System Time Offset Implementation (#1101)

* System Time Offset Implementation

* Addressed @Thog's comments

* Addressed JD's comments

* Addressed @Thog's and @AcK77's comments

* formatting correction

2 files changed, 32 insertions, 2 deletions

diff --git a/Ryujinx.HLE/HOS/Horizon.cs b/Ryujinx.HLE/HOS/Horizon.cs
index f6021ec7..ccb67edf 100644
--- a/Ryujinx.HLE/HOS/Horizon.cs
+++ b/Ryujinx.HLE/HOS/Horizon.cs
@@ -9,6 +9,7 @@ using LibHac.Ns;
 using LibHac.Spl;
 using Ryujinx.Common.Configuration;
 using Ryujinx.Common.Logging;
+using Ryujinx.Configuration;
 using Ryujinx.HLE.FileSystem.Content;
 using Ryujinx.HLE.HOS.Font;
 using Ryujinx.HLE.HOS.Kernel.Common;
@@ -224,8 +225,24 @@ namespace Ryujinx.HLE.HOS
             // We assume the rtc is system time.
             TimeSpanType systemTime = TimeSpanType.FromSeconds((long)rtcValue);
 
+            // Configure and setup internal offset
+            TimeSpanType internalOffset = TimeSpanType.FromSeconds(ConfigurationState.Instance.System.SystemTimeOffset);
+            
+            TimeSpanType systemTimeOffset = new TimeSpanType(systemTime.NanoSeconds + internalOffset.NanoSeconds);
+
+            if (systemTime.IsDaylightSavingTime() && !systemTimeOffset.IsDaylightSavingTime())
+            {
+                internalOffset = internalOffset.AddSeconds(3600L);
+            }
+            else if (!systemTime.IsDaylightSavingTime() && systemTimeOffset.IsDaylightSavingTime())
+            {
+                internalOffset = internalOffset.AddSeconds(-3600L);
+            }
+
+            internalOffset = new TimeSpanType(-internalOffset.NanoSeconds);
+
             // First init the standard steady clock
-            TimeServiceManager.Instance.SetupStandardSteadyClock(null, clockSourceId, systemTime, TimeSpanType.Zero, TimeSpanType.Zero, false);
+            TimeServiceManager.Instance.SetupStandardSteadyClock(null, clockSourceId, systemTime, internalOffset, TimeSpanType.Zero, false);
             TimeServiceManager.Instance.SetupStandardLocalSystemClock(null, new SystemClockContext(), systemTime.ToSeconds());
 
             if (NxSettings.Settings.TryGetValue("time!standard_network_clock_sufficient_accuracy_minutes", out object standardNetworkClockSufficientAccuracyMinutes))
diff --git a/Ryujinx.HLE/HOS/Services/Time/Clock/Types/TimeSpanType.cs b/Ryujinx.HLE/HOS/Services/Time/Clock/Types/TimeSpanType.cs
index c336ad41..89497d82 100644
--- a/Ryujinx.HLE/HOS/Services/Time/Clock/Types/TimeSpanType.cs
+++ b/Ryujinx.HLE/HOS/Services/Time/Clock/Types/TimeSpanType.cs
@@ -1,4 +1,5 @@
-using System.Runtime.InteropServices;
+using System;
+using System.Runtime.InteropServices;
 
 namespace Ryujinx.HLE.HOS.Services.Time.Clock
 {
@@ -9,6 +10,8 @@ namespace Ryujinx.HLE.HOS.Services.Time.Clock
 
         public static readonly TimeSpanType Zero = new TimeSpanType(0);
 
+        private static readonly DateTime UnixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
         public long NanoSeconds;
 
         public TimeSpanType(long nanoSeconds)
@@ -21,6 +24,16 @@ namespace Ryujinx.HLE.HOS.Services.Time.Clock
             return NanoSeconds / NanoSecondsPerSecond;
         }
 
+        public TimeSpanType AddSeconds(long seconds)
+        {
+            return new TimeSpanType(NanoSeconds + (seconds * NanoSecondsPerSecond));
+        }
+
+        public bool IsDaylightSavingTime()
+        {
+            return UnixEpoch.AddSeconds(ToSeconds()).ToLocalTime().IsDaylightSavingTime();
+        }
+
         public static TimeSpanType FromSeconds(long seconds)
         {
             return new TimeSpanType(seconds * NanoSecondsPerSecond);