/*
*
* 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.qpid.server.queue;

import org.apache.qpid.server.message.ServerMessage;
import org.apache.qpid.server.store.MessageEnqueueRecord;

abstract public class PriorityQueueList extends OrderedQueueEntryList
{


    public static PriorityQueueList newInstance(PriorityQueueImpl queue)
    {
        return new PriorityQueueMasterList(queue, queue.getPriorities());
    }

    public PriorityQueueList(final PriorityQueueImpl queue,
                             final HeadCreator headCreator)
    {
        super(queue, headCreator);
    }

    static class PriorityQueueMasterList extends PriorityQueueList
    {
        private static final HeadCreator DUMMY_HEAD_CREATOR =
                new HeadCreator()
                {
                    @Override
                    public PriorityQueueEntry createHead(final QueueEntryList list)
                    {
                        return null;
                    }
                };
        private final PriorityQueueImpl _queue;
        private final PriorityQueueEntrySubList[] _priorityLists;
        private final int _priorities;
        private final int _priorityOffset;

        public PriorityQueueMasterList(PriorityQueueImpl queue, int priorities)
        {
            super(queue, DUMMY_HEAD_CREATOR);
            _queue = queue;
            _priorityLists = new PriorityQueueEntrySubList[priorities];
            _priorities = priorities;
            _priorityOffset = 5-((priorities + 1)/2);
            for(int i = 0; i < priorities; i++)
            {
                _priorityLists[i] = new PriorityQueueEntrySubList(queue, i);
            }
        }

        public int getPriorities()
        {
            return _priorities;
        }

        @Override
        public PriorityQueueImpl getQueue()
        {
            return _queue;
        }

        @Override
        public PriorityQueueEntry add(ServerMessage message, final MessageEnqueueRecord enqueueRecord)
        {
            int index = message.getMessageHeader().getPriority() - _priorityOffset;
            if(index >= _priorities)
            {
                index = _priorities-1;
            }
            else if(index < 0)
            {
                index = 0;
            }
            return (PriorityQueueEntry) _priorityLists[index].add(message, enqueueRecord);

        }

        @Override
        protected PriorityQueueEntry createQueueEntry(final ServerMessage<?> message,
                                                      final MessageEnqueueRecord enqueueRecord)
        {
            throw new UnsupportedOperationException();
        }

        @Override
        public PriorityQueueEntry next(QueueEntry node)
        {
            PriorityQueueEntry next = (PriorityQueueEntry) node.getNextValidEntry();

            if(next == null)
            {
                final PriorityQueueList nodeEntryList = (PriorityQueueList) ((PriorityQueueEntry)node).getQueueEntryList();
                int index;
                for(index = _priorityLists.length-1; _priorityLists[index] != nodeEntryList; index--)
                {
                    // do nothing loop is just to find the index
                }

                while(next == null && index != 0)
                {
                    index--;
                    next = (PriorityQueueEntry) _priorityLists[index].getHead().getNextValidEntry();
                }

            }
            return next;
        }

        private final class PriorityQueueEntryListIterator implements QueueEntryIterator
        {
            private final QueueEntryIterator[] _iterators = new QueueEntryIterator[ _priorityLists.length ];
            private PriorityQueueEntry _lastNode;

            PriorityQueueEntryListIterator()
            {
                for(int i = 0; i < _priorityLists.length; i++)
                {
                    _iterators[i] = _priorityLists[i].iterator();
                }
                _lastNode = (PriorityQueueEntry) _iterators[_iterators.length - 1].getNode();
            }

            @Override
            public boolean atTail()
            {
                for(int i = 0; i < _iterators.length; i++)
                {
                    if(!_iterators[i].atTail())
                    {
                        return false;
                    }
                }
                return true;
            }

            @Override
            public PriorityQueueEntry getNode()
            {
                return _lastNode;
            }

            @Override
            public boolean advance()
            {
                for(int i = _iterators.length-1; i >= 0; i--)
                {
                    if(_iterators[i].advance())
                    {
                        _lastNode = (PriorityQueueEntry) _iterators[i].getNode();
                        return true;
                    }
                }
                return false;
            }
        }

        @Override
        public PriorityQueueEntryListIterator iterator()
        {

            return new PriorityQueueEntryListIterator();
        }

        @Override
        public PriorityQueueEntry getHead()
        {
            return (PriorityQueueEntry) _priorityLists[_priorities-1].getHead();
        }

        @Override
        public PriorityQueueEntry getTail()
        {
            return (PriorityQueueEntry) _priorityLists[0].getTail();
        }


        @Override
        public void entryDeleted(final QueueEntry queueEntry)
        {

        }

        @Override
        public QueueEntry getOldestEntry()
        {
            QueueEntry oldest = null;
            for(PriorityQueueEntrySubList subList : _priorityLists)
            {
                QueueEntry subListOldest = subList.getOldestEntry();
                if(oldest == null || (subListOldest != null && subListOldest.getMessage().getMessageNumber() < oldest.getMessage().getMessageNumber()))
                {
                    oldest = subListOldest;
                }
            }
            return oldest;
        }
    }

    static class PriorityQueueEntrySubList extends PriorityQueueList
    {
        private static final HeadCreator HEAD_CREATOR = new HeadCreator()
        {
            @Override
            public PriorityQueueEntry createHead(final QueueEntryList list)
            {
                return new PriorityQueueEntry((PriorityQueueList) list);
            }
        };
        private int _listPriority;

        public PriorityQueueEntrySubList(PriorityQueueImpl queue, int listPriority)
        {
            super(queue, HEAD_CREATOR);
            _listPriority = listPriority;
        }

        @Override
        protected PriorityQueueEntry createQueueEntry(ServerMessage<?> message,
                                                      final MessageEnqueueRecord enqueueRecord)
        {
            return new PriorityQueueEntry(this, message, enqueueRecord);
        }

        public int getListPriority()
        {
            return _listPriority;
        }
    }

    static class PriorityQueueEntry extends OrderedQueueEntry
    {
        private PriorityQueueEntry(final PriorityQueueList queueEntryList)
        {
            super(queueEntryList);
        }

        public PriorityQueueEntry(PriorityQueueEntrySubList queueEntryList,
                                  ServerMessage<?> message,
                                  final MessageEnqueueRecord messageEnqueueRecord)
        {
            super(queueEntryList, message, messageEnqueueRecord);
        }

        @Override
        public int compareTo(final QueueEntry o)
        {
            PriorityQueueEntry other = (PriorityQueueEntry)o;
            PriorityQueueEntrySubList pqel = (PriorityQueueEntrySubList)other.getQueueEntryList();
            int otherPriority = pqel.getListPriority();
            int thisPriority = ((PriorityQueueEntrySubList) getQueueEntryList()).getListPriority();

            if(thisPriority != otherPriority)
            {
                /*
                 * Different priorities, so answer can only be greater than or less than
                 *
                 * A message with higher priority (e.g. 5) is conceptually 'earlier' in the
                 * priority queue than one with a lower priority (e.g. 4).
                 */
                return thisPriority > otherPriority ? -1 : 1;
            }
            else
            {
                return super.compareTo(o);
            }
        }
    }
}