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   *  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
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   *    https://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
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  package org.apache.cayenne.cache;
  
  import java.io.Serializable;
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.cayenne.CayenneRuntimeException;
  import org.apache.cayenne.query.QueryMetadata;
  import org.apache.cayenne.util.concurrentlinkedhashmap.ConcurrentLinkedHashMap;
  
  /**
   * A default implementation of the {@link QueryCache} interface that stores data in a
   * non-expiring LRUMap.
   * 
   * @since 3.0
   */
  public class MapQueryCache implements QueryCache, Serializable {
  
      public static final int DEFAULT_CACHE_SIZE = 1000;
  
      static final String DEFAULT_CACHE_NAME = "cayenne.default.cache";
  
      protected final Map<String, Map<String, List<?>>> cacheGroups;
  
      private int maxSize;
  
      public MapQueryCache() {
          this(DEFAULT_CACHE_SIZE);
      }
  
      public MapQueryCache(int maxSize) {
          this.cacheGroups = new ConcurrentHashMap<>();
          this.maxSize = maxSize;
      }
  
      public List get(QueryMetadata metadata) {
          String key = metadata.getCacheKey();
          if (key == null) {
              return null;
          }
          Map<String, List<?>> map = createIfAbsent(metadata);
          synchronized (map) {
              return map.get(key);
          }
      }
  
      /**
       * Returns a non-null cached value. If it is not present in the cache, it is obtained
       * by calling {@link QueryCacheEntryFactory#createObject()} without blocking the cache. As
       * a result there is a potential of multiple threads to be updating cache in parallel -
       * this wouldn't lead to corruption of the cache, but can be suboptimal.
       */
      @SuppressWarnings("rawtypes")
      public List get(QueryMetadata metadata, QueryCacheEntryFactory factory) {
          List result = get(metadata);
          if (result == null) {
              List newObject = factory.createObject();
              if (newObject == null) {
                  throw new CayenneRuntimeException("Null on cache rebuilding: %s", metadata.getCacheKey());
              }
  
              result = newObject;
              put(metadata, result);
          }
  
          return result;
      }
  
      public void put(QueryMetadata metadata, List results) {
          String key = metadata.getCacheKey();
          if (key == null) {
              return;
          }
  
          Map<String, List<?>> map = createIfAbsent(metadata);
          synchronized (map) {
              map.put(key, results);
          }
      }
  
      public void remove(String key) {
          if (key == null) {
              return;
          }
  
          for(Map<String, List<?>> map : cacheGroups.values()) {
              synchronized (map) {
                  map.remove(key);
              }
          }
      }
  
      public void removeGroup(String groupKey) {
          if (groupKey != null) {
              cacheGroups.remove(groupKey);
          }
      }
  
      public void removeGroup(String groupKey, Class<?> keyType, Class<?> valueType) {
          removeGroup(groupKey);
      }
  
      public void clear() {
          cacheGroups.clear();
      }
  
      public int size() {
          int size = 0;
          for(Map<String, List<?>> map : cacheGroups.values()) {
              synchronized (map) {
                  size += map.size();
              }
          }
          return size;
      }
  
      protected Map<String, List<?>> createIfAbsent(QueryMetadata metadata) {
          return createIfAbsent(cacheName(metadata));
      }
  
      protected Map<String, List<?>> createIfAbsent(String cacheName) {
          Map<String, List<?>> cache = getCache(cacheName);
          if (cache == null) {
              cache = createCache(cacheName);
          }
  
          return cache;
      }
  
      @SuppressWarnings("unchecked")
      protected synchronized Map<String, List<?>> createCache(String cacheName) {
          Map<String, List<?>> map = getCache(cacheName);
          if(map != null) {
              return map;
          }
  
          map = new ConcurrentLinkedHashMap.Builder<String, List<?>>().maximumWeightedCapacity(maxSize).build();
          cacheGroups.put(cacheName, map);
          return map;
      }
  
      protected Map<String, List<?>> getCache(String name) {
          return cacheGroups.get(name);
      }
  
      protected String cacheName(QueryMetadata metadata) {
  
          String cacheGroup = metadata.getCacheGroup();
          if (cacheGroup != null) {
              return cacheGroup;
          }
  
          // no explicit cache group
          return DEFAULT_CACHE_NAME;
      }
  }
  