SimpleEventBus.java

package org.zaproxy.zap.eventBus;

import java.security.InvalidParameterException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.log4j.Logger;

/**
 * A very simple event bus
 * @author simon
 *
 */
public class SimpleEventBus implements EventBus {
	
	private Map<String, RegisteredPublisher> nameToPublisher = new HashMap<String, RegisteredPublisher>();
	private List<RegisteredConsumer> danglingConsumers = new ArrayList<RegisteredConsumer>();

	/**
	 * The read/write {@code Lock} for registration management and publishing of events.
	 * 
	 * @see #regMgmtLock
	 * @see #publishLock
	 */
	private final ReadWriteLock rwLock = new ReentrantReadWriteLock(true);

	/**
	 * The {@code Lock} for registration management (register and unregister) of publishers and consumers.
	 * 
	 * @see #publishLock
	 */
	private final Lock regMgmtLock = rwLock.writeLock();

	/**
	 * The {@code Lock} for publishing of events.
	 * 
	 * @see #regMgmtLock
	 */
	private final Lock publishLock = rwLock.readLock();

	private static Logger log = Logger.getLogger(SimpleEventBus.class);

	@Override
	public void registerPublisher(EventPublisher publisher, String[] eventTypes) {
		if (publisher == null) {
			throw new InvalidParameterException("Publisher must not be null");
		}
		if (eventTypes == null || eventTypes.length == 0) {
			throw new InvalidParameterException("At least one event type must be specified");
		}
		regMgmtLock.lock();
		try {
			if (this.nameToPublisher.get(publisher.getPublisherName()) != null) {
				throw new InvalidParameterException("Publisher with name " + publisher.getPublisherName() + 
						" already registered by " + this.nameToPublisher.get(publisher.getPublisherName())
							.getPublisher().getClass().getCanonicalName());
			}
			log.debug("registerPublisher " + publisher.getPublisherName());

			RegisteredPublisher regProd = new RegisteredPublisher(publisher, eventTypes);

			this.nameToPublisher.put(publisher.getPublisherName(), regProd);

			// Check to see if there are any cached consumers
			for (RegisteredConsumer regCon : this.danglingConsumers) {
				if (regCon.getPublisherName().equals(publisher.getPublisherName())) {
					regProd.addComsumer(regCon);
					this.danglingConsumers.remove(regCon);
					break;
				}
			}
		} finally {
			regMgmtLock.unlock();
		}

	}

	@Override
	public void unregisterPublisher(EventPublisher publisher) {
		if (publisher == null) {
			throw new InvalidParameterException("Publisher must not be null");
		}

		regMgmtLock.lock();
		try {
			log.debug("unregisterPublisher " + publisher.getPublisherName());
			RegisteredPublisher regPub = nameToPublisher.remove(publisher.getPublisherName());
			if (regPub == null) {
				throw new InvalidParameterException("Publisher with name " + publisher.getPublisherName() + 
						" not registered");
			}
		} finally {
			regMgmtLock.unlock();
		}
	}

	@Override
	public void registerConsumer(EventConsumer consumer, String publisherName) {
		this.registerConsumer(consumer, publisherName, null);
	}

	@Override
	public void registerConsumer(EventConsumer consumer, String publisherName,
			String[] eventTypes) {
		if (consumer == null) {
			throw new InvalidParameterException("Consumer must not be null");
		}

		regMgmtLock.lock();
		try {
			log.debug("registerConsumer " + consumer.getClass().getCanonicalName() + " for " + publisherName);
			RegisteredPublisher publisher = this.nameToPublisher.get(publisherName);
			if (publisher == null) {
				// Cache until the publisher registers
				this.danglingConsumers.add(new RegisteredConsumer(consumer, eventTypes, publisherName));
			} else {
				publisher.addComsumer(consumer, eventTypes);
			}
		} finally {
			regMgmtLock.unlock();
		}
	}

	@Override
	public void unregisterConsumer(EventConsumer consumer, String publisherName) {
		if (consumer == null) {
			throw new InvalidParameterException("Consumer must not be null");
		}

		regMgmtLock.lock();
		try {
			log.debug("unregisterConsumer " + consumer.getClass().getCanonicalName() + " for " + publisherName);
			RegisteredPublisher publisher = this.nameToPublisher.get(publisherName);
			if (publisher != null) {
				publisher.removeComsumer(consumer);
			} else {
				// Check to see if its cached waiting for the publisher
				for (RegisteredConsumer regCon : this.danglingConsumers) {
					if (regCon.getConsumer().equals(consumer)) {
						this.danglingConsumers.remove(regCon);
						break;
					}
				}
			}
		} finally {
			regMgmtLock.unlock();
		}
	}


	@Override
	public void publishSyncEvent(EventPublisher publisher, Event event) {
		if (publisher == null) {
			throw new InvalidParameterException("Publisher must not be null");
		}

		publishLock.lock();
		try {
			RegisteredPublisher regPublisher = this.nameToPublisher.get(publisher.getPublisherName());
			if (regPublisher == null) {
				throw new InvalidParameterException("Publisher not registered: " + publisher.getPublisherName());
			}
			log.debug("publishSyncEvent " + event.getEventType() + " from " + publisher.getPublisherName());
			boolean foundType = false;
			for (String type : regPublisher.getEventTypes()) {
				if (event.getEventType().equals(type)) {
					foundType = true;
					break;
				}
			}
			if (! foundType) {
				throw new InvalidParameterException("Event type: " + event.getEventType() + 
						" not registered for publisher: " + publisher.getPublisherName());
			}

			for (RegisteredConsumer regCon : regPublisher.getConsumers()) {
				String[] eventTypes = regCon.getEventTypes();
				boolean isListeningforEvent = false;
				if (eventTypes == null) {
					// They are listening for all events from this publisher
					isListeningforEvent = true;
				} else {
					for (String type : eventTypes) {
						if (event.getEventType().equals(type)) {
							isListeningforEvent = true;
							break;
						}
					}
				}
				if (isListeningforEvent) {
					try {
						regCon.getConsumer().eventReceived(event);
					} catch (Exception e) {
						log.error(e.getMessage(), e);
					}
				}
			}
		}finally {
			publishLock.unlock();
		}
	}
	
	private static class RegisteredConsumer {
		private EventConsumer consumer;
		private String[] eventTypes;
		private String publisherName;
		
		public RegisteredConsumer(EventConsumer consumer, String[] eventTypes) {
			this.consumer = consumer;
			this.eventTypes = eventTypes;
		}
		public RegisteredConsumer(EventConsumer consumer, String[] eventTypes, String publisherName) {
			this.consumer = consumer;
			this.eventTypes = eventTypes;
			this.publisherName = publisherName;
		}
		public EventConsumer getConsumer() {
			return consumer;
		}
		public String[] getEventTypes() {
			return eventTypes;
		}
		public String getPublisherName() {
			return publisherName;
		}
	}

	private static class RegisteredPublisher {
		private EventPublisher publisher;
		private String[] eventTypes;
		private List<RegisteredConsumer> consumers = new ArrayList<RegisteredConsumer>();
		
		public RegisteredPublisher(EventPublisher publisher, String[] eventTypes) {
			super();
			this.publisher = publisher;
			this.eventTypes = eventTypes;
		}
		public EventPublisher getPublisher() {
			return publisher;
		}
		public String[] getEventTypes() {
			return eventTypes;
		}
		public List<RegisteredConsumer> getConsumers() {
			return consumers;
		}
		public void addComsumer(RegisteredConsumer consumer) {
			this.consumers.add(consumer);
		}
		public void addComsumer(EventConsumer consumer, String [] eventTypes) {
			this.consumers.add(new RegisteredConsumer(consumer, eventTypes));
		}
		public void removeComsumer(EventConsumer consumer) {
			for (RegisteredConsumer cons : consumers) {
				if (cons.getConsumer().equals(consumer)) {
					this.consumers.remove(cons);
					return;
				}
			}
		}
	}

}