From 452954dc1f375aeedbccade53188b4a8b6ad82f1 Mon Sep 17 00:00:00 2001
From: Martchus <martchus@gmx.net>
Date: Wed, 19 Apr 2017 21:48:23 +0200
Subject: [PATCH] Add DateTime::exactGmtNow()

* Provides more precise wall-clock time
* Only available under UNIX so far
---
 chrono/datetime.cpp   | 21 +++++++++++++++++++--
 chrono/datetime.h     | 14 ++++++++++++++
 tests/chronotests.cpp |  6 ++++++
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/chrono/datetime.cpp b/chrono/datetime.cpp
index a5cdce3..ef5c50c 100644
--- a/chrono/datetime.cpp
+++ b/chrono/datetime.cpp
@@ -7,6 +7,10 @@
 #include <iomanip>
 #include <stdexcept>
 
+#if defined(PLATFORM_UNIX)
+# include <time.h>
+#endif
+
 using namespace std;
 using namespace ChronoUtilities;
 using namespace ConversionUtilities;
@@ -49,7 +53,7 @@ inline bool inRangeExclMax(num1 val, num2 min, num3 max)
  */
 
 /*!
- * \brief Constructs a new DateTime object with the local time from the specified \a timeStamp.
+ * \brief Constructs a new DateTime object with the local time from the specified UNIX \a timeStamp.
  */
 DateTime DateTime::fromTimeStamp(time_t timeStamp)
 {
@@ -63,7 +67,7 @@ DateTime DateTime::fromTimeStamp(time_t timeStamp)
 }
 
 /*!
- * \brief Constructs a new DateTime object with the GMT time from the specified \a timeStamp.
+ * \brief Constructs a new DateTime object with the GMT time from the specified UNIX \a timeStamp.
  */
 DateTime DateTime::fromTimeStampGmt(time_t timeStamp)
 {
@@ -286,6 +290,19 @@ const char *DateTime::printDayOfWeek(DayOfWeek dayOfWeek, bool abbreviation)
     return "";
 }
 
+#if defined(PLATFORM_UNIX)
+/*!
+ * \brief Returns a DateTime object that is set to the current date and time on this computer, expressed as the GMT time.
+ * \remarks
+ */
+DateTime DateTime::exactGmtNow()
+{
+    struct timespec t;
+    clock_gettime(CLOCK_REALTIME, &t);
+    return DateTime(DateTime::unixEpochStart().totalTicks() + static_cast<uint64>(t.tv_sec) * TimeSpan::ticksPerSecond + static_cast<uint64>(t.tv_nsec) / 100);
+}
+#endif
+
 /*!
  * \brief Converts the given date expressed in \a year, \a month and \a day to ticks.
  */
diff --git a/chrono/datetime.h b/chrono/datetime.h
index a7fc363..1d98bc8 100644
--- a/chrono/datetime.h
+++ b/chrono/datetime.h
@@ -89,8 +89,12 @@ public:
     static const char *printDayOfWeek(DayOfWeek dayOfWeek, bool abbreviation = false);
 
     static constexpr DateTime eternity();
+    static constexpr DateTime unixEpochStart();
     static DateTime now();
     static DateTime gmtNow();
+#if defined(PLATFORM_UNIX)
+    static DateTime exactGmtNow();
+#endif
     constexpr static bool isLeapYear(int year);
     static int daysInMonth(int year, int month);
 
@@ -352,8 +356,17 @@ constexpr inline DateTime DateTime::eternity()
     return DateTime(std::numeric_limits<decltype(m_ticks)>::max());
 }
 
+/*!
+ * \brief Returns the DateTime object for the "1970-01-01T00:00:00Z".
+ */
+constexpr inline DateTime DateTime::unixEpochStart()
+{
+    return DateTime(621355968000000000);
+}
+
 /*!
  * \brief Returns a DateTime object that is set to the current date and time on this computer, expressed as the local time.
+ * \remarks The time might be rounded to full seconds. Use exactGmtNow() for better precision.
  */
 inline DateTime DateTime::now()
 {
@@ -362,6 +375,7 @@ inline DateTime DateTime::now()
 
 /*!
  * \brief Returns a DateTime object that is set to the current date and time on this computer, expressed as the GMT time.
+ * \remarks The time might be rounded to full seconds. Use exactGmtNow() for better precision.
  */
 inline DateTime DateTime::gmtNow()
 {
diff --git a/tests/chronotests.cpp b/tests/chronotests.cpp
index 68d46b1..c7c3726 100644
--- a/tests/chronotests.cpp
+++ b/tests/chronotests.cpp
@@ -71,6 +71,12 @@ void ChronoTests::testDateTime()
     CPPUNIT_ASSERT_THROW(TimeSpan::fromString("2012-02-29 15:34:34:20.033"), ConversionException);
     const auto test3 = DateTime::fromIsoString("2016-08-29T21:32:31.125+02:00");
     CPPUNIT_ASSERT_EQUAL("2016-08-29T21:32:31.125+02:00"s, test3.first.toIsoString(test3.second));
+
+    // test now() and exactNow() (or at least whether both behave the same)
+#if defined(PLATFORM_UNIX)
+    const auto delta = DateTime::gmtNow() - DateTime::exactGmtNow();
+    CPPUNIT_ASSERT(delta < TimeSpan::fromSeconds(2) && delta > TimeSpan::fromSeconds(-2));
+#endif
 }
 
 /*!