/**
 * Abiquo community edition
 * cloud management application for hybrid clouds
 * Copyright (C) 2008-2010 - Abiquo Holdings S.L.
 * 
 * This application is free software; you can redistribute it and/or
 * modify it under the terms of the GNU LESSER GENERAL PUBLIC
 * LICENSE as published by the Free Software Foundation under
 * version 3 of the License
 * 
 * This software 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 v.3 for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA. */

package com.abiquo.server.core.common.persistence;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;

import org.hibernate.classic.Session;
import org.hibernate.stat.Statistics;

public class HibernateSessionAllocationChecker
{

    private boolean statisticsEnabledOnEntry;

    private long outstandingSessionsOnEntry;

    private int openMySqlConnectionsOnEntry;

    private long sessionsNotReleasedAfterCreation;

    private int mySqlConnectionsNoReleasedAfterCreation;

    private EntityManagerFactory factory;

    private int getMySqlConnectionCount(Connection connection) throws SQLException
    {
        assert connection != null;

        Statement query = connection.createStatement();
        try
        {
            ResultSet rs = query.executeQuery("show global status like 'Threads_connected'");
            try
            {
                boolean found = rs.next();
                assert found;

                String result = rs.getString(2);
                return Integer.parseInt(result);
            }
            finally
            {
                rs.close();
            }
        }
        finally
        {
            query.close();
        }
    }

    public HibernateSessionAllocationChecker(EntityManagerFactory factory)
    {
        assert factory != null;

        this.factory = factory;

        EntityManager em = factory.createEntityManager();
        try
        {
            Session session = (Session) em.getDelegate();
            Statistics statistics = session.getSessionFactory().getStatistics();
            this.statisticsEnabledOnEntry = statistics.isStatisticsEnabled();
            statistics.setStatisticsEnabled(true);
            this.outstandingSessionsOnEntry =
                statistics.getSessionOpenCount() - statistics.getSessionCloseCount();
            try
            {
                this.openMySqlConnectionsOnEntry = getMySqlConnectionCount(session.connection());
            }
            catch (SQLException e)
            {
                throw new RuntimeException(e);
            }
        }
        finally
        {
            em.close();
        }
    }

    private boolean resultObtained;

    private void ensureResultObtained()
    {
        if (!resultObtained)
        {
            EntityManager em = factory.createEntityManager();
            try
            {
                Session session = (Session) em.getDelegate();
                Statistics statistics = session.getSessionFactory().getStatistics();

                assert statistics.isStatisticsEnabled() : "Somebody else disabled the statistics: DON'T do, or do not use this component";

                long outstandingSessionsOnExit =
                    statistics.getSessionOpenCount() - statistics.getSessionCloseCount();
                this.sessionsNotReleasedAfterCreation =
                    outstandingSessionsOnExit - this.outstandingSessionsOnEntry;

                assert sessionsNotReleasedAfterCreation >= 0 : "Somebody else played with the statistics (maybe cleared/disabled them?): DON'T do, or do not use this component";
                // System.err.println( "OUTSTANDING SESSIONS: " +
                // sessionsNotReleasedAfterCreation);

                try
                {
                    this.mySqlConnectionsNoReleasedAfterCreation =
                        getMySqlConnectionCount(session.connection())
                            - this.openMySqlConnectionsOnEntry;
                }
                catch (SQLException e)
                {
                    throw new RuntimeException(e);
                }

                // Reset statistics to the state they were before we started to
                // be interested in open/closed session count
                statistics.setStatisticsEnabled(this.statisticsEnabledOnEntry);
            }
            finally
            {
                em.close();
            }
            resultObtained = true;
        }

    }

    public long getOutstandingMySqlConnections()
    {
        ensureResultObtained();
        return this.mySqlConnectionsNoReleasedAfterCreation;
    }

    public long getOutstandingSessions()
    {
        ensureResultObtained();
        return this.sessionsNotReleasedAfterCreation;
    }
}