From 23572904d24560e1f171c9e0eabca693db197480 Mon Sep 17 00:00:00 2001
From: Kevin Matz <kevin@company235.com>
Date: Mon, 24 Apr 2023 13:04:49 -0400
Subject: [PATCH] timetag values to/from system time

---
 protocol/osc/argument.cpp | 50 +++++++++++++++++++++++++++++++++++++++
 protocol/osc/argument.h   |  4 ++++
 2 files changed, 54 insertions(+)

diff --git a/protocol/osc/argument.cpp b/protocol/osc/argument.cpp
index a77b6d8..fb72149 100644
--- a/protocol/osc/argument.cpp
+++ b/protocol/osc/argument.cpp
@@ -94,6 +94,56 @@ void blob::oStream(std::shared_ptr<bufferstream> stream) const
 }
 
 
+/**
+ * @brief timetag::time_point
+ * @return
+ *
+ * Convert \cite NTPv4 NTP timestamp to a system referanced time_point, with
+ * not greater than nanosecond resolution.
+ *
+ * \warning \cite Spec11 OSC Spec 1.1 leaves unchanged the reliance on the 64-bit NTP
+ * timestamp format.  The NTP Epoch 0 ends on February 7, 2036, at which time OSC
+ * timetag values will rollover.
+ */
+std::chrono::time_point<std::chrono::system_clock> timetag::time() const
+{
+  std::chrono::time_point<std::chrono::system_clock> time;  // POSIX epoch
+  time -= std::chrono::seconds(2208988800);                 // NTP epoch offset
+  time += std::chrono::seconds(seconds);
+  time += std::chrono::nanoseconds(
+      (uint32_t)(((double)fractional
+                   *(1.0/(double)std::numeric_limits<typeof(fractional)>::max()))
+                  *1e9));
+  /// \test validate time conversion from fractional seconds.
+  return time;
+}
+
+
+/**
+ * @brief timetag::setTime
+ * @param time
+ *
+ * Convert system referanced time_point to \cite NTPv4 NTP timestamps, with
+ * not greater than nanosecond resolution.
+ *
+ * \warning \cite Spec11 OSC Spec 1.1 leaves unchanged the reliance on the 64-bit NTP
+ * timestamp format.  The NTP Epoch 0 ends on February 7, 2036, at which time OSC
+ * timetag values will rollover.
+ */
+void timetag::setTime(std::chrono::time_point<std::chrono::system_clock> time)
+{
+  auto t = time.time_since_epoch();                         // POSIX epoch
+  auto s = std::chrono::duration_cast<std::chrono::seconds>(t);
+  auto f = std::chrono::duration_cast<std::chrono::nanoseconds>(t - s);
+  s += std::chrono::seconds(2208988800);                    // NTP epoch offset
+  seconds = s.count();
+  fractional = ((double)f.count()
+                *1e-9)
+               *(1.0/(double)std::numeric_limits<typeof(fractional)>::max());
+  /// \test validate time conversion to fractional seconds.
+}
+
+
 void character::iStream(std::shared_ptr<bufferstream> stream)
 {
   value = stream->readType<int32_t>();
diff --git a/protocol/osc/argument.h b/protocol/osc/argument.h
index 8777867..8f174ac 100644
--- a/protocol/osc/argument.h
+++ b/protocol/osc/argument.h
@@ -24,6 +24,7 @@
 #pragma once
 
 #include <bufferstream.h>
+#include <chrono>
 #include <vector>
 
 namespace OSC {
@@ -136,6 +137,9 @@ struct timetag
 {
   timetag() : Argument('t') {};
 
+  std::chrono::time_point<std::chrono::system_clock> time() const;
+  void setTime(std::chrono::time_point<std::chrono::system_clock> time = std::chrono::system_clock::now());
+
   virtual size_t streamSize() const override { return 8; }
   virtual void iStream(std::shared_ptr<bufferstream> stream) override { *stream >> value; }
   virtual void oStream(std::shared_ptr<bufferstream> stream) const override { *stream << value; }