content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file 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
   *
   *      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.apache.activemq.broker.region.cursors;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.List;
  
  import org.apache.activemq.broker.region.MessageReference;
  import org.apache.activemq.command.MessageId;
  
  /**
   * An abstraction that keeps the correct order of messages that need to be dispatched
   * to consumers, but also hides the fact that there might be redelivered messages that
   * should be dispatched ahead of any other paged in messages.
   *
   * Direct usage of this class is recommended as you can control when redeliveries need
   * to be added vs regular pending messages (the next set of messages that can be dispatched)
   *
   * Created by ceposta
   * <a href="http://christianposta.com/blog>http://christianposta.com/blog</a>.
   */
  public class QueueDispatchPendingList implements PendingList {
  
      private PendingList pagedInPendingDispatch = new OrderedPendingList();
      private PendingList redeliveredWaitingDispatch = new OrderedPendingList();
      private boolean prioritized = false;
  
  
      @Override
      public boolean isEmpty() {
          return pagedInPendingDispatch.isEmpty() && redeliveredWaitingDispatch.isEmpty();
      }
  
      @Override
      public void clear() {
          pagedInPendingDispatch.clear();
          redeliveredWaitingDispatch.clear();
      }
  
      /**
       * Messages added are added directly to the pagedInPendingDispatch set of messages. If
       * you're trying to add a message that is marked redelivered add it using addMessageForRedelivery()
       * method
       * @param message
       *      The MessageReference that is to be added to this list.
       *
       * @return the pending node.
       */
      @Override
      public PendingNode addMessageFirst(MessageReference message) {
          return pagedInPendingDispatch.addMessageFirst(message);
      }
  
      /**
       * Messages added are added directly to the pagedInPendingDispatch set of messages. If
       * you're trying to add a message that is marked redelivered add it using addMessageForRedelivery()
       * method
       * @param message
       *      The MessageReference that is to be added to this list.
       *
       * @return the pending node.
       */
      @Override
      public PendingNode addMessageLast(MessageReference message) {
          return pagedInPendingDispatch.addMessageLast(message);
      }
  
      @Override
      public PendingNode remove(MessageReference message) {
          if (pagedInPendingDispatch.contains(message)) {
              return pagedInPendingDispatch.remove(message);
          } else if (redeliveredWaitingDispatch.contains(message)) {
              return redeliveredWaitingDispatch.remove(message);
          }
          return null;
      }
  
      @Override
      public int size() {
          return pagedInPendingDispatch.size() + redeliveredWaitingDispatch.size();
      }
  
      @Override
      public long messageSize() {
          return pagedInPendingDispatch.messageSize() + redeliveredWaitingDispatch.messageSize();
      }
  
      @Override
      public Iterator<MessageReference> iterator() {
          if (prioritized && hasRedeliveries()) {
              final QueueDispatchPendingList delegate = this;
              final PrioritizedPendingList  priorityOrderedRedeliveredAndPending = new PrioritizedPendingList();
              priorityOrderedRedeliveredAndPending.addAll(redeliveredWaitingDispatch);
              priorityOrderedRedeliveredAndPending.addAll(pagedInPendingDispatch);
  
              return new Iterator<MessageReference>() {
  
                  Iterator<MessageReference> combinedIterator = priorityOrderedRedeliveredAndPending.iterator();
                  MessageReference current = null;
  
                  @Override
                  public boolean hasNext() {
                      return combinedIterator.hasNext();
                  }
  
                  @Override
                  public MessageReference next() {
                      current = combinedIterator.next();
                      return current;
                  }
  
                  @Override
                  public void remove() {
                      if (current!=null) {
                          delegate.remove(current);
                      }
                  }
              };
  
          } else {
  
              return new Iterator<MessageReference>() {
  
                  Iterator<MessageReference> redeliveries = redeliveredWaitingDispatch.iterator();
                  Iterator<MessageReference> pendingDispatch = pagedInPendingDispatch.iterator();
                  Iterator<MessageReference> current = redeliveries;
  
  
                  @Override
                  public boolean hasNext() {
                      if (!redeliveries.hasNext() && (current == redeliveries)) {
                          current = pendingDispatch;
                      }
                      return current.hasNext();
                  }
  
                  @Override
                  public MessageReference next() {
                      return current.next();
                  }
  
                  @Override
                  public void remove() {
                      current.remove();
                  }
              };
          }
      }
  
      @Override
      public boolean contains(MessageReference message) {
          return pagedInPendingDispatch.contains(message) || redeliveredWaitingDispatch.contains(message);
      }
  
      @Override
      public Collection<MessageReference> values() {
          List<MessageReference> messageReferences = new ArrayList<MessageReference>();
          Iterator<MessageReference> iterator = iterator();
          while (iterator.hasNext()) {
              messageReferences.add(iterator.next());
          }
          return messageReferences;
      }
  
      @Override
      public void addAll(PendingList pendingList) {
          pagedInPendingDispatch.addAll(pendingList);
      }
  
      @Override
      public MessageReference get(MessageId messageId) {
          MessageReference rc = pagedInPendingDispatch.get(messageId);
          if (rc == null) {
              return redeliveredWaitingDispatch.get(messageId);
          }
          return rc;
      }
  
      public void setPrioritizedMessages(boolean prioritizedMessages) {
          prioritized = prioritizedMessages;
          if (prioritizedMessages && this.pagedInPendingDispatch instanceof OrderedPendingList) {
              pagedInPendingDispatch = new PrioritizedPendingList();
              redeliveredWaitingDispatch = new PrioritizedPendingList();
          } else if(pagedInPendingDispatch instanceof PrioritizedPendingList) {
              pagedInPendingDispatch = new OrderedPendingList();
              redeliveredWaitingDispatch = new OrderedPendingList();
          }
      }
  
      public boolean hasRedeliveries(){
          return !redeliveredWaitingDispatch.isEmpty();
      }
  
      public void addForRedelivery(List<MessageReference> list, boolean noConsumers) {
          if (noConsumers && redeliveredWaitingDispatch instanceof OrderedPendingList && willBeInOrder(list)) {
              // a single consumer can expect repeatable redelivery order irrespective
              // of transaction or prefetch boundaries
              ((OrderedPendingList)redeliveredWaitingDispatch).insertAtHead(list);
          } else {
              for (MessageReference ref : list) {
                  redeliveredWaitingDispatch.addMessageLast(ref);
              }
          }
      }
  
      private boolean willBeInOrder(List<MessageReference> list) {
          // for a single consumer inserting at head will be in order w.r.t brokerSequence but
          // will not be if there were multiple consumers in the mix even if this is the last
          // consumer to close (noConsumers==true)
          return !redeliveredWaitingDispatch.isEmpty() && list != null && !list.isEmpty() &&
              redeliveredWaitingDispatch.iterator().next().getMessageId().getBrokerSequenceId() > list.get(list.size() - 1).getMessageId().getBrokerSequenceId();
      }
  }
  