src/local_aggregation_1_1/civil_time_manager.h

// Copyright 2022 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_1_1_CIVIL_TIME_MANAGER_H_
#define COBALT_SRC_LOCAL_AGGREGATION_1_1_CIVIL_TIME_MANAGER_H_

#include "src/lib/util/datetime_util.h"
#include "src/public/lib/clock_interfaces.h"
#include "src/public/lib/statusor/status_macros.h"
#include "src/public/lib/statusor/statusor.h"
#include "src/registry/metric_definition.pb.h"

namespace cobalt::local_aggregation {

// A CivilTimeManager converts a specific initial time point to `TimeInfo`s for given time
// zones. It also provides and caches the `TimeInfo`s corresponding to time points at hourly
// increments before the initial time.
class CivilTimeManager {
 public:
  CivilTimeManager(std::chrono::system_clock::time_point initial_time,
                   const util::CivilTimeConverterInterface& civil_time_converter)
      : initial_time_(initial_time), civil_time_converter_(civil_time_converter) {
    cache_["UTC"][0] = util::TimeInfo::FromTimePointUtc(initial_time);
  }

  // Returns the `TimeInfo` at the initial time with respect to UTC.
  util::TimeInfo GetInitialUtc() { return cache_["UTC"][0]; }

  // Returns the `TimeInfo` at the initial time minus `past_hours`, with respect to the time zone
  // policy of `metric`.
  lib::statusor::StatusOr<util::TimeInfo> GetTimeInfo(int past_hours,
                                                      const MetricDefinition& metric) {
    std::string time_zone_id = GetTimeZoneId(metric);
    if (cache_[time_zone_id].count(past_hours) == 0) {
      CB_ASSIGN_OR_RETURN(util::TimeInfo time_info,
                          util::TimeInfo::FromTimePoint(initial_time_ - util::kOneHour * past_hours,
                                                        civil_time_converter_, metric));
      cache_[time_zone_id].try_emplace(past_hours, time_info);
      return time_info;
    }
    return cache_[time_zone_id][past_hours];
  }

 private:
  static std::string GetTimeZoneId(const MetricDefinition& metric) {
    switch (metric.time_zone_policy()) {
      case MetricDefinition::UTC:
        return "UTC";
      case MetricDefinition::LOCAL:
        return "LOCAL";
      case MetricDefinition::OTHER_TIME_ZONE:
        return metric.other_time_zone();
      default:
        return "";
    }
  }

  std::chrono::system_clock::time_point initial_time_;
  const util::CivilTimeConverterInterface& civil_time_converter_;
  // The top-level keys are time zone identifiers. For each time zone id, the entry at index `i`
  // is the TimeInfo corresponding to the hour ID of `initial_time_` minus `i` hours.
  std::map<std::string, std::map<int, util::TimeInfo>> cache_;
};

}  // namespace cobalt::local_aggregation

#endif  // COBALT_SRC_LOCAL_AGGREGATION_1_1_CIVIL_TIME_MANAGER_H_