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Artifact with commonly used I/O functionality and for connection related issues such as receiving or transmitting data in a unified way.
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// /////////////////////////////////////////////////////////////////////////////
// REFCODES.ORG
// =============================================================================
// This code is copyright (c) by Siegfried Steiner, Munich, Germany and licensed
// under the following (see "http://en.wikipedia.org/wiki/Multi-licensing")
// licenses:
// =============================================================================
// GNU General Public License, v3.0 ("http://www.gnu.org/licenses/gpl-3.0.html")
// together with the GPL linking exception applied; as being applied by the GNU
// Classpath ("http://www.gnu.org/software/classpath/license.html")
// =============================================================================
// Apache License, v2.0 ("http://www.apache.org/licenses/LICENSE-2.0")
// =============================================================================
// Please contact the copyright holding author(s) of the software artifacts in
// question for licensing issues not being covered by the above listed licenses,
// also regarding commercial licensing models or regarding the compatibility
// with other open source licenses.
// /////////////////////////////////////////////////////////////////////////////

package org.refcodes.io;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

import org.refcodes.component.AbstractConnectableAutomaton;
import org.refcodes.component.CloseException;
import org.refcodes.component.OpenException;
import org.refcodes.controlflow.RetryCounter;
import org.refcodes.controlflow.RetryCounterImpl;
import org.refcodes.data.IoRetryCount;
import org.refcodes.data.LoopSleepTime;
import org.refcodes.mixin.Loggable;

/**
 * The {@link AbstractReceiver} is a base abstract implementation of the
 * {@link Receiver} interface providing common functionality for concrete real
 * live {@link ByteDatagramReceiver} and {@link ByteBlockReceiver} (=
 * {@link Receiver}) implementations.
 * 
 * A blocking queue is used internally to which received datagrams are put via
 * {@link #pushDatagram(Serializable)} and which can be retrieved via
 * {@link #readDatagram()}. The {@link #pushDatagram(Serializable)} method is
 * your hook when extending this class.
 * 
 * Make sure your code fetches the datagrams quick enough to prevent filling up
 * of the queue. In case the queue is filled up, adding elements via
 * {@link #pushDatagram(Serializable)} to the queue is blocked until elements
 * are taken from the queue via {@link #readDatagram()}. So cautions are taken
 * to prevent a memory leak.
 *
 * @param  The type of the datagram to be operated with.
 */
public abstract class AbstractReceiver extends AbstractConnectableAutomaton implements Receiver, Loggable {

	// /////////////////////////////////////////////////////////////////////////
	// CONSTANTS:
	// /////////////////////////////////////////////////////////////////////////

	public static final int DATAGRAM_QUEUE_SIZE = 1024;

	// /////////////////////////////////////////////////////////////////////////
	// VARIABLES:
	// /////////////////////////////////////////////////////////////////////////

	private LinkedBlockingQueue _datagramQueue;

	// /////////////////////////////////////////////////////////////////////////
	// CONSTRUCTORS:
	// /////////////////////////////////////////////////////////////////////////

	/**
	 * Constructs a {@link AbstractReceiver} with a default sized blocking queue
	 * enabling a maximum of {@link #DATAGRAM_QUEUE_SIZE} datagrams.
	 * -------------------------------------------------------------------------
	 * Make sure your code fetches the datagrams quick enough to prevent filling
	 * up of the queue. In case the queue is filled up, adding elements via
	 * {@link #pushDatagram(Serializable)} to the queue is blocked until
	 * elements are taken from the queue via {@link #readDatagram()}.
	 */
	public AbstractReceiver() {
		_datagramQueue = new LinkedBlockingQueue( DATAGRAM_QUEUE_SIZE );
	}

	/**
	 * Constructs a {@link AbstractReceiver} with a custom sized blocking queue
	 * enabling a maximum of datagrams as specified by the capacity parameter.
	 * -------------------------------------------------------------------------
	 * Make sure your code fetches the datagrams quick enough to prevent filling
	 * up of the queue. In case the queue is filled up, adding elements via
	 * {@link #pushDatagram(Serializable)} to the queue is blocked until
	 * elements are taken from the queue via {@link #readDatagram()}.
	 * 
	 * @param aCapacity The capacity of the queue holding the received
	 *        datagrams.
	 */
	public AbstractReceiver( int aCapacity ) {
		_datagramQueue = new LinkedBlockingQueue( aCapacity );
	}

	// /////////////////////////////////////////////////////////////////////////
	// METHODS:
	// /////////////////////////////////////////////////////////////////////////

	/**
	 * {@inheritDoc}
	 */
	@Override
	public DATA readDatagram() throws OpenException, InterruptedException {
		if ( _datagramQueue.isEmpty() && !isOpened() ) {
			throw new OpenException( "Unable to read datagram  as the connection is NOT OPEN; connection status is " + getConnectionStatus() + "." );
		}
		return _datagramQueue.take();

	}

	/**
	 * Read datagrams.
	 *
	 * @return the DAT a[]
	 * @throws OpenException the open exception
	 * @throws InterruptedException the interrupted exception
	 */
	@SuppressWarnings("unchecked")
	@Override
	public DATA[] readDatagrams() throws OpenException, InterruptedException {
		if ( _datagramQueue.isEmpty() && !isOpened() ) {
			throw new OpenException( "Unable to read datagram  as the connection is NOT OPEN; connection status is " + getConnectionStatus() + "." );
		}
		List theBytes = new ArrayList<>();
		_datagramQueue.drainTo( theBytes );
		return theBytes.toArray( ((DATA[]) new Object[theBytes.size()]) );
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public boolean hasDatagram() throws OpenException {
		// Enable the caller to get all elements from the queue:
		// if ( _datagramQueue.isEmpty() && !isOpened() ) { throw new
		// OpenException( "Unable to read datagram as the connection is NOT
		// OPEN; connection status is " + getConnectionStatus() + "." ); }
		return !_datagramQueue.isEmpty();
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void close() throws CloseException {
		if ( isOpened() ) {
			super.close();
			releaseAll();
		}
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void releaseAll() {
		synchronized ( _datagramQueue ) {
			_datagramQueue.notifyAll();
		}
	}

	// /////////////////////////////////////////////////////////////////////////
	// HOOKS:
	// /////////////////////////////////////////////////////////////////////////

	/**
	 * Pushes a datagram into the receiver and puts it into the blocking queue
	 * containing the so far received datagrams. Them datagrams can be retrieved
	 * via {@link #readDatagram()}: use {@link #hasDatagram()} to test
	 * beforehand whether there is a datagram available.
	 *
	 * @param aDatagram The datagram to be pushed at the end of the blocking
	 *        queue; to be retrieved with the {@link #readDatagram()} method.
	 * @throws OpenException the open exception
	 */
	protected void pushDatagram( DATA aDatagram ) throws OpenException {
		if ( !isOpened() ) {
			throw new OpenException( "Unable to push datagram <" + aDatagram.getClass().getName() + "> as the connection is NOT OPEN; connection status is " + getConnectionStatus() + "." );
		}
		RetryCounter theRetryCounter = new RetryCounterImpl( IoRetryCount.MAX.getValue() );
		try {
			while ( !_datagramQueue.offer( aDatagram, LoopSleepTime.MAX.getMillis(), TimeUnit.MILLISECONDS ) && theRetryCounter.nextRetry() ) {
				warn( "Trying to offer (add) a datagram to the datagram queue, though the queue is full, this is retry # <" + theRetryCounter.getRetryCount() + ">, aborting after <" + theRetryCounter.getRetryNumber() + "> retries. Retrying now after a delay of <" + (LoopSleepTime.MAX.getMillis() / 1000) + "> seconds..." );
				if ( !theRetryCounter.hasNextRetry() ) {
					throw new OpenException( "Unable to process the datagram after <" + theRetryCounter.getRetryNumber() + "> retries, aborting retries, dismissing datagram \"" + aDatagram.toString() + "\"!", null, null );
				}
			}
		}
		catch ( InterruptedException ignored ) {}
	}

	/**
	 * Pushes datagrams into the receiver and puts them into the blocking queue
	 * containing the so far received datagrams. Them datagrams can be retrieved
	 * via {@link #readDatagram()}: use {@link #hasDatagram()} to test
	 * beforehand whether there is a datagram available.
	 *
	 * @param aDatagrams The datagrams to be pushed at the end of the blocking
	 *        queue; to be retrieved with the {@link #readDatagram()} method.
	 * @throws OpenException the open exception
	 */
	protected void pushDatagrams( DATA[] aDatagrams ) throws OpenException {
		for ( DATA eData : aDatagrams ) {
			pushDatagram( eData );
		}
	}

	/**
	 * Pushes datagrams into the receiver and puts them into the blocking queue
	 * containing the so far received datagrams. Them datagrams can be retrieved
	 * via {@link #readDatagram()}: use {@link #hasDatagram()} to test
	 * beforehand whether there is a datagram available.
	 *
	 * @param aDatagrams The datagrams to be pushed at the end of the blocking
	 *        queue; to be retrieved with the {@link #readDatagram()} method.
	 * @param aOffset The offset to start taking data from to be pushed.
	 * @param aLength The number of elements to be pushed from the offset
	 *        onwards.
	 * @throws OpenException the open exception
	 */
	protected void pushDatagrams( DATA[] aDatagrams, int aOffset, int aLength ) throws OpenException {
		for ( int i = aOffset; i < aOffset + aLength; i++ ) {
			pushDatagram( aDatagrams[i] );
		}
	}
}