package jalview.ext.rbvi.chimera;

import java.net.BindException;

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

import jalview.httpserver.AbstractRequestHandler;
import jalview.httpserver.HttpServer;
import jalview.structure.SelectionSource;

/**
 * This is a simple Http handler that can listen for selections in Chimera.
 * <p/>
 * Lifecycle:
 * <ul>
 * <li>Start the Chimera process</li>
 * <li>Start the REST service on Chimera, get the port number it is listening on
 * </li>
 * <li>Start the ChimeraListener, get the port number it is listening on</li>
 * <li>Send a 'listen' command to Chimera with the URL of the listener</li>
 * </ul>
 * 
 * @author gmcarstairs
 *
 */
public class ChimeraListener extends AbstractRequestHandler implements
        SelectionSource
{
  /*
   * A static counter so each listener can be associated with a distinct context
   * root (/chimera0,1,2,3...). This is needed so we can fetch selections from
   * multiple Chimera instances without confusion.
   */
  private static int chimeraId = 0;

  /*
   * Path below context root that identifies this handler
   */
  private static final String LISTENER_PATH = "chimera";

  /*
   * Value of chimeraId (0, 1, 2...) for this instance
   */
  private int myChimeraId = 0;

  /*
   * A reference to the object by which we can talk to Chimera
   */
  private JalviewChimeraBinding chimeraBinding;

  /*
   * The URI of this listener
   */
  private String uri;

  /**
   * Constructor that also registers this as an Http request handler on path
   * /chimeraN, where N is incremented for each instance. Call getUri to get the
   * resulting URI for this handler.
   * 
   * @param chimeraBinding
   * @throws BindException
   *           if no free port can be assigned
   */
  public ChimeraListener(JalviewChimeraBinding binding)
          throws BindException
  {
    myChimeraId = chimeraId++;
    this.chimeraBinding = binding;
    final String path = LISTENER_PATH + myChimeraId;
    this.uri = HttpServer.getInstance().registerHandler(path, this);
  }

  /**
   * Returns the URI on which we are listening
   * 
   * @return
   */
  public String getUri()
  {
    return this.uri;
  }

  /**
   * Process a message from Chimera
   */
  @Override
  protected void processRequest(HttpServletRequest request,
          HttpServletResponse response)
  {
    // dumpRequest(request);
    String message = request.getParameter("chimeraNotification");
    if ("selection changed".equals(message))
    {
      this.chimeraBinding.highlightChimeraSelection();
    }
    else
    {
      System.err.println("Unexpected chimeraNotification: " + message);
      // do it anyway for now!
      this.chimeraBinding.highlightChimeraSelection();
    }
  }

  /**
   * Deregister this listener and close it down
   * 
   * @throws Exception
   */
  public void shutdown()
  {
    try
    {
      HttpServer.getInstance().removeHandler(this);
      stop();
    } catch (Exception e)
    {
      System.err.println("Error stopping chimera listener: "
              + e.getMessage());
    }
  }
}