refactor: std::chrono support refactored for V2

src/core/include/units/chrono.h

@@ -23,35 +23,56 @@
 #pragma once
 
 #include <units/customization_points.h>
-// IWYU pragma: begin_exports
-#include <units/isq/si/time.h>
-#include <units/point_origin.h>
+#include <units/isq/space_and_time.h>
+#include <units/si/prefixes.h>
+#include <units/si/units.h>
 #include <chrono>
-// IWYU pragma: end_exports
 
 namespace units {
 
+namespace detail {
+
+template<typename Period>
+[[nodiscard]] inline consteval auto time_unit_from_chrono_period()
+{
+  using namespace si;
+
+  if constexpr (is_same_v<Period, std::chrono::nanoseconds::period>)
+    return nano<second>;
+  else if constexpr (is_same_v<Period, std::chrono::microseconds::period>)
+    return micro<second>;
+  else if constexpr (is_same_v<Period, std::chrono::milliseconds::period>)
+    return milli<second>;
+  else if constexpr (is_same_v<Period, std::chrono::seconds::period>)
+    return second;
+  else if constexpr (is_same_v<Period, std::chrono::minutes::period>)
+    return minute;
+  else if constexpr (is_same_v<Period, std::chrono::hours::period>)
+    return hour;
+  else if constexpr (is_same_v<Period, std::chrono::days::period>)
+    return day;
+  else
+    return mag<ratio{Period::num, Period::den}> * second;
+}
+
+}  // namespace detail
+
 template<typename Rep, typename Period>
 struct quantity_like_traits<std::chrono::duration<Rep, Period>> {
-private:
-  static constexpr auto mag = ::units::mag<ratio(Period::num, Period::den)>();
-public:
-  using dimension = isq::si::dim_time;
-  using unit = downcast_unit<dimension, mag>;
+  static constexpr auto reference = isq::duration[detail::time_unit_from_chrono_period<Period>()];
   using rep = Rep;
   [[nodiscard]] static constexpr rep number(const std::chrono::duration<Rep, Period>& q) { return q.count(); }
 };
 
 template<typename C>
-struct clock_origin : point_origin<isq::si::dim_time> {};
+struct chrono_point_origin : absolute_point_origin<isq::time> {
+  using clock = C;
+};
 
 template<typename C, typename Rep, typename Period>
 struct quantity_point_like_traits<std::chrono::time_point<C, std::chrono::duration<Rep, Period>>> {
-private:
-  static constexpr auto mag = ::units::mag<ratio(Period::num, Period::den)>();
-public:
-  using origin = clock_origin<C>;
-  using unit = downcast_unit<typename origin::dimension, mag>;
+  static constexpr auto reference = isq::time[detail::time_unit_from_chrono_period<Period>()];
+  static constexpr auto point_origin = chrono_point_origin<C>{};
   using rep = Rep;
   [[nodiscard]] static constexpr auto relative(const std::chrono::time_point<C, std::chrono::duration<Rep, Period>>& qp)
   {
@@ -59,42 +80,24 @@ public:
   }
 };
 
-namespace detail {
-
-template<typename C, typename Rep, typename Period>
-inline constexpr bool is_quantity_point_like<std::chrono::time_point<C, std::chrono::duration<Rep, Period>>> = true;
-
-constexpr std::intmax_t pow_10(std::intmax_t v)
+template<quantity_of<isq::time> Q>
+[[nodiscard]] constexpr auto to_chrono_duration(const Q& q)
 {
-  gsl_Expects(v > 0);
-  std::intmax_t res = 1;
-  for (std::intmax_t i = 0; i < v; i++) res *= 10;
-  return res;
+  constexpr auto canonical = detail::get_canonical_unit(Q::unit);
+  constexpr ratio r = as_ratio(canonical.mag);
+  return std::chrono::duration<typename Q::rep, std::ratio<r.num, r.den>>{q.number()};
 }
 
-template<ratio R>
-constexpr auto to_std_ratio_impl()
+template<quantity_point_of<isq::time> QP>
+  requires is_specialization_of<std::remove_const_t<decltype(QP::absolute_point_origin)>, chrono_point_origin>
+[[nodiscard]] constexpr auto to_chrono_time_point(const QP& qp)
 {
-  return std::ratio<R.num, R.den>{};
-}
-
-}  // namespace detail
-
-// TODO ICE below on gcc-11 when `ratio` is used instead of `auto`
-template<auto R>
-using to_std_ratio = decltype(detail::to_std_ratio_impl<R>());
-
-template<typename U, typename Rep>
-[[nodiscard]] constexpr auto to_std_duration(const quantity<isq::si::dim_time, U, Rep>& q)
-{
-  return std::chrono::duration<Rep, to_std_ratio<as_ratio(U::mag)>>(q.number());
-}
-
-template<typename C, typename U, typename Rep>
-[[nodiscard]] constexpr auto to_std_time_point(const quantity_point<clock_origin<C>, U, Rep>& qp)
-{
-  using ret_type = std::chrono::time_point<C, std::chrono::duration<Rep, to_std_ratio<as_ratio(U::mag)>>>;
-  return ret_type(to_std_duration(qp.relative()));
+  using clock = TYPENAME decltype(QP::absolute_point_origin)::clock;
+  using rep = TYPENAME QP::rep;
+  constexpr auto canonical = detail::get_canonical_unit(QP::unit);
+  constexpr ratio r = as_ratio(canonical.mag);
+  using ret_type = std::chrono::time_point<clock, std::chrono::duration<rep, std::ratio<r.num, r.den>>>;
+  return ret_type(to_std_duration(qp.absolute()));
 }
 
 }  // namespace units