/*
    * Copyright 2008 Simon Martinelli, Rebenweg 32, 3236 Gampelen, Switzerland
    *
    * 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 org.simject.remoting.client;
  
  import java.beans.XMLDecoder;
  import java.beans.XMLEncoder;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.lang.reflect.InvocationHandler;
  import java.lang.reflect.Method;
  import java.net.HttpURLConnection;
  import java.net.MalformedURLException;
  import java.net.URL;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import org.simject.util.Protocol;
  import org.simject.util.SimConstants;
  
  /**
   * Used to provide remote access over HTTP to a resource. HttpClientProxy uses
   * XStream for XML serialization or normal Java serialization for binary
   * protocol
   * 
   * @author Simon Martinelli
   */
  public final class HttpClientProxy implements InvocationHandler {
  
  	private final static Logger logger = Logger.getLogger(HttpClientProxy.class
  			.getName());
  
  	/**
  	 * Holds the requested URL
  	 */
  	final private URL url;
  
  	/**
  	 * Holds the protocol
  	 */
  	final private Protocol protocol;
  
  	/**
  	 * Creates a new instance of a proxy
  	 * 
  	 * @param loader
  	 * @param interfaces
  	 * @param url
  	 * @return an instance of HttpClientProxy
  	 * @throws MalformedURLException
  	 */
  	public static Object newInstance(final ClassLoader loader,
  			final Class<?>[] interfaces, final String target)
  			throws MalformedURLException {
  
  		// Extract the protocol
  		final String protcolString = target.substring(0, 3);
  		Protocol protocol = Protocol.Xml;
  		if (protcolString.equals(Protocol.Binary.getString())) {
  			protocol = Protocol.Binary;
  		}
  		// Extract the URL
  		final String urlString = target.substring(4);
  		final URL url = new URL(urlString);
  
  		logger.info("Creating proxy for URL <" + url + "> using <" + protocol
  				+ "> protocol");
  		// Create an instance of the proxy
  		return java.lang.reflect.Proxy.newProxyInstance(loader, interfaces,
  				new HttpClientProxy(url, protocol));
  	}
  
  	/**
  	 * Private Constructor
  	 * 
  	 * @param url
  	 */
  	private HttpClientProxy(final URL url, final Protocol protocol) {
  		this.url = url;
  		this.protocol = protocol;
  	}
  
  	@Override
  	public Object invoke(final Object proxy, final Method method,
  			final Object[] args) throws Throwable {
  		logger.info("Invoking method <" + method.getName()
  				+ "> with arguments <" + args + ">");
 		Object result;
 		try {
 			if (protocol == Protocol.Binary) {
 				result = this.invokeUrlBinary2(method, args);
 			} else {
 				result = this.invokeUrlXml2(method, args);
 			}
 		} catch (Exception e) {
 			logger.log(Level.SEVERE, e.getMessage(), e);
 			throw e;
 		}
 		return result;
 	}
 
 	/**
 	 * Synchronous call over HTTP using binary protocol
 	 * 
 	 * 1. Serializes the arguments to Binary and make a remote call over HTTP
 	 * with Commons HttpClient to the desired method. 2. Deserializes the binary
 	 * response from the server.
 	 * 
 	 * @param method
 	 * @param args
 	 * @return
 	 * @throws Throwable
 	 */
 	private Object invokeUrlBinary2(final Method method, final Object[] args)
 			throws Throwable {
 
 		HttpURLConnection con = (HttpURLConnection) this.url.openConnection();
 		con.setDoOutput(true);
 
 		// The method name and the parameter types are set to the header
 		this.createHeader2(method, con);
 
 		final ObjectOutputStream oos = new ObjectOutputStream(con
 				.getOutputStream());
 		oos.writeObject(args);
 		oos.close();
 
 		// Get response if the content is > 0
 		Object result = null;
 		if (con.getContentLength() > 0) {
 			final ObjectInputStream ois = new ObjectInputStream(con
 					.getInputStream());
 			result = ois.readObject();
 
 			if (result instanceof Throwable) {
 				throw ((Throwable) result);
 			}
 		}
 
 		con.disconnect();
 
 		return result;
 	}
 
 	/**
 	 * Synchronous call over HTTP using XML protocol
 	 * 
 	 * 1. Serializes the arguments to XML using XMLEncoder and make a remote
 	 * call over HTTP with Commons HttpClient to the desired method. 2.
 	 * Deserializes the XML response from the server using XMLDecoder.
 	 * 
 	 * @param method
 	 * @param args
 	 * @return
 	 * @throws Throwable
 	 */
 	private Object invokeUrlXml2(final Method method, final Object[] args)
 			throws Throwable {
 
 		final HttpURLConnection con = (HttpURLConnection) this.url
 				.openConnection();
 		con.setDoOutput(true);
 
 		// The method name and the parameter types are set to the header
 		this.createHeader2(method, con);
 
 		final XMLEncoder encoder = new XMLEncoder(con.getOutputStream());
 		encoder.writeObject(args);
 
 		// Get response if the content is > 0
 		Object result = null;
 		if (con.getContentLength() > 0) {
 			final XMLDecoder decoder = new XMLDecoder(con.getInputStream());
 			result = decoder.readObject();
 			if (result instanceof Throwable) {
 				throw ((Throwable) result);
 			}
 		}
 
 		con.disconnect();
 
 		return result;
 	}
 
 	/**
 	 * Create the necessairy Header entries
 	 * 
 	 * @param method
 	 * @param post
 	 */
 	private void createHeader2(final Method method, final HttpURLConnection con) {
 		con.setRequestProperty(SimConstants.PARAM_METHOD, method.getName());
 
 		// Get all parameter types and add them to a string delimited by ,
 		final StringBuffer params = new StringBuffer();
 		for (Class<?> param : method.getParameterTypes()) {
 			final String paramString = param.getName()
 					+ SimConstants.PARAM_TYPE_DELIM;
 			params.append(paramString);
 		}
 		if (params.length() > 0) {
 			final String parameters = params.toString();
 			con.setRequestProperty(SimConstants.PARAM_TYPES, parameters);
 		}
 	}
 }