/*
    *   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.directory.server.ldap.replication.provider;
  
  
  import java.io.IOException;
  import java.util.Iterator;
  
  import org.apache.directory.api.ldap.model.constants.Loggers;
  import org.apache.directory.api.ldap.model.constants.SchemaConstants;
  import org.apache.directory.api.ldap.model.cursor.AbstractCursor;
  import org.apache.directory.api.ldap.model.cursor.Cursor;
  import org.apache.directory.api.ldap.model.cursor.CursorException;
  import org.apache.directory.api.ldap.model.cursor.Tuple;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.apache.directory.api.ldap.model.message.controls.ChangeType;
  import org.apache.directory.server.core.api.partition.PartitionTxn;
  import org.apache.directory.server.core.partition.impl.btree.jdbm.JdbmTable;
  import org.apache.directory.server.ldap.replication.ReplicaEventMessage;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * Define a cursor on top of a replication journal.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class ReplicaJournalCursor extends AbstractCursor<ReplicaEventMessage>
  {
      /** Logger for this class */
      private static final Logger LOG = LoggerFactory.getLogger( ReplicaJournalCursor.class );
  
      /** A dedicated log for cursors */
      private static final Logger LOG_CURSOR = LoggerFactory.getLogger( Loggers.CURSOR_LOG.getName() );
  
      /** Speedup for logs */
      private static final boolean IS_DEBUG = LOG_CURSOR.isDebugEnabled();
  
      /** the underlying journal's cursor */
      private Cursor<Tuple<String, ReplicaEventMessage>> tupleCursor;
  
      /** the event log journal */
      private JdbmTable<String, ReplicaEventMessage> journal;
  
      /** the consumer's CSN based on which messages will be qualified for sending */
      private String consumerCsn;
  
      private ReplicaEventMessage qualifiedEvtMsg;
  
      /** used while cleaning up the log */
      private boolean skipQualifying;
      
      /** The partition transaction */
      private PartitionTxn partitionTxn;
      
  
  
      /**
       * Creates a cursor on top of the given journal
       * 
       * @param partitionTxn The Transaction to use
       * @param journal the log journal
       * @param consumerCsn the consumer's CSN taken from cookie
       * @throws Exception If the cursor creation failed
       */
      public ReplicaJournalCursor( PartitionTxn partitionTxn, JdbmTable<String, ReplicaEventMessage> journal, 
              String consumerCsn ) throws Exception
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating ReplicaJournalCursor {}", this );
          }
  
          this.journal = journal;
          this.tupleCursor = journal.cursor();
          this.consumerCsn = consumerCsn;
          this.partitionTxn = partitionTxn;
      }
  
  
     /**
      * {@inheritDoc}
      */
     public void after( ReplicaEventMessage arg0 ) throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void afterLast() throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean available()
     {
         return ( qualifiedEvtMsg != null );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void before( ReplicaEventMessage arg0 ) throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException
     {
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public ReplicaEventMessage get() throws CursorException
     {
         return qualifiedEvtMsg;
     }
 
 
     /**
      * selects the current queue entry if qualified for sending to the consumer
      * 
      * @throws Exception
      */
     private boolean isQualified( String csn, ReplicaEventMessage evtMsg ) throws LdapException
     {
         LOG.debug( "ReplicaEventMessage: {}", evtMsg );
 
         if ( evtMsg.isEventOlderThan( consumerCsn ) )
         {
             if ( LOG.isDebugEnabled() )
             {
                 String evt = "MODDN"; // take this as default cause the event type for MODDN is null
 
                 ChangeType changeType = evtMsg.getChangeType();
 
                 if ( changeType != null )
                 {
                     evt = changeType.name();
                 }
 
                 LOG.debug( "event {} for dn {} is not qualified for sending", evt, evtMsg.getEntry().getDn() );
             }
 
             return false;
         }
 
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean next() throws LdapException, CursorException
     {
         while ( tupleCursor.next() )
         {
             Tuple<String, ReplicaEventMessage> tuple = tupleCursor.get();
 
             String csn = tuple.getKey();
             ReplicaEventMessage message = tuple.getValue();
 
             if ( skipQualifying )
             {
                 qualifiedEvtMsg = message;
                 return true;
             }
 
             boolean qualified = isQualified( csn, message );
 
             if ( qualified )
             {
                 qualifiedEvtMsg = message;
                 return true;
             }
             else
             {
                 journal.remove( partitionTxn, csn );
             }
         }
 
         qualifiedEvtMsg = null;
 
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean previous() throws LdapException, CursorException
     {
         throw new UnsupportedOperationException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close() throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing ReplicaJournalCursor {}", this );
         }
 
         tupleCursor.close();
         super.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause ) throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing ReplicaJournalCursor {}", this );
         }
 
         tupleCursor.close();
         super.close( cause );
     }
 
 
     /**
      * sets the flag to skip CSN based checking while traversing
      * used for internal log cleanup ONLY 
      */
     protected void skipQualifyingWhileFetching()
     {
         skipQualifying = true;
     }
 
 
     /**
      * delete the current message
      * used for internal log cleanup ONLY
      */
     protected void delete()
     {
         try
         {
             if ( qualifiedEvtMsg != null )
             {
                 journal.remove( partitionTxn, qualifiedEvtMsg.getEntry().get( SchemaConstants.ENTRY_CSN_AT ).getString() );
             }
         }
         catch ( Exception e )
         {
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public Iterator<ReplicaEventMessage> iterator()
     {
         throw new UnsupportedOperationException();
     }
 }