From a2fa0c11cb56c7265322f6a3db5caebec7c96c96 Mon Sep 17 00:00:00 2001
From: Claudio Schaad <c.schaad@pog.ch>
Date: Sat, 6 Sep 2025 21:37:59 +0200
Subject: [PATCH] Fix google calendar time zone

---
 .github/copilot-instructions.md   |  7 +++++++
 Services/ConfigurationService.cs  | 11 ++++++++---
 Services/GoogleCalendarService.cs | 18 +++++++-----------
 3 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 467dd12..6fa9d76 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -170,6 +170,13 @@ void Foo(params IReadOnlyList<string> values) => // actual implementation here.`
 - Use proper null checks in equality methods
 - Consider `ReferenceEquals` optimization for reference types
 
+### Date, Time and TimeZone
+- Don't use DateTime for a date with time, use DateTimeOffset instead
+- When only a date is needed, use DateOnly
+- When only a time is needed, use TimeOnly
+- Always use a specific local timezone for the DateTimeOffset
+- If nothing specified, use Europe/Zurich
+
 ### Architecture
 - Proper separation of concerns
 - Following established patterns in the codebase
diff --git a/Services/ConfigurationService.cs b/Services/ConfigurationService.cs
index a4c7cac..aa2fe61 100644
--- a/Services/ConfigurationService.cs
+++ b/Services/ConfigurationService.cs
@@ -5,7 +5,7 @@ namespace ShiftScheduler.Services
 {
     public interface IConfigurationService
     {
-        string GetTimeZone();
+        (DateTimeOffset StartTime, DateTimeOffset EndTime) GetZurichTime(DateOnly date, string timeRange);
         ApplicationConfiguration GetConfiguration();
         void UpdateConfiguration(ApplicationConfiguration configuration);
         Task<string> ExportConfigurationAsync();
@@ -32,9 +32,14 @@ namespace ShiftScheduler.Services
 
         private readonly TimeZoneInfo localTimeZone = TimeZoneInfo.FindSystemTimeZoneById("Europe/Zurich");
 
-        public string GetTimeZone()
+        public (DateTimeOffset StartTime, DateTimeOffset EndTime) GetZurichTime(DateOnly date, string timeRange)
         {
-            return localTimeZone.Id;
+            var times = timeRange.Split('-'); ;
+            var startTime = TimeOnly.Parse(times[0]);
+            var endTime = TimeOnly.Parse(times[1]);
+            
+            TimeSpan offset = localTimeZone.GetUtcOffset(DateTime.UtcNow);
+            return (new DateTimeOffset(date, startTime, offset), new DateTimeOffset(date, endTime, offset));
         }
 
         public ConfigurationService(ApplicationConfiguration initialConfiguration)
diff --git a/Services/GoogleCalendarService.cs b/Services/GoogleCalendarService.cs
index 5c7186c..4fc9312 100644
--- a/Services/GoogleCalendarService.cs
+++ b/Services/GoogleCalendarService.cs
@@ -101,24 +101,22 @@ public class GoogleCalendarService(IHttpContextAccessor httpContextAccessor, ICo
         // Create morning event if it exists
         if (!string.IsNullOrEmpty(shift.MorningTime))
         {
-            var morningEvent = CreateEventFromShift(shift, date, shift.MorningTime, shiftWithTransport.MorningTransport);
+            var (startTime, endTime) = configurationService.GetZurichTime(DateOnly.FromDateTime(date), shift.MorningTime);
+            var morningEvent = CreateEventFromShift(shift, startTime, endTime, shiftWithTransport.MorningTransport);
             await ExecuteWithRetryAsync(async () => await service.Events.Insert(morningEvent, calendarId).ExecuteAsync());
         }
 
         // Create afternoon event if it exists
         if (!string.IsNullOrEmpty(shift.AfternoonTime))
         {
-            var afternoonEvent = CreateEventFromShift(shift, date, shift.AfternoonTime, shiftWithTransport.AfternoonTransport);
+            var (startTime, endTime) = configurationService.GetZurichTime(DateOnly.FromDateTime(date), shift.AfternoonTime);
+            var afternoonEvent = CreateEventFromShift(shift, startTime, endTime, shiftWithTransport.AfternoonTransport);
             await ExecuteWithRetryAsync(async () => await service.Events.Insert(afternoonEvent, calendarId).ExecuteAsync());
         }
     }
 
-    private Event CreateEventFromShift(Shift shift, DateTime date, string timeRange, TransportConnection? transport)
+    private Event CreateEventFromShift(Shift shift, DateTimeOffset startTime, DateTimeOffset endTime, TransportConnection? transport)
     {
-        var times = timeRange.Split('-');
-        var startTime = date.Add(TimeSpan.Parse(times[0]));
-        var endTime = date.Add(TimeSpan.Parse(times[1]));
-        
         var summary = $"{shift.Name}";
         var description = "";
 
@@ -134,13 +132,11 @@ public class GoogleCalendarService(IHttpContextAccessor httpContextAccessor, ICo
             Description = description,
             Start = new EventDateTime
             {
-                DateTimeDateTimeOffset = startTime,
-                TimeZone = configurationService.GetTimeZone()
+                DateTimeDateTimeOffset = startTime
             },
             End = new EventDateTime
             {
-                DateTimeDateTimeOffset = endTime,
-                TimeZone = configurationService.GetTimeZone()
+                DateTimeDateTimeOffset = endTime
             },
             ExtendedProperties = new Event.ExtendedPropertiesData
             {