the-biergarten-app/pipeline/includes/services/date_time_provider.h

#ifndef BIERGARTEN_PIPELINE_INCLUDES_SERVICES_DATE_TIME_PROVIDER_H_
#define BIERGARTEN_PIPELINE_INCLUDES_SERVICES_DATE_TIME_PROVIDER_H_

/**
 * @file services/date_time_provider.h
 * @brief Abstraction for UTC timestamp generation.
 */

#include <chrono>
#include <ctime>
#include <iomanip>
#include <sstream>
#include <stdexcept>
#include <string>

/**
 * @brief Interface for UTC timestamp providers.
 */
class IDateTimeProvider {
 public:
  /// @brief Virtual destructor for polymorphic cleanup.
  virtual ~IDateTimeProvider() = default;

  IDateTimeProvider() = default;
  IDateTimeProvider(const IDateTimeProvider&) = delete;
  IDateTimeProvider& operator=(const IDateTimeProvider&) = delete;
  IDateTimeProvider(IDateTimeProvider&&) = delete;
  IDateTimeProvider& operator=(IDateTimeProvider&&) = delete;

  /**
   * @brief Returns the current UTC timestamp in a file-safe format.
   *
   * @return UTC timestamp string.
   */
  virtual std::string GetUtcTimestamp() = 0;
};

/**
 * @brief Timestamp provider backed by the system clock.
 */
class SystemDateTimeProvider final : public IDateTimeProvider {
 public:
  std::string GetUtcTimestamp() override {
    constexpr int kFractionalSecondWidth = 6;

    const auto now = std::chrono::system_clock::now();
    const auto now_time = std::chrono::system_clock::to_time_t(now);
    const std::tm* utc_time_ptr = std::gmtime(&now_time);
    if (utc_time_ptr == nullptr) {
      throw std::runtime_error("Failed to format UTC timestamp");
    }

    const auto fractional_seconds =
        std::chrono::duration_cast<std::chrono::microseconds>(
            now.time_since_epoch()) %
        std::chrono::seconds(1);

    std::ostringstream output;
    output << std::put_time(utc_time_ptr, "%Y-%m-%dT%H-%M-%S");
    output << '.' << std::setw(kFractionalSecondWidth) << std::setfill('0')
           << fractional_seconds.count() << 'Z';
    return output.str();
  }
};

#endif  // BIERGARTEN_PIPELINE_INCLUDES_SERVICES_DATE_TIME_PROVIDER_H_