package flowersinthesand.example;



import java.io.IOException;

import java.io.PrintWriter;

import java.util.LinkedHashMap;

import java.util.Map;

import java.util.UUID;

import java.util.concurrent.BlockingQueue;

import java.util.concurrent.ConcurrentHashMap;

import java.util.concurrent.LinkedBlockingQueue;



import javax.servlet.AsyncContext;

import javax.servlet.AsyncEvent;

import javax.servlet.AsyncListener;

import javax.servlet.ServletConfig;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import com.google.gson.Gson;



@WebServlet(urlPatterns = "/chat", asyncSupported = true)

public class ChatServlet extends HttpServlet {



	private static final long serialVersionUID = -2919167206889576860L;

	private Map<String, AsyncContext> contexts = new ConcurrentHashMap<String, AsyncContext>();

	private BlockingQueue<String> messages = new LinkedBlockingQueue<String>();

	private Thread notifier = new Thread(new Runnable() {

		public void run() {

			boolean done = false;

			while (!done) {

				String message = null;

				try {

					message = messages.take();

					for (AsyncContext ac : contexts.values()) {

						try {

							sendMessage(ac.getResponse().getWriter(), message);

						} catch (IOException e) {

							contexts.remove(ac);

						}

					}

				} catch (InterruptedException e) {

					done = true;

				}

			}

		}

	});

	

	private void sendMessage(PrintWriter writer, String message) {

		// Sends a message according to the message format(message-size ; message-data ;) 

		writer.print(message.length());

		writer.print(";");

		writer.print(message);

		writer.print(";");

		writer.flush();

	}



	@Override

	public void init(ServletConfig config) throws ServletException {

		super.init(config);

		notifier.start();

	}



	// GET method is used to open stream

	@Override

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException,

			IOException {

		response.setCharacterEncoding("utf-8");

		

		// Sets the Content-Type header to 'text/plain' that is the only one satisfying all streaming transport

		response.setContentType("text/plain");

		

		// For XDomainRequest transport, sets the Access-Control-Allow-Origin header

		response.setHeader("Access-Control-Allow-Origin", "*");



		// Prints the stream connection id for further communication and one kilobyte padding at the top of the response

		// each part must end with a semicolon

		PrintWriter writer = response.getWriter();

		

		// UUID is very suitable

		final String id = UUID.randomUUID().toString();

		writer.print(id);

		writer.print(';');

		

		// The padding is needed by XMLHttpRequest of WebKit, XDomainRequest and Hidden iframe transport

		for (int i = 0; i < 1024; i++) {

			writer.print(' ');

		}

		writer.print(';');

		writer.flush();

		

		System.out.println(id + ": open");

		

		// Starts asynchronous mode

		final AsyncContext ac = request.startAsync();

		ac.setTimeout(5 * 60 * 1000);

		ac.addListener(new AsyncListener() {

			public void onComplete(AsyncEvent event) throws IOException {

				contexts.remove(id);

			}



			public void onTimeout(AsyncEvent event) throws IOException {

				contexts.remove(id);

			}



			public void onError(AsyncEvent event) throws IOException {

				contexts.remove(id);

			}



			public void onStartAsync(AsyncEvent event) throws IOException {



			}

		});

		contexts.put(id, ac);

	}



	// POST method is used to handle data sent by user through the stream

	@Override

	protected void doPost(HttpServletRequest request, HttpServletResponse response)

			throws ServletException, IOException {

		request.setCharacterEncoding("utf-8");



		// POST request always has metadata parameters

		

		// The stream connection id generated by the server 

		String id = request.getParameter("metadata.id");

		

		// Request type such as send and close

		String type = request.getParameter("metadata.type");

		

		System.out.println(id + ": " + type);

		

		// Handles a special case

		if ("close".equals(type)) {

			// Closes connection by its id

			AsyncContext ac = contexts.get(id);

			if (ac != null) {

				ac.complete();

			}

			

			return;

		}



		// Handles data sent from a client

		Map<String, String> data = new LinkedHashMap<String, String>();

		data.put("username", request.getParameter("username"));

		data.put("message", request.getParameter("message"));



		try {

			messages.put(new Gson().toJson(data));

		} catch (Exception e) {

			throw new IOException(e);

		}

	}



	@Override

	public void destroy() {

		messages.clear();

		contexts.clear();

		notifier.interrupt();

	}



}