/*
    * The contents of this file are subject to the terms of the Common Development and
    * Distribution License (the License). You may not use this file except in compliance with the
    * License.
    *
    * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
    * specific language governing permission and limitations under the License.
    *
    * When distributing Covered Software, include this CDDL Header Notice in each file and include
   * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
   * Header, with the fields enclosed by brackets [] replaced by your own identifying
   * information: "Portions copyright [year] [name of copyright owner]".
   *
   * Copyright 2015-2016 ForgeRock AS.
   */
  
  package org.forgerock.util;
  
  // Java SE
  import java.util.Collection;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * A map with lazy initialization. The factory is called to initialize the map
   * on the first call to one of this object's methods.
   *
   * @param <K>
   *            The type of key.
   * @param <V>
   *            The type of value.
   */
  public class LazyMap<K, V> implements Map<K, V> {
  
      /** The map that this lazy map exposes, once initialized. */
      private Map<K, V> map;
  
      /** Factory to create the instance of the map to expose. */
      protected Factory<Map<K, V>> factory;
  
      /**
       * Constructs a new lazy map. Allows factory to be set in subclass
       * constructor.
       */
      protected LazyMap() {
      }
  
      /**
       * Constructs a new lazy map.
       *
       * @param factory
       *            factory to create the map instance to expose.
       */
      public LazyMap(Factory<Map<K, V>> factory) {
          this.factory = factory;
      }
  
      /**
       * Performs lazy initialization of the map if not already performed, and
       * returns the initialized map.
       */
      private Map<K, V> lazy() {
          if (map == null) {
              synchronized (this) {
                  if (map == null) {
                      map = factory.newInstance();
                  }
              }
          }
          return map;
      }
  
      /**
       * Returns the number of key-value mappings in this map.
       */
      @Override
      public int size() {
          return lazy().size();
      }
  
      /**
       * Returns {@code true} if the map contains no key-value mappings.
       */
      @Override
      public boolean isEmpty() {
          return lazy().isEmpty();
      }
  
      /**
       * Returns {@code true} if this map contains a mapping for the specified
       * key.
       *
       * @param key
       *            the key whose presence in this map is to be tested.
       * @return {@code true} if this map contains a mapping for the specified
       *         key.
       */
      @Override
      public boolean containsKey(Object key) {
         return lazy().containsKey(key);
     }
 
     /**
      * Returns {@code true} if the map maps one or more keys to the specified
      * value.
      *
      * @param value
      *            the value whose presence in the map is to be tested.
      * @return {@code true} if the map maps one or more keys to the specified
      *         value.
      */
     @Override
     public boolean containsValue(Object value) {
         return lazy().containsValue(value);
     }
 
     /**
      * Returns the value to which the specified key is mapped, or {@code null}
      * if the map contains no mapping for the key.
      *
      * @param key
      *            the key whose associated value is to be returned.
      * @return the value to which the specified key is mapped, or {@code null}
      *         if no mapping.
      */
     @Override
     public V get(Object key) {
         return lazy().get(key);
     }
 
     /**
      * Associates the specified value with the specified key in the map.
      *
      * @param key
      *            key with which the specified value is to be associated.
      * @param value
      *            value to be associated with the specified key.
      * @return the previous value associated with key, or {@code null} if no
      *         mapping.
      */
     @Override
     public V put(K key, V value) {
         return lazy().put(key, value);
     }
 
     /**
      * Removes the mapping for a key from the map if it is present.
      *
      * @param key
      *            key whose mapping is to be removed from the map.
      * @return the previous value associated with key, or {@code null} if no
      *         mapping.
      */
     @Override
     public V remove(Object key) {
         return lazy().remove(key);
     }
 
     /**
      * Copies all of the mappings from the specified map to the map.
      *
      * @param m
      *            mappings to be stored in the map.
      */
     @Override
     public void putAll(Map<? extends K, ? extends V> m) {
         lazy().putAll(m);
     }
 
     /**
      * Removes all of the mappings from the map.
      */
     @Override
     public void clear() {
         lazy().clear();
     }
 
     /**
      * Returns a {@link Set} view of the keys contained in the map.
      */
     @Override
     public Set<K> keySet() {
         return lazy().keySet();
     }
 
     /**
      * Returns a {@link Collection} view of the values contained in the map.
      */
     @Override
     public Collection<V> values() {
         return lazy().values();
     }
 
     /**
      * Returns a {@link Set} view of the mappings contained in the map.
      */
     @Override
     public Set<Map.Entry<K, V>> entrySet() {
         return lazy().entrySet();
     }
 
     /**
      * Returns the hash code value for the map.
      */
     @Override
     public int hashCode() {
         return lazy().hashCode();
     }
 
     /**
      * Compares the specified object with the map for equality.
      *
      * @param o
      *            object to be compared for equality with the map.
      * @return {@code true} if the specified object is equal to the map.
      */
     @Override
     public boolean equals(Object o) {
         return lazy().equals(o);
     }
 }