Add support for time zones when calculating alarm trigger times

lib/src/main/kotlin/at/bitfire/ical4android/ICalendar.kt

@@ -11,27 +11,16 @@ import at.bitfire.synctools.BuildConfig
 import at.bitfire.synctools.exception.InvalidICalendarException
 import at.bitfire.synctools.icalendar.ICalendarParser
 import at.bitfire.synctools.icalendar.validation.ICalPreprocessor
-import at.bitfire.synctools.util.AndroidTimeUtils.toInstant
 import net.fortuna.ical4j.data.CalendarBuilder
 import net.fortuna.ical4j.data.ParserException
 import net.fortuna.ical4j.model.Calendar
-import net.fortuna.ical4j.model.Parameter
 import net.fortuna.ical4j.model.Property
-import net.fortuna.ical4j.model.component.VAlarm
 import net.fortuna.ical4j.model.component.VTimeZone
-import net.fortuna.ical4j.model.parameter.Related
 import net.fortuna.ical4j.model.property.Color
-import net.fortuna.ical4j.model.property.DateProperty
-import net.fortuna.ical4j.model.property.DtStart
 import net.fortuna.ical4j.model.property.ProdId
-import net.fortuna.ical4j.model.property.Trigger
 import net.fortuna.ical4j.validate.ValidationException
 import java.io.Reader
 import java.io.StringReader
-import java.time.Duration
-import java.time.Instant
-import java.time.Period
-import java.time.temporal.Temporal
 import java.util.LinkedList
 import java.util.UUID
 import java.util.logging.Level
@@ -156,104 +145,6 @@ open class ICalendar {
             }
         }
 
-
-        // misc. iCalendar helpers
-
-        /**
-         * Calculates the minutes before/after an event/task to know when a given alarm occurs.
-         *
-         * @param alarm         the alarm to calculate the minutes from
-         * @param refStart      reference `DTSTART` from the calendar component
-         * @param refEnd        reference `DTEND` (`VEVENT`) or `DUE` (`VTODO`) from the calendar component
-         * @param allowRelEnd   *true*: caller accepts minutes related to the end;
-         * *false*: caller only accepts minutes related to the start
-         *
-         * Android's alarm granularity is minutes. This methods calculates with milliseconds, but the result
-         * is rounded down to minutes (seconds cut off).
-         *
-         * @return Pair of values:
-         *
-         * 1. whether the minutes are related to the start or end (always [Related.START] if [allowRelEnd] is *false*)
-         * 2. number of minutes before start/end (negative value means number of minutes *after* start/end)
-         *
-         * May be *null* if there's not enough information to calculate the number of minutes.
-         */
-        fun vAlarmToMin(
-            alarm: VAlarm,
-            refStart: DtStart<*>?,
-            refEnd: DateProperty<*>?,
-            refDuration: net.fortuna.ical4j.model.property.Duration?,
-            allowRelEnd: Boolean
-        ): Pair<Related, Int>? {
-            val trigger = alarm.getProperty<Trigger>(Property.TRIGGER).getOrNull() ?: return null
-
-            // Note: big method – maybe split?
-
-            val minutes: Int    // minutes before/after the event
-            var related: Related = trigger.getParameter<Related>(Parameter.RELATED).getOrNull() ?: Related.START
-
-            // event/task start/end time
-            val start = refStart?.date?.toInstant()
-            var end = refEnd?.date?.toInstant()
-
-            // event/task end time
-            if (end == null && start != null)
-                end = when (val refDur = refDuration?.duration) {
-                    is Duration -> start + refDur
-                    is Period -> start + Duration.between(start, start + refDur)
-                    else -> null
-                }
-
-            // event/task duration
-            val duration: Duration? =
-                if (start != null && end != null)
-                    Duration.between(start, end)
-                else
-                    null
-
-            val triggerDur = trigger.duration
-            val triggerTime = trigger.date
-
-            if (triggerDur != null) {
-                // TRIGGER value is a DURATION. Important:
-                // 1) Negative values in TRIGGER mean positive values in Reminders.MINUTES and vice versa.
-                // 2) Android doesn't know alarm seconds, but only minutes. Cut off seconds from the final result.
-                // 3) DURATION can be a Duration (time-based) or a Period (date-based), which have to be treated differently.
-                var millisBefore =
-                    when (triggerDur) {
-                        is Duration -> -triggerDur.toMillis()
-                        is Period -> {
-                            // TODO: Take time zones into account (will probably be possible with ical4j 4.x).
-                            // For instance, an alarm one day before the DST change should be 23/25 hours before the event.
-                            -Duration.ofDays(triggerDur.days.toLong()).toMillis()     // months and years are not used in DURATION values; weeks are calculated to days
-                        }
-                        else -> throw AssertionError("triggerDur must be Duration or Period")
-                    }
-
-                if (related == Related.END && !allowRelEnd) {
-                    if (duration == null) {
-                        logger.warning("Event/task without duration; can't calculate END-related alarm")
-                        return null
-                    }
-                    // move alarm towards end
-                    related = Related.START
-                    millisBefore -= duration.toMillis()
-                }
-                minutes = (millisBefore / 60000).toInt()
-
-            } else if (triggerTime != null && start != null) {
-                // TRIGGER value is a DATE-TIME, calculate minutes from start time
-                related = Related.START
-                minutes = Duration.between(triggerTime, start).toMinutes().toInt()
-
-            } else {
-                logger.log(Level.WARNING, "VALARM TRIGGER type is not DURATION or DATE-TIME (requires event DTSTART for Android), ignoring alarm", alarm)
-                return null
-            }
-
-            return Pair(related, minutes)
-        }
-
     }
 
 

lib/src/main/kotlin/at/bitfire/ical4android/Task.kt

@@ -8,6 +8,7 @@ package at.bitfire.ical4android
 
 import androidx.annotation.IntRange
 import at.bitfire.ical4android.util.DateUtils
+import at.bitfire.synctools.util.AndroidTimeUtils.toInstant
 import net.fortuna.ical4j.model.Property
 import net.fortuna.ical4j.model.component.VAlarm
 import net.fortuna.ical4j.model.property.Clazz
@@ -23,6 +24,7 @@ import net.fortuna.ical4j.model.property.RDate
 import net.fortuna.ical4j.model.property.RRule
 import net.fortuna.ical4j.model.property.RelatedTo
 import net.fortuna.ical4j.model.property.Status
+import java.time.Instant
 import java.util.LinkedList
 
 /**
@@ -75,4 +77,28 @@ data class Task(
             ?: true
     }
 
+    /**
+     * The "end date" of this task.
+     *
+     * Returns…
+     * - [due] if present, otherwise…
+     * - [Due] instance containing the end date as [Instant] calculated from [dtStart] and
+     *   [duration] if both present, otherwise…
+     * - `null`.
+     */
+    val end: Due<*>?
+        get() {
+            if (due != null) {
+                return due
+            }
+
+            val start = dtStart?.date?.toInstant()
+            val duration = duration?.duration
+            if (start != null && duration != null) {
+                val end = start + duration
+                return Due(end)
+            }
+
+            return null
+        }
 }

lib/src/main/kotlin/at/bitfire/synctools/mapping/calendar/builder/RemindersBuilder.kt

@@ -10,15 +10,13 @@ import android.content.ContentValues
 import android.content.Entity
 import android.provider.CalendarContract.Reminders
 import androidx.core.content.contentValuesOf
-import at.bitfire.ical4android.ICalendar
 import at.bitfire.synctools.icalendar.dtStart
+import at.bitfire.synctools.util.AlarmTriggerCalculator
 import net.fortuna.ical4j.model.Property
 import net.fortuna.ical4j.model.component.VAlarm
 import net.fortuna.ical4j.model.component.VEvent
 import net.fortuna.ical4j.model.property.Action
-import net.fortuna.ical4j.model.property.DtEnd
 import java.time.temporal.Temporal
-import java.util.Locale
 import kotlin.jvm.optionals.getOrNull
 
 class RemindersBuilder: AndroidEntityBuilder {
@@ -39,11 +37,10 @@ class RemindersBuilder: AndroidEntityBuilder {
             else -> Reminders.METHOD_DEFAULT                // won't trigger an alarm on the Android device
         }
 
-        val minutes = ICalendar.vAlarmToMin(
+        val minutes = AlarmTriggerCalculator.alarmTriggerToMinutes(
             alarm = alarm,
             refStart = event.dtStart<Temporal>(),
-            refEnd = event.getEndDate<Temporal>().getOrNull(),
-            refDuration = event.duration,
+            refEnd = event.getEndDate<Temporal>(true).getOrNull(),
             allowRelEnd = false
         )?.second ?: Reminders.MINUTES_DEFAULT
 

lib/src/main/kotlin/at/bitfire/synctools/mapping/tasks/DmfsTaskBuilder.kt

@@ -8,7 +8,6 @@ package at.bitfire.synctools.mapping.tasks
 
 import android.content.ContentValues
 import android.content.Entity
-import at.bitfire.ical4android.ICalendar
 import at.bitfire.ical4android.Task
 import at.bitfire.ical4android.UnknownProperty
 import at.bitfire.synctools.icalendar.DatePropertyTzMapper.normalizedDate
@@ -20,6 +19,7 @@ import at.bitfire.synctools.storage.tasks.DmfsTask.Companion.COLUMN_FLAGS
 import at.bitfire.synctools.storage.tasks.DmfsTask.Companion.UNKNOWN_PROPERTY_DATA
 import at.bitfire.synctools.storage.tasks.DmfsTaskList
 import at.bitfire.synctools.storage.tasks.TasksBatchOperation
+import at.bitfire.synctools.util.AlarmTriggerCalculator
 import at.bitfire.synctools.util.AndroidTimeUtils
 import at.bitfire.synctools.util.AndroidTimeUtils.toTimestamp
 import net.fortuna.ical4j.model.Parameter
@@ -93,7 +93,7 @@ class DmfsTaskBuilder(
             builder .withValue(Tasks.LIST_ID, taskList.id)
 
         // new builders
-        
+
         val entity = Entity(ContentValues())
         for (fieldBuilder in fieldBuilders)
             fieldBuilder.build(task, entity)
@@ -224,11 +224,10 @@ class DmfsTaskBuilder(
 
     private fun insertAlarms(batch: TasksBatchOperation, idxTask: Int?) {
         for (alarm in task.alarms) {
-            val (alarmRef, minutes) = ICalendar.vAlarmToMin(
+            val (alarmRef, minutes) = AlarmTriggerCalculator.alarmTriggerToMinutes(
                 alarm = alarm,
                 refStart = task.dtStart,
-                refEnd = task.due,
-                refDuration = task.duration,
+                refEnd = task.end,
                 allowRelEnd = true
             ) ?: continue
             val ref = when (alarmRef) {