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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
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   *
   *    https://www.apache.org/licenses/LICENSE-2.0
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   *  Unless required by applicable law or agreed to in writing,
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  package org.apache.cayenne.configuration.xml;
  
  import org.apache.cayenne.configuration.ConfigurationNode;
  
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * <p>
   *     Default implementation of {@link DataChannelMetaData} that stores data in Map.
   * </p>
   * <p>
   *     This implementation is thread safe.
   * </p>
   *
   * @see NoopDataChannelMetaData
   * @since 4.1
   */
  public class DefaultDataChannelMetaData implements DataChannelMetaData {
  
      private Map<ConfigurationNode, Map<Class<?>, Object>> map;
  
      public DefaultDataChannelMetaData() {
          map = new ConcurrentHashMap<>();
      }
  
      /**
       * value.getClass() will be used under the hood to associate data with the key object.
       *
       * @param key object for which we want to store data
       * @param value data to store
       */
      @Override
      public void add(ConfigurationNode key, Object value) {
          if(key == null || value == null) {
              return;
          }
  
          Map<Class<?>, Object> data = map.get(key);
          if(data == null) {
              data = new ConcurrentHashMap<>();
              Map<Class<?>, Object> old = map.put(key, data);
              // extra check in case if someone was fast enough
              if(old != null) {
                  data.putAll(old);
              }
          }
          data.put(value.getClass(), value);
      }
  
      /**
       * If either key or value is {@code null} then {@code null} will be returned.
       *
       * @param key object for wich we want meta data
       * @param type meta data type class
       * @param <T> data type
       * @return value or {@code null}
       */
      @Override
      public <T> T get(ConfigurationNode key, Class<T> type) {
          if(key == null || type == null) {
              return null;
          }
  
          Map<Class<?>, Object> data = map.get(key);
          if(data == null) {
              return null;
          }
  
          return type.cast(data.get(type));
      }
  
      /**
       *
       * @param key object for wich we want meta data
       * @param type meta data type class
       * @param <T> data type
       * @return removed value or {@code null}
       */
      @Override
      public <T> T remove(ConfigurationNode key, Class<T> type) {
          if(key == null || type == null) {
              return null;
          }
  
          Map<Class<?>, Object> data = map.get(key);
          if(data == null) {
              return null;
          }
  
          return type.cast(data.remove(type));
      }
  }
  