From 2896cd51562102af459138628199bf323ad9c274 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20M=C3=BCller?= <straightshoota@gmail.com>
Date: Thu, 21 Dec 2017 01:01:27 +0100
Subject: [PATCH] Implement Crystal::System::Time for win32

* `compute_utc_offset`: Always returns the **current** UTC offset for now.
  There seems to be no easy method to access UTC offset at an arbitrary
  point in time.
* `compute_utc_seconds_and_nanoseconds`: Precision is currently only
  100 nanoseconds because `FILE_TIME` has no higher resolution.
* `monotonic`
---
 src/crystal/system/win32/time.cr           | 45 +++++++++++++++++++++-
 src/lib_c/x86_64-windows-msvc/c/win_def.cr |  4 ++
 src/lib_c/x86_64-windows-msvc/c/win_nt.cr  |  2 +
 src/lib_c/x86_64-windows-msvc/c/winbase.cr | 34 ++++++++++++++++
 4 files changed, 83 insertions(+), 2 deletions(-)
 create mode 100644 src/lib_c/x86_64-windows-msvc/c/win_def.cr

diff --git a/src/crystal/system/win32/time.cr b/src/crystal/system/win32/time.cr
index 6755adb0a71a..55c6d147f39d 100644
--- a/src/crystal/system/win32/time.cr
+++ b/src/crystal/system/win32/time.cr
@@ -1,9 +1,50 @@
+require "c/winbase"
+require "winerror"
+
 module Crystal::System::Time
+  # Win32 epoch is 1601-01-01 00:00:00 UTC
+  WINDOWS_EPOCH_IN_SECONDS = 50_491_123_200_i64
+
+  # Resolution of FILETIME is 100 nanoseconds
+  NANOSECONDS_PER_FILETIME_TICK = 100
+
+  NANOSECONDS_PER_SECOND    = 1_000_000_000
+  FILETIME_TICKS_PER_SECOND = NANOSECONDS_PER_SECOND / NANOSECONDS_PER_FILETIME_TICK
+
+  # TODO: For now, this method returns the UTC offset currently in place, ignoring *seconds*.
   def self.compute_utc_offset(seconds : Int64) : Int32
-    raise NotImplementedError.new("Crystal::System::Time.compute_utc_offset")
+    ret = LibC.GetTimeZoneInformation(out zone_information)
+    raise WinError.new("GetTimeZoneInformation") if ret == -1
+
+    zone_information.bias.to_i32 * -60
   end
 
   def self.compute_utc_seconds_and_nanoseconds : {Int64, Int32}
-    raise NotImplementedError.new("Crystal::System::Time.compute_utc_seconds_and_nanoseconds")
+    # TODO: Needs a check if `GetSystemTimePreciseAsFileTime` is actually available (only >= Windows 8)
+    # and use `GetSystemTimeAsFileTime` as fallback.
+    LibC.GetSystemTimePreciseAsFileTime(out filetime)
+    since_epoch = (filetime.dwHighDateTime.to_u64 << 32) | filetime.dwLowDateTime.to_u64
+
+    seconds = (since_epoch / FILETIME_TICKS_PER_SECOND).to_i64 + WINDOWS_EPOCH_IN_SECONDS
+    nanoseconds = since_epoch.remainder(FILETIME_TICKS_PER_SECOND).to_i32 * NANOSECONDS_PER_FILETIME_TICK
+
+    {seconds, nanoseconds}
+  end
+
+  @@performance_frequency : Int64 = begin
+    ret = LibC.QueryPerformanceFrequency(out frequency)
+    if ret == 0
+      raise WinError.new("QueryPerformanceFrequency")
+    end
+
+    frequency
+  end
+
+  def self.monotonic : {Int64, Int32}
+    if LibC.QueryPerformanceCounter(out ticks) == 0
+      raise WinError.new("QueryPerformanceCounter")
+    end
+
+    {ticks / @@performance_frequency, (ticks.remainder(NANOSECONDS_PER_SECOND) * NANOSECONDS_PER_SECOND / @@performance_frequency).to_i32}
   end
 end
diff --git a/src/lib_c/x86_64-windows-msvc/c/win_def.cr b/src/lib_c/x86_64-windows-msvc/c/win_def.cr
new file mode 100644
index 000000000000..56258f7501fc
--- /dev/null
+++ b/src/lib_c/x86_64-windows-msvc/c/win_def.cr
@@ -0,0 +1,4 @@
+lib LibC
+  alias WORD = UInt16
+  alias BOOL = Int32
+end
diff --git a/src/lib_c/x86_64-windows-msvc/c/win_nt.cr b/src/lib_c/x86_64-windows-msvc/c/win_nt.cr
index bc378a4211e1..ab7aa9256a48 100644
--- a/src/lib_c/x86_64-windows-msvc/c/win_nt.cr
+++ b/src/lib_c/x86_64-windows-msvc/c/win_nt.cr
@@ -1,3 +1,5 @@
 lib LibC
   alias LPSTR = Char*
+  alias LONG = Int32
+  alias WCHAR = UInt16
 end
diff --git a/src/lib_c/x86_64-windows-msvc/c/winbase.cr b/src/lib_c/x86_64-windows-msvc/c/winbase.cr
index c1936a92259f..18586c8d5fa5 100644
--- a/src/lib_c/x86_64-windows-msvc/c/winbase.cr
+++ b/src/lib_c/x86_64-windows-msvc/c/winbase.cr
@@ -1,4 +1,5 @@
 require "c/win_nt"
+require "c/win_def"
 require "c/int_safe"
 
 lib LibC
@@ -13,4 +14,37 @@ lib LibC
 
   fun FormatMessageA(dwFlags : DWORD, lpSource : Void*, dwMessageId : DWORD, dwLanguageId : DWORD,
                      lpBuffer : LPSTR, nSize : DWORD, arguments : Void*) : DWORD
+
+  struct FILETIME
+    dwLowDateTime : DWORD
+    dwHighDateTime : DWORD
+  end
+
+  struct SYSTEMTIME
+    wYear : WORD
+    wMonth : WORD
+    wDayOfWeek : WORD
+    wDay : WORD
+    wHour : WORD
+    wMinute : WORD
+    wSecond : WORD
+    wMilliseconds : WORD
+  end
+
+  struct TIME_ZONE_INFORMATION
+    bias : LONG
+    standardName : StaticArray(WCHAR, 32)
+    standardDate : SYSTEMTIME
+    standardBias : LONG
+    daylightName : StaticArray(WCHAR, 32)
+    daylightDate : SYSTEMTIME
+    daylightBias : LONG
+  end
+
+  fun GetTimeZoneInformation(tz_info : TIME_ZONE_INFORMATION*) : DWORD
+  fun GetSystemTimeAsFileTime(time : FILETIME*)
+  fun GetSystemTimePreciseAsFileTime(time : FILETIME*)
+
+  fun QueryPerformanceCounter(performance_count : Int64*) : BOOL
+  fun QueryPerformanceFrequency(frequency : Int64*) : BOOL
 end