/*

 * Copyright 2010 Jeff McHugh (Segue Development LLC)

 * 

 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except

 * in compliance with the License. You may obtain a copy of the License at

 * 

 * http://www.apache.org/licenses/LICENSE-2.0

 * 

 * Unless required by applicable law or agreed to in writing, software distributed under the License

 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express

 * or implied. See the License for the specific language governing permissions and limitations under

 * the License.

 */

package com.googlecode.gwtrpccommlayer.server;





import com.google.gwt.user.server.rpc.RemoteServiceServlet;

import com.googlecode.gwtrpccommlayer.shared.GwtRpcCommLayerPojoConstants;

import com.googlecode.gwtrpccommlayer.shared.GwtRpcCommLayerPojoRequest;

import com.googlecode.gwtrpccommlayer.shared.GwtRpcCommLayerPojoResponse;



import javax.servlet.ServletConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.*;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import java.util.LinkedList;



/**

 * This class can either sit above your servlet (i.e. your servlet extends this) or it can wrap

 * your servlet (i.e. it will receive the calls and delegate it to the respective methods

 * @author jeff mchugh

 *

 */

public abstract class AbstractGwtRpcCommLayerServlet extends RemoteServiceServlet

{



	private static final long	serialVersionUID	= -8829760243946113688L;



	Object servletInstance = null;



    public AbstractGwtRpcCommLayerServlet() { }

    //@Inject

    //Can be extended and injected Guice



	public AbstractGwtRpcCommLayerServlet(Object servletImplementation)

	{

        this.servletInstance = servletImplementation;



        //this.servletImplementation = servletImplementation;

	}



	/**

	 * Initializes the servlet

	 */

	public void init(ServletConfig config) throws ServletException

	{

		super.init(config);





		/*

		 * The default is to assume this instance is the selected servlet

		 */

		servletInstance = this;





		/*

		 * Check to see another servlet should be the target

		 */

        //todo: this is currently configured using an init param in web.xml.  We need to change this to use something guice-friendly!

        //maybe use @Inject(optional=true) @Named("CommLayerImplClass") String strImplmentationClass;



		String servletImplClassName = config.getInitParameter(GwtRpcCommLayerPojoConstants.GWT_RPC_COMM_LAYER_SERVLET_IMPL_CLASS);

        //Use guice injected name instead of init parameter

        //if ( servletImplementation != null)

		if ( servletImplClassName != null && !servletImplClassName.trim().equals(""))

		{

			try

			{

				Class clzz = Class.forName(servletImplClassName);

				servletInstance = clzz.newInstance();

			}

			catch(Throwable t)

			{

				throw new ServletException(t);

			}

		}

	}





	/**

	 * any servlet that extends can opt to deny these request

	 * either explicitly or using web.xml

	 * @return

	 */

	protected boolean allowGwtRpcPojoRequest()

	{

		return true;

	}



	protected void initalizePerRequestPerResponseIfNeeded()

	{

		if ( super.perThreadRequest == null )

		{

			super.perThreadRequest = new ThreadLocal<HttpServletRequest>();

		}

		if ( super.perThreadResponse == null )

		{

			super.perThreadResponse = new ThreadLocal<HttpServletResponse>();

		}

	}





	/**

	 * Override the main service call and implement the special handling here

	 */

	public void service(ServletRequest req, ServletResponse resp) throws ServletException, IOException

	{

        //need some function intercept <ServletRequest,Boolean>



		HttpServletRequest request 		= (HttpServletRequest) req;

		HttpServletResponse response 	= (HttpServletResponse) resp;



		/*

		 * If the GwtRpcCommLayerClient has made this request, this header should be provided

		 */

		String gwtClientUserAgent 		= request.getHeader(GwtRpcCommLayerPojoConstants.GWT_RPC_COMM_LAYER_CLIENT_KEY);





		/*

		 * Only execute this block if:

		 *  - allowGwtRpcPojoRequest() is true

		 *  - is POST

		 *  - gwtClientUserAgent = 'GwtRpcCommLayerPojoRequest'

		 */

		if ( allowGwtRpcPojoRequest()

                && request.getMethod().equals("POST")

                && gwtClientUserAgent != null

                && gwtClientUserAgent.equalsIgnoreCase(GwtRpcCommLayerPojoConstants.GWT_RPC_COMM_LAYER_POJO_CLIENT))

		{

			try

			{



				/*

				 * This might not be initialized.

				 * So do it if needed

				 */

				initalizePerRequestPerResponseIfNeeded();



				super.perThreadRequest.set(request);

			    super.perThreadResponse.set(response);



				doServicePojoRequest(request,response);

			}

			finally

			{

			    super.perThreadRequest.set(null);

			    super.perThreadResponse.set(null);

			}



		}

		else

		{

			/*

			 * Call up the chain and allow one of the implementations handle the request accordingly.

			 * For an

			 */

			super.service(req, resp);

		}

	}



	/**

	 * Reads the request's InputStream and cast it to the correct Object type(s)

	 * @param req

	 * @param resp

	 * @throws javax.servlet.ServletException

	 * @throws java.io.IOException

	 */

	protected abstract void doServicePojoRequest(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException;



    protected Object getImplementation() {

       return this.servletInstance;

    }



	/**

	 * Execute the actual method within the GwtRpc servlet

	 * @param pojoRequest

	 * @param req

	 * @param resp

	 * @throws Throwable

	 */

	public void executePojoRequest(GwtRpcCommLayerPojoRequest pojoRequest,HttpServletRequest req, HttpServletResponse resp) throws Throwable

	{

		try

		{

			/*

			 * extract the appropriate method

			 */

			Method method = getMethod(pojoRequest);



			/*

			 * invoke the method

			 */

			Object returnedInstance = invokeMethod(pojoRequest, method);



			/*

			 * wrap response within a response object

			 */

			GwtRpcCommLayerPojoResponse pojoResp = new GwtRpcCommLayerPojoResponse();

			pojoResp.setResponseInstance( (Serializable) returnedInstance);



			/*

			 * send back the result as a stream set of bytes

			 */

			serializeResponse(req,resp,pojoRequest,pojoResp);

		}

		catch(NoSuchMethodException e)

		{

			log("Method does not found.", e);

			resp.sendError(500, e.toString() );

		}

		catch(InvocationTargetException e)

		{

			log("Error executing method.", e.getCause());

			resp.sendError(500, e.toString() );

		}

		catch(IllegalAccessException e)

		{

			log("Error accessing method.", e);

			resp.sendError(500, e.toString() );

		}

	}



	/**

	 * Write the appropriate response

	 * @param req

	 * @param resp

	 * @param pojoRequest

	 * @param pojoResp

	 * @throws java.io.IOException

	 */

	protected void serializeResponse(HttpServletRequest req, HttpServletResponse resp, GwtRpcCommLayerPojoRequest pojoRequest, GwtRpcCommLayerPojoResponse pojoResp) throws IOException

	{

		ByteArrayOutputStream bos = new ByteArrayOutputStream();

		ObjectOutputStream objOut = new ObjectOutputStream(bos);

		objOut.writeObject(pojoResp);

		objOut.flush();

		objOut.close();



		resp.setContentType("binary/octet-stream");

		resp.setContentLength(bos.toByteArray().length);

		OutputStream out = resp.getOutputStream();

		out.write(bos.toByteArray());

		out.flush();

	}



	/**

	 *

	 * @param stressTestRequest

	 * @return

	 * @throws NoSuchMethodException

	 */

	protected Method getMethod(GwtRpcCommLayerPojoRequest stressTestRequest) throws NoSuchMethodException, ClassNotFoundException {

		int count = 0;

		Class<?> paramClasses[] = new Class[stressTestRequest.getMethodParameters().size()];



        LinkedList<Class<?>> lstParameterClasses = new LinkedList<Class<?>>();

        for (String methodName: stressTestRequest.getParameterClassNames()) {

            lstParameterClasses.add(Class.forName(methodName));

        }



        Class[] arrParameterClasses = lstParameterClasses.toArray(new Class[0]);

        return getClass().getMethod(stressTestRequest.getMethodName(), arrParameterClasses);

    }



	/**

	 *

	 * @param stressTestRequest

	 * @param method

	 * @return

	 * @throws java.lang.reflect.InvocationTargetException

	 * @throws IllegalAccessException

	 */

	protected Object invokeMethod(GwtRpcCommLayerPojoRequest stressTestRequest, Method method) throws InvocationTargetException, IllegalAccessException

	{

        //todo: call toArray with correct size Object Array

		Object paramsAsObjects[] = stressTestRequest.getMethodParameters().toArray( new Object[0]);

		Object instance = method.invoke(servletInstance, paramsAsObjects);

		return instance;

	}

	

	

}