/**
 * Copyright 2005-2014 Restlet
 * 
 * The contents of this file are subject to the terms of one of the following
 * open source licenses: Apache 2.0 or or EPL 1.0 (the "Licenses"). You can
 * select the license that you prefer but you may not use this file except in
 * compliance with one of these Licenses.
 * 
 * You can obtain a copy of the Apache 2.0 license at
 * http://www.opensource.org/licenses/apache-2.0
 * 
 * You can obtain a copy of the EPL 1.0 license at
 * http://www.opensource.org/licenses/eclipse-1.0
 * 
 * See the Licenses for the specific language governing permissions and
 * limitations under the Licenses.
 * 
 * Alternatively, you can obtain a royalty free commercial license with less
 * limitations, transferable or non-transferable, directly at
 * http://restlet.com/products/restlet-framework
 * 
 * Restlet is a registered trademark of Restlet S.A.S.
 */

package org.restlet.ext.spring;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.restlet.Application;
import org.restlet.Context;
import org.restlet.Restlet;
import org.restlet.ext.servlet.ServletAdapter;
import org.springframework.beans.BeansException;
import org.springframework.web.servlet.FrameworkServlet;

/**
 * A Servlet which provides an automatic Restlet integration with an existing
 * {@link org.springframework.web.context.WebApplicationContext}. The usage is
 * similar to Spring's {@link org.springframework.web.servlet.DispatcherServlet}
 * . In the web.xml file, declare the Servlet and map its root URL like this:
 * 
 * <pre>
 * <servlet>
 *    <servlet-name>api</servlet-name>
 *    <servlet-class>org.restlet.ext.spring.RestletFrameworkServlet</servlet-class>
 *    <load-on-startup>1</load-on-startup>
 * </servlet>
 * 
 * <servlet-mapping>
 *    <servlet-name>api</servlet-name>
 *    <url-pattern>/api/v1/*</url-pattern>
 * </servlet-mapping>
 * </pre>
 * 
 * <p>
 * Then, create a beans XML file called
 * <code>/WEB-INF/[servlet-name]-servlet.xml</code> — in this case,
 * <code>/WEB-INF/api-servlet.xml</code> — and define your restlets and
 * resources in it.
 * <p>
 * All requests to this servlet will be delegated to a single top-level restlet
 * loaded from the Spring application context. By default, this servlet looks
 * for a bean named "root". You can override that by passing in the
 * <code>targetRestletBeanName</code> parameter. For example:
 * 
 * <pre>
 * <servlet>
 *    <servlet-name>api</servlet-name>
 *    <servlet-class>org.restlet.ext.spring.RestletFrameworkServlet</servlet-class>
 *    <load-on-startup>1</load-on-startup>
 *    <init-param>
 *       <param-name>targetRestletBeanName</param-name>
 *       <param-value>guard</param-value>
 *    </init-param>
 * </servlet>
 * </pre>
 * <p>
 * If the target restlet is an {@link org.restlet.Application}, it will be used
 * directly. Otherwise, it will be wrapped in an instance of {@link Application}.
 * 
 * @author Rhett Sutphin
 */
public class RestletFrameworkServlet extends FrameworkServlet {
    /** The default bean name for the target Restlet. */
    private static final String DEFAULT_TARGET_RESTLET_BEAN_NAME = "root";

    private static final long serialVersionUID = 1L;

    /** The adapter of Servlet calls into Restlet equivalents. */
    private volatile ServletAdapter adapter;

    /** The bean name of the target Restlet. */
    private volatile String targetRestletBeanName;

    /**
     * Creates the Restlet {@link Context} to use if the target application does
     * not already have a context associated, or if the target restlet is not an
     * {@link Application} at all.
     * <p>
     * Uses a simple {@link Context} by default.
     * 
     * @return A new instance of {@link Context}
     */
    protected Context createContext() {
        return new Context();
    }

    @Override
    protected void doService(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        getAdapter().service(request, response);
    }

    /**
     * Provides access to the {@link ServletAdapter} used to handle requests.
     * Exposed so that subclasses may do additional configuration, if necessary,
     * by overriding {@link #initFrameworkServlet()}.
     * 
     * @return The adapter of Servlet calls into Restlet equivalents.
     */
    protected ServletAdapter getAdapter() {
        return this.adapter;
    }

    /**
     * Returns the target Restlet from Spring's Web application context.
     * 
     * @return The target Restlet.
     */
    protected Restlet getTargetRestlet() {
        return (Restlet) getWebApplicationContext().getBean(
                getTargetRestletBeanName());
    }

    /**
     * Returns the bean name of the target Restlet. Returns "root" by default.
     * 
     * @return The bean name.
     */
    public String getTargetRestletBeanName() {
        return (this.targetRestletBeanName == null) ? DEFAULT_TARGET_RESTLET_BEAN_NAME
                : this.targetRestletBeanName;
    }

    @Override
    protected void initFrameworkServlet() throws ServletException,
            BeansException {
        super.initFrameworkServlet();
        this.adapter = new ServletAdapter(getServletContext());

        org.restlet.Application application;

        if (getTargetRestlet() instanceof Application) {
            application = (Application) getTargetRestlet();
        } else {
            application = new Application();
            application.setInboundRoot(getTargetRestlet());
        }

        if (application.getContext() == null) {
            application.setContext(createContext());
        }

        this.adapter.setNext(application);
    }

    /**
     * Sets the bean name of the target Restlet.
     * 
     * @param targetRestletBeanName
     *            The bean name.
     */
    public void setTargetRestletBeanName(String targetRestletBeanName) {
        this.targetRestletBeanName = targetRestletBeanName;
    }
}