/*
    * 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 org.apache.logging.log4j.Logger;
  import org.apache.logging.log4j.core.AbstractLifeCycle;
  import org.apache.logging.log4j.core.async.DaemonThreadFactory;
  import org.apache.logging.log4j.core.util.CronExpression;
  import org.apache.logging.log4j.status.StatusLogger;
  
  import java.util.Date;
  import java.util.concurrent.Callable;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  
  /**
   *
   */
  public class ConfigurationScheduler extends AbstractLifeCycle {
  
      private static final Logger LOGGER = StatusLogger.getLogger();
      private ScheduledExecutorService executorService;
  
      private int scheduledItems = 0;
  
  
      @Override
      public void start() {
          super.start();
          if (scheduledItems > 0) {
              LOGGER.debug("Starting {} Log4j2Scheduled threads", scheduledItems);
              if (scheduledItems > 5) {
                  scheduledItems = 5;
              }
              executorService = new ScheduledThreadPoolExecutor(scheduledItems, new DaemonThreadFactory("Log4j2Scheduled-"));
          } else {
              LOGGER.debug("No scheduled items");
          }
      }
  
      @Override
      public void stop() {
          if (executorService != null) {
              LOGGER.debug("Stopping Log4j2Scheduled threads.");
              executorService.shutdown();
          }
          super.stop();
      }
  
      /**
       * Increment the number of threads in the pool.
       */
      public void incrementScheduledItems() {
          if (!isStarted()) {
              ++scheduledItems;
          } else {
              LOGGER.error("Attempted to increment scheduled items after start");
          }
      }
  
      /**
       * Decrement the number of threads in the pool
       */
      public void decrementScheduledItems() {
          if (!isStarted() && scheduledItems > 0) {
              --scheduledItems;
          }
      }
  
      /**
       * Creates and executes a ScheduledFuture that becomes enabled after the given delay.
       * @param callable the function to execute.
       * @param delay the time from now to delay execution.
       * @param unit the time unit of the delay parameter.
       * @return a ScheduledFuture that can be used to extract result or cancel.
       *
       */
      public <V> ScheduledFuture<V> schedule(final Callable<V> callable, final long delay, final TimeUnit unit) {
          return executorService.schedule(callable, delay, unit);
      }
  
      /**
       * Creates and executes a one-shot action that becomes enabled after the given delay.
      * @param command the task to execute.
      * @param delay the time from now to delay execution.
      * @param unit the time unit of the delay parameter.
      * @return a ScheduledFuture representing pending completion of the task and whose get() method will return null
      * upon completion.
      */
     public ScheduledFuture<?> schedule(final Runnable command, final long delay, final TimeUnit unit) {
         return executorService.schedule(command, delay, unit);
     }
 
 
     /**
      * Creates and executes an action that first based on a cron expression.
      * @param cronExpression the cron expression describing the schedule.
      * @param command The Runnable to run,
      * @return a ScheduledFuture representing the next time the command will run.
      */
     public CronScheduledFuture<?> scheduleWithCron(final CronExpression cronExpression, final Runnable command) {
         final CronRunnable runnable = new CronRunnable(command, cronExpression);
         final ScheduledFuture<?> future = schedule(runnable, nextFireInterval(cronExpression), TimeUnit.MILLISECONDS);
         final CronScheduledFuture<?> cronScheduledFuture = new CronScheduledFuture<>(future);
         runnable.setScheduledFuture(cronScheduledFuture);
         return cronScheduledFuture;
     }
 
 
     /**
      * Creates and executes a periodic action that becomes enabled first after the given initial delay, and subsequently
      * with the given period; that is executions will commence after initialDelay then initialDelay+period,
      * then initialDelay + 2 * period, and so on.
      * @param command the task to execute.
      * @param initialDelay the time to delay first execution.
      * @param period the period between successive executions.
      * @param unit the time unit of the initialDelay and period parameters.
      * @return a ScheduledFuture representing pending completion of the task, and whose get() method will throw an
      * exception upon cancellation
      */
     public ScheduledFuture<?> scheduleAtFixedRate(final Runnable command, final long initialDelay, final long period, final TimeUnit unit) {
         return executorService.scheduleAtFixedRate(command, initialDelay, period, unit);
     }
 
     /**
      * Creates and executes a periodic action that becomes enabled first after the given initial delay, and
      * subsequently with the given delay between the termination of one execution and the commencement of the next.
      * @param command the task to execute.
      * @param initialDelay the time to delay first execution.
      * @param delay the delay between the termination of one execution and the commencement of the next.
      * @param unit the time unit of the initialDelay and delay parameters
      * @return a ScheduledFuture representing pending completion of the task, and whose get() method will throw an
      * exception upon cancellation
      */
     public ScheduledFuture<?> scheduleWithFixedDelay(final Runnable command, final long initialDelay, final long delay, final TimeUnit unit) {
         return executorService.scheduleWithFixedDelay(command, initialDelay, delay, unit);
     }
 
     private class CronRunnable implements Runnable {
 
         private final CronExpression cronExpression;
         private final Runnable runnable;
         private CronScheduledFuture<?> scheduledFuture;
 
         public CronRunnable(final Runnable runnable, final CronExpression cronExpression) {
             this.cronExpression = cronExpression;
             this.runnable = runnable;
         }
 
         public void setScheduledFuture(final CronScheduledFuture<?> future) {
             this.scheduledFuture = future;
         }
 
         @Override
         public void run() {
             try {
                 runnable.run();
             } catch(final Throwable ex) {
                 LOGGER.error("Error running command", ex);
             } finally {
                 final ScheduledFuture<?> future = schedule(this, nextFireInterval(cronExpression), TimeUnit.MILLISECONDS);
                 scheduledFuture.setScheduledFuture(future);
             }
         }
     }
 
     private long nextFireInterval(final CronExpression cronExpression) {
         final Date now = new Date();
         final Date fireDate = cronExpression.getNextValidTimeAfter(now);
         return fireDate.getTime() - now.getTime();
     }
 
 }