/* -*- Mode: C++; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/*
 *   Copyright 2021 Couchbase, Inc.
 *
 *   Licensed 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.
 */

#include "logging_meter.hxx"

#include "couchbase/build_info.hxx"

#include "core/logger/logger.hxx"
#include "core/utils/json.hxx"
#include "noop_meter.hxx"

#include <gsl/assert>
#include <hdr/hdr_histogram.h>
#include <tao/json/value.hpp>

#include <memory>
#include <utility>

namespace couchbase::core::metrics
{
class logging_value_recorder : public couchbase::metrics::value_recorder
{
private:
  std::string name_;
  std::map<std::string, std::string> tags_;
  hdr_histogram* histogram_{ nullptr };

  void initialize_histogram()
  {
    histogram_ = nullptr;
    hdr_init(/* minimum - 1 ns*/ 1,
             /* maximum - 30 s*/ 30'000'000'000LL,
             /* significant figures */ 3,
             /* pointer */ &histogram_);
    Expects(histogram_ != nullptr);
  }

public:
  logging_value_recorder(std::string name, std::map<std::string, std::string> tags)
    : value_recorder()
    , name_(std::move(name))
    , tags_(std::move(tags))
  {
    initialize_histogram();
  }

  logging_value_recorder(const logging_value_recorder& other)
    : value_recorder()
    , name_(other.name_)
    , tags_(other.tags_)
  {
    initialize_histogram();
  }

  logging_value_recorder(logging_value_recorder&& other) noexcept
    : value_recorder()
    , name_(std::move(other.name_))
    , tags_(std::move(other.tags_))
  {
    initialize_histogram();
  }

  auto operator=(const logging_value_recorder& other) -> logging_value_recorder&
  {
    if (this == &other) {
      return *this;
    }
    name_ = other.name_;
    tags_ = other.tags_;
    initialize_histogram();
    return *this;
  }

  auto operator=(logging_value_recorder&& other) noexcept -> logging_value_recorder&
  {
    if (this == &other) {
      return *this;
    }
    name_ = std::move(other.name_);
    tags_ = std::move(other.tags_);
    initialize_histogram();
    return *this;
  }

  ~logging_value_recorder() override
  {
    if (histogram_ != nullptr) {
      hdr_close(histogram_);
      histogram_ = nullptr;
    }
  }

  void record_value(std::int64_t value) override
  {
    if (histogram_ == nullptr) {
      return;
    }
    hdr_record_value_atomic(histogram_, value);
  }

  [[nodiscard]] auto emit() const -> tao::json::value
  {
    auto total_count = histogram_->total_count;
    auto val_50_0 = hdr_value_at_percentile(histogram_, 50.0);
    auto val_90_0 = hdr_value_at_percentile(histogram_, 90.0);
    auto val_99_0 = hdr_value_at_percentile(histogram_, 99.0);
    auto val_99_9 = hdr_value_at_percentile(histogram_, 99.9);
    auto val_100_0 = hdr_value_at_percentile(histogram_, 100.0);

    hdr_reset(histogram_);

    return {
      { "total_count", total_count },
      { "percentiles_us",
        {
          { "50.0", val_50_0 },
          { "90.0", val_90_0 },
          { "99.0", val_99_0 },
          { "99.9", val_99_9 },
          { "100.0", val_100_0 },
        } },
    };
  }
};

void
logging_meter::log_report() const
{
  tao::json::value report{
    {
      "meta",
      {

        { "emit_interval_s",
          std::chrono::duration_cast<std::chrono::seconds>(options_.emit_interval).count() },
#if COUCHBASE_CXX_CLIENT_DEBUG_BUILD
        { "emit_interval_ms", options_.emit_interval.count() },
#endif
      },
    },
  };
  for (const auto& [service, operations] : recorders_) {
    for (const auto& [operation, recorder] : operations) {
      report["operations"][service][operation] = recorder->emit();
    }
  }
  if (report.find("operations") != nullptr) {
    CB_LOG_INFO("Metrics: {}", utils::json::generate(report));
  }
}

logging_meter::logging_meter(asio::io_context& ctx, logging_meter_options options)
  : emit_report_(ctx)
  , options_(options)
{
}

logging_meter::~logging_meter()
{
  emit_report_.cancel();
  log_report();
}

void
logging_meter::rearm_reporter()
{
  emit_report_.expires_after(options_.emit_interval);
  emit_report_.async_wait([self = shared_from_this()](std::error_code ec) {
    if (ec == asio::error::operation_aborted) {
      return;
    }
    self->log_report();
    self->rearm_reporter();
  });
}

void
logging_meter::start()
{
  rearm_reporter();
}

void
logging_meter::stop()
{
  emit_report_.cancel();
}

auto
logging_meter::get_value_recorder(const std::string& name,
                                  const std::map<std::string, std::string>& tags)
  -> std::shared_ptr<couchbase::metrics::value_recorder>
{
  static std::shared_ptr<noop_value_recorder> noop_recorder{
    std::make_shared<noop_value_recorder>()
  };

  if (static const std::string meter_name = "db.couchbase.operations"; name != meter_name) {
    return noop_recorder;
  }

  static const std::string service_tag = "db.couchbase.service";
  auto service = tags.find(service_tag);
  if (service == tags.end()) {
    return noop_recorder;
  }

  static const std::string operation_tag = "db.operation";
  auto operation = tags.find(operation_tag);
  if (operation == tags.end()) {
    return noop_recorder;
  }

  std::scoped_lock lock(recorders_mutex_);
  auto& service_recorders = recorders_[service->second];

  auto recorder = service_recorders.find(operation->second);
  if (recorder != service_recorders.end()) {
    return recorder->second;
  }

  service_recorders.try_emplace(operation->second,
                                std::make_shared<logging_value_recorder>(operation->second, tags));
  recorder = service_recorders.find(operation->second);
  return recorder->second;
}
} // namespace couchbase::core::metrics
