.Entry<K, V>> iterator() {
            return new EntrySetIterator(this.decorated().iterator(), parent);
        }

        @Override
        @SuppressWarnings("unchecked")
        public Object[] toArray() {
            final Object[] array = this.decorated().toArray();
            for (int i = 0; i < array.length; i++) {
                array[i] = new MapEntry((Map.Entry<K, V>) array[i], parent);
            }
            return array;
        }

        @Override
        @SuppressWarnings("unchecked")
        public <T> T[] toArray(final T[] array) {
            Object[] result = array;
            if (array.length > 0) {
                // we must create a new array to handle multithreaded situations
                // where another thread could access data before we decorate it
                result = (Object[]) Array.newInstance(array.getClass().getComponentType(), 0);
            }
            result = this.decorated().toArray(result);
            for (int i = 0; i < result.length; i++) {
                result[i] = new MapEntry((Map.Entry<K, V>) result[i], parent);
            }

            // check to see if result should be returned straight
            if (result.length > array.length) {
                return (T[]) result;
            }

            // copy back into input array to fulfil the method contract
            System.arraycopy(result, 0, array, 0, result.length);
            if (array.length > result.length) {
                array[result.length] = null;
            }
            return array;
        }
    }

    /**
     * Implementation of an entry set iterator that checks additions via setValue.
     */
    private final class EntrySetIterator extends AbstractIteratorDecorator<Map.Entry<K, V>> {

        /** The parent map */
        private final AbstractInputCheckedMapDecorator<K, V> parent;

        protected EntrySetIterator(final Iterator<Map.Entry<K, V>> iterator,
                                   final AbstractInputCheckedMapDecorator<K, V> parent) {
            super(iterator);
            this.parent = parent;
        }

        @Override
        public Map.Entry<K, V> next() {
            final Map.Entry<K, V> entry = getIterator().next();
            return new MapEntry(entry, parent);
        }
    }

    /**
     * Implementation of a map entry that checks additions via setValue.
     */
    private final class MapEntry extends AbstractMapEntryDecorator<K, V> {

        /** The parent map */
        private final AbstractInputCheckedMapDecorator<K, V> parent;

        protected MapEntry(final Map.Entry<K, V> entry, final AbstractInputCheckedMapDecorator<K, V> parent) {
            super(entry);
            this.parent = parent;
        }

        @Override
        public V setValue(V value) {
            value = parent.checkSetValue(value);
            return getMapEntry().setValue(value);
        }
    }

    /**
     * Constructor only used in deserialization, do not use otherwise.
     */
    protected AbstractInputCheckedMapDecorator() {
    }

    /**
     * Constructor that wraps (not copies).
     *
     * @param map  the map to decorate, must not be null
     * @throws NullPointerException if map is null
     */
    protected AbstractInputCheckedMapDecorator(final Map<K, V> map) {
        super(map);
    }

    /**
     * Hook method called when a value is being set using {@code setValue}.
     * <p>
     * An implementation may validate the value and throw an exception
     * or it may transform the value into another object.
     * </p>
     * <p>
     * This implementation returns the input value.
     * </p>
     *
     * @param value  the value to check
     * @return the input value
     * @throws UnsupportedOperationException if the map may not be changed by setValue
     * @throws IllegalArgumentException if the specified value is invalid
     * @throws ClassCastException if the class of the specified value is invalid
     * @throws NullPointerException if the specified value is null and nulls are invalid
     */
    protected abstract V checkSetValue(V value);

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

    /**
     * Hook method called to determine if {@code checkSetValue} has any effect.
     * <p>
     * An implementation should return false if the {@code checkSetValue} method
     * has no effect as this optimizes the implementation.
     * <p>
     * This implementation returns {@code true}.
     *
     * @return true always
     */
    protected boolean isSetValueChecking() {
        return true;
    }

}