/*
 * 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 java.util.Comparator;

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;


/**
 * Cursor over a set of values for the same key which are store in another
 * BTree.  This Cursor is limited to the same key and it's tuples will always
 * return the same key.
 *
 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
 */
public class KeyTupleBTreeCursor<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 Comparator<V> comparator;
    private final BTree btree;
    private final K key;

    private jdbm.helper.Tuple<K, V> valueTuple = new jdbm.helper.Tuple<K, V>();
    private Tuple<K, V> returnedTuple = new Tuple<K, V>();
    private TupleBrowser<K, V> browser;
    private boolean valueAvailable;


    /**
     * Creates a Cursor over the tuples of a JDBM BTree.
     *
     * @param btree the JDBM BTree to build a Cursor over
     * @param key the constant key for which values are returned
     * @param comparator the Comparator used to determine <b>key</b> ordering
     * @throws Exception of there are problems accessing the BTree
     */
    public KeyTupleBTreeCursor( BTree btree, K key, Comparator<V> comparator ) throws Exception
    {
        if ( IS_DEBUG )
        {
            LOG_CURSOR.debug( "Creating KeyTupleBTreeCursor {}", this );
        }

        this.key = key;
        this.btree = btree;
        this.comparator = comparator;
        this.browser = btree.browse();
    }


    private void clearValue()
    {
        returnedTuple.setKey( key );
        returnedTuple.setValue( null );
        valueAvailable = false;
    }


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


    public void beforeKey( K key ) throws Exception
    {
        throw new UnsupportedOperationException( I18n.err( I18n.ERR_446 ) );
    }


    /**
     * {@inheritDoc}
     */
    public void afterKey( K key ) throws Exception
    {
        throw new UnsupportedOperationException( I18n.err( I18n.ERR_446 ) );
    }


    /**
     * {@inheritDoc}
     */
    public void beforeValue( K key, V value ) throws Exception
    {
        checkNotClosed( "beforeValue()" );
        if ( key != null && !key.equals( this.key ) )
        {
            throw new UnsupportedOperationException( I18n.err( I18n.ERR_446 ) );
        }

        browser = btree.browse( value );
        clearValue();
    }


    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public void afterValue( K key, V value ) throws LdapException, CursorException
    {
        if ( key != null && !key.equals( this.key ) )
        {
            throw new UnsupportedOperationException( I18n.err( I18n.ERR_446 ) );
        }

        try
        {
        	browser = btree.browse( value );
        	
        	/*
        	 * 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( valueTuple ) )
        	{
        		checkNotClosed( "afterValue" );
        		
        		V next = ( V ) valueTuple.getKey();
        		
        		int nextCompared = comparator.compare( next, value );
        		
        		if ( nextCompared > 0 )
        		{
        			/*
        			 * If we just have values greater than the element argument
        			 * then we are before the first element and cannot backup, and
        			 * the call below to getPrevious() will fail.  In this special
        			 * case we just reset the Cursor's browser and return.
        			 */
        			if ( !browser.getPrevious( valueTuple ) )
        			{
        				browser = btree.browse( this.key );
        			}
        			
        			clearValue();
        			
        			return;
        		}
        	}
        	
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * Positions this Cursor over the same keys before the value of the
     * supplied valueTuple.  The supplied element Tuple's key is not considered at
     * all.
     *
     * @param element the valueTuple who's value is used to position this Cursor
     * @throws Exception if there are failures to position the Cursor
     */
    public void before( Tuple<K, V> element ) throws LdapException, CursorException
    {
        checkNotClosed( "before()" );
        try
        {
        	browser = btree.browse( element.getValue() );
        	clearValue();
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public void after( Tuple<K, V> element ) throws LdapException, CursorException
    {
        afterValue( key, element.getValue() );
    }


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


    /**
     * {@inheritDoc}
     */
    public void afterLast() throws LdapException, CursorException
    {
        checkNotClosed( "afterLast()" );
        try
        {
        	browser = btree.browse( null );
        }
        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}
     */
    @SuppressWarnings("unchecked")
    public boolean previous() throws LdapException, CursorException
    {
        checkNotClosed( "previous()" );

        try
        {
        	if ( browser.getPrevious( valueTuple ) )
        	{
        		// work around to fix direction change problem with jdbm browser
        		if ( ( returnedTuple.getValue() != null ) &&
        				( comparator.compare( ( V ) valueTuple.getKey(), returnedTuple.getValue() ) == 0 ) )
        		{
        			browser.getPrevious( valueTuple );
        		}
        		returnedTuple.setKey( key );
        		returnedTuple.setValue( ( V ) valueTuple.getKey() );
        		
        		return valueAvailable = true;
        	}
        	else
        	{
        		clearValue();
        		
        		return false;
        	}
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


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

        try
        {
        	if ( browser.getNext( valueTuple ) )
        	{
        		// work around to fix direction change problem with jdbm browser
        		if ( returnedTuple.getValue() != null &&
        				comparator.compare( ( V ) valueTuple.getKey(), returnedTuple.getValue() ) == 0 )
        		{
        			browser.getNext( valueTuple );
        		}
        		
        		returnedTuple.setKey( key );
        		returnedTuple.setValue( ( V ) valueTuple.getKey() );
        		
        		return valueAvailable = true;
        	}
        	else
        	{
        		clearValue();
        		
        		return false;
        	}
        }
        catch( IOException e )
        {
        	throw new CursorException( e );
        }
    }


    /**
     * {@inheritDoc}
     */
    public Tuple<K, 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 KeyTupleBTreeCursor {}", this );
        }

        super.close();
    }


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

        super.close( cause );
    }
}