/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jms.connection;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.ExceptionListener;
import javax.jms.JMSException;
import javax.jms.QueueConnection;
import javax.jms.QueueConnectionFactory;
import javax.jms.Session;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.util.Assert;

/**
 * A JMS ConnectionFactory adapter that returns the same Connection
 * from all {@link #createConnection()} calls, and ignores calls to
 * {@link javax.jms.Connection#close()}. According to the JMS Connection
 * model, this is perfectly thread-safe (in contrast to e.g. JDBC). The
 * shared Connection can be automatically recovered in case of an Exception.
 *
 * <p>You can either pass in a specific JMS Connection directly or let this
 * factory lazily create a Connection via a given target ConnectionFactory.
 * This factory generally works with JMS 1.1 as well as the JMS 1.0.2 API.
 *
 * <p>Note that when using the JMS 1.0.2 API, this ConnectionFactory will switch
 * into queue/topic mode according to the JMS API methods used at runtime:
 * {@code createQueueConnection} and {@code createTopicConnection} will
 * lead to queue/topic mode, respectively; generic {@code createConnection}
 * calls will lead to a JMS 1.1 connection which is able to serve both modes.
 *
 * <p>Useful for testing and standalone environments in order to keep using the
 * same Connection for multiple {@link org.springframework.jms.core.JmsTemplate}
 * calls, without having a pooling ConnectionFactory underneath. This may span
 * any number of transactions, even concurrently executing transactions.
 *
 * <p>Note that Spring's message listener containers support the use of
 * a shared Connection within each listener container instance. Using
 * SingleConnectionFactory in combination only really makes sense for
 * sharing a single JMS Connection <i>across multiple listener containers</i>.
 *
 * @author Juergen Hoeller
 * @author Mark Pollack
 * @since 1.1
 * @see org.springframework.jms.core.JmsTemplate
 * @see org.springframework.jms.listener.SimpleMessageListenerContainer
 * @see org.springframework.jms.listener.DefaultMessageListenerContainer#setCacheLevel
 */
public class SingleConnectionFactory implements ConnectionFactory, QueueConnectionFactory,
		TopicConnectionFactory, ExceptionListener, InitializingBean, DisposableBean {

	protected final Log logger = LogFactory.getLog(getClass());

	private ConnectionFactory targetConnectionFactory;

	private String clientId;

	private ExceptionListener exceptionListener;

	private boolean reconnectOnException = false;

	/** The target Connection */
	private Connection connection;

	/** A hint whether to create a queue or topic connection */
	private Boolean pubSubMode;

	/** An internal aggregator allowing for per-connection ExceptionListeners */
	private AggregatedExceptionListener aggregatedExceptionListener;

	/** Whether the shared Connection has been started */
	private int startedCount = 0;

	/** Synchronization monitor for the shared Connection */
	private final Object connectionMonitor = new Object();


	/**
	 * Create a new SingleConnectionFactory for bean-style usage.
	 * @see #setTargetConnectionFactory
	 */
	public SingleConnectionFactory() {
	}

	/**
	 * Create a new SingleConnectionFactory that always returns the given Connection.
	 * @param targetConnection the single Connection
	 */
	public SingleConnectionFactory(Connection targetConnection) {
		Assert.notNull(targetConnection, "Target Connection must not be null");
		this.connection = targetConnection;
	}

	/**
	 * Create a new SingleConnectionFactory that always returns a single Connection
	 * that it will lazily create via the given target ConnectionFactory.
	 * @param targetConnectionFactory the target ConnectionFactory
	 */
	public SingleConnectionFactory(ConnectionFactory targetConnectionFactory) {
		Assert.notNull(targetConnectionFactory, "Target ConnectionFactory must not be null");
		this.targetConnectionFactory = targetConnectionFactory;
	}


	/**
	 * Set the target ConnectionFactory which will be used to lazily
	 * create a single Connection.
	 */
	public void setTargetConnectionFactory(ConnectionFactory targetConnectionFactory) {
		this.targetConnectionFactory = targetConnectionFactory;
	}

	/**
	 * Return the target ConnectionFactory which will be used to lazily
	 * create a single Connection, if any.
	 */
	public ConnectionFactory getTargetConnectionFactory() {
		return this.targetConnectionFactory;
	}

	/**
	 * Specify a JMS client ID for the single Connection created and exposed
	 * by this ConnectionFactory.
	 * <p>Note that client IDs need to be unique among all active Connections
	 * of the underlying JMS provider. Furthermore, a client ID can only be
	 * assigned if the original ConnectionFactory hasn't already assigned one.
	 * @see javax.jms.Connection#setClientID
	 * @see #setTargetConnectionFactory
	 */
	public void setClientId(String clientId) {
		this.clientId = clientId;
	}

	/**
	 * Return a JMS client ID for the single Connection created and exposed
	 * by this ConnectionFactory, if any.
	 */
	protected String getClientId() {
		return this.clientId;
	}

	/**
	 * Specify an JMS ExceptionListener implementation that should be
	 * registered with the single Connection created by this factory.
	 * @see #setReconnectOnException
	 */
	public void setExceptionListener(ExceptionListener exceptionListener) {
		this.exceptionListener = exceptionListener;
	}

	/**
	 * Return the JMS ExceptionListener implementation that should be registered
	 * with the single Connection created by this factory, if any.
	 */
	protected ExceptionListener getExceptionListener() {
		return this.exceptionListener;
	}

	/**
	 * Specify whether the single Connection should be reset (to be subsequently renewed)
	 * when a JMSException is reported by the underlying Connection.
	 * <p>Default is "false". Switch this to "true" to automatically trigger
	 * recovery based on your JMS provider's exception notifications.
	 * <p>Internally, this will lead to a special JMS ExceptionListener
	 * (this SingleConnectionFactory itself) being registered with the
	 * underlying Connection. This can also be combined with a
	 * user-specified ExceptionListener, if desired.
	 * @see #setExceptionListener
	 */
	public void setReconnectOnException(boolean reconnectOnException) {
		this.reconnectOnException = reconnectOnException;
	}

	/**
	 * Return whether the single Connection should be renewed when
	 * a JMSException is reported by the underlying Connection.
	 */
	protected boolean isReconnectOnException() {
		return this.reconnectOnException;
	}

	/**
	 * Make sure a Connection or ConnectionFactory has been set.
	 */
	@Override
	public void afterPropertiesSet() {
		if (this.connection == null && getTargetConnectionFactory() == null) {
			throw new IllegalArgumentException("Target Connection or ConnectionFactory is required");
		}
	}


	@Override
	public Connection createConnection() throws JMSException {
		return getSharedConnectionProxy(getConnection());
	}

	@Override
	public Connection createConnection(String username, String password) throws JMSException {
		throw new javax.jms.IllegalStateException(
				"SingleConnectionFactory does not support custom username and password");
	}

	@Override
	public QueueConnection createQueueConnection() throws JMSException {
		Connection con;
		synchronized (this.connectionMonitor) {
			this.pubSubMode = Boolean.FALSE;
			con = createConnection();
		}
		if (!(con instanceof QueueConnection)) {
			throw new javax.jms.IllegalStateException(
					"This SingleConnectionFactory does not hold a QueueConnection but rather: " + con);
		}
		return ((QueueConnection) con);
	}

	@Override
	public QueueConnection createQueueConnection(String username, String password) throws JMSException {
		throw new javax.jms.IllegalStateException(
				"SingleConnectionFactory does not support custom username and password");
	}

	@Override
	public TopicConnection createTopicConnection() throws JMSException {
		Connection con;
		synchronized (this.connectionMonitor) {
			this.pubSubMode = Boolean.TRUE;
			con = createConnection();
		}
		if (!(con instanceof TopicConnection)) {
			throw new javax.jms.IllegalStateException(
					"This SingleConnectionFactory does not hold a TopicConnection but rather: " + con);
		}
		return ((TopicConnection) con);
	}

	@Override
	public TopicConnection createTopicConnection(String username, String password) throws JMSException {
		throw new javax.jms.IllegalStateException(
				"SingleConnectionFactory does not support custom username and password");
	}


	/**
	 * Obtain an initialized shared Connection.
	 * @return the Connection (never {@code null})
	 * @throws javax.jms.JMSException if thrown by JMS API methods
	 * @see #initConnection()
	 */
	protected Connection getConnection() throws JMSException {
		synchronized (this.connectionMonitor) {
			if (this.connection == null) {
				initConnection();
			}
			return this.connection;
		}
	}

	/**
	 * Initialize the underlying shared Connection.
	 * <p>Closes and reinitializes the Connection if an underlying
	 * Connection is present already.
	 * @throws javax.jms.JMSException if thrown by JMS API methods
	 * @see #prepareConnection
	 */
	public void initConnection() throws JMSException {
		if (getTargetConnectionFactory() == null) {
			throw new IllegalStateException(
					"'targetConnectionFactory' is required for lazily initializing a Connection");
		}
		synchronized (this.connectionMonitor) {
			if (this.connection != null) {
				closeConnection(this.connection);
			}
			this.connection = doCreateConnection();
			prepareConnection(this.connection);
			if (this.startedCount > 0) {
				this.connection.start();
			}
			if (logger.isInfoEnabled()) {
				logger.info("Established shared JMS Connection: " + this.connection);
			}
		}
	}

	/**
	 * Exception listener callback that renews the underlying single Connection.
	 * @see #resetConnection()
	 */
	@Override
	public void onException(JMSException ex) {
		logger.warn("Encountered a JMSException - resetting the underlying JMS Connection", ex);
		resetConnection();
	}

	/**
	 * Close the underlying shared connection.
	 * The provider of this ConnectionFactory needs to care for proper shutdown.
	 * <p>As this bean implements DisposableBean, a bean factory will
	 * automatically invoke this on destruction of its cached singletons.
	 * @see #resetConnection()
	 */
	@Override
	public void destroy() {
		resetConnection();
	}

	/**
	 * Reset the underlying shared Connection, to be reinitialized on next access.
	 * @see #closeConnection
	 */
	public void resetConnection() {
		synchronized (this.connectionMonitor) {
			if (this.connection != null) {
				closeConnection(this.connection);
			}
			this.connection = null;
		}
	}

	/**
	 * Create a JMS Connection via this template's ConnectionFactory.
	 * @return the new JMS Connection
	 * @throws javax.jms.JMSException if thrown by JMS API methods
	 */
	protected Connection doCreateConnection() throws JMSException {
		ConnectionFactory cf = getTargetConnectionFactory();
		if (Boolean.FALSE.equals(this.pubSubMode) && cf instanceof QueueConnectionFactory) {
			return ((QueueConnectionFactory) cf).createQueueConnection();
		}
		else if (Boolean.TRUE.equals(this.pubSubMode) && cf instanceof TopicConnectionFactory) {
			return ((TopicConnectionFactory) cf).createTopicConnection();
		}
		else {
			return getTargetConnectionFactory().createConnection();
		}
	}

	/**
	 * Prepare the given Connection before it is exposed.
	 * <p>The default implementation applies ExceptionListener and client id.
	 * Can be overridden in subclasses.
	 * @param con the Connection to prepare
	 * @throws JMSException if thrown by JMS API methods
	 * @see #setExceptionListener
	 * @see #setReconnectOnException
	 */
	protected void prepareConnection(Connection con) throws JMSException {
		if (getClientId() != null) {
			con.setClientID(getClientId());
		}
		if (this.aggregatedExceptionListener != null) {
			con.setExceptionListener(this.aggregatedExceptionListener);
		}
		else if (getExceptionListener() != null || isReconnectOnException()) {
			ExceptionListener listenerToUse = getExceptionListener();
			if (isReconnectOnException()) {
				this.aggregatedExceptionListener = new AggregatedExceptionListener();
				this.aggregatedExceptionListener.delegates.add(this);
				if (listenerToUse != null) {
					this.aggregatedExceptionListener.delegates.add(listenerToUse);
				}
				listenerToUse = this.aggregatedExceptionListener;
			}
			con.setExceptionListener(listenerToUse);
		}
	}

	/**
	 * Template method for obtaining a (potentially cached) Session.
	 * <p>The default implementation always returns {@code null}.
	 * Subclasses may override this for exposing specific Session handles,
	 * possibly delegating to {@link #createSession} for the creation of raw
	 * Session objects that will then get wrapped and returned from here.
	 * @param con the JMS Connection to operate on
	 * @param mode the Session acknowledgement mode
	 * ({@code Session.TRANSACTED} or one of the common modes)
	 * @return the Session to use, or {@code null} to indicate
	 * creation of a raw standard Session
	 * @throws JMSException if thrown by the JMS API
	 */
	protected Session getSession(Connection con, Integer mode) throws JMSException {
		return null;
	}

	/**
	 * Create a default Session for this ConnectionFactory,
	 * adapting to JMS 1.0.2 style queue/topic mode if necessary.
	 * @param con the JMS Connection to operate on
	 * @param mode the Session acknowledgement mode
	 * ({@code Session.TRANSACTED} or one of the common modes)
	 * @return the newly created Session
	 * @throws JMSException if thrown by the JMS API
	 */
	protected Session createSession(Connection con, Integer mode) throws JMSException {
		// Determine JMS API arguments...
		boolean transacted = (mode == Session.SESSION_TRANSACTED);
		int ackMode = (transacted ? Session.AUTO_ACKNOWLEDGE : mode);
		// Now actually call the appropriate JMS factory method...
		if (Boolean.FALSE.equals(this.pubSubMode) && con instanceof QueueConnection) {
			return ((QueueConnection) con).createQueueSession(transacted, ackMode);
		}
		else if (Boolean.TRUE.equals(this.pubSubMode) && con instanceof TopicConnection) {
			return ((TopicConnection) con).createTopicSession(transacted, ackMode);
		}
		else {
			return con.createSession(transacted, ackMode);
		}
	}

	/**
	 * Close the given Connection.
	 * @param con the Connection to close
	 */
	protected void closeConnection(Connection con) {
		if (logger.isDebugEnabled()) {
			logger.debug("Closing shared JMS Connection: " + con);
		}
		try {
			try {
				if (this.startedCount > 0) {
					con.stop();
				}
			}
			finally {
				con.close();
			}
		}
		catch (javax.jms.IllegalStateException ex) {
			logger.debug("Ignoring Connection state exception - assuming already closed: " + ex);
		}
		catch (Throwable ex) {
			logger.debug("Could not close shared JMS Connection", ex);
		}
	}

	/**
	 * Wrap the given Connection with a proxy that delegates every method call to it
	 * but suppresses close calls. This is useful for allowing application code to
	 * handle a special framework Connection just like an ordinary Connection from a
	 * JMS ConnectionFactory.
	 * @param target the original Connection to wrap
	 * @return the wrapped Connection
	 */
	protected Connection getSharedConnectionProxy(Connection target) {
		List<Class<?>> classes = new ArrayList<Class<?>>(3);
		classes.add(Connection.class);
		if (target instanceof QueueConnection) {
			classes.add(QueueConnection.class);
		}
		if (target instanceof TopicConnection) {
			classes.add(TopicConnection.class);
		}
		return (Connection) Proxy.newProxyInstance(
				Connection.class.getClassLoader(),
				classes.toArray(new Class<?>[classes.size()]),
				new SharedConnectionInvocationHandler());
	}


	/**
	 * Invocation handler for a cached JMS Connection proxy.
	 */
	private class SharedConnectionInvocationHandler implements InvocationHandler {

		private ExceptionListener localExceptionListener;

		private boolean locallyStarted = false;

		@Override
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			if (method.getName().equals("equals")) {
				Object other = args[0];
				if (proxy == other) {
					return true;
				}
				if (other == null || !Proxy.isProxyClass(other.getClass())) {
					return false;
				}
				InvocationHandler otherHandler = Proxy.getInvocationHandler(other);
				return (otherHandler instanceof SharedConnectionInvocationHandler &&
						factory() == ((SharedConnectionInvocationHandler) otherHandler).factory());
			}
			else if (method.getName().equals("hashCode")) {
				// Use hashCode of containing SingleConnectionFactory.
				return System.identityHashCode(factory());
			}
			else if (method.getName().equals("toString")) {
				return "Shared JMS Connection: " + getConnection();
			}
			else if (method.getName().equals("setClientID")) {
				// Handle setClientID method: throw exception if not compatible.
				String currentClientId = getConnection().getClientID();
				if (currentClientId != null && currentClientId.equals(args[0])) {
					return null;
				}
				else {
					throw new javax.jms.IllegalStateException(
							"setClientID call not supported on proxy for shared Connection. " +
							"Set the 'clientId' property on the SingleConnectionFactory instead.");
				}
			}
			else if (method.getName().equals("setExceptionListener")) {
				// Handle setExceptionListener method: add to the chain.
				synchronized (connectionMonitor) {
					if (aggregatedExceptionListener != null) {
						ExceptionListener listener = (ExceptionListener) args[0];
						if (listener != this.localExceptionListener) {
							if (this.localExceptionListener != null) {
								aggregatedExceptionListener.delegates.remove(this.localExceptionListener);
							}
							if (listener != null) {
								aggregatedExceptionListener.delegates.add(listener);
							}
							this.localExceptionListener = listener;
						}
						return null;
					}
					else {
						throw new javax.jms.IllegalStateException(
								"setExceptionListener call not supported on proxy for shared Connection. " +
								"Set the 'exceptionListener' property on the SingleConnectionFactory instead. " +
								"Alternatively, activate SingleConnectionFactory's 'reconnectOnException' feature, " +
								"which will allow for registering further ExceptionListeners to the recovery chain.");
					}
				}
			}
			else if (method.getName().equals("getExceptionListener")) {
				synchronized (connectionMonitor) {
					if (this.localExceptionListener != null) {
						return this.localExceptionListener;
					}
					else {
						return getExceptionListener();
					}
				}
			}
			else if (method.getName().equals("start")) {
				localStart();
				return null;
			}
			else if (method.getName().equals("stop")) {
				localStop();
				return null;
			}
			else if (method.getName().equals("close")) {
				localStop();
				synchronized (connectionMonitor) {
					if (this.localExceptionListener != null) {
						if (aggregatedExceptionListener != null) {
							aggregatedExceptionListener.delegates.remove(this.localExceptionListener);
						}
						this.localExceptionListener = null;
					}
				}
				return null;
			}
			else if (method.getName().equals("createSession") || method.getName().equals("createQueueSession") ||
					method.getName().equals("createTopicSession")) {
				// Default: JMS 2.0 createSession() method
				Integer mode = Session.AUTO_ACKNOWLEDGE;
				if (args != null) {
					if (args.length == 1) {
						// JMS 2.0 createSession(int) method
						mode = (Integer) args[0];
					}
					else if (args.length == 2) {
						// JMS 1.1 createSession(boolean, int) method
						boolean transacted = (Boolean) args[0];
						Integer ackMode = (Integer) args[1];
						mode = (transacted ? Session.SESSION_TRANSACTED : ackMode);
					}
				}
				Session session = getSession(getConnection(), mode);
				if (session != null) {
					if (!method.getReturnType().isInstance(session)) {
						String msg = "JMS Session does not implement specific domain: " + session;
						try {
							session.close();
						}
						catch (Throwable ex) {
							logger.trace("Failed to close newly obtained JMS Session", ex);
						}
						throw new javax.jms.IllegalStateException(msg);
					}
					return session;
				}
			}
			try {
				return method.invoke(getConnection(), args);
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
		}

		private void localStart() throws JMSException {
			synchronized (connectionMonitor) {
				if (!this.locallyStarted) {
					this.locallyStarted = true;
					if (startedCount == 0 && connection != null) {
						connection.start();
					}
					startedCount++;
				}
			}
		}

		private void localStop() throws JMSException {
			synchronized (connectionMonitor) {
				if (this.locallyStarted) {
					this.locallyStarted = false;
					if (startedCount == 1 && connection != null) {
						connection.stop();
					}
					if (startedCount > 0) {
						startedCount--;
					}
				}
			}
		}

		private SingleConnectionFactory factory() {
			return SingleConnectionFactory.this;
		}
	}


	/**
	 * Internal aggregated ExceptionListener for handling the internal
	 * recovery listener in combination with user-specified listeners.
	 */
	private class AggregatedExceptionListener implements ExceptionListener {

		final Set<ExceptionListener> delegates = new LinkedHashSet<ExceptionListener>(2);

		@Override
		public void onException(JMSException ex) {
			synchronized (connectionMonitor) {
				// Iterate over temporary copy in order to avoid ConcurrentModificationException,
				// since listener invocations may in turn trigger registration of listeners...
				for (ExceptionListener listener : new LinkedHashSet<ExceptionListener>(this.delegates)) {
					listener.onException(ex);
				}
			}
		}
	}

}
