//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

//

#pragma once

#include "monitoring/statistics_impl.h"

#include "rocksdb/system_clock.h"

namespace ROCKSDB_NAMESPACE {

// Auto-scoped.

// When statistics is not nullptr, records the measured time into any enabled

// histograms supplied to the constructor. A histogram argument may be omitted

// by setting it to Histograms::HISTOGRAM_ENUM_MAX. It is also saved into

// *elapsed if the pointer is not nullptr and overwrite is true, it will be

// added to *elapsed if overwrite is false.

class StopWatch {

 public:

  StopWatch(SystemClock* clock, Statistics* statistics,

            const uint32_t hist_type_1,

            const uint32_t hist_type_2 = Histograms::HISTOGRAM_ENUM_MAX,

            uint64_t* elapsed = nullptr, bool overwrite = true,

            bool delay_enabled = false)

      : clock_(clock),

        statistics_(statistics),

        hist_type_1_(statistics && statistics->HistEnabledForType(hist_type_1)

                         ? hist_type_1

                         : Histograms::HISTOGRAM_ENUM_MAX),

        hist_type_2_(statistics && statistics->HistEnabledForType(hist_type_2)

                         ? hist_type_2

                         : Histograms::HISTOGRAM_ENUM_MAX),

        elapsed_(elapsed),

        overwrite_(overwrite),

        stats_enabled_(statistics &&

                       statistics->get_stats_level() >

                           StatsLevel::kExceptTimers &&

                       (hist_type_1_ != Histograms::HISTOGRAM_ENUM_MAX ||

                        hist_type_2_ != Histograms::HISTOGRAM_ENUM_MAX)),

        delay_enabled_(delay_enabled),

        total_delay_(0),

        delay_start_time_(0),

        start_time_((stats_enabled_ || elapsed != nullptr) ? clock->NowMicros()

                                                           : 0) {}

  ~StopWatch() {

    if (elapsed_) {

      if (overwrite_) {

        *elapsed_ = clock_->NowMicros() - start_time_;

      } else {

        *elapsed_ += clock_->NowMicros() - start_time_;

      }

    }

    if (elapsed_ && delay_enabled_) {

      *elapsed_ -= total_delay_;

    }

    if (stats_enabled_) {

      const auto time = (elapsed_ != nullptr)

                            ? *elapsed_

                            : (clock_->NowMicros() - start_time_);

      if (hist_type_1_ != Histograms::HISTOGRAM_ENUM_MAX) {

        statistics_->reportTimeToHistogram(hist_type_1_, time);

      }

      if (hist_type_2_ != Histograms::HISTOGRAM_ENUM_MAX) {

        statistics_->reportTimeToHistogram(hist_type_2_, time);

      }

    }

  }

  void DelayStart() {

    // if delay_start_time_ is not 0, it means we are already tracking delay,

    // so delay_start_time_ should not be overwritten

    if (elapsed_ && delay_enabled_ && delay_start_time_ == 0) {

      delay_start_time_ = clock_->NowMicros();

    }

  }

  void DelayStop() {

    if (elapsed_ && delay_enabled_ && delay_start_time_ != 0) {

      total_delay_ += clock_->NowMicros() - delay_start_time_;

    }

    // reset to 0 means currently no delay is being tracked, so two consecutive

    // calls to DelayStop will not increase total_delay_

    delay_start_time_ = 0;

  }

  uint64_t GetDelay() const { return delay_enabled_ ? total_delay_ : 0; }

  uint64_t start_time() const { return start_time_; }

 private:

  SystemClock* clock_;

  Statistics* statistics_;

  const uint32_t hist_type_1_;

  const uint32_t hist_type_2_;

  uint64_t* elapsed_;

  bool overwrite_;

  bool stats_enabled_;

  bool delay_enabled_;

  uint64_t total_delay_;

  uint64_t delay_start_time_;

  const uint64_t start_time_;

};

// a nano second precision stopwatch

class StopWatchNano {

 public:

  explicit StopWatchNano(SystemClock* clock, bool auto_start = false)

      : clock_(clock), start_(0) {

    if (auto_start) {

      Start();

    }

  }

  void Start() { start_ = clock_->NowNanos(); }

  uint64_t ElapsedNanos(bool reset = false) {

    auto now = clock_->NowNanos();

    auto elapsed = now - start_;

    if (reset) {

      start_ = now;

    }

    return elapsed;

  }

  uint64_t ElapsedNanosSafe(bool reset = false) {

    return (clock_ != nullptr) ? ElapsedNanos(reset) : 0U;

  }

  bool IsStarted() { return start_ != 0; }

 private:

  SystemClock* clock_;

  uint64_t start_;

};

}  // namespace ROCKSDB_NAMESPACE