/*
    *   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.avltree;
  
  
  import java.io.IOException;
  
  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.exception.LdapException;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * A Cursor for an AvlTree.
   *
   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
   */
  public class AvlTreeCursor<E> extends AbstractCursor<E>
  {
      /** 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 AVL tree */
      private AvlTree<E> tree;
  
      /** The current node */
      private LinkedAvlNode<E> node;
  
      /** The current position of this cursor, relative to the node */
      private Position position = Position.BEFORE_FIRST;
  
  
      public AvlTreeCursor( AvlTree<E> tree )
      {
          if ( IS_DEBUG )
          {
              LOG_CURSOR.debug( "Creating AvlTreeCursor {}", this );
          }
  
          this.tree = tree;
      }
  
  
      /**
       * {@inheritDoc}
       */
      public void after( E element ) throws LdapException, CursorException
      {
          checkNotClosed();
  
          if ( element == null )
          {
              afterLast();
              return;
          }
  
          node = tree.findGreater( element );
  
          if ( node == null )
          {
              position = Position.AFTER_LAST;
          }
          else
          {
              // the cursor should be positioned after the given element
              // we just fetched the next greater element so the cursor
              // is positioned before the fetched element
              position = Position.BEFORE_NODE;
          }
      }
  
  
      /**
       * {@inheritDoc}
       */
     public void afterLast() throws LdapException, CursorException
     {
         checkNotClosed();
         node = null;
         position = Position.AFTER_LAST;
     }
 
 
     public boolean available()
     {
         return position == Position.ON_NODE;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void before( E element ) throws LdapException, CursorException
     {
         checkNotClosed();
 
         if ( element == null )
         {
             beforeFirst();
             return;
         }
 
         node = tree.findLess( element );
 
         if ( node == null )
         {
             position = Position.BEFORE_FIRST;
         }
         else
         {
             // the cursor should be positioned before the given element
             // we just fetched the next less element so the cursor
             // is positioned after the fetched element
             position = Position.AFTER_NODE;
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public void beforeFirst() throws LdapException, CursorException
     {
         checkNotClosed();
         node = null;
         position = Position.BEFORE_FIRST;
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean first() throws LdapException, CursorException
     {
         checkNotClosed();
 
         node = tree.getFirst();
 
         if ( node == null )
         {
             position = Position.BEFORE_FIRST;
             return false;
         }
         else
         {
             position = Position.ON_NODE;
             return true;
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public E get() throws CursorException
     {
         checkNotClosed();
 
         if ( position == Position.ON_NODE )
         {
             return node.getKey();
         }
 
         throw new InvalidCursorPositionException();
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean last() throws LdapException, CursorException
     {
         checkNotClosed();
 
         node = tree.getLast();
 
         if ( node == null )
         {
             position = Position.AFTER_LAST;
             return false;
         }
         else
         {
             position = Position.ON_NODE;
             return true;
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean next() throws LdapException, CursorException
     {
         checkNotClosed();
 
         switch ( position )
         {
             case BEFORE_FIRST:
                 return first();
 
             case BEFORE_NODE:
                 position = Position.ON_NODE;
                 return true;
 
             case ON_NODE:
             case AFTER_NODE:
                 node = node.next;
                 if ( node == null )
                 {
                     afterLast();
                     return false;
                 }
                 else
                 {
                     position = Position.ON_NODE;
                     return true;
                 }
 
             case AFTER_LAST:
                 return false;
 
             default:
                 throw new IllegalStateException( "Unexpected position " + position );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     public boolean previous() throws LdapException, CursorException
     {
         checkNotClosed();
 
         switch ( position )
         {
             case BEFORE_FIRST:
                 return false;
 
             case BEFORE_NODE:
             case ON_NODE:
                 node = node.previous;
                 if ( node == null )
                 {
                     beforeFirst();
                     return false;
                 }
                 else
                 {
                     position = Position.ON_NODE;
                     return true;
                 }
 
             case AFTER_NODE:
                 position = Position.ON_NODE;
                 return true;
 
             case AFTER_LAST:
                 return last();
 
             default:
                 throw new IllegalStateException( "Unexpected position " + position );
         }
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close() throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing AvlTreeCursor {}", this );
         }
 
         super.close();
     }
 
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void close( Exception reason ) throws IOException
     {
         if ( IS_DEBUG )
         {
             LOG_CURSOR.debug( "Closing AvlTreeCursor {}", this );
         }
 
         super.close( reason );
     }
 }