import javax.servlet.*;
import javax.servlet.http.*;

import java.io.RandomAccessFile;
import java.io.FileOutputStream;
import java.io.PrintWriter;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;

import java.net.URLDecoder;
/*
 * [todo 2006.06.06] integrate exception message into response instead 
 *                   of to System.err.
 */
public class ModuleAccessHandlerServlet extends HttpServlet {

    public void doGet(HttpServletRequest request,
		      HttpServletResponse response) throws IOException {
        String requestText = request.getQueryString();
	if (requestText != null)
	    requestText = URLDecoder.decode(requestText, "UTF-8");
        doEither(request, response, requestText);
    }//end (doGet)

    public void doPost(HttpServletRequest request,
		      HttpServletResponse response) throws IOException {

        BufferedReader in = request.getReader();
        String line, requestText = new String();
        while ((line = in.readLine()) != null) {
            requestText += line;
        }
        doEither(request, response, requestText);
    }//end (doPost)

    public void doEither(HttpServletRequest request, 
                         HttpServletResponse response,
                         String requestText) throws IOException {
	/*
	 * The driverName can be specified in the URL as follows:
	 * http://142.88.2.43/mah?driver=aDriverName&<recirculator ...
	 *
	 */
	String driverName = request.getParameter("driver");
	if (driverName == null || driverName.equals(""))
	    driverName = "/dev/widar/cmibxml";

	/*
	 * The actual request XML starts after the last '&', if any.
	 */
	int requestStart = requestText.lastIndexOf('&');
	if (requestStart > -1) 
	    requestText = requestText.substring(requestStart + 1);
	try {
	    /*
	     * This way is 2-3 times faster than first opening read-only to
	     * throw an exception if the file does not exist ...
	     */
	    java.io.File checkExists = new java.io.File(driverName);
	    if (!checkExists.exists()) throw new IOException
		("The driver does not exist on this server");
	    RandomAccessFile driver =
		new RandomAccessFile(driverName, "rwd");
	    FileOutputStream writer = new FileOutputStream(driver.getFD());
	    FileReader reader = new FileReader(driver.getFD());
	    
	    PrintWriter mahOut = new PrintWriter(writer);
	    mahOut.println(requestText);
	    mahOut.flush();
	    
	    BufferedReader mahIn = new BufferedReader(reader);
	    driver.seek(0);
	    
	    PrintWriter responseMessage = response.getWriter();
	    responseMessage = response.getWriter();
	    //response.setHeader("Content-Type", "text/xml");
	    
	    String line;
	    while((line = mahIn.readLine()) != null) {
		responseMessage.println(line);
	    }
	    driver.close();
	}
	catch (java.io.UnsupportedEncodingException uee) {
	    try {
		response.sendError
		    (500, "ModuleAccessHandlerServlet." +
		     "UnsupportedEncodingException: The content-type " + 
		     "'charset' property was set to a value not " +
		     "supported by the server:\n" + uee.getMessage());
	    } catch (IOException ioe) {
		response.setStatus(500);
	    } catch (IllegalStateException ise) {
		response.setStatus(500);
	    }
	}
	// if a Writer already exists on the response
	catch (IllegalStateException ise) {
	    response.setStatus(500);
	}
	catch (IOException e) {
	    try {
		response.sendError
		    (500, "ModuleAccessHandlerServlet.IOException " +
		     "while attempting to communicate with CMIB " +
		     "driver software: '" + driverName + "':\n" +
		     e.getMessage());
	    } catch (IOException ioe) {
		response.setStatus(500);
	    } catch (IllegalStateException ise) {
		response.setStatus(500);
	    }
	}
    }// end (doEither)
} //end (ModuleAccessHandlerServlet.java)