/*
 * Copyright 2002-2012 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.orm.hibernate4.support;

import org.hibernate.FlushMode;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.orm.hibernate4.SessionFactoryUtils;
import org.springframework.orm.hibernate4.SessionHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.filter.OncePerRequestFilter;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Servlet 2.3 Filter that binds a Hibernate Session to the thread for the entire
 * processing of the request. Intended for the "Open Session in View" pattern,
 * i.e. to allow for lazy loading in web views despite the original transactions
 * already being completed.
 *
 * <p>This filter makes Hibernate Sessions available via the current thread, which
 * will be autodetected by transaction managers. It is suitable for service layer
 * transactions via {@link org.springframework.orm.hibernate4.HibernateTransactionManager}
 * as well as for non-transactional execution (if configured appropriately).
 *
 * <p><b>NOTE</b>: This filter will by default <i>not</i> flush the Hibernate Session,
 * with the flush mode set to {@code FlushMode.NEVER}. It assumes to be used
 * in combination with service layer transactions that care for the flushing: The
 * active transaction manager will temporarily change the flush mode to
 * {@code FlushMode.AUTO} during a read-write transaction, with the flush
 * mode reset to {@code FlushMode.NEVER} at the end of each transaction.
 *
 * <p><b>WARNING:</b> Applying this filter to existing logic can cause issues that
 * have not appeared before, through the use of a single Hibernate Session for the
 * processing of an entire request. In particular, the reassociation of persistent
 * objects with a Hibernate Session has to occur at the very beginning of request
 * processing, to avoid clashes with already loaded instances of the same objects.
 *
 * <p>Looks up the SessionFactory in Spring's root web application context.
 * Supports a "sessionFactoryBeanName" filter init-param in {@code web.xml};
 * the default bean name is "sessionFactory". Looks up the SessionFactory on each
 * request, to avoid initialization order issues (when using ContextLoaderServlet,
 * the root application context will get initialized <i>after</i> this filter).
 *
 * @author Juergen Hoeller
 * @since 3.1
 * @see #lookupSessionFactory
 * @see OpenSessionInViewInterceptor
 * @see org.springframework.orm.hibernate4.HibernateTransactionManager
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 */
public class OpenSessionInViewFilter extends OncePerRequestFilter {

	public static final String DEFAULT_SESSION_FACTORY_BEAN_NAME = "sessionFactory";

	private String sessionFactoryBeanName = DEFAULT_SESSION_FACTORY_BEAN_NAME;


	/**
	 * Set the bean name of the SessionFactory to fetch from Spring's
	 * root application context. Default is "sessionFactory".
	 * @see #DEFAULT_SESSION_FACTORY_BEAN_NAME
	 */
	public void setSessionFactoryBeanName(String sessionFactoryBeanName) {
		this.sessionFactoryBeanName = sessionFactoryBeanName;
	}

	/**
	 * Return the bean name of the SessionFactory to fetch from Spring's
	 * root application context.
	 */
	protected String getSessionFactoryBeanName() {
		return this.sessionFactoryBeanName;
	}

	/**
	 * Returns "false" so that the filter may re-bind the opened Hibernate
	 * {@code Session} to each asynchronously dispatched thread and postpone
	 * closing it until the very last asynchronous dispatch.
	 */
	@Override
	protected boolean shouldNotFilterAsyncDispatch() {
		return false;
	}

	/**
	 * Returns "false" so that the filter may provide a Hibernate
	 * {@code Session} to each error dispatches.
	 */
	@Override
	protected boolean shouldNotFilterErrorDispatch() {
		return false;
	}

	@Override
	protected void doFilterInternal(
			HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		SessionFactory sessionFactory = lookupSessionFactory(request);
		boolean participate = false;

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		String key = getAlreadyFilteredAttributeName();

		if (TransactionSynchronizationManager.hasResource(sessionFactory)) {
			// Do not modify the Session: just set the participate flag.
			participate = true;
		}
		else {
			boolean isFirstRequest = !isAsyncDispatch(request);
			if (isFirstRequest || !applySessionBindingInterceptor(asyncManager, key)) {
				logger.debug("Opening Hibernate Session in OpenSessionInViewFilter");
				Session session = openSession(sessionFactory);
				SessionHolder sessionHolder = new SessionHolder(session);
				TransactionSynchronizationManager.bindResource(sessionFactory, sessionHolder);

				AsyncRequestInterceptor interceptor = new AsyncRequestInterceptor(sessionFactory, sessionHolder);
				asyncManager.registerCallableInterceptor(key, interceptor);
				asyncManager.registerDeferredResultInterceptor(key, interceptor);
			}
		}

		try {
			filterChain.doFilter(request, response);
		}

		finally {
			if (!participate) {
				SessionHolder sessionHolder =
						(SessionHolder) TransactionSynchronizationManager.unbindResource(sessionFactory);
				if (!isAsyncStarted(request)) {
					logger.debug("Closing Hibernate Session in OpenSessionInViewFilter");
					SessionFactoryUtils.closeSession(sessionHolder.getSession());
				}
			}
		}
	}

	/**
	 * Look up the SessionFactory that this filter should use,
	 * taking the current HTTP request as argument.
	 * <p>The default implementation delegates to the {@link #lookupSessionFactory()}
	 * variant without arguments.
	 * @param request the current request
	 * @return the SessionFactory to use
	 */
	protected SessionFactory lookupSessionFactory(HttpServletRequest request) {
		return lookupSessionFactory();
	}

	/**
	 * Look up the SessionFactory that this filter should use.
	 * <p>The default implementation looks for a bean with the specified name
	 * in Spring's root application context.
	 * @return the SessionFactory to use
	 * @see #getSessionFactoryBeanName
	 */
	protected SessionFactory lookupSessionFactory() {
		if (logger.isDebugEnabled()) {
			logger.debug("Using SessionFactory '" + getSessionFactoryBeanName() + "' for OpenSessionInViewFilter");
		}
		WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
		return wac.getBean(getSessionFactoryBeanName(), SessionFactory.class);
	}

	/**
	 * Open a Session for the SessionFactory that this filter uses.
	 * <p>The default implementation delegates to the
	 * {@code SessionFactory.openSession} method and
	 * sets the {@code Session}'s flush mode to "MANUAL".
	 * @param sessionFactory the SessionFactory that this filter uses
	 * @return the Session to use
	 * @throws DataAccessResourceFailureException if the Session could not be created
	 * @see org.hibernate.FlushMode#MANUAL
	 */
	protected Session openSession(SessionFactory sessionFactory) throws DataAccessResourceFailureException {
		try {
			Session session = sessionFactory.openSession();
			session.setFlushMode(FlushMode.MANUAL);
			return session;
		}
		catch (HibernateException ex) {
			throw new DataAccessResourceFailureException("Could not open Hibernate Session", ex);
		}
	}

	private boolean applySessionBindingInterceptor(WebAsyncManager asyncManager, String key) {
		if (asyncManager.getCallableInterceptor(key) == null) {
			return false;
		}
		((AsyncRequestInterceptor) asyncManager.getCallableInterceptor(key)).bindSession();
		return true;
	}

}
