package auction.web.filter;

import org.apache.commons.logging.*;
import org.hibernate.*;
import auction.persistence.HibernateUtil;
import org.hibernate.context.ManagedSessionContext;

import javax.servlet.Filter;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * Filter that manages a Hibernate Session for a conversation.
 * <p>
 * This filter should be used if your <tt>hibernate.current_session_context_class</tt>
 * configuration is set to <tt>managed</tt> and you are not using JTA or CMT.
 * <p>
 * With JTA you'd replace transaction demarcation with calls to the <tt>UserTransaction</tt> API.
 * With CMT you would remove transaction demarcation code from this filter.
 * <p>
 * Use this filter for the <b>session-per-conversation</b> pattern
 * with an extended <tt>Session</tt>. Don't forget to set conversation boundaries
 * in your code! One way to do this is to put a marker attribute in the request, and let
 * the filter handle flushing and closing of the Session at the end of a conversation.
 * <p>
 * We recommend the JBoss Seam framework with built-in support for conversations in
 * all environments.
 * <p>
 * Note that you should not use this interceptor out-of-the-box with enabled optimistic
 * concurrency control. Apply your own compensation logic for failed conversations, this
 * is totally dependent on your applications design.
 *
 * @author Christian Bauer
 */
public class HibernateSessionConversationFilter
        implements Filter {

    private static Log log = LogFactory.getLog(HibernateSessionConversationFilter.class);

    private SessionFactory sf;

    public static final String HIBERNATE_SESSION_KEY = "hibernateSession";
    public static final String END_OF_CONVERSATION_FLAG = "endOfConversation";

    public void doFilter(ServletRequest request,
                         ServletResponse response,
                         FilterChain chain)
            throws IOException, ServletException {

        org.hibernate.classic.Session currentSession;

        // Try to get a Hibernate Session from the HttpSession
        HttpSession httpSession =
                ((HttpServletRequest) request).getSession();
        Session disconnectedSession =
                (Session) httpSession.getAttribute(HIBERNATE_SESSION_KEY);

        try {

            // Start a new conversation or in the middle?
            if (disconnectedSession == null) {
                log.debug(">>> New conversation");
                log.debug("Opening Session, disabling automatic flushing");
                currentSession = sf.openSession();
                currentSession.setFlushMode(FlushMode.MANUAL);
            } else {
                log.debug("< Continuing conversation");
                currentSession = (org.hibernate.classic.Session) disconnectedSession;
            }

            log.debug("Binding the current Session");
            ManagedSessionContext.bind(currentSession);

            log.debug("Starting a database transaction");
            currentSession.beginTransaction();

            log.debug("Processing the event");
            chain.doFilter(request, response);

            log.debug("Unbinding Session after processing");
            currentSession = ManagedSessionContext.unbind(sf);

            // End or continue the long-running conversation?
            if (request.getAttribute(END_OF_CONVERSATION_FLAG) != null ||
                request.getParameter(END_OF_CONVERSATION_FLAG) != null) {

                log.debug("Flushing Session");
                currentSession.flush();

                log.debug("Committing the database transaction");
                currentSession.getTransaction().commit();

                log.debug("Closing the Session");
                currentSession.close();

                log.debug("Cleaning Session from HttpSession");
                httpSession.setAttribute(HIBERNATE_SESSION_KEY, null);

                log.debug("<<< End of conversation");

            } else {

                log.debug("Committing database transaction");
                currentSession.getTransaction().commit();

                log.debug("Storing Session in the HttpSession");
                httpSession.setAttribute(HIBERNATE_SESSION_KEY, currentSession);

                log.debug("> Returning to user in conversation");
            }

        } catch (StaleObjectStateException staleEx) {
            log.error("This interceptor does not implement optimistic concurrency control!");
            log.error("Your application will not work until you add compensation actions!");
            // Rollback, close everything, possibly compensate for any permanent changes
            // during the conversation, and finally restart business conversation. Maybe
            // give the user of the application a chance to merge some of his work with
            // fresh data... what you do here depends on your applications design.
            throw staleEx;
        } catch (Throwable ex) {
            // Rollback only
            try {
                if (sf.getCurrentSession().getTransaction().isActive()) {
                    log.debug("Trying to rollback database transaction after exception");
                    sf.getCurrentSession().getTransaction().rollback();
                }
            } catch (Throwable rbEx) {
                log.error("Could not rollback transaction after exception!", rbEx);
            } finally {
                log.error("Cleanup after exception!");

                // Cleanup
                log.debug("Unbinding Session after exception");
                currentSession = ManagedSessionContext.unbind(sf);

                log.debug("Closing Session after exception");
                currentSession.close();

                log.debug("Removing Session from HttpSession");
                httpSession.setAttribute(HIBERNATE_SESSION_KEY, null);

            }

            // Let others handle it... maybe another interceptor for exceptions?
            throw new ServletException(ex);
        }

    }

    public void init(FilterConfig filterConfig) throws ServletException {
        log.debug("Initializing filter...");
        log.debug("Obtaining SessionFactory from HibernateUtil");
        sf = HibernateUtil.getSessionFactory();
    }

    public void destroy() {}

}