/**
 *   GRANITE DATA SERVICES
 *   Copyright (C) 2006-2013 GRANITE DATA SERVICES S.A.S.
 *
 *   This file is part of the Granite Data Services Platform.
 *
 *   Granite Data Services 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 2.1 of the License, or (at your option) any later version.
 *
 *   Granite Data Services 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 this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 *   USA, or see <http://www.gnu.org/licenses/>.
 */
package org.granite.gravity;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;

import org.granite.config.ConfigProvider;
import org.granite.config.GraniteConfig;
import org.granite.config.GraniteConfigListener;
import org.granite.config.ServletGraniteConfig;
import org.granite.config.flex.ServicesConfig;
import org.granite.config.flex.ServletServicesConfig;
import org.granite.util.TypeUtil;

/**
 * @author Franck WOLFF
 */
public class GravityManager {

        private static final String GRAVITY_KEY = Gravity.class.getName();
        
        /**
         * Parse gravity configuration (granite-config.xml), start gravity by using the specified factory and put it
         * in ServletContext. If Gravity is already started, returns the previous instance from the servlet context.
         * <br><br>
         * This method is intended to be used in {@link HttpServlet#init(ServletConfig)} methods only and
         * synchronizes on the current ServletContext instance.
         * 
         * @param servletConfig the servlet config passed in HttpServlet.init(ServletConfig config) method.
         * @return a newly created and started Gravity instance or previously started one.
         * @throws ServletException if something goes wrong (GravityFactory not found, Gravity.start() error, etc.)
         */
    public static Gravity start(ServletConfig servletConfig) throws ServletException {
        return start(servletConfig.getServletContext());
    }
    
    public static Gravity start(ServletContext context) throws ServletException {
        Gravity gravity = null;
        
        synchronized (context) {
                
                gravity = (Gravity)context.getAttribute(GRAVITY_KEY);
                
                if (gravity == null) {
                        GraniteConfig graniteConfig = ServletGraniteConfig.loadConfig(context);
                        ServicesConfig servicesConfig = ServletServicesConfig.loadConfig(context);
                    
                        GravityServiceConfigurator serviceConfigurator = (GravityServiceConfigurator)context.getAttribute(GraniteConfigListener.GRANITE_CONFIG_ATTRIBUTE);
                        if (serviceConfigurator != null)
                                serviceConfigurator.configureGravityServices(context);
                    
                        GravityConfig gravityConfig = new GravityConfig(graniteConfig);
                        
                        String gravityFactory = gravityConfig.getGravityFactory();
                        try {
                                        GravityFactory factory = TypeUtil.newInstance(gravityFactory, GravityFactory.class);
                                        gravity = factory.newGravity(gravityConfig, servicesConfig, graniteConfig, GraniteConfigListener.getSharedContext(context));
                                } 
                        catch (Exception e) {
                                        throw new ServletException("Could not create Gravity instance with factory: " + gravityFactory, e);
                                }
                
                        try {
                            gravity.start();
                            context.setAttribute(GRAVITY_KEY, gravity);

                    if (context.getAttribute(GraniteConfigListener.GRANITE_CONFIG_PROVIDER_ATTRIBUTE) != null)
                        ((ConfigProvider)context.getAttribute(GraniteConfigListener.GRANITE_CONFIG_PROVIDER_ATTRIBUTE)).initGravity(gravity);

                            GraniteConfigListener.registerShutdownListener(context, gravity);
                        }
                        catch (Exception e) {
                            throw new ServletException("Gravity initialization error", e);
                        }
                }
        }

        return gravity;
    }
    
    
    public static interface GravityServiceConfigurator {
        
        public void configureGravityServices(ServletContext context) throws ServletException;
    }
    
    
    /**
     * Reconfigure gravity with the new supplied configuration (after reloading granite-config.xml).
     * <br><br>
     * Only these configuration options are taken into account when reconfiguring Gravity:
     * <ul>
     *  <li>channelIdleTimeoutMillis</li>
     *  <li>longPollingTimeout</li>
     *  <li>retryOnError</li>
     *  <li>maxMessagesQueuedPerChannel</li>
     *  <li>corePoolSize</li>
     *  <li>maximumPoolSize</li>
     *  <li>keepAliveTimeMillis</li>
     * </ul>
     * 
     * @param context the ServletContext where the gravity instance is registered.
     * @param gravityConfig the new (reloaded) GravityConfig. 
     */
    public static void reconfigure(ServletContext context, GravityConfig gravityConfig) {
        synchronized (context) {
                Gravity gravity = getGravity(context);
                gravity.reconfigure(gravityConfig, ServletGraniteConfig.getConfig(context));
        }
    }
    
    /**
     * Returns a previously started Gravity instance. This method isn't synchronized and should be used in
     * HttpServlet.doPost(...) methods only.
     * 
     * @param context the ServletContext from which to retrieve the Gravity instance. 
     * @return the unique and started Gravity instance (or null if {@link #start(ServletConfig)}
     *          has never been called).
     */
    public static Gravity getGravity(ServletContext context) {
        return (Gravity)context.getAttribute(GRAVITY_KEY);
    }
    
}