text: /*
     +----------------------------------------------------------------------+
     | HipHop for PHP                                                       |
     +----------------------------------------------------------------------+
     | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
     +----------------------------------------------------------------------+
     | This source file is subject to version 3.01 of the PHP license,      |
     | that is bundled with this package in the file LICENSE, and is        |
     | available through the world-wide-web at the following url:           |
     | http://www.php.net/license/3_01.txt                                  |
     | If you did not receive a copy of the PHP license and are unable to   |
     | obtain it through the world-wide-web, please send a note to          |
     | license@php.net so we can mail you a copy immediately.               |
     +----------------------------------------------------------------------+
  */
  
  #ifndef incl_HPHP_HOST_HEALTH_MONITOR_TYPES_H_
  #define incl_HPHP_HOST_HEALTH_MONITOR_TYPES_H_
  
  #include <string>
  
  #include <folly/Likely.h>
  
  namespace HPHP {
  ////////////////////////////////////////////////////////////////////////////////
  
  /*
   * The enum type for describing various system health level.  The
   * system health monitor will expose one of the listed health level.
   *
   * Beware if you change the order or the numerical values, as we
   * assume smaller numbers indicating better health condition here.
   */
  enum class HealthLevel {
    Bold = 0,
    Moderate = 1,
    Cautious = 2,
    NoMore = 3,
    BackOff = 4,
    NumLevels = 5                  // insert new values before NumLevels
  };
  
  /*
   * The interface of specific system metrics used by the system health
   * monitor.
   */
  struct IHealthMonitorMetric {
    virtual ~IHealthMonitorMetric() {}
    virtual HealthLevel evaluate() = 0;
    virtual bool enabled() = 0;
    void registerSelf();           // register the metric in the monitor
  };
  
  /*
   * The interface for observers which subscribe the output of the
   * system health monitor.
   */
  struct IHostHealthObserver {
    virtual ~IHostHealthObserver() {}
    virtual void notifyNewStatus(HealthLevel newStatus) = 0;
    virtual HealthLevel getHealthLevel() = 0;
  };
  
  /*
   * Helper function to convert HealthLevel enum value to integer number that is
   * bigger for better health condition.
   */
  inline int64_t healthLeveltToInt(HealthLevel level) {
    constexpr int32_t kMaxHealth = 100;
    // Smaller HealthLevel indicates better health condition, under
    // which this function returns a bigger number.
    static_assert(static_cast<int>(HealthLevel::Bold) == 0, "");
    constexpr int32_t kMaxLevel =
      static_cast<int32_t>(HealthLevel::NumLevels) - 1;
    if (LIKELY(level == HealthLevel::Bold)) {
      return kMaxHealth;
    }
    auto const result = kMaxHealth *
      (kMaxLevel - static_cast<int32_t>(level)) / kMaxLevel;
    return result;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  }
  
  #endif
  