outlook: correctly create events using UTC timezone

When creating an event, the timestamp's timezone was silently dropped and
replaced with the timezone of the local system. Timestamps returned by
outlook are in UTC, such that syncing from outlook to outlook resulted
in shifted events on non-UTC systems.

Explicitly convert timestamps to UTC to ensure correctness.

go.mod

@@ -14,7 +14,6 @@ require (
 	github.com/microcosm-cc/bluemonday v1.0.27
 	github.com/pkg/browser v0.0.0-20210911075715-681adbf594b8
 	github.com/stretchr/testify v1.9.0
-	github.com/thlib/go-timezone-local v0.0.3
 	github.com/urfave/cli/v2 v2.27.2
 	go.uber.org/ratelimit v0.3.1
 	golang.org/x/oauth2 v0.22.0

go.sum

@@ -120,8 +120,6 @@ github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8
 github.com/teambition/rrule-go v1.7.2/go.mod h1:mBJ1Ht5uboJ6jexKdNUJg2NcwP8uUMNvStWXlJD3MvU=
 github.com/teambition/rrule-go v1.8.2 h1:lIjpjvWTj9fFUZCmuoVDrKVOtdiyzbzc93qTmRVe/J8=
 github.com/teambition/rrule-go v1.8.2/go.mod h1:Ieq5AbrKGciP1V//Wq8ktsTXwSwJHDD5mD/wLBGl3p4=
-github.com/thlib/go-timezone-local v0.0.3 h1:ie5XtZWG5lQ4+1MtC5KZ/FeWlOKzW2nPoUnXYUbV/1s=
-github.com/thlib/go-timezone-local v0.0.3/go.mod h1:/Tnicc6m/lsJE0irFMA0LfIwTBo4QP7A8IfyIv4zZKI=
 github.com/urfave/cli/v2 v2.27.2 h1:6e0H+AkS+zDckwPCUrZkKX38mRaau4nL2uipkJpbkcI=
 github.com/urfave/cli/v2 v2.27.2/go.mod h1:g0+79LmHHATl7DAcHO99smiR/T7uGLw84w8Y42x+4eM=
 github.com/xrash/smetrics v0.0.0-20240312152122-5f08fbb34913 h1:+qGGcbkzsfDQNPPe9UDgpxAWQrhbbBXOYJFQDq/dtJw=
@@ -171,7 +169,6 @@ golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210616045830-e2b7044e8c71/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20210831042530-f4d43177bf5e/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.24.0 h1:Twjiwq9dn6R1fQcyiK+wQyHWfaz/BJB+YIpzU/Cv3Xg=
 golang.org/x/sys v0.24.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

internal/adapter/outlook_http/client.go

@@ -12,7 +12,6 @@ import (
 	"time"
 
 	"github.com/charmbracelet/log"
-	"github.com/thlib/go-timezone-local/tzlocal"
 
 	"github.com/inovex/CalendarSync/internal/models"
 )
@@ -190,16 +189,10 @@ func (o OutlookClient) eventToOutlookEvent(e models.Event) (oe Event) {
 	outlookEvent := Event{}
 	outlookEvent.Location.Name = e.Location
 
-	// microsoft expects iana time zone codes, but the go standard library returns abbreviations like "CET"
-	// NOTE: This may not work when events get imported from other time zones, i would expect golang to properly format the time strings correctly using the local runtime timezone
-	tzname, err := tzlocal.RuntimeTZ()
-	if err != nil {
-		tzname = "UTC"
-	}
-	outlookEvent.Start.DateTime = e.StartTime.Format(timeFormat)
-	outlookEvent.Start.TimeZone = tzname
-	outlookEvent.End.DateTime = e.EndTime.Format(timeFormat)
-	outlookEvent.End.TimeZone = tzname
+	outlookEvent.Start.DateTime = e.StartTime.UTC().Format(timeFormat)
+	outlookEvent.Start.TimeZone = "UTC"
+	outlookEvent.End.DateTime = e.EndTime.UTC().Format(timeFormat)
+	outlookEvent.End.TimeZone = "UTC"
 
 	outlookEvent.Subject = e.Title
 	outlookEvent.ID = e.ID