/*
 * Copyright 2002-2016 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
 *
 *      https://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.hibernate5.support;

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

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.hibernate5.SessionFactoryUtils;
import org.springframework.orm.hibernate5.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;

/**
 * Servlet 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.hibernate5.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".
 *
 * @author Juergen Hoeller
 * @since 4.2
 * @see #lookupSessionFactory
 * @see OpenSessionInViewInterceptor
 * @see OpenSessionInterceptor
 * @see org.springframework.orm.hibernate5.HibernateTransactionManager
 * @see TransactionSynchronizationManager
 * @see SessionFactory#getCurrentSession()
 */
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 {@link SessionFactory#openSession}
         * method and sets the {@link 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 FlushMode#MANUAL
         */
        @SuppressWarnings("deprecation")
        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;
        }

}