Nth.java

package org.epics.archiverappliance.retrieval.postprocessors;

import java.io.IOException;
import java.sql.Timestamp;
import java.util.LinkedList;
import java.util.concurrent.Callable;

import javax.servlet.http.HttpServletRequest;

import org.apache.log4j.Logger;
import org.epics.archiverappliance.Event;
import org.epics.archiverappliance.EventStream;
import org.epics.archiverappliance.common.POJOEvent;
import org.epics.archiverappliance.common.TimeSpan;
import org.epics.archiverappliance.common.TimeUtils;
import org.epics.archiverappliance.config.PVTypeInfo;
import org.epics.archiverappliance.data.AlarmInfo;
import org.epics.archiverappliance.engine.membuf.ArrayListEventStream;
import org.epics.archiverappliance.retrieval.RemotableEventStreamDesc;

/**
 * 
 * <code>Nth</code> is a post processor which returns every n-th value.
 *
 * @author <a href="mailto:jaka.bobnar@cosylab.com">Jaka Bobnar</a>
 *
 */
public class Nth implements PostProcessor, PostProcessorWithConsolidatedEventStream {
	
	private static final String IDENTITY = "nth";
	public static final int MAX_COUNT = Integer.MAX_VALUE/1000;
	
	private static Logger logger = Logger.getLogger(Nth.class.getName());
	
	private int everyNth = PostProcessors.DEFAULT_SUMMARIZING_INTERVAL;
	private int count;
	private long startTime;
	private long endTime;
	private ArrayListEventStream data;
	private Timestamp previousEventTimestamp = new Timestamp(1);
	private int i = 0;
	
	@Override
	public String getIdentity() {
		return IDENTITY;
	}

	@Override
	public String getExtension() {
		String identity = this.getIdentity();
		if(everyNth == PostProcessors.DEFAULT_SUMMARIZING_INTERVAL) {
			return identity;
		} else {
			return identity + "_" + Integer.toString(everyNth);
		}
	}

	@Override
	public void initialize(String userarg, String pvName) throws IOException {
		if(userarg != null && userarg.contains("_")) {
			String[] userparams = userarg.split("_");
			String everyNthStr = userparams[1];
			everyNth = Integer.parseInt(everyNthStr);
			logger.debug("Using the supplied n " + everyNthStr);
		} else {
			logger.debug("Using the default n " + everyNth + " as the user has not specified the n argument.");
		}
		
	}

	@Override
	public long estimateMemoryConsumption(String pvName, PVTypeInfo typeInfo, Timestamp start, Timestamp end, HttpServletRequest req) {
		this.startTime = start.getTime();
		this.endTime = end.getTime();
		long startTime = TimeUtils.convertToEpochSeconds(start);
		long endTime = TimeUtils.convertToEpochSeconds(end);
		count = (int)((endTime - startTime)/typeInfo.getSamplingPeriod())/everyNth;
		//limit the count to ~2M (2.147.483) to avoid out of memory errors		
		if (count > MAX_COUNT)
			logger.warn("Too many points expected (" + count + "). The returned data array will be cut off at " + MAX_COUNT +" points.");
	
		if (count < 0) count = 1;
		else count = Math.min(MAX_COUNT,count);
		logger.debug(count + " number of points expected.");
		return (long) (typeInfo.getComputedStorageRate()*(endTime - startTime)*2/everyNth);
	}

	@Override
	public Callable<EventStream> wrap(final Callable<EventStream> callable) {
		//This method might be called several times with different parameter, each containing a subset of points
		//To handle the points correctly and to ensure that the points are ordered by the timestamps, hold
		//the running integer (i) and the previous timestamp (previousEventTimestamp) globally.
		return new Callable<EventStream>() {
			@Override
			public EventStream call() throws Exception {
				try(EventStream strm = callable.call()) {
					if(data == null) {
						data = new ArrayListEventStream(count,(RemotableEventStreamDesc)strm.getDescription());
					}
					for(Event e : strm) {
						if(e.getEventTimeStamp().after(previousEventTimestamp)) { 
							previousEventTimestamp = e.getEventTimeStamp();
						} else {
							if(logger.isDebugEnabled()) { 
								logger.debug("Skipping older event " + TimeUtils.convertToHumanReadableString(e.getEventTimeStamp()) + " previous " + TimeUtils.convertToHumanReadableString(previousEventTimestamp));
							}
							continue;
						}
						long s = e.getEventTimeStamp().getTime();
						if (s < startTime || s > endTime) {
							logger.debug("Skipping event that is out of selected boundaries. Time: " + TimeUtils.convertToHumanReadableString(s));
						} else {
    						if (i++ % everyNth == 0) {
    							//Transform events to POJOEvent. Using the incomming events causes troubles when
    							//transferring data to the client (client only sees one sample).
    							if (e instanceof AlarmInfo) {
    								data.add(new POJOEvent(e.getDBRType(),e.getEventTimeStamp(),e.getSampleValue(),((AlarmInfo)e).getStatus(),((AlarmInfo)e).getSeverity()));
    							} else {
    								data.add(new POJOEvent(e.getDBRType(),e.getEventTimeStamp(),e.getSampleValue(),0,0));
    							}
    						}
						}
						if (data.size() == MAX_COUNT) {
							logger.warn("Too many points. Truncating the data array at " + MAX_COUNT);
							break;
						}
						
					}
					return new ArrayListEventStream(0,(RemotableEventStreamDesc)strm.getDescription());
				}
			}
		};
	}
	
	@Override
	public LinkedList<TimeSpan> getBinTimestamps() {
		LinkedList<TimeSpan> list = new LinkedList<>();
		if (data == null) return list;
		for (int i = 0; i < data.size() - 1; i++) {
			list.add(new TimeSpan(data.get(i).getEventTimeStamp(),data.get(i+1).getEventTimeStamp()));
		}
		return list;
	}
	
	@Override
	public EventStream getConsolidatedEventStream() {
		return data;
	}
	
	@Override
	public long getEndBinEpochSeconds() {
		return TimeUtils.convertToEpochSeconds(new Timestamp(endTime));
	}
	
	@Override
	public long getStartBinEpochSeconds() {
		return TimeUtils.convertToEpochSeconds(new Timestamp(startTime));
	}
}