/*
 * FZI - Information Process Engineering 
 * Created on 22.12.2007 by zach
 */
package de.fzi.ipe.pipesSparqlr;

import java.io.BufferedInputStream;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.json.JSONException;
import org.json.JSONObject;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

@SuppressWarnings("serial")
public class SparqlrServlet extends HttpServlet{
	
	@Override
	protected void doGet(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
		doPost(arg0, arg1);
	}
	
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        try {
            String data = request.getParameter("data");
            if (data == null) { 
                response.setContentType("text/xml");
                out.println(" \n No input data!\n");
            }
            else {
            	JSONObject jsonObj = new JSONObject(data);
            	jsonObj = jsonObj.getJSONArray("items").getJSONObject(0);
            	String query = jsonObj.getString("query");
            	String endpoint = jsonObj.getString("endpoint");
            	
            	Document doc = getResultDocument(endpoint, query);
            	JSONObject result = makeJSON(doc);
            	
            	response.setContentType("application/sparql-results+xml");
            	out.println(result.toString());
            }
        } catch (Exception e) {
        	response.setContentType("text/xml");
        	e.printStackTrace(out);
        }
	}
	
	
	private static Document getResultDocument(String endpoint, String query) throws IOException, SAXException, ParserConfigurationException {
	    URLConnection urlConn = new URL(endpoint).openConnection();
	    urlConn.setDoOutput (true);
	    urlConn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
	    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(urlConn.getOutputStream ()));
		writer.write("query="+URLEncoder.encode(query,"UTF-8"));
		writer.close();
        DocumentBuilderFactory fact = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = fact.newDocumentBuilder();
        Document doc = builder.parse(new BufferedInputStream(urlConn.getInputStream()));
        return doc;
	}
	
	private static JSONObject makeJSON(Document doc) throws JSONException {
		JSONObject resultObject = new JSONObject();
		NodeList results = doc.getDocumentElement().getElementsByTagName("results").item(0).getChildNodes();
        for (int i=0;i<results.getLength();i++) {
        	Node currentResult = results.item(i);
        	if (currentResult.getNodeName().equals("result")) {
        		resultObject.append("items",processResult(currentResult.getChildNodes()));
        	}
        }
		return resultObject;
	}

	private static JSONObject processResult( NodeList bindings) throws JSONException{
		JSONObject currentResultJSON = new JSONObject();		
		for (int b=0;b<bindings.getLength();b++) {
			Node currentBinding = bindings.item(b);
			if (currentBinding.getNodeName().equals("binding")) {
				String variableName = currentBinding.getAttributes().getNamedItem("name").getNodeValue();        				
				NodeList values= currentBinding.getChildNodes();
				for (int a=0;a<values.getLength();a++) {
					Node valueNode = values.item(a);
					if (valueNode.getNodeType() == Node.ELEMENT_NODE) {
						String variableBinding = valueNode.getTextContent();
						currentResultJSON.put(variableName, variableBinding);
					}
				}
			}
		}
		return currentResultJSON; 
	}	
	
}