/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2008-2011, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.context.internal;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.transaction.Synchronization;
import javax.transaction.Transaction;
import javax.transaction.TransactionManager;

import org.hibernate.ConnectionReleaseMode;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.context.spi.AbstractCurrentSessionContext;
import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.engine.transaction.internal.jta.JtaStatusHelper;
import org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform;
import org.hibernate.internal.CoreMessageLogger;

import org.jboss.logging.Logger;

An implementation of CurrentSessionContext which scopes the notion of a current session to a JTA transaction. Because JTA gives us a nice tie-in to clean up after ourselves, this implementation will generate Sessions as needed provided a JTA transaction is in effect. If a session is not already associated with the current JTA transaction at the time currentSession() is called, a new session will be opened and it will be associated with that JTA transaction. Note that the sessions returned from this method are automatically configured with both the auto-flush and auto-close attributes set to true, meaning that the Session will be automatically flushed and closed as part of the lifecycle for the JTA transaction to which it is associated. Additionally, it will also be configured to aggressively release JDBC connections after each statement is executed. These settings are governed by the isAutoFlushEnabled(), isAutoCloseEnabled(), and getConnectionReleaseMode() methods; these are provided (along with the buildOrObtainSession() method) for easier subclassing for custom JTA-based session tracking logic (like maybe long-session semantics). 
Author:
Steve Ebersole/**
 * An implementation of {@link org.hibernate.context.spi.CurrentSessionContext} which scopes the notion
 * of a current session to a JTA transaction.  Because JTA gives us a nice tie-in to clean up after
 * ourselves, this implementation will generate Sessions as needed provided a JTA transaction is in
 * effect.  If a session is not already associated with the current JTA transaction at the time
 * {@link #currentSession()} is called, a new session will be opened and it will be associated with that
 * JTA transaction.
 *
 * Note that the sessions returned from this method are automatically configured with both the
 * {@link org.hibernate.cfg.Environment#FLUSH_BEFORE_COMPLETION auto-flush} and
 * {@link org.hibernate.cfg.Environment#AUTO_CLOSE_SESSION auto-close} attributes set to true, meaning
 * that the Session will be automatically flushed and closed as part of the lifecycle for the JTA
 * transaction to which it is associated.  Additionally, it will also be configured to aggressively
 * release JDBC connections after each statement is executed.  These settings are governed by the
 * {@link #isAutoFlushEnabled()}, {@link #isAutoCloseEnabled()}, and {@link #getConnectionReleaseMode()}
 * methods; these are provided (along with the {@link #buildOrObtainSession()} method) for easier
 * subclassing for custom JTA-based session tracking logic (like maybe long-session semantics).
 *
 * @author Steve Ebersole
 */
public class JTASessionContext extends AbstractCurrentSessionContext {
	private static final CoreMessageLogger LOG = Logger.getMessageLogger(
			CoreMessageLogger.class,
			JTASessionContext.class.getName()
	);

	private transient Map<Object, Session> currentSessionMap = new ConcurrentHashMap<Object, Session>();

	
Constructs a JTASessionContext
Params:
factory – The factory this context will service/**
	 * Constructs a JTASessionContext
	 *
	 * @param factory The factory this context will service
	 */
	public JTASessionContext(SessionFactoryImplementor factory) {
		super( factory );
	}

	@Override
	public Session currentSession() throws HibernateException {
		final JtaPlatform jtaPlatform = factory().getServiceRegistry().getService( JtaPlatform.class );
		final TransactionManager transactionManager = jtaPlatform.retrieveTransactionManager();
		if ( transactionManager == null ) {
			throw new HibernateException( "No TransactionManagerLookup specified" );
		}

		Transaction txn;
		try {
			txn = transactionManager.getTransaction();
			if ( txn == null ) {
				throw new HibernateException( "Unable to locate current JTA transaction" );
			}
			if ( !JtaStatusHelper.isActive( txn.getStatus() ) ) {
				// We could register the session against the transaction even though it is
				// not started, but we'd have no guarantee of ever getting the map
				// entries cleaned up (aside from spawning threads).
				throw new HibernateException( "Current transaction is not in progress" );
			}
		}
		catch ( HibernateException e ) {
			throw e;
		}
		catch ( Throwable t ) {
			throw new HibernateException( "Problem locating/validating JTA transaction", t );
		}

		final Object txnIdentifier = jtaPlatform.getTransactionIdentifier( txn );

		Session currentSession = currentSessionMap.get( txnIdentifier );

		if ( currentSession == null ) {
			currentSession = buildOrObtainSession();

			try {
				txn.registerSynchronization( buildCleanupSynch( txnIdentifier ) );
			}
			catch ( Throwable t ) {
				try {
					currentSession.close();
				}
				catch ( Throwable ignore ) {
					LOG.debug( "Unable to release generated current-session on failed synch registration", ignore );
				}
				throw new HibernateException( "Unable to register cleanup Synchronization with TransactionManager" );
			}

			currentSessionMap.put( txnIdentifier, currentSession );
		}
		else {
			validateExistingSession( currentSession );
		}

		return currentSession;
	}

	
Builds a CleanupSync capable of cleaning up the the current session map as an after transaction callback. 
Params:
transactionIdentifier – The transaction identifier under which the current session is registered.
Returns:
The cleanup synch./**
	 * Builds a {@link org.hibernate.context.internal.JTASessionContext.CleanupSync} capable of cleaning up the the current session map as an after transaction
	 * callback.
	 *
	 * @param transactionIdentifier The transaction identifier under which the current session is registered.
	 * @return The cleanup synch.
	 */
	private CleanupSync buildCleanupSynch(Object transactionIdentifier) {
		return new CleanupSync( transactionIdentifier, this );
	}

	
Strictly provided for subclassing purposes; specifically to allow long-session
support.  This implementation always just opens a new session.
Returns:
the built or (re)obtained session./**
	 * Strictly provided for subclassing purposes; specifically to allow long-session
	 * support.  This implementation always just opens a new session.
	 *
	 * @return the built or (re)obtained session.
	 */
	@SuppressWarnings("deprecation")
	protected Session buildOrObtainSession() {
		return baseSessionBuilder()
				.autoClose( isAutoCloseEnabled() )
				.connectionReleaseMode( getConnectionReleaseMode() )
				.flushBeforeCompletion( isAutoFlushEnabled() )
				.openSession();
	}

	
Mainly for subclass usage.  This impl always returns true.
Returns:
Whether or not the the session should be closed by transaction completion./**
	 * Mainly for subclass usage.  This impl always returns true.
	 *
	 * @return Whether or not the the session should be closed by transaction completion.
	 */
	protected boolean isAutoCloseEnabled() {
		return true;
	}

	
Mainly for subclass usage.  This impl always returns true.
Returns:
Whether or not the the session should be flushed prior transaction completion./**
	 * Mainly for subclass usage.  This impl always returns true.
	 *
	 * @return Whether or not the the session should be flushed prior transaction completion.
	 */
	protected boolean isAutoFlushEnabled() {
		return true;
	}

	
Mainly for subclass usage.  This impl always returns after_statement.
Returns:
The connection release mode for any built sessions./**
	 * Mainly for subclass usage.  This impl always returns after_statement.
	 *
	 * @return The connection release mode for any built sessions.
	 */
	protected ConnectionReleaseMode getConnectionReleaseMode() {
		return ConnectionReleaseMode.AFTER_STATEMENT;
	}

	
JTA transaction sync used for cleanup of the internal session map.
/**
	 * JTA transaction sync used for cleanup of the internal session map.
	 */
	protected static class CleanupSync implements Synchronization {
		private Object transactionIdentifier;
		private JTASessionContext context;

		public CleanupSync(Object transactionIdentifier, JTASessionContext context) {
			this.transactionIdentifier = transactionIdentifier;
			this.context = context;
		}

		@Override
		public void beforeCompletion() {
		}

		@Override
		public void afterCompletion(int i) {
			context.currentSessionMap.remove( transactionIdentifier );
		}
	}
}