package pt.ist.renderers.servlets.ajax;

import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.concurrent.ConcurrentHashMap;

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

import org.joda.time.DateTime;

import pt.ist.bennu.core.security.Authenticate.SessionUserWrapper;
import pt.ist.bennu.core.security.UserView;
import pt.ist.renderers.servlets.json.JsonObject;

public class JsonServlet extends HttpServlet {

    public static final String PURGE_METHOD = "purge";
    public static final String REQUEST_OBJECT_METHOD = "request";
    public static final String TOKEN_PARAMETER_NAME = "token";
    public static final String ACTION_PARAMETER_NAME = "action";

    private static ConcurrentHashMap<String, JsonObject> tokenMap = new ConcurrentHashMap<String, JsonObject>();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
	process(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
	process(req, resp);
    }

    private void process(HttpServletRequest req, HttpServletResponse resp) {
	String actionToPerform = req.getParameter(ACTION_PARAMETER_NAME);
	if (actionToPerform.equals(PURGE_METHOD)) {
	    purge(req, resp);
	} else if (actionToPerform.equals(REQUEST_OBJECT_METHOD)) {
	    serve(req, resp);
	}
    }

    private void serve(HttpServletRequest req, HttpServletResponse resp) {
	resp.setContentType("text/html");
	String token = req.getParameter(TOKEN_PARAMETER_NAME);
	if (token != null) {
	    JsonObject object = tokenMap.get(token);
	    try {
		if (object != null) {
		    resp.getWriter().write(object.getJsonString());
		}
	    } catch (IOException e) {
		e.printStackTrace();
	    }
	}
    }

    private void purge(HttpServletRequest req, HttpServletResponse resp) {
	String token = req.getParameter(TOKEN_PARAMETER_NAME);
	if (token != null) {
	    tokenMap.remove(token);
	}
    }

    public static String getTokenFor(JsonObject jsonObject) {
	SessionUserWrapper user = UserView.getSessionUserWrapper();
	if (user == null) {
	    throw new RuntimeException("access.control.error.only.authenticated.users.can.request.tokens");
	}
	StringBuilder hash = new StringBuilder(user.getPrivateConstantForDigestCalculation());
	hash.append(user.getUser().getUsername());
	hash.append(user.getUserCreationDateTime().toString());
	hash.append(new DateTime());

	String digest;
	try {
	    MessageDigest algorithm = MessageDigest.getInstance("MD5");
	    algorithm.reset();
	    algorithm.update(hash.toString().getBytes());
	    byte messageDigest[] = algorithm.digest();

	    StringBuffer hexString = new StringBuffer();
	    for (int i = 0; i < messageDigest.length; i++) {
		hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
	    }
	    digest = hexString.toString();

	} catch (NoSuchAlgorithmException e) {
	    throw new RuntimeException(e);
	}

	tokenMap.put(digest, jsonObject);
	return digest;
    }

}