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CloudGraph(tm) is a suite of Service Data Object (SDO) 2.1 services designed for relational and big-table style "cloud" databases, such as HBase and others.
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package org.cloudgraph.hbase.service;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.util.Bytes;
import org.cloudgraph.hbase.graph.HBaseGraphAssembler;
import org.cloudgraph.hbase.io.TableReader;
import org.cloudgraph.query.expr.Expr;
import org.cloudgraph.recognizer.GraphRecognizerContext;
import org.cloudgraph.state.GraphState;
import org.plasma.sdo.PlasmaDataGraph;
import org.plasma.sdo.helper.PlasmaXMLHelper;
import org.plasma.sdo.xml.DefaultOptions;

import commonj.sdo.helper.XMLDocument;

/**
 * Assembler which determines whether results can be ignored under the current context then
 * "slides" past results not within the given range, avoiding the 
 * overhead of assembling a graph. When a graph recognizer 
 * is present for the current context, no result can be bypassed as the recognizer
 * requires an assembled graph to evaluate and make its determination. 
 * @author Scott Cinnamond
 * @since 0.5.9
 * @see HBaseGraphAssembler
 * @see Expr
 * @see GraphRecognizerContext
 */
public class SlidingResultsAssembler implements ResultsAssembler {
	private static final Log log = LogFactory.getLog(SlidingResultsAssembler.class);
    private Set graphs = new HashSet();
    
    private Expr graphRecognizerRootExpr;
    private GraphRecognizerContext recognizerContext;
    private Comparator orderingComparator;
    private TableReader rootTableReader;
    private HBaseGraphAssembler graphAssembler;
    private Integer startRange;
    private Integer endRange;
    private boolean resultEndRangeReached = false;
    private int unrecognizedRsults;
    private int ignoredResults;
    private int ignoredResultsPreceedingRange;
    private int range;
    
 	private SlidingResultsAssembler() {}
    
    public SlidingResultsAssembler(Expr graphRecognizerRootExpr,
			Comparator orderingComparator,
			TableReader rootTableReader, 
			HBaseGraphAssembler graphAssembler,
			Integer startRange, Integer endRange) {
		this();
		this.graphRecognizerRootExpr = graphRecognizerRootExpr;
		this.orderingComparator = orderingComparator;
		this.rootTableReader = rootTableReader;
		this.graphAssembler = graphAssembler;
		this.startRange = startRange;
		this.endRange = endRange;
		if (startRange != null && endRange != null) {
			range = endRange.intValue() - startRange.intValue();
			range++; // inclusive
		}
	}

	public boolean collect(Result resultRow) throws IOException {
    	if (resultRow.containsColumn(rootTableReader.getTableConfig().getDataColumnFamilyNameBytes(), 
    			GraphState.TOUMBSTONE_COLUMN_NAME_BYTES)) {
    		return false; // ignore toumbstone roots
    	}
        	
    	if (canIgnoreResults()) {
        	if (startRange != null && endRange != null) {
        		int current = ignoredResultsPreceedingRange + 1;    		
        		if (current < startRange.intValue()) {
        			ignoredResultsPreceedingRange++;
        			ignoredResults++;
        			return false;       			 
        		}
        		
        		current = this.graphs.size() + 1; 
        		if (current > range) {
        			ignoredResults++;
        			this.resultEndRangeReached = true;
        			return false;       			 
        		}
        	}
    	}
    	
  	    this.graphAssembler.assemble(resultRow); 
  	    PlasmaDataGraph graph = this.graphAssembler.getDataGraph();
    	this.graphAssembler.clear();

        if (this.graphRecognizerRootExpr != null) {
        	if (this.recognizerContext == null)
        		this.recognizerContext = new GraphRecognizerContext();
        	this.recognizerContext.setGraph(graph);
        	if (!this.graphRecognizerRootExpr.evaluate(this.recognizerContext)) {
        		if (log.isDebugEnabled())
        			log.debug("recognizer excluded: " + Bytes.toString(
        					resultRow.getRow()));
        		if (log.isDebugEnabled())
        			log.debug(serializeGraph(graph));   
        		this.unrecognizedRsults++;
        		return false;
        	}
        }
        this.graphs.add(graph);
    	
    	return true;
    }

	@Override
	public int getUnrecognizedResults() {
		return unrecognizedRsults;
	}

	@Override
	public int getIgnoredResults() {
		return ignoredResults;
	}

	@Override
	public boolean isResultEndRangeReached() {
		return resultEndRangeReached;
	}

	@Override
	public PlasmaDataGraph[] getResults() {
        PlasmaDataGraph[] array = new PlasmaDataGraph[graphs.size()]; 
        this.graphs.toArray(array);
        if (this.orderingComparator != null) 
        	Arrays.sort(array, this.orderingComparator);
        return array;
	}

	@Override
	public boolean canIgnoreResults() {
		return this.graphRecognizerRootExpr == null;
	}
	
	@Override
	public int size() {
		return this.graphs.size();
	}

    private String serializeGraph(commonj.sdo.DataGraph graph) throws IOException
    {
        DefaultOptions options = new DefaultOptions(
        		graph.getRootObject().getType().getURI());
        options.setRootNamespacePrefix("debug");
        
        XMLDocument doc = PlasmaXMLHelper.INSTANCE.createDocument(graph.getRootObject(), 
        		graph.getRootObject().getType().getURI(), 
        		null);
        ByteArrayOutputStream os = new ByteArrayOutputStream();
	    PlasmaXMLHelper.INSTANCE.save(doc, os, options);        
        os.flush();
        os.close(); 
        String xml = new String(os.toByteArray());
        return xml;
    }

}