package gov.usgs.geotools.util;

import java.lang.reflect.Field;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * Application Lifecycle Listener implementation class WeakCollectionCleanerCleaner
 *
 */
public class WeakCollectionCleanerCleaner implements ServletContextListener {

	public final static String CLASS_WeakCollectionCleaner = "org.geotools.util.WeakCollectionCleaner";
	public final static String FIELD_DEFAULT = "DEFAULT";
	public final static String FIELD_referenceQueue = "referenceQueue";

	private final static String LOG_MSG_WARNING = "Unable to stop WeakCollectionCleaner thread gracefully";
	private final static String LOG_MSG_SEVERE = "Unable to stop WeakCollectionCleaner thread, probable PermGen leak...";
    /**
     * Default constructor. 
     */
    public WeakCollectionCleanerCleaner() {
        // DO NOT REMOVE: default constructor must be explicitly declared for
		// container to instantiate.
    }

	/**
     * @see ServletContextListener#contextInitialized(ServletContextEvent)
     */
    public void contextInitialized(ServletContextEvent sce) {
        // nothing to do...
    }

	/**
     * @see ServletContextListener#contextDestroyed(ServletContextEvent)
     */
    @SuppressWarnings("deprecation")
	public void contextDestroyed(ServletContextEvent sce) {
		try {
			// NOTE: If the thread we are trying to kill hasn't started
			// (class never loaded and initialized) we are are going to start
			// it with reflection calls, shucks...  JVM Specification 12.4.1
			// No way that I know of to test whether a class has been
			// initialized by JVM so that we could punt...

			// Pull out class fields we need to manipulate.
			Field defaultField = fieldForName(CLASS_WeakCollectionCleaner, FIELD_DEFAULT);
			Field referenceQueueField = fieldForName(CLASS_WeakCollectionCleaner, FIELD_referenceQueue);

			// get handle to singleton instance
			Object cleanerObject = defaultField.get(null);

			if (cleanerObject != null && cleanerObject instanceof Thread) {

				Thread cleanerThread = (Thread)cleanerObject;

				// Make sure we're only cleaning up an instance associated with
				// the this app's classload.
				// 1) If one has GeoTools installed in the container libs
				//    directory, stopping the cleaner thread  would be *bad*
				//    for subsequent app deploys...
				// 2) If the cleaner isn't associated with this classloader it's
				//    not going to address the PermGen leak so why mess with it...
				if(cleanerThread.getClass().getClassLoader() == Thread.currentThread().getContextClassLoader()) {

					// heavy exception catching so we can attempt a fallback method
					try {
						// First try a gracefull stop (will result in log output)
						// the cleaner thread tests for (referenceQueue != null)
						// as a continuation condition.  This is good...
						referenceQueueField.set(cleanerObject, null);

						// interrupt clean thread as it sleeps for 15s between sweeps
						cleanerThread.interrupt();
						cleanerThread.join(500);
					} catch (InterruptedException ex) {
						// swallow, we are exiting and need to clean up...
					} catch (IllegalArgumentException ex) {
						Logger.getLogger(getClass().getName()).log(Level.WARNING, LOG_MSG_WARNING, ex);
					} catch (IllegalAccessException ex) {
						Logger.getLogger(getClass().getName()).log(Level.WARNING, LOG_MSG_WARNING, ex);
					}
					if(referenceQueueField.get(cleanerObject) != null || cleanerThread.isAlive()) {

						// This is bad form, but what else are we to do?
						cleanerThread.stop();

						try {
							cleanerThread.join(500);
						} catch (InterruptedException ex) {
							// swallow, we are exiting and need to clean up...
						}

						if (cleanerThread.isAlive()) {
							Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE);
						} else {
							Logger.getLogger(getClass().getName()).log(Level.INFO, "Successfully stopped WeakCollectionCleaner with brute force");
						}

					} else {
						Logger.getLogger(getClass().getName()).log(Level.INFO, "Successfully stopped WeakCollectionCleaner, gracefully");
					}
				}
			}
		} catch (IllegalArgumentException ex) {
			Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE, ex);
		} catch (IllegalAccessException ex) {
			Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE, ex);
		} catch (NoSuchFieldException ex) {
			Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE, ex);
		} catch (SecurityException ex) {
			Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE, ex);
		} catch (ClassNotFoundException ex) {
			Logger.getLogger(getClass().getName()).log(Level.SEVERE, LOG_MSG_SEVERE, ex);
		}
    }

	static Field fieldForName(String className, String fieldName)
			throws ClassNotFoundException, NoSuchFieldException {
		Class<?> clazz = Class.forName(className);
		Field field = clazz.getDeclaredField(fieldName);
		field.setAccessible(true);
		return field;
	}

}