Use recurrence timezone for ics exports (#5206)

<!-- PR description-->

---

#### Does this PR need a docs update or release note?

- [x] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [ ] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #<issue>

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Handle the case where an email or event cannot be retrieved from Exchange due to an `ErrorCorruptData` error. Corso will skip over the item but report it in the backup summary.
 - Emails attached within other emails are now correctly exported
 - Gracefully handle email and post attachments without name when exporting to eml
+- Use correct timezone for event start and end times in Exchange exports (helps fix issues in relative recurrence patterns)
 
 ## [v0.19.0] (beta) - 2024-02-06
 

src/internal/converters/eml/eml_test.go

@@ -266,11 +266,11 @@ func (suite *EMLUnitSuite) TestConvert_eml_ics() {
 
 	assert.Equal(
 		t,
-		msg.GetCreatedDateTime().Format(ics.ICalDateTimeFormat),
+		msg.GetCreatedDateTime().Format(ics.ICalDateTimeFormatUTC),
 		event.GetProperty(ical.ComponentPropertyCreated).Value)
 	assert.Equal(
 		t,
-		msg.GetLastModifiedDateTime().Format(ics.ICalDateTimeFormat),
+		msg.GetLastModifiedDateTime().Format(ics.ICalDateTimeFormatUTC),
 		event.GetProperty(ical.ComponentPropertyLastModified).Value)
 
 	st, err := ics.GetUTCTime(
@@ -285,11 +285,11 @@ func (suite *EMLUnitSuite) TestConvert_eml_ics() {
 
 	assert.Equal(
 		t,
-		st.Format(ics.ICalDateTimeFormat),
+		st.Format(ics.ICalDateTimeFormatUTC),
 		event.GetProperty(ical.ComponentPropertyDtStart).Value)
 	assert.Equal(
 		t,
-		et.Format(ics.ICalDateTimeFormat),
+		et.Format(ics.ICalDateTimeFormatUTC),
 		event.GetProperty(ical.ComponentPropertyDtEnd).Value)
 
 	tos := msg.GetToRecipients()

src/internal/converters/ics/consts.go

@@ -166,3 +166,20 @@ var GraphTimeZoneToTZ = map[string]string{
 	"Yukon Standard Time":             "America/Whitehorse",
 	"tzone://Microsoft/Utc":           "Etc/UTC",
 }
+
+// Map from alternatives to the canonical time zone name
+// There mapping are currently generated by manually going on the
+// values in the GraphTimeZoneToTZ which is not available in the tzdb
+var CanonicalTimeZoneMap = map[string]string{
+	"Africa/Asmara":        "Africa/Asmera",
+	"Asia/Calcutta":        "Asia/Kolkata",
+	"Asia/Rangoon":         "Asia/Yangon",
+	"Asia/Saigon":          "Asia/Ho_Chi_Minh",
+	"Europe/Kiev":          "Europe/Kyiv",
+	"Europe/Warsaw":        "Europe/Warszawa",
+	"America/Buenos_Aires": "America/Argentina/Buenos_Aires",
+	"America/Godthab":      "America/Nuuk",
+	// NOTE: "Atlantic/Raykjavik" missing in tzdb but is in MS list
+
+	"Etc/UTC": "UTC", // simplifying the time zone name
+}

src/internal/converters/ics/ics.go

@@ -17,6 +17,7 @@ import (
 
 	"github.com/alcionai/corso/src/internal/common/ptr"
 	"github.com/alcionai/corso/src/internal/common/str"
+	"github.com/alcionai/corso/src/internal/converters/ics/tzdata"
 	"github.com/alcionai/corso/src/pkg/dttm"
 	"github.com/alcionai/corso/src/pkg/logger"
 	"github.com/alcionai/corso/src/pkg/services/m365/api"
@@ -32,7 +33,8 @@ import (
 // TODO locations: https://github.com/alcionai/corso/issues/5003
 
 const (
-	ICalDateTimeFormat = "20060102T150405Z"
+	ICalDateTimeFormat    = "20060102T150405"
+	ICalDateTimeFormatUTC = "20060102T150405Z"
 	ICalDateFormat        = "20060102"
 )
 
@@ -173,6 +175,17 @@ func getRecurrencePattern(
 		recurComponents = append(recurComponents, "BYDAY="+prefix+strings.Join(dowComponents, ","))
 	}
 
+	// This is necessary to compute when weekly events recur
+	fdow := pat.GetFirstDayOfWeek()
+	if fdow != nil {
+		icalday, ok := GraphToICalDOW[fdow.String()]
+		if !ok {
+			return "", clues.NewWC(ctx, "unknown first day of week").With("day", fdow)
+		}
+
+		recurComponents = append(recurComponents, "WKST="+icalday)
+	}
+
 	rrange := recurrence.GetRangeEscaped()
 	if rrange != nil {
 		switch ptr.Val(rrange.GetTypeEscaped()) {
@@ -196,7 +209,7 @@ func getRecurrencePattern(
 					return "", clues.WrapWC(ctx, err, "parsing end time")
 				}
 
-				recurComponents = append(recurComponents, "UNTIL="+endTime.Format(ICalDateTimeFormat))
+				recurComponents = append(recurComponents, "UNTIL="+endTime.Format(ICalDateTimeFormatUTC))
 			}
 		case models.NOEND_RECURRENCERANGETYPE:
 			// Nothing to do
@@ -225,10 +238,15 @@ func FromEventable(ctx context.Context, event models.Eventable) (string, error)
 	cal := ics.NewCalendar()
 	cal.SetProductId("-//Alcion//Corso") // Does this have to be customizable?
 
+	err := addTimeZoneComponents(ctx, cal, event)
+	if err != nil {
+		return "", clues.Wrap(err, "adding timezone components")
+	}
+
 	id := ptr.Val(event.GetId())
 	iCalEvent := cal.AddEvent(id)
 
-	err := updateEventProperties(ctx, event, iCalEvent)
+	err = updateEventProperties(ctx, event, iCalEvent)
 	if err != nil {
 		return "", clues.Wrap(err, "updating event properties")
 	}
@@ -259,7 +277,7 @@ func FromEventable(ctx context.Context, event models.Eventable) (string, error)
 		exICalEvent := cal.AddEvent(id)
 		start := exception.GetOriginalStart() // will always be in UTC
 
-		exICalEvent.AddProperty(ics.ComponentProperty(ics.PropertyRecurrenceId), start.Format(ICalDateTimeFormat))
+		exICalEvent.AddProperty(ics.ComponentProperty(ics.PropertyRecurrenceId), start.Format(ICalDateTimeFormatUTC))
 
 		err = updateEventProperties(ctx, exception, exICalEvent)
 		if err != nil {
@@ -270,6 +288,91 @@ func FromEventable(ctx context.Context, event models.Eventable) (string, error)
 	return cal.Serialize(), nil
 }
 
+func getTZDataKeyValues(ctx context.Context, timezone string) (map[string]string, error) {
+	template, ok := tzdata.TZData[timezone]
+	if !ok {
+		return nil, clues.NewWC(ctx, "timezone not found in tz database").
+			With("timezone", timezone)
+	}
+
+	keyValues := map[string]string{}
+
+	for _, line := range strings.Split(template, "\n") {
+		splits := strings.SplitN(line, ":", 2)
+		if len(splits) != 2 {
+			return nil, clues.NewWC(ctx, "invalid tzdata line").
+				With("line", line).
+				With("timezone", timezone)
+		}
+
+		keyValues[splits[0]] = splits[1]
+	}
+
+	return keyValues, nil
+}
+
+func addTimeZoneComponents(ctx context.Context, cal *ics.Calendar, event models.Eventable) error {
+	// Handling of timezone get a bit tricky when we have to deal with
+	// relative recurrence. The issue comes up when we set a recurrence
+	// to be something like "repeat every 3rd Tuesday". Tuesday in UTC
+	// and in IST will be different and so we cannot just always use UTC.
+	//
+	// The way this is solved is by using the timezone in the
+	// recurrence for start and end timezones as we have to use UTC
+	// for UNTIL(mostly).
+	// https://www.rfc-editor.org/rfc/rfc5545#section-3.3.10
+	timezone, err := getRecurrenceTimezone(ctx, event)
+	if err != nil {
+		return clues.Stack(err)
+	}
+
+	if timezone != time.UTC {
+		kvs, err := getTZDataKeyValues(ctx, timezone.String())
+		if err != nil {
+			return clues.Stack(err)
+		}
+
+		tz := cal.AddTimezone(timezone.String())
+
+		for k, v := range kvs {
+			tz.AddProperty(ics.ComponentProperty(k), v)
+		}
+	}
+
+	return nil
+}
+
+// getRecurrenceTimezone get the timezone specified by the recurrence
+// in the calendar.  It does a normalization pass where we always convert
+// the timezone to the value in tzdb If we don't have a recurrence
+// timezone, we don't have to use a specific timezone in the export and
+// is safe to return UTC from this method.
+func getRecurrenceTimezone(ctx context.Context, event models.Eventable) (*time.Location, error) {
+	if event.GetRecurrence() != nil {
+		timezone := ptr.Val(event.GetRecurrence().GetRangeEscaped().GetRecurrenceTimeZone())
+
+		ctz, ok := GraphTimeZoneToTZ[timezone]
+		if ok {
+			timezone = ctz
+		}
+
+		cannon, ok := CanonicalTimeZoneMap[timezone]
+		if ok {
+			timezone = cannon
+		}
+
+		loc, err := time.LoadLocation(timezone)
+		if err != nil {
+			return nil, clues.WrapWC(ctx, err, "unknown timezone").
+				With("timezone", timezone)
+		}
+
+		return loc, nil
+	}
+
+	return time.UTC, nil
+}
+
 func isASCII(s string) bool {
 	for _, c := range s {
 		if c > unicode.MaxASCII {
@@ -299,6 +402,11 @@ func updateEventProperties(ctx context.Context, event models.Eventable, iCalEven
 		iCalEvent.SetModifiedAt(ptr.Val(modified))
 	}
 
+	timezone, err := getRecurrenceTimezone(ctx, event)
+	if err != nil {
+		return err
+	}
+
 	// DTSTART - https://www.rfc-editor.org/rfc/rfc5545#section-3.8.2.4
 	allDay := ptr.Val(event.GetIsAllDay())
 	startString := event.GetStart().GetDateTime()
@@ -310,11 +418,7 @@ func updateEventProperties(ctx context.Context, event models.Eventable, iCalEven
 			return clues.WrapWC(ctx, err, "parsing start time")
 		}
 
-		if allDay {
+		addTime(iCalEvent, ics.ComponentPropertyDtStart, start, allDay, timezone)
-			iCalEvent.SetStartAt(start, ics.WithValue(string(ics.ValueDataTypeDate)))
-		} else {
-			iCalEvent.SetStartAt(start)
-		}
 	}
 
 	// DTEND - https://www.rfc-editor.org/rfc/rfc5545#section-3.8.2.2
@@ -327,11 +431,7 @@ func updateEventProperties(ctx context.Context, event models.Eventable, iCalEven
 			return clues.WrapWC(ctx, err, "parsing end time")
 		}
 
-		if allDay {
+		addTime(iCalEvent, ics.ComponentPropertyDtEnd, end, allDay, timezone)
-			iCalEvent.SetEndAt(end, ics.WithValue(string(ics.ValueDataTypeDate)))
-		} else {
-			iCalEvent.SetEndAt(end)
-		}
 	}
 
 	recurrence := event.GetRecurrence()
@@ -630,6 +730,26 @@ func updateEventProperties(ctx context.Context, event models.Eventable, iCalEven
 	return nil
 }
 
+func addTime(iCalEvent *ics.VEvent, prop ics.ComponentProperty, tm time.Time, allDay bool, tzLoc *time.Location) {
+	if allDay {
+		if tzLoc == time.UTC {
+			iCalEvent.SetProperty(prop, tm.Format(ICalDateFormat), ics.WithValue(string(ics.ValueDataTypeDate)))
+		} else {
+			iCalEvent.SetProperty(
+				prop,
+				tm.In(tzLoc).Format(ICalDateFormat),
+				ics.WithValue(string(ics.ValueDataTypeDate)),
+				keyValues("TZID", tzLoc.String()))
+		}
+	} else {
+		if tzLoc == time.UTC {
+			iCalEvent.SetProperty(prop, tm.Format(ICalDateTimeFormatUTC))
+		} else {
+			iCalEvent.SetProperty(prop, tm.In(tzLoc).Format(ICalDateTimeFormat), keyValues("TZID", tzLoc.String()))
+		}
+	}
+}
+
 func getCancelledDates(ctx context.Context, event models.Eventable) ([]time.Time, error) {
 	dateStrings, err := api.GetCancelledEventDateStrings(event)
 	if err != nil {

src/internal/converters/ics/ics_test.go

@@ -13,6 +13,7 @@ import (
 	"testing"
 	"time"
 
+	ics "github.com/arran4/golang-ical"
 	"github.com/microsoft/kiota-abstractions-go/serialization"
 	kjson "github.com/microsoft/kiota-serialization-json-go"
 	"github.com/microsoftgraph/msgraph-sdk-go/models"
@@ -21,6 +22,7 @@ import (
 	"github.com/stretchr/testify/suite"
 
 	"github.com/alcionai/corso/src/internal/common/ptr"
+	"github.com/alcionai/corso/src/internal/converters/ics/tzdata"
 	"github.com/alcionai/corso/src/internal/tester"
 )
 
@@ -32,7 +34,7 @@ func TestICSUnitSuite(t *testing.T) {
 	suite.Run(t, &ICSUnitSuite{Suite: tester.NewUnitSuite(t)})
 }
 
-func (suite *ICSUnitSuite) TestGetLocationString() {
+func (s *ICSUnitSuite) TestGetLocationString() {
 	table := []struct {
 		name   string
 		loc    func() models.Locationable
@@ -110,13 +112,13 @@ func (suite *ICSUnitSuite) TestGetLocationString() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			assert.Equal(suite.T(), tt.expect, getLocationString(tt.loc()))
+			assert.Equal(s.T(), tt.expect, getLocationString(tt.loc()))
 		})
 	}
 }
 
-func (suite *ICSUnitSuite) TestGetUTCTime() {
+func (s *ICSUnitSuite) TestGetUTCTime() {
 	table := []struct {
 		name      string
 		timestamp string
@@ -162,18 +164,18 @@ func (suite *ICSUnitSuite) TestGetUTCTime() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
 			t, err := GetUTCTime(tt.timestamp, tt.timezone)
-			tt.errCheck(suite.T(), err)
+			tt.errCheck(s.T(), err)
 
 			if !tt.time.Equal(time.Time{}) {
-				assert.Equal(suite.T(), tt.time, t)
+				assert.Equal(s.T(), tt.time, t)
 			}
 		})
 	}
 }
 
-func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
+func (s *ICSUnitSuite) TestGetRecurrencePattern() {
 	table := []struct {
 		name       string
 		recurrence func() models.PatternedRecurrenceable
@@ -187,16 +189,37 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("daily")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rec.SetPattern(pat)
 
 				return rec
 			},
-			expect:   "FREQ=DAILY;INTERVAL=1",
+			expect:   "FREQ=DAILY;INTERVAL=1;WKST=SU",
+			errCheck: require.NoError,
+		},
+		{
+			name: "daily different start of week",
+			recurrence: func() models.PatternedRecurrenceable {
+				rec := models.NewPatternedRecurrence()
+				pat := models.NewRecurrencePattern()
+
+				typ, err := models.ParseRecurrencePatternType("daily")
+				require.NoError(s.T(), err)
+
+				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
+				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.MONDAY_DAYOFWEEK))
+
+				rec.SetPattern(pat)
+
+				return rec
+			},
+			expect:   "FREQ=DAILY;INTERVAL=1;WKST=MO",
 			errCheck: require.NoError,
 		},
 		{
@@ -206,15 +229,16 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("daily")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rng := models.NewRecurrenceRange()
 
 				rrtype, err := models.ParseRecurrenceRangeType("endDate")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				rng.SetTypeEscaped(rrtype.(*models.RecurrenceRangeType))
 
@@ -227,7 +251,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=DAILY;INTERVAL=1;UNTIL=20210101T182959Z",
+			expect:   "FREQ=DAILY;INTERVAL=1;WKST=SU;UNTIL=20210101T182959Z",
 			errCheck: require.NoError,
 		},
 		{
@@ -237,16 +261,17 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("weekly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rec.SetPattern(pat)
 
 				return rec
 			},
-			expect:   "FREQ=WEEKLY;INTERVAL=1",
+			expect:   "FREQ=WEEKLY;INTERVAL=1;WKST=SU",
 			errCheck: require.NoError,
 		},
 		{
@@ -256,15 +281,16 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("weekly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rng := models.NewRecurrenceRange()
 
 				rrtype, err := models.ParseRecurrenceRangeType("endDate")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				rng.SetTypeEscaped(rrtype.(*models.RecurrenceRangeType))
 
@@ -277,7 +303,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=WEEKLY;INTERVAL=1;UNTIL=20210101T235959Z",
+			expect:   "FREQ=WEEKLY;INTERVAL=1;WKST=SU;UNTIL=20210101T235959Z",
 			errCheck: require.NoError,
 		},
 		{
@@ -287,15 +313,16 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("weekly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rng := models.NewRecurrenceRange()
 
 				rrtype, err := models.ParseRecurrenceRangeType("numbered")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				rng.SetTypeEscaped(rrtype.(*models.RecurrenceRangeType))
 
@@ -307,7 +334,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=WEEKLY;INTERVAL=1;COUNT=10",
+			expect:   "FREQ=WEEKLY;INTERVAL=1;WKST=SU;COUNT=10",
 			errCheck: require.NoError,
 		},
 		{
@@ -317,10 +344,11 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("weekly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				days := []models.DayOfWeek{
 					models.MONDAY_DAYOFWEEK,
@@ -334,7 +362,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=WEEKLY;INTERVAL=1;BYDAY=MO,WE,TH",
+			expect:   "FREQ=WEEKLY;INTERVAL=1;BYDAY=MO,WE,TH;WKST=SU",
 			errCheck: require.NoError,
 		},
 		{
@@ -344,16 +372,17 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("daily")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(2)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				rec.SetPattern(pat)
 
 				return rec
 			},
-			expect:   "FREQ=DAILY;INTERVAL=2",
+			expect:   "FREQ=DAILY;INTERVAL=2;WKST=SU",
 			errCheck: require.NoError,
 		},
 		{
@@ -363,10 +392,11 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("absoluteMonthly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				pat.SetDayOfMonth(ptr.To(int32(5)))
 
@@ -374,7 +404,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=5",
+			expect:   "FREQ=MONTHLY;INTERVAL=1;BYMONTHDAY=5;WKST=SU",
 			errCheck: require.NoError,
 		},
 		{
@@ -384,10 +414,11 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("absoluteYearly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(3)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				pat.SetMonth(ptr.To(int32(8)))
 
@@ -395,7 +426,7 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 
 				return rec
 			},
-			expect:   "FREQ=YEARLY;INTERVAL=3;BYMONTH=8",
+			expect:   "FREQ=YEARLY;INTERVAL=3;BYMONTH=8;WKST=SU",
 			errCheck: require.NoError,
 		},
 		{
@@ -405,37 +436,38 @@ func (suite *ICSUnitSuite) TestGetRecurrencePattern() {
 				pat := models.NewRecurrencePattern()
 
 				typ, err := models.ParseRecurrencePatternType("relativeYearly")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
 
 				pat.SetMonth(ptr.To(int32(8)))
 				pat.SetDaysOfWeek([]models.DayOfWeek{models.FRIDAY_DAYOFWEEK})
 
 				wi, err := models.ParseWeekIndex("first")
-				require.NoError(suite.T(), err)
+				require.NoError(s.T(), err)
 				pat.SetIndex(wi.(*models.WeekIndex))
 
 				rec.SetPattern(pat)
 
 				return rec
 			},
-			expect:   "FREQ=YEARLY;INTERVAL=1;BYMONTH=8;BYDAY=1FR",
+			expect:   "FREQ=YEARLY;INTERVAL=1;BYMONTH=8;BYDAY=1FR;WKST=SU",
 			errCheck: require.NoError,
 		},
 		// TODO(meain): could still use more tests for edge cases of time
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			ctx, flush := tester.NewContext(suite.T())
+			ctx, flush := tester.NewContext(s.T())
 			defer flush()
 
 			rec, err := getRecurrencePattern(ctx, tt.recurrence())
-			tt.errCheck(suite.T(), err)
+			tt.errCheck(s.T(), err)
 
-			assert.Equal(suite.T(), tt.expect, rec)
+			assert.Equal(s.T(), tt.expect, rec)
 		})
 	}
 }
@@ -460,8 +492,8 @@ func baseEvent() *models.Event {
 	return e
 }
 
-func (suite *ICSUnitSuite) TestEventConversion() {
+func (s *ICSUnitSuite) TestEventConversion() {
-	t := suite.T()
+	t := s.T()
 
 	table := []struct {
 		name  string
@@ -546,14 +578,19 @@ func (suite *ICSUnitSuite) TestEventConversion() {
 
 				rec := models.NewPatternedRecurrence()
 				pat := models.NewRecurrencePattern()
+				rng := models.NewRecurrenceRange()
 
 				typ, err := models.ParseRecurrencePatternType("daily")
 				require.NoError(t, err)
 
 				pat.SetTypeEscaped(typ.(*models.RecurrencePatternType))
 				pat.SetInterval(ptr.To(int32(1)))
+				pat.SetFirstDayOfWeek(ptr.To(models.SUNDAY_DAYOFWEEK))
+
+				rng.SetRecurrenceTimeZone(ptr.To("UTC"))
 
 				rec.SetPattern(pat)
+				rec.SetRangeEscaped(rng)
 
 				e.SetRecurrence(rec)
 
@@ -830,8 +867,8 @@ func (suite *ICSUnitSuite) TestEventConversion() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			t := suite.T()
+			t := s.T()
 
 			ctx, flush := tester.NewContext(t)
 			defer flush()
@@ -881,8 +918,8 @@ func checkAttendee(t *testing.T, out, check, msg string) {
 	assert.ElementsMatch(t, as, bs, fmt.Sprintf("fields %s", msg))
 }
 
-func (suite *ICSUnitSuite) TestAttendees() {
+func (s *ICSUnitSuite) TestAttendees() {
-	t := suite.T()
+	t := s.T()
 
 	table := []struct {
 		name  string
@@ -949,8 +986,8 @@ func (suite *ICSUnitSuite) TestAttendees() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			t := suite.T()
+			t := s.T()
 
 			ctx, flush := tester.NewContext(t)
 			defer flush()
@@ -1071,8 +1108,8 @@ func checkAttachment(t *testing.T, out, check, msg string) {
 	assert.ElementsMatch(t, as, bs, fmt.Sprintf("fields %s", msg))
 }
 
-func (suite *ICSUnitSuite) TestAttachments() {
+func (s *ICSUnitSuite) TestAttachments() {
-	t := suite.T()
+	t := s.T()
 
 	type attachment struct {
 		cid     string // contentid
@@ -1128,8 +1165,8 @@ func (suite *ICSUnitSuite) TestAttachments() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			t := suite.T()
+			t := s.T()
 
 			ctx, flush := tester.NewContext(t)
 			defer flush()
@@ -1172,7 +1209,7 @@ func (suite *ICSUnitSuite) TestAttachments() {
 	}
 }
 
-func (suite *ICSUnitSuite) TestCancellations() {
+func (s *ICSUnitSuite) TestCancellations() {
 	table := []struct {
 		name         string
 		cancelledIds []string
@@ -1196,8 +1233,8 @@ func (suite *ICSUnitSuite) TestCancellations() {
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			t := suite.T()
+			t := s.T()
 
 			ctx, flush := tester.NewContext(t)
 			defer flush()
@@ -1260,7 +1297,7 @@ func eventToJSON(e *models.Event) ([]byte, error) {
 	return bts, err
 }
 
-func (suite *ICSUnitSuite) TestEventExceptions() {
+func (s *ICSUnitSuite) TestEventExceptions() {
 	table := []struct {
 		name  string
 		event func() *models.Event
@@ -1282,7 +1319,7 @@ func (suite *ICSUnitSuite) TestEventExceptions() {
 				exception.SetEnd(newEnd)
 
 				parsed, err := eventToMap(exception)
-				require.NoError(suite.T(), err, "parsing exception")
+				require.NoError(s.T(), err, "parsing exception")
 
 				// add exception event to additional data
 				e.SetAdditionalData(map[string]any{
@@ -1301,15 +1338,15 @@ func (suite *ICSUnitSuite) TestEventExceptions() {
 					}
 				}
 
-				assert.Equal(suite.T(), 2, events, "number of events")
+				assert.Equal(s.T(), 2, events, "number of events")
 
-				assert.Contains(suite.T(), out, "RECURRENCE-ID:20210101T120000Z", "recurrence id")
+				assert.Contains(s.T(), out, "RECURRENCE-ID:20210101T120000Z", "recurrence id")
 
-				assert.Contains(suite.T(), out, "SUMMARY:Subject", "original event")
+				assert.Contains(s.T(), out, "SUMMARY:Subject", "original event")
-				assert.Contains(suite.T(), out, "SUMMARY:Exception", "exception event")
+				assert.Contains(s.T(), out, "SUMMARY:Exception", "exception event")
 
-				assert.Contains(suite.T(), out, "DTSTART:20210101T130000Z", "new start time")
+				assert.Contains(s.T(), out, "DTSTART:20210101T130000Z", "new start time")
-				assert.Contains(suite.T(), out, "DTEND:20210101T140000Z", "new end time")
+				assert.Contains(s.T(), out, "DTEND:20210101T140000Z", "new end time")
 			},
 		},
 		{
@@ -1338,10 +1375,10 @@ func (suite *ICSUnitSuite) TestEventExceptions() {
 				exception2.SetEnd(newEnd)
 
 				parsed1, err := eventToMap(exception1)
-				require.NoError(suite.T(), err, "parsing exception 1")
+				require.NoError(s.T(), err, "parsing exception 1")
 
 				parsed2, err := eventToMap(exception2)
-				require.NoError(suite.T(), err, "parsing exception 2")
+				require.NoError(s.T(), err, "parsing exception 2")
 
 				// add exception event to additional data
 				e.SetAdditionalData(map[string]any{
@@ -1360,36 +1397,230 @@ func (suite *ICSUnitSuite) TestEventExceptions() {
 					}
 				}
 
-				assert.Equal(suite.T(), 3, events, "number of events")
+				assert.Equal(s.T(), 3, events, "number of events")
 
-				assert.Contains(suite.T(), out, "RECURRENCE-ID:20210101T120000Z", "recurrence id 1")
+				assert.Contains(s.T(), out, "RECURRENCE-ID:20210101T120000Z", "recurrence id 1")
-				assert.Contains(suite.T(), out, "RECURRENCE-ID:20210102T120000Z", "recurrence id 2")
+				assert.Contains(s.T(), out, "RECURRENCE-ID:20210102T120000Z", "recurrence id 2")
 
-				assert.Contains(suite.T(), out, "SUMMARY:Subject", "original event")
+				assert.Contains(s.T(), out, "SUMMARY:Subject", "original event")
-				assert.Contains(suite.T(), out, "SUMMARY:Exception 1", "exception event 1")
+				assert.Contains(s.T(), out, "SUMMARY:Exception 1", "exception event 1")
-				assert.Contains(suite.T(), out, "SUMMARY:Exception 2", "exception event 2")
+				assert.Contains(s.T(), out, "SUMMARY:Exception 2", "exception event 2")
 
-				assert.Contains(suite.T(), out, "DTSTART:20210101T130000Z", "new start time 1")
+				assert.Contains(s.T(), out, "DTSTART:20210101T130000Z", "new start time 1")
-				assert.Contains(suite.T(), out, "DTEND:20210101T140000Z", "new end time 1")
+				assert.Contains(s.T(), out, "DTEND:20210101T140000Z", "new end time 1")
 
-				assert.Contains(suite.T(), out, "DTSTART:20210102T130000Z", "new start time 2")
+				assert.Contains(s.T(), out, "DTSTART:20210102T130000Z", "new start time 2")
-				assert.Contains(suite.T(), out, "DTEND:20210102T140000Z", "new end time 2")
+				assert.Contains(s.T(), out, "DTEND:20210102T140000Z", "new end time 2")
 			},
 		},
 	}
 
 	for _, tt := range table {
-		suite.Run(tt.name, func() {
+		s.Run(tt.name, func() {
-			ctx, flush := tester.NewContext(suite.T())
+			ctx, flush := tester.NewContext(s.T())
 			defer flush()
 
 			bts, err := eventToJSON(tt.event())
-			require.NoError(suite.T(), err, "getting serialized content")
+			require.NoError(s.T(), err, "getting serialized content")
 
 			out, err := FromJSON(ctx, bts)
-			require.NoError(suite.T(), err, "converting to ics")
+			require.NoError(s.T(), err, "converting to ics")
 
 			tt.check(out)
 		})
 	}
 }
+
+func (s *ICSUnitSuite) TestGetRecurrenceTimezone() {
+	table := []struct {
+		name  string
+		intz  string
+		outtz string
+	}{
+		{
+			name:  "empty",
+			intz:  "",
+			outtz: "UTC",
+		},
+		{
+			name:  "utc",
+			intz:  "UTC",
+			outtz: "UTC",
+		},
+		{
+			name:  "simple",
+			intz:  "Asia/Kolkata",
+			outtz: "Asia/Kolkata",
+		},
+		{
+			name:  "windows tz",
+			intz:  "India Standard Time",
+			outtz: "Asia/Kolkata",
+		},
+		{
+			name:  "non canonical",
+			intz:  "Asia/Calcutta",
+			outtz: "Asia/Kolkata",
+		},
+	}
+
+	for _, tt := range table {
+		s.Run(tt.name, func() {
+			ctx, flush := tester.NewContext(s.T())
+			defer flush()
+
+			event := baseEvent()
+			if len(tt.intz) > 0 {
+				recur := models.NewPatternedRecurrence()
+				rp := models.NewRecurrenceRange()
+				rp.SetRecurrenceTimeZone(ptr.To(tt.intz))
+
+				recur.SetRangeEscaped(rp)
+				event.SetRecurrence(recur)
+			}
+
+			timezone, err := getRecurrenceTimezone(ctx, event)
+			require.NoError(s.T(), err)
+			assert.Equal(s.T(), tt.outtz, timezone.String())
+		})
+	}
+}
+
+func (s *ICSUnitSuite) TestAddTimezoneComponents() {
+	event := baseEvent()
+	recur := models.NewPatternedRecurrence()
+	rp := models.NewRecurrenceRange()
+	rp.SetRecurrenceTimeZone(ptr.To("Asia/Kolkata"))
+
+	recur.SetRangeEscaped(rp)
+	event.SetRecurrence(recur)
+
+	ctx, flush := tester.NewContext(s.T())
+	defer flush()
+
+	cal := ics.NewCalendar()
+
+	err := addTimeZoneComponents(ctx, cal, event)
+	require.NoError(s.T(), err)
+
+	text := cal.Serialize()
+	assert.Contains(s.T(), text, "BEGIN:VTIMEZONE", "beginning of timezone")
+	assert.Contains(s.T(), text, "TZID:Asia/Kolkata", "timezone id")
+	assert.Contains(s.T(), text, "END:VTIMEZONE", "end of timezone")
+}
+
+func (s *ICSUnitSuite) TestAddTime() {
+	locak, err := time.LoadLocation("Asia/Kolkata")
+	require.NoError(s.T(), err)
+
+	table := []struct {
+		name   string
+		prop   ics.ComponentProperty
+		time   time.Time
+		allDay bool
+		loc    *time.Location
+		exp    string
+	}{
+		{
+			name:   "utc",
+			prop:   ics.ComponentPropertyDtStart,
+			time:   time.Date(2021, 1, 2, 3, 4, 5, 0, time.UTC),
+			allDay: false,
+			loc:    time.UTC,
+			exp:    "DTSTART:20210102T030405Z",
+		},
+		{
+			name:   "local",
+			prop:   ics.ComponentPropertyDtStart,
+			time:   time.Date(2021, 1, 2, 3, 4, 5, 0, time.UTC),
+			allDay: false,
+			loc:    locak,
+			exp:    "DTSTART;TZID=Asia/Kolkata:20210102T083405",
+		},
+		{
+			name:   "all day",
+			prop:   ics.ComponentPropertyDtStart,
+			time:   time.Date(2021, 1, 2, 0, 0, 0, 0, time.UTC),
+			allDay: true,
+			loc:    time.UTC,
+			exp:    "DTSTART;VALUE=DATE:20210102",
+		},
+		{
+			name:   "all day local",
+			prop:   ics.ComponentPropertyDtStart,
+			time:   time.Date(2021, 1, 2, 0, 0, 0, 0, time.UTC),
+			allDay: true,
+			loc:    locak,
+			exp:    "DTSTART;VALUE=DATE;TZID=Asia/Kolkata:20210102",
+		},
+		{
+			name:   "end",
+			prop:   ics.ComponentPropertyDtEnd,
+			time:   time.Date(2021, 1, 2, 3, 4, 5, 0, time.UTC),
+			allDay: false,
+			loc:    time.UTC,
+			exp:    "DTEND:20210102T030405Z",
+		},
+		{
+			// This won't happen, but a good test to have to test loc handling
+			name:   "windows tz",
+			prop:   ics.ComponentPropertyDtStart,
+			time:   time.Date(2021, 1, 2, 3, 4, 5, 0, time.UTC),
+			allDay: false,
+			loc:    time.FixedZone("India Standard Time", 5*60*60+30*60),
+			exp:    "DTSTART;TZID=India Standard Time:20210102T083405",
+		},
+	}
+
+	for _, tt := range table {
+		s.Run(tt.name, func() {
+			cal := ics.NewCalendar()
+			evt := cal.AddEvent("id")
+
+			addTime(evt, tt.prop, tt.time, tt.allDay, tt.loc)
+
+			expSplits := strings.FieldsFunc(tt.exp, func(c rune) bool {
+				return c == ':' || c == ';'
+			})
+
+			text := cal.Serialize()
+			checkLine := ""
+
+			for _, l := range strings.Split(text, "\r\n") {
+				if strings.HasPrefix(l, string(tt.prop)) {
+					checkLine = l
+					break
+				}
+			}
+
+			actSplits := strings.FieldsFunc(checkLine, func(c rune) bool {
+				return c == ':' || c == ';'
+			})
+
+			assert.Greater(s.T(), len(checkLine), 0, "line not found")
+			assert.Equal(s.T(), len(expSplits), len(actSplits), "length of fields")
+			assert.ElementsMatch(s.T(), expSplits, actSplits, "fields")
+		})
+	}
+}
+
+// This tests and ensures that the generated data is int he format
+// that we expect
+func (s *ICSUnitSuite) TestGetTZDataKeyValues() {
+	for key := range tzdata.TZData {
+		s.Run(key, func() {
+			ctx, flush := tester.NewContext(s.T())
+			defer flush()
+
+			data, err := getTZDataKeyValues(ctx, key)
+			require.NoError(s.T(), err)
+
+			assert.NotEmpty(s.T(), data, "data")
+			assert.NotContains(s.T(), data, "BEGIN", "beginning of timezone") // should be stripped
+			assert.NotContains(s.T(), data, "END", "end of timezone")         // should be stripped
+			assert.NotContains(s.T(), data, "TZID", "timezone id")            // should be stripped
+			assert.Contains(s.T(), data, "DTSTART", "start time")
+			assert.Contains(s.T(), data, "TZOFFSETFROM", "offset from")
+		})
+	}
+}

src/internal/converters/ics/tzdata/fetch.sh

@@ -0,0 +1,35 @@
+#!/bin/sh
+
+set -eo pipefail
+
+if ! echo "$PWD" | grep -q '/tzdata$'; then
+    echo "Please run this script from the tzdata dir"
+    exit 1
+fi
+
+# TODO: Generate from https://www.iana.org/time-zones
+if [ ! -d /tmp/corso-tzdata ]; then
+    git clone --depth 1 https://github.com/add2cal/timezones-ical-library.git /tmp/corso-tzdata
+else
+    cd /tmp/corso-tzdata
+    git pull
+    cd -
+fi
+
+# Generate a huge go file with all the timezones
+echo "package tzdata" >data.go
+echo "" >>data.go
+
+echo "var TZData = map[string]string{" >>data.go
+
+find /tmp/corso-tzdata/ -name '*.ics' | while read -r f; do
+    tz=$(echo "$f" | sed 's|/tmp/corso-tzdata/api/||;s|\.ics$||')
+    echo "Processing $tz"
+    printf "\t\"%s\": \`" "$tz" >>data.go
+    cat "$f" | grep -Ev "(BEGIN:|END:|TZID:)" |
+        sed 's|`|\\`|g;s|\r||;s|TZID:/timezones-ical-library/|TZID:|' |
+        perl -pe 'chomp if eof' >>data.go
+    echo "\`," >>data.go
+done
+
+echo "}" >>data.go