// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COBALT_SRC_LOCAL_AGGREGATION_OBSERVATION_GENERATOR_H_
#define COBALT_SRC_LOCAL_AGGREGATION_OBSERVATION_GENERATOR_H_

#include <condition_variable>
#include <thread>

#include "src/lib/util/clock.h"
#include "src/local_aggregation/aggregation_procedures/aggregation_procedure.h"
#include "src/local_aggregation/backfill_manager.h"
#include "src/local_aggregation/civil_time_manager.h"
#include "src/local_aggregation/local_aggregate_storage/local_aggregate_storage.h"
#include "src/logger/observation_writer.h"
#include "src/logger/privacy_encoder.h"
#include "src/logger/project_context_factory.h"
#include "src/pb/metadata_builder.h"
#include "src/public/lib/clock_interfaces.h"
#include "src/public/lib/status.h"
#include "src/registry/report_definition.pb.h"
#include "src/system_data/system_data.h"

namespace cobalt::local_aggregation {

const uint32_t kDefaultBackfillManagerDays = 3;

// ObservationGenerator manages the background task that is responsible for generating observations
// and writing them to |observation_writer| on a regular schedule (~once per hour).
//
// There should be only one ObservationGenerator per system.
//
// Once the system clock has become accurate, the Start() method should be called with the
// SystemClockInterface exactly once. After that point, the ObservationGenerator will generate
// observations on a regular schedule until ShutDown() is called.
class ObservationGenerator {
 public:
  // Constructor for ObservationGenerator
  //
  // |aggregate_storage|: The file-backed storage for MetricAggregate objects.
  // |global_project_context_factory|: The current global registry.
  // |system_data|: Used to retrieve global SystemProfile data.
  // |observation_writer|: Used for writing generated observations to observation storage.
  // |privacy_encoder|: Used for encoding generated observations using privacy algorithms.
  // |civil_time_converter|: Converts a `time_point` to a civil time for a given time zone.
  // |generate_observations_with_current_system_profile|: If set, any missing system profile fields
  // should be taken from the current system profile.
  // |dont_backfill_empty_reports|: If set, reports that have never had any events will be skipped.
  // Only enable this in tests.
  ObservationGenerator(LocalAggregateStorage& aggregate_storage,
                       const logger::ProjectContextFactory& global_project_context_factory,
                       system_data::SystemDataInterface& system_data,
                       const logger::ObservationWriter& observation_writer,
                       std::unique_ptr<logger::PrivacyEncoder> privacy_encoder,
                       util::CivilTimeConverterInterface& civil_time_converter,
                       bool generate_observations_with_current_system_profile,
                       bool test_dont_backfill_empty_reports,
                       uint32_t backfill_manager_days = kDefaultBackfillManagerDays);

  // Start begins the background thread to generate observations on a fixed schedule. This method
  // should only be called once when the system clock has become accurate.
  void Start(util::SystemClockInterface* clock);

  // ShutDown halts the background thread, allowing the ObservationGenerator to be destroyed.
  void ShutDown();

  // GenerateObservationsOnce iterates through all of the metrics/reports in the global registry and
  // attempts to generate observations for them. Any generated observations will be written to the
  // |observation_writer_|.
  //
  // |system_time|: The most recent time that should be considered for any report. In general,
  //                GenerateObservationsOnce generates observations for time periods that have
  //                ended before `system_time`. For expedited reports, observations are also
  //                generated for the time period containing `system_time`.
  //
  // This method is called automatically in the background thread by 'GenerateObservations()', but
  // can be called manually while testing to avoid having to wait.
  Status GenerateObservationsOnce(std::chrono::system_clock::time_point system_time);

  void ResetInternalMetrics(logger::InternalMetrics* internal_metrics) {
    internal_metrics_.reset(internal_metrics);
  }

 private:
  void Run(util::SystemClockInterface* clock);

  // GenerateObservations calculates TimeInfos for UTC and LOCAL timezones, and passes them in to
  // InnerGenerateObservations().
  Status GenerateObservations(std::chrono::system_clock::time_point system_time,
                              std::chrono::steady_clock::time_point steady_time);

  // GenerateObservationsForReportAggregate generates all needed observations for a given
  // ReportAggregate, returning a Status::OK if all observations were generated.
  Status GenerateObservationsForReportAggregate(
      const LocalAggregateStorage::MetricAggregateRef& aggregate, ReportAggregate& report_aggregate,
      AggregationProcedure& procedure, CivilTimeManager* civil_time_mgr,
      const MetricDefinition& metric, const logger::MetricRef& metric_ref,
      const ReportDefinition& report);

  Status WriteObservations(ReportAggregate& report_aggregate, AggregationProcedure& procedure,
                           util::TimeInfo time_info, const logger::MetricRef& metric_ref,
                           const ReportDefinition& report,
                           const std::vector<std::unique_ptr<Observation>>& private_observations,
                           const SystemProfile& system_profile,
                           std::optional<uint64_t> commit_system_profile_hash);

  const SystemProfile* GetSystemProfile(uint64_t system_profile_hash,
                                        std::map<uint64_t, SystemProfile>* system_profile_cache,
                                        const LocalAggregateStorage::MetricAggregateRef& aggregate,
                                        const SystemProfile& current_filtered_system_profile) const;

  // Merge any unset fields in |to| with the values in |from|.
  static void MergeSystemProfiles(SystemProfile* to, const SystemProfile& from);

  LocalAggregateStorage& aggregate_storage_;
  const logger::ProjectContextFactory& global_project_context_factory_;
  system_data::SystemDataInterface& system_data_;
  const logger::ObservationWriter& observation_writer_;
  logger::InternalMetricsPtr internal_metrics_;
  std::unique_ptr<util::SteadyClockInterface> steady_clock_;
  std::chrono::steady_clock::time_point next_generate_obs_;
  std::chrono::seconds generate_obs_interval_;
  BackfillManager backfill_manager_;
  std::unique_ptr<logger::PrivacyEncoder> privacy_encoder_;
  util::CivilTimeConverterInterface& civil_time_converter_;
  bool generate_observations_with_current_system_profile_;
  bool test_dont_backfill_empty_reports_;

  std::thread worker_thread_;
  struct ProtectedFields {
    bool shut_down;

    std::condition_variable_any wakeup_notifier;
  };
  util::ProtectedFields<ProtectedFields> protected_fields_;
};

}  // namespace cobalt::local_aggregation

#endif  // COBALT_SRC_LOCAL_AGGREGATION_OBSERVATION_GENERATOR_H_