/*
    * 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.core.partition.impl.btree.jdbm;
  
  
  import java.io.IOException;
  
  import jdbm.helper.TupleBrowser;
  
  import org.apache.directory.api.ldap.model.constants.Loggers;
  import org.apache.directory.api.ldap.model.cursor.AbstractCursor;
  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.cursor.Tuple;
  import org.apache.directory.api.ldap.model.exception.LdapException;
  import org.apache.directory.server.i18n.I18n;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * Cursor over the Tuples of a JDBM BTree.  Duplicate keys are not supported
   * by JDBM natively so you will not see duplicate keys.  For this reason as
   * well before() and after() positioning only considers the key of the Tuple
   * arguments provided.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  class NoDupsCursor<K, V> extends AbstractCursor<Tuple<K, 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 final JdbmTable<K, V> table;
  
      private jdbm.helper.Tuple jdbmTuple = new jdbm.helper.Tuple();
      private Tuple<K, V> returnedTuple = new Tuple<K, V>();
      private TupleBrowser browser;
      private boolean valueAvailable;
  
  
      /**
       * Creates a Cursor over the tuples of a JDBM table.
       *
       * @param table the JDBM Table to build a Cursor over
       * @throws IOException of there are problems accessing the BTree
       */
      public NoDupsCursor( JdbmTable<K, V> table )
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating NoDupsCursor {}", this );
          }
  
          this.table = table;
      }
  
  
      private void clearValue()
      {
          returnedTuple.setKey( null );
          returnedTuple.setValue( null );
          jdbmTuple.setKey( null );
          jdbmTuple.setValue( null );
          valueAvailable = false;
      }
  
  
      public boolean available()
      {
          return valueAvailable;
      }
  
  
      public void beforeKey( K key ) throws LdapException, CursorException, IOException
      {
          checkNotClosed( "beforeKey()" );
          browser = table.getBTree().browse( key );
          clearValue();
      }
 
 
     @SuppressWarnings("unchecked")
     public void afterKey( K key ) throws LdapException, CursorException, IOException
     {
         browser = table.getBTree().browse( key );
 
         /*
          * While the next value is less than or equal to the element keep
          * advancing forward to the next item.  If we cannot advance any
          * further then stop and return.  If we find a value greater than
          * the element then we stop, backup, and return so subsequent calls
          * to getNext() will return a value greater than the element.
          */
         while ( browser.getNext( jdbmTuple ) )
         {
             checkNotClosed( "afterKey()" );
             K next = ( K ) jdbmTuple.getKey();
 
             int nextCompared = table.getKeyComparator().compare( next, key );
 
             if ( nextCompared > 0 )
             {
                 browser.getPrevious( jdbmTuple );
                 clearValue();
                 return;
             }
         }
 
         clearValue();
     }
 
 
     public void beforeValue( K key, V value ) throws Exception
     {
         throw new UnsupportedOperationException( I18n.err( I18n.ERR_596 ) );
     }
 
 
     public void afterValue( K key, V value ) throws Exception
     {
         throw new UnsupportedOperationException( I18n.err( I18n.ERR_596 ) );
     }
 
 
     /**
      * Positions this Cursor before the key of the supplied tuple.
      *
      * @param element the tuple who's key is used to position this Cursor
      * @throws IOException if there are failures to position the Cursor
      */
     public void before( Tuple<K, V> element ) throws LdapException, CursorException, IOException
     {
         beforeKey( element.getKey() );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void after( Tuple<K, V> element ) throws LdapException, CursorException, IOException
     {
         afterKey( element.getKey() );
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException, IOException
     {
         checkNotClosed( "beforeFirst()" );
         browser = table.getBTree().browse();
         clearValue();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void afterLast() throws LdapException, CursorException, IOException
     {
         checkNotClosed( "afterLast()" );
         browser = table.getBTree().browse( null );
         clearValue();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException, IOException
     {
         beforeFirst();
         return next();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException, IOException
     {
         afterLast();
         return previous();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @SuppressWarnings("unchecked")
     public boolean previous() throws LdapException, CursorException, IOException
     {
         checkNotClosed( "previous()" );
         if ( browser == null )
         {
             afterLast();
         }
 
         if ( browser.getPrevious( jdbmTuple ) )
         {
             if ( returnedTuple.getKey() != null && table.getKeyComparator().compare(
                 ( K ) jdbmTuple.getKey(), returnedTuple.getKey() ) == 0 )
             {
                 browser.getPrevious( jdbmTuple );
             }
 
             returnedTuple.setKey( ( K ) jdbmTuple.getKey() );
             returnedTuple.setValue( ( V ) jdbmTuple.getValue() );
             return valueAvailable = true;
         }
         else
         {
             clearValue();
             return false;
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     @SuppressWarnings("unchecked")
     public boolean next() throws LdapException, CursorException, IOException
     {
         checkNotClosed( "previous()" );
 
         if ( browser == null )
         {
             beforeFirst();
         }
 
         if ( browser.getNext( jdbmTuple ) )
         {
             if ( returnedTuple.getKey() != null && table.getKeyComparator().compare(
                 ( K ) jdbmTuple.getKey(), returnedTuple.getKey() ) == 0 )
             {
                 browser.getNext( jdbmTuple );
             }
 
             returnedTuple.setKey( ( K ) jdbmTuple.getKey() );
             returnedTuple.setValue( ( V ) jdbmTuple.getValue() );
             return valueAvailable = true;
         }
         else
         {
             clearValue();
             return false;
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public Tuple<K, V> get() throws CursorException, IOException
     {
         checkNotClosed( "get()" );
         if ( valueAvailable )
         {
             return returnedTuple;
         }
 
         throw new InvalidCursorPositionException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close()
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing NoDupsCursor {}", this );
         }
 
         super.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception cause )
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing NoDupsCursor {}", this );
         }
 
         super.close( cause );
     }
 }