/*
    * 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.xdbm;
  
  
  import java.io.IOException;
  
  import org.apache.directory.api.ldap.model.constants.Loggers;
  import org.apache.directory.api.ldap.model.cursor.CursorException;
  import org.apache.directory.api.ldap.model.cursor.InvalidCursorPositionException;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.apache.directory.server.core.api.partition.PartitionTxn;
  import org.apache.directory.server.i18n.I18n;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * A Cursor over a single element.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class SingletonIndexCursor<V> extends AbstractIndexCursor<V>
  {
      /** 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();
  
      private boolean beforeFirst = true;
      private boolean afterLast;
      private boolean onSingleton;
      private final IndexEntry<V, String> singleton;
  
  
      public SingletonIndexCursor( PartitionTxn partitionTxn, IndexEntry<V, String> singleton )
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating SingletonIndexCursor {}", this );
          }
  
          this.singleton = singleton;
          this.partitionTxn = partitionTxn;
      }
  
  
      /**
       * {@inheritDoc}
       */
      protected String getUnsupportedMessage()
      {
          return UNSUPPORTED_MSG;
      }
  
  
      /**
       * {@inheritDoc}
       */
      @Override
      public boolean available()
      {
          return onSingleton;
      }
  
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void beforeFirst() throws LdapException, CursorException
      {
          checkNotClosed();
          beforeFirst = true;
          afterLast = false;
          onSingleton = false;
      }
  
  
      /**
       * {@inheritDoc}
       */
     @Override
     public void afterLast() throws LdapException, CursorException
     {
         checkNotClosed();
         beforeFirst = false;
         afterLast = true;
         onSingleton = false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean first() throws LdapException, CursorException
     {
         checkNotClosed();
         beforeFirst = false;
         onSingleton = true;
         afterLast = false;
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean last() throws LdapException, CursorException
     {
         checkNotClosed();
         beforeFirst = false;
         onSingleton = true;
         afterLast = false;
         return true;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isFirst()
     {
         return onSingleton;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isLast()
     {
         return onSingleton;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isAfterLast()
     {
         return afterLast;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean isBeforeFirst()
     {
         return beforeFirst;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean previous() throws LdapException, CursorException
     {
         checkNotClosed();
         if ( beforeFirst )
         {
             return false;
         }
 
         if ( afterLast )
         {
             beforeFirst = false;
             onSingleton = true;
             afterLast = false;
             return true;
         }
 
         // must be on the singleton
         beforeFirst = true;
         onSingleton = false;
         afterLast = false;
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean next() throws LdapException, CursorException
     {
         checkNotClosed();
         
         if ( beforeFirst )
         {
             beforeFirst = false;
             onSingleton = true;
             afterLast = false;
             return true;
         }
 
         if ( afterLast )
         {
             return false;
         }
 
         // must be on the singleton
         beforeFirst = false;
         onSingleton = false;
         afterLast = true;
         return false;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public IndexEntry<V, String> get() throws CursorException
     {
         checkNotClosed();
 
         if ( onSingleton )
         {
             return singleton;
         }
 
         if ( beforeFirst )
         {
             throw new InvalidCursorPositionException( I18n.err( I18n.ERR_705 ) );
         }
         else
         {
             throw new InvalidCursorPositionException( I18n.err( I18n.ERR_706 ) );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close() throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SingletonIndexCursor {}", this );
         }
 
         super.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause ) throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing SingletonIndexCursor {}", this );
         }
 
         super.close( cause );
     }
 }