/**
 * Licensed to Apereo under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright ownership. Apereo
 * 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 the
 * following location:
 *
 * <p>http://www.apache.org/licenses/LICENSE-2.0
 *
 * <p>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.apereo.portal.utils;

import com.google.common.base.Function;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * Utilities for working with concurrent maps
 *
 */
public final class ConcurrentMapUtils {
    private ConcurrentMapUtils() {}

    /**
     * How putIfAbsent should work, returns the one value that actually ends up in the {@link
     * ConcurrentMap}
     *
     * @param map The map
     * @param key The key
     * @param value The value to put
     * @return The value that exists in the Map for this key at the point in time that {@link
     *     ConcurrentMap#putIfAbsent(Object, Object)} is called
     */
    public static <K, V> V putIfAbsent(ConcurrentMap<K, V> map, K key, V value) {
        final V existingValue = map.putIfAbsent(key, value);
        if (existingValue == null) {
            return value;
        }

        return existingValue;
    }

    /**
     * Make a {@link ConcurrentMap} that when {@link ConcurrentMap#get(Object)} is called an null is
     * returned the creator function is called and the value returned is used with {@link
     * ConcurrentMap#putIfAbsent(Object, Object)}. The value that ends up in the {@link
     * ConcurrentMap} is returned by the get function.
     */
    public static <K, V> ConcurrentMap<K, V> makeDefaultsMap(final Function<K, V> creator) {
        return new ConcurrentHashMap<K, V>() {
            @Override
            public V get(Object keyObj) {
                V value = super.get(keyObj);
                if (value == null) {
                    K key = (K) keyObj;
                    value = creator.apply(key);
                    final V existingValue = super.putIfAbsent(key, value);
                    if (existingValue != null) {
                        value = existingValue;
                    }
                }
                return value;
            }
        };
    }
}