Move EXDATE with the series when its times change (#248) (#249)

Reviewed-on: https://codeberg.org/jlmakiola/calendula/pulls/249

CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- **A deleted occurrence no longer comes back when the series is re-timed.**
+  Delete a single occurrence of a repeating event, then change the time of the
+  whole series, and the occurrence you had removed reappeared. Doing it the
+  other way round — "This and all following events" — lost every removal in the
+  part of the series being changed. Removals now travel with the event: they
+  keep their place in the series across a time change, a move to a different
+  day, a timezone change and a switch to or from an all-day event, and they
+  carry over when a series is split. Repeating events on your device's own
+  calendars are affected, including the birthday and anniversary calendars
+  Calendula creates from your contacts ([#248]).
+
 ## [2.19.3] — 2026-08-22
 
 ### Added
@@ -1471,3 +1483,4 @@ automatically, with zero telemetry and no internet permission.
 [#192]: https://codeberg.org/jlmakiola/calendula/issues/192
 [#196]: https://codeberg.org/jlmakiola/calendula/issues/196
 [#214]: https://codeberg.org/jlmakiola/calendula/issues/214
+[#248]: https://codeberg.org/jlmakiola/calendula/issues/248

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt

@@ -976,10 +976,12 @@ class AndroidCalendarDataSource @Inject constructor(
         updated: EventForm,
         allDayReminderTimeMinutes: Int,
     ) {
+        val row = querySeriesRow(eventId)
         val values = buildEventUpdateValues(
             original = original,
             updated = updated,
-            seriesDtStartMillis = querySeriesRow(eventId).dtStartMillis,
+            seriesDtStartMillis = row.dtStartMillis,
+            seriesExdate = row.exdate,
             zone = ZoneId.systemDefault(),
         )
         if (values.isNotEmpty()) {
@@ -1228,10 +1230,66 @@ class AndroidCalendarDataSource @Inject constructor(
         }
         // Insert the new series first: if it fails, the original is untouched.
         val newEventId = insertEvent(updated, allDayReminderTimeMinutes)
+        carrySplitExdate(newEventId, row, beginMillis, original, updated)
         truncateSeries(eventId, row, beginMillis)
         return newEventId
     }
 
+    /**
+     * Carry the [parent]'s exclusions for occurrences past [beginMillis] onto the
+     * series [newEventId] that now owns them, re-timed by the shift the split
+     * applied ([shiftedExdate]/[exdateAfter]). [insertEvent] builds the new row
+     * from the form, which knows nothing about them, so without this every
+     * occurrence the user had deleted from the tail of the series comes back.
+     *
+     * The whole time/recurrence set rides along with EXDATE for the reason
+     * [buildOccurrenceExdateValues] documents: on its own the provider does not
+     * read an EXDATE write as a recurrence change, and leaves the instances it
+     * expanded on insert standing.
+     *
+     * A failure rolls the new series back and throws, so the split fails whole
+     * rather than landing with the exclusions quietly dropped — the parent is
+     * still untruncated at this point, so the event is left exactly as it was.
+     */
+    private fun carrySplitExdate(
+        newEventId: Long,
+        parent: SeriesRow,
+        beginMillis: Long,
+        original: EventForm,
+        updated: EventForm,
+    ) {
+        // Dropping the recurrence in the same save leaves a one-off tail, and an
+        // exclusion means nothing on a row that doesn't recur.
+        if (updated.rrule.isNullOrBlank()) return
+        val carried = shiftedExdate(
+            existingExdate = exdateAfter(parent.exdate, beginMillis, original.isAllDay),
+            original = original,
+            updated = updated,
+            zone = ZoneId.systemDefault(),
+        ) ?: return
+        val row = querySeriesRow(newEventId)
+        val values = ContentValues().apply {
+            put(CalendarContract.Events.EXDATE, carried)
+            put(CalendarContract.Events.DTSTART, row.dtStartMillis)
+            put(CalendarContract.Events.RRULE, row.rrule)
+            put(CalendarContract.Events.DURATION, row.duration)
+            put(CalendarContract.Events.EVENT_TIMEZONE, row.timezone)
+            put(CalendarContract.Events.ALL_DAY, row.allDay)
+        }
+        try {
+            val rows = resolver.update(
+                ContentUris.withAppendedId(CalendarContract.Events.CONTENT_URI, newEventId),
+                values, null, null,
+            )
+            if (rows == 0) {
+                throw WriteFailedException("carry exdate onto split series id=$newEventId")
+            }
+        } catch (t: Throwable) {
+            runCatching { deleteEvent(newEventId) }
+            throw t
+        }
+    }
+
     override fun deleteEventFromOccurrence(eventId: Long, beginMillis: Long) {
         val row = querySeriesRow(eventId)
         // From the first occurrence on = the whole series; also the fallback

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapper.kt

@@ -10,6 +10,9 @@ import java.time.Duration
 import java.time.Instant
 import java.time.ZoneId
 import java.time.ZoneOffset
+import java.time.format.DateTimeFormatter
+import java.time.format.ResolverStyle
+import java.time.LocalDate as JavaLocalDate
 import java.time.LocalDateTime as JavaLocalDateTime
 
 /** Provider-ready DTSTART / DTEND / EVENT_TIMEZONE for an event write. */
@@ -134,18 +137,21 @@ internal fun buildEventInsertValues(
  *
  * Time fields travel together (the provider validates them as a unit):
  * - unchanged times, all-day flag and rrule → no time columns at all;
- * - non-recurring result → DTSTART/DTEND, DURATION and RRULE cleared;
+ * - non-recurring result → DTSTART/DTEND, DURATION, RRULE and EXDATE cleared;
  * - recurring result → the *series* DTSTART moves by the same **wall-clock**
  *   shift the user applied to the displayed occurrence and is re-resolved in the
  *   event's zone ([seriesDtStartMillis] is the row's current DTSTART), DURATION
- *   replaces DTEND, RRULE is written. This keeps past occurrences intact when
- *   someone edits a later occurrence's time, and keeps the anchor's time-of-day
- *   stable across a DST boundary or a zone change between the two.
+ *   replaces DTEND, RRULE is written, and the row's exclusions
+ *   ([seriesExdate], the current EXDATE) travel with the anchor. This keeps past
+ *   occurrences intact when someone edits a later occurrence's time, and keeps
+ *   the anchor's time-of-day stable across a DST boundary or a zone change
+ *   between the two.
  */
 internal fun buildEventUpdateValues(
     original: EventForm,
     updated: EventForm,
     seriesDtStartMillis: Long,
+    seriesExdate: String?,
     zone: ZoneId,
 ): Map<String, Any?> = buildMap {
     if (updated.title.trim() != original.title.trim()) {
@@ -185,6 +191,10 @@ internal fun buildEventUpdateValues(
         put(CalendarContract.Events.DTEND, newTimes.dtEndMillis)
         put(CalendarContract.Events.RRULE, null)
         put(CalendarContract.Events.DURATION, null)
+        // The exclusions named occurrences of a series that no longer exists.
+        // Left behind they are dormant rather than harmless: adding a recurrence
+        // back later would punch the old holes into the new one.
+        put(CalendarContract.Events.EXDATE, null)
     } else {
         // Move the series anchor by the *wall-clock* shift the user applied to the
         // displayed occurrence, then re-resolve it in the event's (possibly new)
@@ -206,6 +216,14 @@ internal fun buildEventUpdateValues(
         put(CalendarContract.Events.DTEND, null)
         put(CalendarContract.Events.RRULE, updated.rrule)
         put(CalendarContract.Events.DURATION, newTimes.toRfc2445Duration(updated.isAllDay))
+        // An EXDATE stamp is an absolute instant, so it excludes an occurrence
+        // only while the series keeps generating one at exactly that instant. The
+        // anchor has just moved, so every occurrence regenerates elsewhere and a
+        // stamp left behind matches none of them — the occurrence the user deleted
+        // comes back. Move the stamps the same way the anchor moved.
+        shiftedExdate(seriesExdate, original, updated, zone)
+            ?.takeIf { it != seriesExdate }
+            ?.let { put(CalendarContract.Events.EXDATE, it) }
     }
 }
 
@@ -420,11 +438,7 @@ internal fun buildOccurrenceExdateValues(
     allDay: Int,
 ): Map<String, Any?> {
     val stamp = formatExdateStamp(occurrenceMillis, isAllDay = allDay != 0)
-    val existing = existingExdate?.split(',')
-        ?.map { it.trim() }
-        ?.filter { it.isNotEmpty() }
-        .orEmpty()
-    val merged = (existing + stamp).distinct().joinToString(",")
+    val merged = (exdateStamps(existingExdate) + stamp).distinct().joinToString(",")
     return mapOf(
         CalendarContract.Events.EXDATE to merged,
         CalendarContract.Events.DTSTART to dtStartMillis,
@@ -435,22 +449,122 @@ internal fun buildOccurrenceExdateValues(
     )
 }
 
+/**
+ * [existingExdate] with every stamp re-timed by the same **wall-clock** shift the
+ * series anchor takes from [original] to [updated] — the exclusions' half of the
+ * anchor move [buildEventUpdateValues] performs, and what carries them onto the
+ * new series when "this and following" splits one.
+ *
+ * A stamp is an absolute instant, so it keeps naming its occurrence only if it
+ * moves exactly as the occurrence does: shifted in wall clock and re-resolved in
+ * the event's (possibly new) zone. A millisecond delta would instead bake in the
+ * offset that happened to apply at the edited occurrence — an hour off for any
+ * exclusion on the far side of a DST boundary. All-day-ness is read from
+ * [original] and written from [updated], so the `VALUE=DATE` and date-time forms
+ * convert into each other when the event switches.
+ *
+ * Null when there is nothing to carry: no stamps, or a stamp in a form Calendula
+ * never writes (a `TZID=`-parameterised or floating one from a sync adapter). Those
+ * are left exactly as they are rather than guessed at — a stale stamp excludes
+ * nothing, but a mangled one could exclude the wrong occurrence.
+ */
+internal fun shiftedExdate(
+    existingExdate: String?,
+    original: EventForm,
+    updated: EventForm,
+    zone: ZoneId,
+): String? {
+    val stamps = exdateStamps(existingExdate)
+    if (stamps.isEmpty()) return null
+    val fromZone = original.writeZone(zone)
+    val toZone = updated.writeZone(zone)
+    val wallClockShift = Duration.between(original.anchorLocal(), updated.anchorLocal())
+    return stamps
+        .map { stamp ->
+            val local = parseExdateStamp(stamp, original.isAllDay, fromZone) ?: return null
+            formatExdateStamp(local.plus(wallClockShift), updated.isAllDay, toZone)
+        }
+        .distinct()
+        .joinToString(",")
+}
+
+/**
+ * The stamps of [existingExdate] naming occurrences after [beginMillis] — the ones
+ * that belong to the *new* series once "this and following" splits a recurring
+ * event there. The parent keeps the full list; its stamps past the split point are
+ * simply inert once it stops generating those occurrences.
+ *
+ * The occurrence at [beginMillis] itself is never carried. It is the one the user
+ * is editing, so it exists by definition, and honouring a stale exclusion for it
+ * would swallow the edit whole.
+ *
+ * Null when nothing qualifies, or when a stamp can't be read (see [shiftedExdate]).
+ */
+internal fun exdateAfter(existingExdate: String?, beginMillis: Long, isAllDay: Boolean): String? {
+    val stamps = exdateStamps(existingExdate)
+    if (stamps.isEmpty()) return null
+    return stamps
+        .filter { stamp ->
+            val utc = parseExdateStamp(stamp, isAllDay, ZoneOffset.UTC) ?: return null
+            utc.toInstant(ZoneOffset.UTC).toEpochMilli() > beginMillis
+        }
+        .takeIf { it.isNotEmpty() }
+        ?.joinToString(",")
+}
+
+/** The individual stamps of an EXDATE column value; it is a comma-separated list. */
+private fun exdateStamps(exdate: String?): List<String> = exdate
+    ?.split(',')
+    ?.map { it.trim() }
+    ?.filter { it.isNotEmpty() }
+    .orEmpty()
+
 /**
  * One EXDATE entry for the occurrence starting at [occurrenceMillis]. Both forms
  * are UTC: the provider stores an all-day DTSTART at UTC midnight, so its date
  * reads off the UTC calendar day.
  */
-private fun formatExdateStamp(occurrenceMillis: Long, isAllDay: Boolean): String {
-    val utc = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC)
-    return if (isAllDay) {
-        "%04d%02d%02d".format(utc.year, utc.monthValue, utc.dayOfMonth)
+private fun formatExdateStamp(occurrenceMillis: Long, isAllDay: Boolean): String =
+    formatExdateStamp(
+        local = Instant.ofEpochMilli(occurrenceMillis).atZone(ZoneOffset.UTC).toLocalDateTime(),
+        isAllDay = isAllDay,
+        zone = ZoneOffset.UTC,
+    )
+
+/**
+ * One EXDATE entry for the occurrence whose wall clock in [zone] is [local]. An
+ * all-day entry keeps only the date (its time-of-day is the anchor's, not the
+ * occurrence's); a timed one is resolved in [zone] and written as a UTC instant.
+ */
+private fun formatExdateStamp(local: JavaLocalDateTime, isAllDay: Boolean, zone: ZoneId): String =
+    if (isAllDay) {
+        local.toLocalDate().format(ALL_DAY_EXDATE)
     } else {
-        "%04d%02d%02dT%02d%02d%02dZ".format(
-            utc.year, utc.monthValue, utc.dayOfMonth,
-            utc.hour, utc.minute, utc.second,
-        )
+        local.atZone(zone).withZoneSameInstant(ZoneOffset.UTC).format(TIMED_EXDATE)
     }
-}
+
+/**
+ * [stamp] as the wall clock it names in [zone] — the inverse of
+ * [formatExdateStamp]. Null for anything but the two forms Calendula writes, so a
+ * caller can tell "not ours, leave it alone" from a value it may safely re-time.
+ */
+private fun parseExdateStamp(stamp: String, isAllDay: Boolean, zone: ZoneId): JavaLocalDateTime? =
+    runCatching {
+        if (isAllDay) {
+            JavaLocalDate.parse(stamp, ALL_DAY_EXDATE).atStartOfDay()
+        } else {
+            JavaLocalDateTime.parse(stamp, TIMED_EXDATE)
+                .atZone(ZoneOffset.UTC).withZoneSameInstant(zone).toLocalDateTime()
+        }
+    }.getOrNull()
+
+/** `VALUE=DATE` EXDATE form, for an all-day series. */
+private val ALL_DAY_EXDATE: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("uuuuMMdd").withResolverStyle(ResolverStyle.STRICT)
+
+/** UTC date-time EXDATE form, for a timed series. */
+private val TIMED_EXDATE: DateTimeFormatter =
+    DateTimeFormatter.ofPattern("uuuuMMdd'T'HHmmss'Z'").withResolverStyle(ResolverStyle.STRICT)
 
 /**
  * The `EVENT_COLOR` / `EVENT_COLOR_KEY` columns for a colour selection. A

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapperTest.kt

@@ -128,7 +128,8 @@ class EventWriteMapperTest {
         original: EventForm,
         updated: EventForm,
         series: Long = seriesStart,
-    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, berlin)
+        exdate: String? = null,
+    ): Map<String, Any?> = buildEventUpdateValues(original, updated, series, exdate, berlin)
 
     /** The instant [local] names in [zoneId], as the provider would store it. */
     private fun instantAt(local: String, zoneId: String): Long =
@@ -558,6 +559,239 @@ class EventWriteMapperTest {
         assertThat(values[CalendarContract.Events.ALL_DAY]).isEqualTo(1)
     }
 
+    // --- EXDATE follows the series when its times change (Codeberg #248) ---
+
+    /** A weekly series whose displayed occurrence runs 15 July 2026, 09:00–10:00. */
+    private fun julySeries(): EventForm = form(
+        start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+        end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+    ).copy(rrule = "FREQ=WEEKLY")
+
+    /** [julySeries] pushed to [hour]:00, the shift an "all events" time edit makes. */
+    private fun EventForm.atHour(hour: Int): EventForm = copy(
+        start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(hour, 0)),
+        end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(hour + 1, 0)),
+    )
+
+    @Test
+    fun `a series time edit moves its exclusions with the anchor`() {
+        // The bug: the stamp stayed at the old instant, which the moved series no
+        // longer generates, so the occurrence the user deleted came back.
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        // 8 July 09:00 Berlin (CEST, +2) == 07:00Z; at 10:00 it must read 08:00Z.
+        val values = update(original, original.atHour(10), series, "20260708T070000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260708T080000Z")
+    }
+
+    @Test
+    fun `an exclusion keeps its wall clock across a DST boundary`() {
+        // Anchor and edited occurrence are in July (CEST, +2); the excluded
+        // occurrence sits in January (CET, +1). Shifting by the millisecond delta
+        // measured at the edited occurrence would leave it an hour off.
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = julySeries()
+        // 14 January 09:00 Berlin == 08:00Z; at 10:00 it must read 09:00Z.
+        val values = update(original, original.atHour(10), series, "20260114T080000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260114T090000Z")
+    }
+
+    @Test
+    fun `pinning a series to another zone re-resolves its exclusions there`() {
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val values = update(
+            original,
+            original.copy(timezone = "Asia/Tokyo"),
+            series,
+            "20260716T070000Z",
+        )
+        // The exclusion still reads 09:00 — now 09:00 in Tokyo (+9) == 00:00Z.
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260716T000000Z")
+    }
+
+    @Test
+    fun `an all-day series move shifts its exclusions by whole days`() {
+        val series = instantAt("2026-07-01T00:00", "UTC")
+        val original = form(
+            isAllDay = true,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(0, 0)),
+        )
+
+        assertThat(update(original, moved, series, "20260722")[CalendarContract.Events.EXDATE])
+            .isEqualTo("20260724")
+    }
+
+    @Test
+    fun `switching a series to all-day rewrites its exclusions as dates`() {
+        // The two forms aren't interchangeable: a date-time stamp on an all-day
+        // series matches no occurrence, so the exclusion would be lost.
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val values = update(original, original.copy(isAllDay = true), series, "20260722T070000Z")
+        assertThat(values[CalendarContract.Events.EXDATE]).isEqualTo("20260722")
+    }
+
+    @Test
+    fun `switching a series back to timed rewrites its exclusions as instants`() {
+        val series = instantAt("2026-07-01T00:00", "UTC")
+        val original = form(
+            isAllDay = true,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(0, 0)),
+        ).copy(rrule = "FREQ=WEEKLY")
+        val timed = original.copy(
+            isAllDay = false,
+            start = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(9, 0)),
+            end = LocalDateTime(LocalDate(2026, 7, 15), LocalTime(10, 0)),
+        )
+        // The excluded day gains the new 09:00 Berlin time-of-day == 07:00Z.
+        assertThat(update(original, timed, series, "20260722")[CalendarContract.Events.EXDATE])
+            .isEqualTo("20260722T070000Z")
+    }
+
+    @Test
+    fun `a text-only edit leaves the exclusions alone`() {
+        val original = julySeries()
+        val values = update(original, original.copy(title = "Renamed"), exdate = "20260722T070000Z")
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `changing only the rule rewrites no exclusions`() {
+        // The times are untouched, so every surviving occurrence keeps its instant
+        // and the stamps still name the right ones.
+        val original = julySeries()
+        val values = update(original, original.copy(rrule = "FREQ=DAILY"), exdate = "20260722T070000Z")
+        assertThat(values[CalendarContract.Events.RRULE]).isEqualTo("FREQ=DAILY")
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `an exdate form we do not write is left untouched`() {
+        // A sync adapter may store a TZID-parameterised or floating stamp. A stale
+        // stamp excludes nothing; a mangled one could exclude the wrong occurrence.
+        val original = julySeries()
+        val values = update(
+            original,
+            original.atHour(10),
+            instantAt("2026-07-01T09:00", "Europe/Berlin"),
+            "TZID=Europe/Berlin;20260722T090000",
+        )
+        assertThat(values).doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    @Test
+    fun `removing the recurrence clears the exclusions with it`() {
+        // Dormant, not harmless: adding a recurrence back later would punch the old
+        // holes into the new one.
+        val original = julySeries()
+        val values = update(original, original.copy(rrule = null), exdate = "20260722T070000Z")
+        assertThat(values).containsEntry(CalendarContract.Events.EXDATE, null)
+    }
+
+    @Test
+    fun `undoing a series move lands the exclusions back where they started`() {
+        val series = instantAt("2026-01-07T09:00", "Europe/Berlin")
+        val original = julySeries()
+        val moved = original.copy(
+            start = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(14, 30)),
+            end = LocalDateTime(LocalDate(2026, 7, 17), LocalTime(15, 30)),
+        )
+        val exdate = "20260722T070000Z"
+
+        val forward = update(original, moved, series, exdate)
+        val movedExdate = forward[CalendarContract.Events.EXDATE] as String
+        assertThat(movedExdate).isNotEqualTo(exdate)
+
+        val back = update(
+            moved,
+            original,
+            forward[CalendarContract.Events.DTSTART] as Long,
+            movedExdate,
+        )
+        assertThat(back[CalendarContract.Events.EXDATE]).isEqualTo(exdate)
+    }
+
+    @Test
+    fun `a series with no exclusions writes no exdate column`() {
+        val series = instantAt("2026-07-01T09:00", "Europe/Berlin")
+        val original = julySeries()
+        assertThat(update(original, original.atHour(10), series, exdate = null))
+            .doesNotContainKey(CalendarContract.Events.EXDATE)
+    }
+
+    // --- exdateAfter (the exclusions a "this and following" split inherits) ---
+
+    @Test
+    fun `a split carries only the exclusions past the split point`() {
+        // The occurrence at the split point is the one being edited, so it exists
+        // by definition — a stale exclusion for it would swallow the edit whole.
+        assertThat(
+            exdateAfter(
+                existingExdate = "20260708T080000Z,20260715T080000Z,20260722T080000Z",
+                beginMillis = instantAt("2026-07-15T08:00", "UTC"),
+                isAllDay = false,
+            ),
+        ).isEqualTo("20260722T080000Z")
+    }
+
+    @Test
+    fun `a split carries nothing when every exclusion is behind it`() {
+        assertThat(
+            exdateAfter("20260708T080000Z", instantAt("2026-07-15T08:00", "UTC"), isAllDay = false),
+        ).isNull()
+        assertThat(exdateAfter(null, 0L, isAllDay = false)).isNull()
+    }
+
+    @Test
+    fun `all-day exclusions split on their UTC date`() {
+        assertThat(
+            exdateAfter("20260708,20260722", instantAt("2026-07-15T00:00", "UTC"), isAllDay = true),
+        ).isEqualTo("20260722")
+    }
+
+    @Test
+    fun `an unreadable exclusion carries nothing across a split`() {
+        assertThat(
+            exdateAfter(
+                "20260722T080000Z,TZID=Europe/Berlin;20260729T100000",
+                instantAt("2026-07-15T08:00", "UTC"),
+                isAllDay = false,
+            ),
+        ).isNull()
+    }
+
+    @Test
+    fun `split exclusions move by the same shift as the new series start`() {
+        // What the split path composes: filter to the tail, then re-time it by the
+        // shift the user applied to the occurrence they split at.
+        val original = julySeries()
+        val carried = shiftedExdate(
+            existingExdate = exdateAfter(
+                "20260716T070000Z",
+                instantAt("2026-07-15T07:00", "UTC"),
+                isAllDay = false,
+            ),
+            original = original,
+            updated = original.atHour(11),
+            zone = berlin,
+        )
+        // 16 July 09:00 Berlin, pushed two hours, is 11:00 Berlin == 09:00Z.
+        assertThat(carried).isEqualTo("20260716T090000Z")
+    }
+
+    @Test
+    fun `nothing to shift yields no exdate`() {
+        assertThat(shiftedExdate(null, julySeries(), julySeries().atHour(10), berlin)).isNull()
+        assertThat(shiftedExdate("  ", julySeries(), julySeries().atHour(10), berlin)).isNull()
+    }
+
     // --- per-event colour ---
 
     @Test