/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements. See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache license, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License. You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the license for the specific language governing permissions and
   * limitations under the license.
   */
  package org.apache.logging.log4j.core.config;
  
  import java.io.File;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantLock;
  
  /**
   * Configuration monitor that periodically checks the timestamp of the configuration file and calls the
   * ConfigurationListeners when an update occurs.
   */
  public class FileConfigurationMonitor implements ConfigurationMonitor {
  
      private static final int MASK = 0x0f;
  
      private static final int MIN_INTERVAL = 5;
  
      private static final int MILLIS_PER_SECOND = 1000;
  
      private final File file;
  
      private long lastModified;
  
      private final List<ConfigurationListener> listeners;
  
      private final int intervalSeconds;
  
      private long nextCheck;
  
      private final AtomicInteger counter = new AtomicInteger(0);
  
      private static final Lock LOCK = new ReentrantLock();
  
      private final Reconfigurable reconfigurable;
  
      /**
       * Constructor.
       * @param reconfigurable The Configuration that can be reconfigured.
       * @param file The File to monitor.
       * @param listeners The List of ConfigurationListeners to notify upon a change.
       * @param intervalSeconds The monitor interval in seconds. The minimum interval is 5 seconds.
       */
      public FileConfigurationMonitor(final Reconfigurable reconfigurable, final File file,
                                      final List<ConfigurationListener> listeners,
                                      final int intervalSeconds) {
          this.reconfigurable = reconfigurable;
          this.file = file;
          this.lastModified = file.lastModified();
          this.listeners = listeners;
          this.intervalSeconds = (intervalSeconds < MIN_INTERVAL ? MIN_INTERVAL : intervalSeconds) * MILLIS_PER_SECOND;
          this.nextCheck = System.currentTimeMillis() + intervalSeconds;
      }
  
      /**
       * Called to determine if the configuration has changed.
       */
      @Override
      public void checkConfiguration() {
          final long current = System.currentTimeMillis();
          if (((counter.incrementAndGet() & MASK) == 0) && (current >= nextCheck)) {
              LOCK.lock();
              try {
                  nextCheck = current + intervalSeconds;
                  if (file.lastModified() > lastModified) {
                      lastModified = file.lastModified();
                      for (final ConfigurationListener listener : listeners) {
                          final Thread thread = new Thread(new ReconfigurationWorker(listener, reconfigurable));
                          thread.setDaemon(true);
                          thread.start();
                      }
                  }
              } finally {
                  LOCK.unlock();
              }
          }
      }
  
      private class ReconfigurationWorker implements Runnable {
  
          private final ConfigurationListener listener;
          private final Reconfigurable reconfigurable;
  
         public ReconfigurationWorker(final ConfigurationListener listener, final Reconfigurable reconfigurable) {
             this.listener = listener;
             this.reconfigurable = reconfigurable;
         }
 
         @Override
         public void run() {
             listener.onChange(reconfigurable);
         }
     }
 }