trunk/jdbm-partition/src/main/java/org/apache/directory/server/core/partition/impl/btree/jdbm/DupsContainerCursor.java

/*
 *  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.btree.BTree;
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;


/**
 * A cursor for browsing tables with duplicates which returns the container
 * for values rather than just the value.
 *
 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
 * @param K The Key
 * @param V The associated value
 */
public class DupsContainerCursor<K, V> extends AbstractCursor<Tuple<K, DupsContainer<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();

    /** The JDBM table we are building a cursor over */
    private final JdbmTable<K, V> table;

    /** A container to pass to the underlying JDBM to get back a tuple */
    private jdbm.helper.Tuple<K, V> jdbmTuple = new jdbm.helper.Tuple<K, V>();

    private Tuple<K, DupsContainer<V>> returnedTuple = new Tuple<K, DupsContainer<V>>();

    /** A browser over the JDBM Table */
    private TupleBrowser<K, V> browser;

    /** Tells if we have a tuple to return */
    private boolean valueAvailable;

    /** TODO : do we need this flag ??? */
    private Boolean forwardDirection;


    /**
     * Creates a Cursor over the tuples of a JDBM table.
     *
     * @param table the JDBM Table to build a Cursor over
     * @throws java.io.IOException of there are problems accessing the BTree or if this table
     * does not allow duplicate values
     */
    public DupsContainerCursor( JdbmTable<K, V> table )
    {
        if ( IS_DEBUG )
        {
            LOG_CURSOR.debug( "Creating DupsContainerCursor {}", this );
        }

        if ( !table.isDupsEnabled() )
        {
            throw new IllegalStateException( I18n.err( I18n.ERR_572 ) );
        }

        this.table = table;
    }


    /**
     * Clean the tuples we use to store the returned resut.
     */
    private void clearValue()
    {
        returnedTuple.setKey( null );
        returnedTuple.setValue( null );
        jdbmTuple.setKey( null );
        jdbmTuple.setValue( null );
        valueAvailable = false;
    }


    /**
     * {@inheritDoc}
     */
    public boolean available()
    {
        return valueAvailable;
    }


    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public void beforeKey( K key ) throws LdapException, CursorException
    {
        checkNotClosed( "beforeKey()" );
        try
        {
        	browser = ( ( BTree<K, V> ) table.getBTree() ).browse( key );
        	forwardDirection = null;
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public void afterKey( K key ) throws LdapException, CursorException
    {
        checkNotClosed( "afterKey()" );

        try
        {
        	browser = ( ( BTree<K, V> ) table.getBTree() ).browse( key );
        	forwardDirection = null;
        	
        	/*
        	 * 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 = jdbmTuple.getKey();
        		
        		int nextCompared = table.getKeyComparator().compare( next, key );
        		
        		if ( nextCompared > 0 )
        		{
        			browser.getPrevious( jdbmTuple );
        			
        			// switch in direction bug workaround: when a JDBM browser
        			// switches direction with next then previous as is occurring
        			// here then two previous moves are needed.
        			browser.getPrevious( jdbmTuple );
        			forwardDirection = false;
        			clearValue();
        			
        			return;
        		}
        	}
        	
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public void beforeValue( K key, DupsContainer<V> value ) throws Exception
    {
        throw new UnsupportedOperationException( I18n.err( I18n.ERR_573 ) );
    }


    /**
     * {@inheritDoc}
     */
    public void afterValue( K key, DupsContainer<V> value ) throws Exception
    {
        throw new UnsupportedOperationException( I18n.err( I18n.ERR_573 ) );
    }


    /**
     * 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, DupsContainer<V>> element ) throws LdapException, CursorException
    {
        beforeKey( element.getKey() );
    }


    /**
     * {@inheritDoc}
     */
    public void after( Tuple<K, DupsContainer<V>> element ) throws LdapException, CursorException
    {
        afterKey( element.getKey() );
    }


    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public void beforeFirst() throws LdapException, CursorException
    {
        checkNotClosed( "beforeFirst()" );
        try
        {
        	browser = table.getBTree().browse();
        	forwardDirection = null;
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public void afterLast() throws LdapException, CursorException
    {
        checkNotClosed( "afterLast()" );
        try
        {
        	browser = table.getBTree().browse( null );
        	forwardDirection = null;
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public boolean first() throws LdapException, CursorException
    {
        beforeFirst();

        return next();
    }


    /**
     * {@inheritDoc}
     */
    public boolean last() throws LdapException, CursorException
    {
        afterLast();

        return previous();
    }


    /**
     * {@inheritDoc}
     */
    public boolean previous() throws LdapException, CursorException
    {
        checkNotClosed( "previous()" );

        if ( browser == null )
        {
            afterLast();
        }

        try
        {
        	boolean advanceSuccess = browser.getPrevious( jdbmTuple );
        	
        	// only want to set this if the advance is a success which means we
        	// are not at front
        	if ( forwardDirection == null )
        	{
        		if ( advanceSuccess )
        		{
        			forwardDirection = false;
        		}
        		else
        		{
        			clearValue();
        			
        			return false;
        		}
        	}
        	else if ( forwardDirection )
        	{
        		advanceSuccess = browser.getPrevious( jdbmTuple );
        		forwardDirection = false;
        	}
        	
        	valueAvailable = advanceSuccess;
        	
        	if ( valueAvailable )
        	{
        		returnedTuple.setKey( jdbmTuple.getKey() );
        		returnedTuple.setValue( table.getDupsContainer( ( byte[] ) jdbmTuple.getValue() ) );
        	}
        	else
        	{
        		clearValue();
        	}
        	
        	return valueAvailable;
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public boolean next() throws LdapException, CursorException
    {
        checkNotClosed( "next()" );

        if ( browser == null )
        {
            // The tuple browser is not initialized : set it to the beginning of the cursor
            beforeFirst();
        }

        try
        {
        	// Check if we can move forward and grab a tuple
        	boolean advanceSuccess = browser.getNext( jdbmTuple );
        	
        	// only want to set this if the advance is a success which means
        	// we are not at end
        	if ( forwardDirection == null )
        	{
        		if ( advanceSuccess )
        		{
        			forwardDirection = true;
        		}
        		else
        		{
        			clearValue();
        			
        			// No value available
        			return false;
        		}
        	}
        	
        	if ( !forwardDirection )
        	{
        		advanceSuccess = browser.getNext( jdbmTuple );
        		forwardDirection = true;
        	}
        	
        	valueAvailable = advanceSuccess;
        	
        	if ( valueAvailable )
        	{
        		// create the fetched tuple containing the key and the deserialized value
        		returnedTuple.setKey( jdbmTuple.getKey() );
        		returnedTuple.setValue( table.getDupsContainer( ( byte[] ) jdbmTuple.getValue() ) );
        	}
        	else
        	{
        		clearValue();
        	}
        	
        	return valueAvailable;
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public Tuple<K, DupsContainer<V>> get() throws CursorException
    {
        checkNotClosed( "get()" );

        if ( valueAvailable )
        {
            return returnedTuple;
        }

        throw new InvalidCursorPositionException();
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void close()
    {
        if ( IS_DEBUG )
        {
            LOG_CURSOR.debug( "Closing DupsContainerCursor {}", this );
        }

        super.close();
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void close( Exception cause )
    {
        if ( IS_DEBUG )
        {
            LOG_CURSOR.debug( "Closing DupsContainerCursor {}", this );
        }

        super.close( cause );
    }
}