/*
    * Copyright 2009 Red Hat, Inc.
    *
    * Red Hat 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.jboss.netty.util;
  
  import java.lang.reflect.Field;
  import java.lang.reflect.Modifier;
  import java.nio.ByteBuffer;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.concurrent.ConcurrentMap;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.util.internal.ConcurrentIdentityWeakKeyHashMap;
  
  /**
   * The default {@link ObjectSizeEstimator} implementation for general purpose.
   *
   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
   *
   * @version $Rev: 2080 $, $Date: 2010-01-26 18:04:19 +0900 (Tue, 26 Jan 2010) $
   *
   */
  public class DefaultObjectSizeEstimator implements ObjectSizeEstimator {
  
      private final ConcurrentMap<Class<?>, Integer> class2size =
          new ConcurrentIdentityWeakKeyHashMap<Class<?>, Integer>();
  
      /**
       * Creates a new instance.
       */
      public DefaultObjectSizeEstimator() {
          class2size.put(boolean.class, 4); // Probably an integer.
          class2size.put(byte.class, 1);
          class2size.put(char.class, 2);
          class2size.put(int.class, 4);
          class2size.put(short.class, 2);
          class2size.put(long.class, 8);
          class2size.put(float.class, 4);
          class2size.put(double.class, 8);
          class2size.put(void.class, 0);
      }
  
      public int estimateSize(Object o) {
          if (o == null) {
              return 8;
          }
  
          int answer = 8 + estimateSize(o.getClass(), null);
  
          if (o instanceof EstimatableObjectWrapper) {
              answer += estimateSize(((EstimatableObjectWrapper) o).unwrap());
          } else if (o instanceof MessageEvent) {
              answer += estimateSize(((MessageEvent) o).getMessage());
          } else if (o instanceof ChannelBuffer) {
              answer += ((ChannelBuffer) o).capacity();
          } else if (o instanceof byte[]) {
              answer += ((byte[]) o).length;
          } else if (o instanceof ByteBuffer) {
              answer += ((ByteBuffer) o).remaining();
          } else if (o instanceof CharSequence) {
              answer += ((CharSequence) o).length() << 1;
          } else if (o instanceof Iterable<?>) {
              for (Object m : (Iterable<?>) o) {
                  answer += estimateSize(m);
              }
          }
  
          return align(answer);
      }
  
      private int estimateSize(Class<?> clazz, Set<Class<?>> visitedClasses) {
          Integer objectSize = class2size.get(clazz);
          if (objectSize != null) {
              return objectSize;
          }
  
          if (visitedClasses != null) {
              if (visitedClasses.contains(clazz)) {
                  return 0;
              }
          } else {
              visitedClasses = new HashSet<Class<?>>();
          }
  
         visitedClasses.add(clazz);
 
         int answer = 8; // Basic overhead.
         for (Class<?> c = clazz; c != null; c = c.getSuperclass()) {
             Field[] fields = c.getDeclaredFields();
             for (Field f : fields) {
                 if ((f.getModifiers() & Modifier.STATIC) != 0) {
                     // Ignore static fields.
                     continue;
                 }
 
                 answer += estimateSize(f.getType(), visitedClasses);
             }
         }
 
         visitedClasses.remove(clazz);
 
         // Some alignment.
         answer = align(answer);
 
         // Put the final answer.
         class2size.putIfAbsent(clazz, answer);
         return answer;
     }
 
     private static int align(int size) {
         int r = size % 8;
         if (r != 0) {
             size += 8 - r;
         }
         return size;
     }
 }