/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package ch.qos.logback.classic.turbo;
  
  import static ch.qos.logback.core.CoreConstants.MILLIS_IN_ONE_SECOND;
  
  import java.io.File;
  import java.net.URL;
  import java.util.List;
  
  import org.slf4j.Marker;
  
  import ch.qos.logback.classic.Level;
  import ch.qos.logback.classic.Logger;
  import ch.qos.logback.classic.LoggerContext;
  import ch.qos.logback.classic.joran.JoranConfigurator;
  import ch.qos.logback.core.CoreConstants;
  import ch.qos.logback.core.joran.spi.ConfigurationWatchList;
  import ch.qos.logback.core.joran.spi.JoranException;
  import ch.qos.logback.core.joran.util.ConfigurationWatchListUtil;
  import ch.qos.logback.core.model.Model;
  import ch.qos.logback.core.model.ModelUtil;
  import ch.qos.logback.core.spi.FilterReply;
  import ch.qos.logback.core.status.StatusUtil;
  
  /**
   * Reconfigure a LoggerContext when the configuration file changes.
   *
   * @author Ceki Gulcu
   */
  public class ReconfigureOnChangeFilter extends TurboFilter {
  
      /**
       * Scan for changes in configuration file once every minute.
       */
      // 1 minute - value mentioned in documentation
      public final static long DEFAULT_REFRESH_PERIOD = 60 * MILLIS_IN_ONE_SECOND;
  
      long refreshPeriod = DEFAULT_REFRESH_PERIOD;
      URL mainConfigurationURL;
      protected volatile long nextCheck;
  
      ConfigurationWatchList configurationWatchList;
  
      @Override
      public void start() {
          configurationWatchList = ConfigurationWatchListUtil.getConfigurationWatchList(context);
          if (configurationWatchList != null) {
              mainConfigurationURL = configurationWatchList.getMainURL();
              if (mainConfigurationURL == null) {
                  addWarn("Due to missing top level configuration file, automatic reconfiguration is impossible.");
                  return;
              }
              List<File> watchList = configurationWatchList.getCopyOfFileWatchList();
              long inSeconds = refreshPeriod / 1000;
              addInfo("Will scan for changes in [" + watchList + "] every " + inSeconds + " seconds. ");
              synchronized (configurationWatchList) {
                  updateNextCheck(System.currentTimeMillis());
              }
              super.start();
          } else {
              addWarn("Empty ConfigurationWatchList in context");
          }
      }
  
      @Override
      public String toString() {
          return "ReconfigureOnChangeFilter{" + "invocationCounter=" + invocationCounter + '}';
      }
  
      // The next fields counts the number of time the decide method is called
      //
      // IMPORTANT: This field can be updated by multiple threads. It follows that
      // its values may *not* be incremented sequentially. However, we don't care
      // about the actual value of the field except that from time to time the
      // expression (invocationCounter++ & mask) == mask) should be true.
      private long invocationCounter = 0;
  
      private volatile long mask = 0xF;
      private volatile long lastMaskCheck = System.currentTimeMillis();
  
      @Override
      public FilterReply decide(Marker marker, Logger logger, Level level, String format, Object[] params, Throwable t) {
          if (!isStarted()) {
              return FilterReply.NEUTRAL;
          }
  
          // for performance reasons, skip change detection (MASK-1) times out of MASK.
         // Only once every MASK calls is change detection code executed
         // Note that MASK is a variable itself.
         if (((invocationCounter++) & mask) != mask) {
             return FilterReply.NEUTRAL;
         }
 
         long now = System.currentTimeMillis();
 
         synchronized (configurationWatchList) {
             updateMaskIfNecessary(now);
             if (changeDetected(now)) {
                 // Even though reconfiguration involves resetting the loggerContext,
                 // which clears the list of turbo filters including this instance, it is
                 // still possible for this instance to be subsequently invoked by another
                 // thread if it was already executing when the context was reset.
                 disableSubsequentReconfiguration();
                 detachReconfigurationToNewThread();
             }
         }
 
         return FilterReply.NEUTRAL;
     }
 
     // experiments indicate that even for CPU intensive applications with 200 or
     // more threads MASK
     // values in the order of 0xFFFF is appropriate
     private static final int MAX_MASK = 0xFFFF;
 
     // if less than MASK_INCREASE_THRESHOLD milliseconds elapse between invocations
     // of updateMaskIfNecessary() method,
     // then the mask should be increased
     private static final long MASK_INCREASE_THRESHOLD = 100;
 
     // if more than MASK_DECREASE_THRESHOLD milliseconds elapse between invocations
     // of updateMaskIfNecessary() method,
     // then the mask should be decreased
     private static final long MASK_DECREASE_THRESHOLD = MASK_INCREASE_THRESHOLD * 8;
 
     // update the mask so as to execute change detection code about once every 100
     // to 8000 milliseconds.
     private void updateMaskIfNecessary(long now) {
         final long timeElapsedSinceLastMaskUpdateCheck = now - lastMaskCheck;
         lastMaskCheck = now;
         if (timeElapsedSinceLastMaskUpdateCheck < MASK_INCREASE_THRESHOLD && (mask < MAX_MASK)) {
             mask = (mask << 1) | 1;
         } else if (timeElapsedSinceLastMaskUpdateCheck > MASK_DECREASE_THRESHOLD) {
             mask = mask >>> 2;
         }
     }
 
     // by detaching reconfiguration to a new thread, we release the various
     // locks held by the current thread, in particular, the AppenderAttachable
     // reader lock.
     void detachReconfigurationToNewThread() {
         addInfo("Detected change in [" + configurationWatchList.getCopyOfFileWatchList() + "]");
         context.getExecutorService().submit(new ReconfiguringThread());
     }
 
     void updateNextCheck(long now) {
         nextCheck = now + refreshPeriod;
     }
 
     protected boolean changeDetected(long now) {
         if (now >= nextCheck) {
             updateNextCheck(now);
             return configurationWatchList.changeDetected();
         }
         return false;
     }
 
     void disableSubsequentReconfiguration() {
         nextCheck = Long.MAX_VALUE;
     }
 
     public long getRefreshPeriod() {
         return refreshPeriod;
     }
 
     public void setRefreshPeriod(long refreshPeriod) {
         this.refreshPeriod = refreshPeriod;
     }
 
     class ReconfiguringThread implements Runnable {
         public void run() {
             if (mainConfigurationURL == null) {
                 addInfo("Due to missing top level configuration file, skipping reconfiguration");
                 return;
             }
             LoggerContext lc = (LoggerContext) context;
             addInfo(CoreConstants.RESET_MSG_PREFIX + "named [" + context.getName() + "]");
             if (mainConfigurationURL.toString().endsWith("xml")) {
                 performXMLConfiguration(lc);
             } else if (mainConfigurationURL.toString().endsWith("groovy")) {
                 addError("Groovy configuration disabled due to Java 9 compilation issues.");
             }
         }
 
         private void performXMLConfiguration(LoggerContext lc) {
             JoranConfigurator jc = new JoranConfigurator();
             jc.setContext(context);
             StatusUtil statusUtil = new StatusUtil(context);
             Model failSafeTop = jc.recallSafeConfiguration();
             URL mainURL = ConfigurationWatchListUtil.getMainWatchURL(context);
             lc.reset();
             long threshold = System.currentTimeMillis();
             try {
                 jc.doConfigure(mainConfigurationURL);
                 if (statusUtil.hasXMLParsingErrors(threshold)) {
                     fallbackConfiguration(lc, failSafeTop, mainURL);
                 }
             } catch (JoranException e) {
                 fallbackConfiguration(lc, failSafeTop, mainURL);
             }
         }
 
         private void fallbackConfiguration(LoggerContext lc, Model failSafeTop, URL mainURL) {
             JoranConfigurator joranConfigurator = new JoranConfigurator();
             joranConfigurator.setContext(context);
             if (failSafeTop != null) {
                 addWarn("Falling back to previously registered safe configuration.");
                 try {
                     lc.reset();
                     JoranConfigurator.informContextOfURLUsedForConfiguration(context, mainURL);
                     ModelUtil.resetForReuse(failSafeTop);
                     joranConfigurator.processModel(failSafeTop);
                     addInfo("Re-registering previous fallback configuration once more as a fallback configuration point");
                     joranConfigurator.registerSafeConfiguration(failSafeTop);
                 } catch (Exception e) {
                     addError("Unexpected exception thrown by a configuration considered safe.", e);
                 }
             } else {
                 addWarn("No previous configuration to fall back on.");
             }
         }
     }
 }