streams/src/main/java/org/gcube/data/streams/adapters/ResultsetStream.java

package org.gcube.data.streams.adapters;

import gr.uoa.di.madgik.grs.buffer.IBuffer.Status;
import gr.uoa.di.madgik.grs.reader.ForwardReader;
import gr.uoa.di.madgik.grs.reader.GRS2ReaderException;
import gr.uoa.di.madgik.grs.record.Record;
import gr.uoa.di.madgik.grs.record.exception.GRS2UncheckedException;

import java.net.URI;
import java.util.Iterator;
import java.util.concurrent.TimeUnit;

import org.gcube.data.streams.LookAheadStream;
import org.gcube.data.streams.Stream;
import org.gcube.data.streams.exceptions.StreamException;
import org.gcube.data.streams.exceptions.StreamOpenException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * A {@link Stream} adapter for gRS2 resultsets.
 * <p>
 * This implementation is not thread safe.
 * 
 * @author Fabio Simeoni
 *
 */
public class ResultsetStream<E extends Record> extends LookAheadStream<E> {

	private static Logger log =LoggerFactory.getLogger(ResultsetStream.class);	
	
	public static final int default_timeout = 30;
	public static final TimeUnit default_timeout_unit=TimeUnit.SECONDS;
	
	private final URI locator;
	
	private long timeout = default_timeout;
	private TimeUnit timeoutUnit = default_timeout_unit;
	
	private boolean open=false;
	private boolean closed=false;
	private RuntimeException lookAheadFailure;
	
	private ForwardReader<E> reader;
	private Iterator<E> iterator;

	
	/**
	 * Creates a new instance with a result set locator.
	 * @param locator the locator.
	 * @throws IllegalArgumentException if the locator is <code>null</code>.
	 * */
	public ResultsetStream(URI locator) throws IllegalArgumentException {
		
		if (locator==null)
			throw new IllegalArgumentException("invalid or null locator");
		
		this.locator=locator;
		
	}
	
	public void setTimeout(long timeout, TimeUnit unit) throws IllegalArgumentException {
		
		if (timeout<=0 || timeoutUnit==null)
			throw new IllegalArgumentException("invalid timeout or null timeout unit");
		
		this.timeout = timeout;
		this.timeoutUnit = unit;
	}

	@Override
	protected E delegateNext() {
		
		try {
			if (lookAheadFailure!=null)
				throw lookAheadFailure;
			else
				try {
					return iterator.next();
				}
				catch(GRS2UncheckedException e) {
					
					//get underlying cause
					Throwable cause = e.getCause();
					
					//rewrap checked cause as appropriate to this layer
					if (cause instanceof RuntimeException)
						throw (RuntimeException) cause;
					else
					 throw new StreamException(cause);
				}
		}
		finally {
			lookAheadFailure=null;
		}
	}
	
	@Override
	protected boolean delegateHasNext() {
		
		if (closed)
			return false;
		
		if (!open) {
			
			try {
				reader = new ForwardReader<E>(locator);
				reader.setIteratorTimeout(timeout);
				reader.setIteratorTimeUnit(timeoutUnit);
			}
			catch (Throwable t) { 
				lookAheadFailure= new StreamOpenException("cannot open resultset "+locator,t);
				return true;
			}
		
			iterator = reader.iterator();
		
			log.info("initialised resultset at "+locator);
			
			open=true;
		}
		
		//infer outage if reader has been dismissed remotely 
		if (reader.getStatus()==Status.Dispose && !closed)
			lookAheadFailure= new RuntimeException("unrecoverable failure in resultset ");

		boolean hasNext =  iterator.hasNext();
		
		return hasNext;
	}
	
	
	@Override
	public void close() {

		if (open) {
			try {
				reader.close();
				log.info("closed resultset at "+locator);
			}
			catch(GRS2ReaderException e) {
				log.error("could not close resultset",e);
			}
			open=false;
		}
		closed=true;
	}
	
	@Override
	public URI locator() throws IllegalStateException {
		
		if (open)
			throw new IllegalStateException("locator is invalid as result set has already been opened");
		else
			return locator;
		
	}

	@Override
	public void remove() {
		iterator.remove();
	}
	
	@Override
	public boolean isClosed() {
		return closed;
	}
}