/**
    * This file Copyright (c) 2013-2018 Magnolia International
    * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
    *
    *
    * This file is dual-licensed under both the Magnolia
    * Network Agreement and the GNU General Public License.
    * You may elect to use one or the other of these licenses.
    *
   * This file is distributed in the hope that it will be
   * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
   * implied warranty of MERCHANTABILITY or FITNESS FOR A
   * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
   * Redistribution, except as permitted by whichever of the GPL
   * or MNA you select, is prohibited.
   *
   * 1. For the GPL license (GPL), you can redistribute and/or
   * modify this file under the terms of the GNU General
   * Public License, Version 3, as published by the Free Software
   * Foundation.  You should have received a copy of the GNU
   * General Public License, Version 3 along with this program;
   * if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * 2. For the Magnolia Network Agreement (MNA), this file
   * and the accompanying materials are made available under the
   * terms of the MNA which accompanies this distribution, and
   * is available at http://www.magnolia-cms.com/mna.html
   *
   * Any modifications to this file must keep this entire header
   * intact.
   *
   */
  package info.magnolia.monitoring;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.inject.Singleton;
  
  /**
   * Allows to monitor the system.
   */
  @Singleton
  public class SystemMonitor {
  
      public static final String MEMORY_LIMIT_IS_REACHED_STRING_FORMAT = "Your server is currently low on memory. %s. Please try again later or contact your administrator if this happens frequently.";
  
      public static final String MEMORY_VALUES_STRING_FORMAT = "Memory values: max = {}mb, total = {}mb, free = {}mb -> remaining = {}mb / thresholds = {}mb or {}%";
  
      public static final long BYTE_TO_MEGABYTE_FACTOR = 1024 * 1024;
  
      public static final int MEMORY_THRESHOLD_PERCENTAGE = 10;
  
      public static final int MEMORY_THRESHOLD_IN_MB = 50;
  
      private final static Logger log = LoggerFactory.getLogger(SystemMonitor.class);
  
      /**
       * Evaluates whether the memory limit is reached. This is the case when system memory is absolutely below {@link #MEMORY_THRESHOLD_IN_MB} and relatively below {@link #MEMORY_THRESHOLD_PERCENTAGE}.
       *
       * @return whether the memory limit is reached or not.
       */
      public boolean isMemoryLimitReached() {
          Runtime runtime = Runtime.getRuntime();
          return isBelowAllThresholds(runtime.maxMemory() / BYTE_TO_MEGABYTE_FACTOR, runtime.totalMemory() / BYTE_TO_MEGABYTE_FACTOR, runtime.freeMemory() / BYTE_TO_MEGABYTE_FACTOR);
      }
  
      /**
       * @param maxMemoryInMb maximum amount the JVM can grow to
       * @param totalMemoryInMb current size of the JVM
       * @param freeMemoryInMb amount left of the current size
       */
      protected boolean isBelowAllThresholds(final long maxMemoryInMb, final long totalMemoryInMb, final long freeMemoryInMb) {
  
          final long remainingInMB = freeMemoryInMb + (maxMemoryInMb - totalMemoryInMb);
          final boolean isLowerThanThresholdInMB = remainingInMB < MEMORY_THRESHOLD_IN_MB;
          final boolean isLowerThanThresholdPercentage = (100 * remainingInMB / maxMemoryInMb) < MEMORY_THRESHOLD_PERCENTAGE;
          final boolean isMemoryLimitReached = isLowerThanThresholdInMB && isLowerThanThresholdPercentage;
  
          log.debug(MEMORY_VALUES_STRING_FORMAT, maxMemoryInMb, totalMemoryInMb, freeMemoryInMb, remainingInMB, MEMORY_THRESHOLD_IN_MB, MEMORY_THRESHOLD_PERCENTAGE);
  
          if (isMemoryLimitReached) {
              log.warn(MEMORY_VALUES_STRING_FORMAT, maxMemoryInMb, totalMemoryInMb, freeMemoryInMb, remainingInMB, MEMORY_THRESHOLD_IN_MB, MEMORY_THRESHOLD_PERCENTAGE);
          }
  
          return isMemoryLimitReached;
      }
  }