/*
 * Copyright (C) 2005-2010 Alfresco Software Limited.
 *
 * This file is part of Alfresco
 *
 * Alfresco 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, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Alfresco 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 Alfresco. If not, see <http://www.gnu.org/licenses/>.
 */
package org.alfresco.repo.cache;

import java.io.FileNotFoundException;
import java.net.URL;
import java.util.Properties;

import net.sf.ehcache.CacheManager;

import org.alfresco.error.AlfrescoRuntimeException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.cache.Cache;
import org.hibernate.cache.CacheException;
import org.hibernate.cache.CacheProvider;
import org.hibernate.cache.EhCache;
import org.hibernate.cache.EhCacheProvider;
import org.hibernate.cache.Timestamper;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.util.ResourceUtils;

/**
 * Alfresco-specific cache manager factory.
 * <p>
 * The purpose of this bean is to provide a common point from which the system-wide
 * EHCache <code>CacheManager</code> singleton is created.  Hibernate and Spring
 * will all pick up the same <code>CacheManager</code> instance.  It then becomes
 * possible to initialise this instance in whichever way we require, provided it
 * is done in a well-known (non-configurable) way.
 * <p>
 * For Alfresco purposes, there are two files that are looked for:
 * <ul>
 *   <li><b>classpath:alfresco/extension/ehcache-custom.xml</b>, which will take precedence</li>
 *   <li><b>classpath:alfresco/ehcache-default.xml</b>, which is the default shipped with Alfresco</li>
 * </ul>
 * <p>
 * The EHCache static singleton instance is used but ensuring that all access to the
 * instance goes through the required initialization code first.
 * <p>
 * TODO: Provide mixing of config so that cache definitions in the custom file override
 *       those in the default file
 * 
 * @see #getInstance()
 * 
 * @author Derek Hulley
 */
public class InternalEhCacheManagerFactoryBean implements FactoryBean<CacheManager>, CacheProvider
{
    public static final String CUSTOM_CONFIGURATION_FILE = "classpath:alfresco/extension/ehcache-custom.xml";
    public static final String DEFAULT_CONFIGURATION_FILE = "classpath:alfresco/ehcache-default.xml";
    
    private static Log logger = LogFactory.getLog(InternalEhCacheManagerFactoryBean.class);
    
    /** keep track of the singleton status to avoid work */
    private static boolean initialized;
    /** the <code>CacheManager</code> */
    private static CacheManager cacheManager;
    /** used to ensure that the existing Hibernate logic is maintained */
    private static EhCacheProvider hibernateEhCacheProvider = new EhCacheProvider();
    
    /**
     * Default constructor required by Hibernate.  In fact, we anticipate several
     * instances of this class to be created.
     */
    public InternalEhCacheManagerFactoryBean()
    {
    }
    
    /**
     * News up the singleton cache manager according to the rules set out
     * in the class comments.
     */
    private static synchronized void initCacheManager()
    {
        if (initialized)
        {
            return;
        }
        try
        {
            boolean defaultLocation = false;
            try
            {
                URL configUrl = ResourceUtils.getURL(CUSTOM_CONFIGURATION_FILE);
                InternalEhCacheManagerFactoryBean.cacheManager = CacheManager.create(configUrl);
            }
            catch (FileNotFoundException e)
            {
                // try the alfresco default
                URL configUrl = ResourceUtils.getURL(DEFAULT_CONFIGURATION_FILE);
                if (configUrl == null)
                {
                    throw new AlfrescoRuntimeException("Missing default cache config: " + DEFAULT_CONFIGURATION_FILE);
                }
                InternalEhCacheManagerFactoryBean.cacheManager = new CacheManager(configUrl);
                defaultLocation = true;
            }
            // done
            if (logger.isDebugEnabled())
            {
                logger.debug("Created EHCache CacheManager instance: \n" +
                        "   configuration: " + (defaultLocation ? DEFAULT_CONFIGURATION_FILE : CUSTOM_CONFIGURATION_FILE));
            }
            initialized = true;
        }
        catch (Throwable e)
        {
            throw new AlfrescoRuntimeException("EHCache configuration failed", e);
        }
    }
    
    /**
     * @return Returns the properly initialized instance for Alfresco internal use
     * 
     * @see #initCacheManager()
     */
    public static CacheManager getInstance()
    {
        if (!InternalEhCacheManagerFactoryBean.initialized)
        {
            InternalEhCacheManagerFactoryBean.initCacheManager();
        }
        return InternalEhCacheManagerFactoryBean.cacheManager;
    }

    public Cache buildCache(String regionName, Properties properties) throws CacheException
    {
        CacheManager manager = InternalEhCacheManagerFactoryBean.getInstance();
        try
        {
            net.sf.ehcache.Cache cache = manager.getCache(regionName);
            if (cache == null)
            {
                logger.info("Using default cache configuration: " + regionName);
                manager.addCache(regionName);
                cache = manager.getCache(regionName);
                logger.debug("Started EHCache region: " + regionName);
            }
            return new EhCache(cache);
        }
        catch (net.sf.ehcache.CacheException e)
        {
            throw new CacheException(e);
        }
    }

    /**
     * @see #hibernateEhCacheProvider
     */
    public boolean isMinimalPutsEnabledByDefault()
    {
        return false;
    }

    /**
     * @see #hibernateEhCacheProvider
     */
    public long nextTimestamp()
    {
        return Timestamper.next();
    }

    /**
     * @see #initCacheManager()
     */
    public void start(Properties properties) throws CacheException
    {
        InternalEhCacheManagerFactoryBean.initCacheManager();
    }

    /**
     * @see #initCacheManager()
     */
    public void stop()
    {
        // TODO: Does this port over different Locales?
        // Better to override DbPersistenceServiceFactory#close to put a marker on the thread.
        if (Thread.currentThread().getName().contains("Finalizer"))
        {
            // Probably JBPM's finalizer code ... we rely on Spring context calls rather
            return;
        }
        
        synchronized (getClass())
        {
            if(logger.isDebugEnabled()) {
               String[] caches = InternalEhCacheManagerFactoryBean.getInstance().getCacheNames();
               for(String regionName : caches) {
                  logger.debug("Stopped EHCache region: " + regionName);
               }
            }
            
            if (initialized)            // Avoid re-initialization if it has already been shut down
            {
                InternalEhCacheManagerFactoryBean.getInstance().shutdown();
                initialized = false;
            }
        }
    }

    /**
     * @return Returns the singleton cache manager
     * 
     * @see #initCacheManager()
     */
    public CacheManager getObject() throws Exception
    {
        return InternalEhCacheManagerFactoryBean.getInstance();
    }

    /**
     * @return Returns the singleton cache manager type
     */
    public Class<CacheManager> getObjectType()
    {
        return CacheManager.class;
    }

    /**
     * @return Returns true always
     */
    public boolean isSingleton()
    {
        return true;
    }
}