fix: match reminder paring with caldav spec and tasks.org code

Follow the RFC more strictly:
https://icalendar.org/iCalendar-RFC-5545/3-8-6-3-trigger.html

Compare with tasks.org, to make sure their alarms will be correctly synced:
https://github.com/tasks/tasks/blob/main/app/src/main/java/org/tasks/caldav/extensions/VAlarm.kt

pkg/caldav/caldav.go

@@ -204,13 +204,10 @@ func ParseAlarms(alarms []Alarm, taskDescription string) (caldavalarms string) {
 		caldavalarms += `
 BEGIN:VALARM`
 		switch a.RelativeTo {
-		case models.ReminderRelationDueDate:
-			caldavalarms += `
-TRIGGER:` + makeCalDavDuration(a.Duration)
 		case models.ReminderRelationStartDate:
 			caldavalarms += `
 TRIGGER;RELATED=START:` + makeCalDavDuration(a.Duration)
-		case models.ReminderRelationEndDate:
+		case models.ReminderRelationEndDate, models.ReminderRelationDueDate:
 			caldavalarms += `
 TRIGGER;RELATED=END:` + makeCalDavDuration(a.Duration)
 		default:

pkg/caldav/caldav_test.go

@@ -311,7 +311,7 @@ ACTION:DISPLAY
 DESCRIPTION:alarm description
 END:VALARM
 BEGIN:VALARM
-TRIGGER:-PT2H0M0S
+TRIGGER;RELATED=END:-PT2H0M0S
 ACTION:DISPLAY
 DESCRIPTION:Todo #1
 END:VALARM

pkg/caldav/parsing.go

@@ -141,53 +141,56 @@ func ParseTaskFromVTODO(content string) (vTask *models.Task, err error) {
 		vTask.EndDate = vTask.StartDate.Add(duration)
 	}
 
-	reminders := make([]*models.TaskReminder, 0)
 	for _, vAlarm := range vTodo.SubComponents() {
 		if vAlarm, ok := vAlarm.(*ics.VAlarm); ok {
-			reminders = parseVAlarm(vAlarm, reminders)
+			vTask = parseVAlarm(vAlarm, vTask)
 		}
 	}
-	if len(reminders) > 0 {
-		vTask.Reminders = reminders
-	}
 
 	return
 }
 
-func parseVAlarm(vAlarm *ics.VAlarm, reminders []*models.TaskReminder) []*models.TaskReminder {
+func parseVAlarm(vAlarm *ics.VAlarm, vTask *models.Task) *models.Task {
 	for _, property := range vAlarm.UnknownPropertiesIANAProperties() {
 		if property.IANAToken == "TRIGGER" {
-			switch {
+			if contains(property.ICalParameters["VALUE"], "DATE-TIME") {
-			case len(property.ICalParameters["VALUE"]) > 0:
+				// Example: TRIGGER;VALUE=DATE-TIME:20181201T011210Z
-				if property.ICalParameters["VALUE"][0] == "DATE-TIME" {
+				vTask.Reminders = append(vTask.Reminders, &models.TaskReminder{
-					// Example: TRIGGER;VALUE=DATE-TIME:20181201T011210Z
+					Reminder: caldavTimeToTimestamp(property.Value)})
-					reminders = append(reminders, &models.TaskReminder{
+			} else {
-						Reminder: caldavTimeToTimestamp(property.Value)})
+				if contains(property.ICalParameters["RELATED"], "END") {
-				}
+					// Example: TRIGGER;RELATED=END:-P2D
-			case len(property.ICalParameters["RELATED"]) > 0:
+					duration := utils.ParseISO8601Duration(property.Value)
-				duration := utils.ParseISO8601Duration(property.Value)
+					if vTask.EndDate.IsZero() {
-				switch property.ICalParameters["RELATED"][0] {
+						vTask.Reminders = append(vTask.Reminders, &models.TaskReminder{
-				case "START":
+							RelativePeriod: int64(duration.Seconds()),
+							RelativeTo:     models.ReminderRelationDueDate})
+					} else {
+						vTask.Reminders = append(vTask.Reminders, &models.TaskReminder{
+							RelativePeriod: int64(duration.Seconds()),
+							RelativeTo:     models.ReminderRelationEndDate})
+					}
+				} else {
 					// Example: TRIGGER;RELATED=START:-P2D
-					reminders = append(reminders, &models.TaskReminder{
+					// Example: TRIGGER:-PT60M
+					duration := utils.ParseISO8601Duration(property.Value)
+					vTask.Reminders = append(vTask.Reminders, &models.TaskReminder{
 						RelativePeriod: int64(duration.Seconds()),
 						RelativeTo:     models.ReminderRelationStartDate})
-				case "END":
-					// Example: TRIGGER;RELATED=END:-P2D
-					reminders = append(reminders, &models.TaskReminder{
-						RelativePeriod: int64(duration.Seconds()),
-						RelativeTo:     models.ReminderRelationEndDate})
 				}
-			default:
-				duration := utils.ParseISO8601Duration(property.Value)
-				// Example: TRIGGER:-PT60M
-				reminders = append(reminders, &models.TaskReminder{
-					RelativePeriod: int64(duration.Seconds()),
-					RelativeTo:     models.ReminderRelationDueDate})
 			}
 		}
 	}
-	return reminders
+	return vTask
+}
+
+func contains(array []string, str string) bool {
+	for _, value := range array {
+		if value == str {
+			return true
+		}
+	}
+	return false
 }
 
 // https://tools.ietf.org/html/rfc5545#section-3.3.5

pkg/caldav/parsing_test.go

@@ -170,7 +170,11 @@ TRIGGER:PT0S
 ACTION:DISPLAY
 END:VALARM
 BEGIN:VALARM
-TRIGGER:-PT60M
+TRIGGER;VALUE=DURATION:-PT60M
+ACTION:DISPLAY
+END:VALARM
+BEGIN:VALARM
+TRIGGER:-PT61M
 ACTION:DISPLAY
 END:VALARM
 BEGIN:VALARM
@@ -192,19 +196,23 @@ END:VCALENDAR`,
 				DueDate:     time.Date(2023, 3, 4, 15, 0, 0, 0, config.GetTimeZone()),
 				Reminders: []*models.TaskReminder{
 					{
-						RelativeTo:     models.ReminderRelationDueDate,
+						RelativeTo:     models.ReminderRelationStartDate,
 						RelativePeriod: 0,
 					},
 					{
-						RelativeTo:     models.ReminderRelationDueDate,
+						RelativeTo:     models.ReminderRelationStartDate,
 						RelativePeriod: -3600,
 					},
+					{
+						RelativeTo:     models.ReminderRelationStartDate,
+						RelativePeriod: -3660,
+					},
 					{
 						RelativeTo:     models.ReminderRelationStartDate,
 						RelativePeriod: -86400,
 					},
 					{
-						RelativeTo:     models.ReminderRelationEndDate,
+						RelativeTo:     models.ReminderRelationDueDate,
 						RelativePeriod: -1800,
 					},
 				},
@@ -309,7 +317,7 @@ ACTION:DISPLAY
 DESCRIPTION:Task 1
 END:VALARM
 BEGIN:VALARM
-TRIGGER:-PT1H0M0S
+TRIGGER;RELATED=END:-PT1H0M0S
 ACTION:DISPLAY
 DESCRIPTION:Task 1
 END:VALARM