yacy_search_server/source/net/yacy/kelondro/rwi/AbstractIndex.java

// AbstractIndex.java
// -----------------------------
// (C) 2009 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
// first published 15.3.2009 on http://yacy.net
//
// This is a part of YaCy, a peer-to-peer based web search engine
//
// $LastChangedDate: 2006-04-02 22:40:07 +0200 (So, 02 Apr 2006) $
// $LastChangedRevision: 1986 $
// $LastChangedBy: orbiter $
//
// LICENSE
// 
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

package net.yacy.kelondro.rwi;

import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

import net.yacy.kelondro.index.RowSpaceExceededException;
import net.yacy.kelondro.logging.Log;
import net.yacy.kelondro.order.Order;

public abstract class AbstractIndex <ReferenceType extends Reference> implements Index<ReferenceType> {
    
    final protected ReferenceFactory<ReferenceType> factory;

    public AbstractIndex(final ReferenceFactory<ReferenceType> factory) {
        this.factory = factory;
    }
    
    public int remove(final TreeSet<byte[]> termHashes, final byte[] urlHashBytes) throws IOException {
        // remove the same url hashes for multiple words
        // this is mainly used when correcting a index after a search
        final Iterator<byte[]> i = termHashes.iterator();
        int c = 0;
        while (i.hasNext()) {
            if (remove(i.next(), urlHashBytes)) c++;
        }
        return c;
    }
    
    public synchronized TreeSet<ReferenceContainer<ReferenceType>> references(final byte[] startHash, final boolean rot, int count) throws IOException {
        // creates a set of indexContainers
        // this does not use the cache
        final Order<ReferenceContainer<ReferenceType>> containerOrder = new ReferenceContainerOrder<ReferenceType>(factory, this.ordering().clone());
        final ReferenceContainer<ReferenceType> emptyContainer = ReferenceContainer.emptyContainer(factory, startHash);
        containerOrder.rotate(emptyContainer);
        final TreeSet<ReferenceContainer<ReferenceType>> containers = new TreeSet<ReferenceContainer<ReferenceType>>(containerOrder);
        final Iterator<ReferenceContainer<ReferenceType>> i = references(startHash, rot);
        //if (ram) count = Math.min(size(), count);
        ReferenceContainer<ReferenceType> container;
        // this loop does not terminate using the i.hasNex() predicate when rot == true
        // because then the underlying iterator is a rotating iterator without termination
        // in this case a termination must be ensured with a counter
        // It must also be ensured that the counter is in/decreased every loop
        while ((count > 0) && (i.hasNext())) {
            container = i.next();
            if (container != null && !container.isEmpty()) {
                containers.add(container);
            }
            count--; // decrease counter even if the container was null or empty to ensure termination
        }
        return containers; // this may return less containers as demanded
    }
    
    
    // methods to search in the index
    
    /**
     * collect containers for given word hashes.
     * This collection stops if a single container does not contain any references.
     * In that case only a empty result is returned.
     * @param wordHashes
     * @param urlselection
     * @return map of wordhash:indexContainer
     */
    public HashMap<byte[], ReferenceContainer<ReferenceType>> searchConjunction(final TreeSet<byte[]> wordHashes, final Set<String> urlselection) {
    	// first check if there is any entry that has no match; this uses only operations in ram
    	/*
    	Iterator<byte[]> i = wordHashes.iterator();
        while (i.hasNext()) {
            if (!this.has(i.next())); return new HashMap<byte[], ReferenceContainer<ReferenceType>>(0);
        }
        */
    	// retrieve entities that belong to the hashes
        final HashMap<byte[], ReferenceContainer<ReferenceType>> containers = new HashMap<byte[], ReferenceContainer<ReferenceType>>(wordHashes.size());
        byte[] singleHash;
        ReferenceContainer<ReferenceType> singleContainer;
        final Iterator<byte[]> i = wordHashes.iterator();
        while (i.hasNext()) {
        
            // get next word hash:
            singleHash = i.next();
        
            // retrieve index
            try {
                singleContainer = this.get(singleHash, urlselection);
            } catch (IOException e) {
                Log.logException(e);
                continue;
            }
        
            // check result
            if ((singleContainer == null || singleContainer.isEmpty())) return new HashMap<byte[], ReferenceContainer<ReferenceType>>(0);
        
            containers.put(singleHash, singleContainer);
        }
        return containers;
    }
    
    /**
     * collect containers for given word hashes and join them as they are retrieved.
     * This collection stops if a single container does not contain any references
     * or the current result of the container join results in an empty container.
     * In any fail case only a empty result container is returned.
     * @param wordHashes
     * @param urlselection
     * @param maxDistance the maximum distance that the words in the result may have
     * @return ReferenceContainer the join result
     * @throws RowSpaceExceededException 
     */
    public ReferenceContainer<ReferenceType> searchJoin(final TreeSet<byte[]> wordHashes, final Set<String> urlselection, final int maxDistance) throws RowSpaceExceededException {
        // first check if there is any entry that has no match;
        // this uses only operations in ram
        for (byte[] wordHash: wordHashes) {
            if (!this.has(wordHash)) return ReferenceContainer.emptyContainer(factory, null, 0);
        }
        
        // retrieve entities that belong to the hashes
        ReferenceContainer<ReferenceType> resultContainer = null;
        ReferenceContainer<ReferenceType> singleContainer;
        for (byte[] wordHash: wordHashes) {
            // retrieve index
            try {
                singleContainer = this.get(wordHash, urlselection);
            } catch (IOException e) {
                Log.logException(e);
                continue;
            }
        
            // check result
            if ((singleContainer == null || singleContainer.isEmpty())) return ReferenceContainer.emptyContainer(factory, null, 0);
            if (resultContainer == null) resultContainer = singleContainer; else {
                resultContainer = ReferenceContainer.joinConstructive(factory, resultContainer, singleContainer, maxDistance);
            }
            
            // finish if the result is empty
            if (resultContainer.isEmpty()) return resultContainer;
        }
        return resultContainer;
    }
    
    public TermSearch<ReferenceType> query(
            final TreeSet<byte[]> queryHashes,
            final TreeSet<byte[]> excludeHashes,
            final Set<String> urlselection,
            final ReferenceFactory<ReferenceType> termFactory,
            final int maxDistance) throws RowSpaceExceededException {

        return new TermSearch<ReferenceType>(this, queryHashes, excludeHashes, urlselection, termFactory, maxDistance);
    }
}