time.h

#ifndef SOURCEMETA_CORE_TIME_H_
#define SOURCEMETA_CORE_TIME_H_
 
#ifndef SOURCEMETA_CORE_TIME_EXPORT
#include <sourcemeta/core/time_export.h>
#endif
 
#include <array>       // std::array
#include <cassert>     // assert
#include <chrono>      // std::chrono::system_clock::time_point
#include <cstdint>     // std::uint8_t, std::uint16_t
#include <optional>    // std::optional
#include <string>      // std::string
#include <string_view> // std::string_view

 
namespace sourcemeta::core {

SOURCEMETA_CORE_TIME_EXPORT
auto to_imf_fixdate(const std::chrono::system_clock::time_point time)
    -> std::string;

SOURCEMETA_CORE_TIME_EXPORT
auto from_imf_fixdate(const std::string_view value) noexcept
    -> std::optional<std::chrono::system_clock::time_point>;

SOURCEMETA_CORE_TIME_EXPORT
auto to_rfc850_date(const std::chrono::system_clock::time_point time)
    -> std::string;

SOURCEMETA_CORE_TIME_EXPORT
auto from_rfc850_date(const std::string_view value) noexcept
    -> std::optional<std::chrono::system_clock::time_point>;

SOURCEMETA_CORE_TIME_EXPORT
auto to_asctime(const std::chrono::system_clock::time_point time)
    -> std::string;

SOURCEMETA_CORE_TIME_EXPORT
auto from_asctime(const std::string_view value) noexcept
    -> std::optional<std::chrono::system_clock::time_point>;

SOURCEMETA_CORE_TIME_EXPORT
auto to_iso8601_basic(const std::chrono::system_clock::time_point time)
    -> std::string;

SOURCEMETA_CORE_TIME_EXPORT
auto from_iso8601_basic(const std::string_view value) noexcept
    -> std::optional<std::chrono::system_clock::time_point>;

SOURCEMETA_CORE_TIME_EXPORT
auto from_unix_timestamp(const std::chrono::duration<double> seconds) noexcept
    -> std::optional<std::chrono::system_clock::time_point>;

SOURCEMETA_CORE_TIME_EXPORT
auto to_unix_timestamp(
    const std::chrono::system_clock::time_point time) noexcept
    -> std::chrono::duration<double>;

SOURCEMETA_CORE_TIME_EXPORT
auto clock_shift_backward(const std::chrono::system_clock::time_point time,
                          const std::chrono::seconds span) noexcept
    -> std::chrono::system_clock::time_point;

SOURCEMETA_CORE_TIME_EXPORT
auto clock_shift_forward(const std::chrono::system_clock::time_point time,
                         const std::chrono::seconds span) noexcept
    -> std::chrono::system_clock::time_point;

SOURCEMETA_CORE_TIME_EXPORT
auto is_rfc3339_datetime(const std::string_view value) -> bool;

SOURCEMETA_CORE_TIME_EXPORT
auto is_rfc3339_fulldate(const std::string_view value) -> bool;

SOURCEMETA_CORE_TIME_EXPORT
auto is_rfc3339_fulltime(const std::string_view value) -> bool;

SOURCEMETA_CORE_TIME_EXPORT
auto is_rfc3339_partialtime_no_secfrac(const std::string_view value) -> bool;

SOURCEMETA_CORE_TIME_EXPORT
auto is_rfc3339_duration(const std::string_view value) -> bool;

inline constexpr auto is_leap_year(const std::uint16_t year) -> bool {
  return (year % 4 == 0) && (year % 100 != 0 || year % 400 == 0);
}

inline constexpr auto max_day_in_month(const std::uint8_t month,
                                       const std::uint16_t year)
    -> std::uint8_t {
  assert(month >= 1 && month <= 12);
  constexpr std::array<std::uint8_t, 13> days{
      {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};
  if (month == 2 && is_leap_year(year)) {
    return 29;
  }
  return days[month];
}
 
} // namespace sourcemeta::core
 
#endif