feat(ics): import core — parser, dedup-aware bulk import, form prefill

v2.7 Branch 2 (core, no UI yet). The read side of the .ics engine:

- domain/ics: IcsParser (inverse of IcsWriter) — unfold/unescape/param
  parsing, VALUE=DATE / UTC-Z / TZID date handling resolved against the OS
  tz db, VEVENT walk → ParsedIcsEvent + typed warnings. Liberal-in/
  strict-out: a malformed VEVENT is skipped, RECURRENCE-ID overrides /
  attendees / unresolved TZIDs are reported, not silently dropped.
- Promoted parseRfc2445DurationMillis into domain/ics (shared by writer-
  side mapper and parser); IcsDuration + test.
- Datasource existingUids()/insertImportedEvent(); repository
  importEvents() with UID dedup (skip known UIDs → idempotent restore) →
  IcsImportSummary. IcsImporter reads a Uri's text.
- ParsedIcsEvent.toEventForm() for the single-event "open into the create
  form" path.

Parser round-trips against IcsWriter; dedup + form-adapter unit-tested.
Intent filter, routing and import UI land in the next commit.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -445,4 +445,35 @@ class CalendarRepositoryImplTest {
             .containsExactly(EventColorOption("5", 0xFF33B679.toInt()))
         assertThat(repo.eventColorPalette(8L)).isEmpty()
     }
+
+    @Test
+    fun `importEvents skips events whose UID already exists and inserts the rest`(
+        @TempDir tempDir: Path,
+    ) = runTest {
+        val fake = FakeCalendarDataSource().apply {
+            existingUidsResult = setOf("dup@x")
+        }
+        val repo = CalendarRepositoryImpl(fake, newPrefs(tempDir), newSettings(tempDir), Dispatchers.Unconfined)
+        val events = listOf(
+            parsedEvent("dup@x"), // already present → skipped
+            parsedEvent("new@x"), // inserted
+            parsedEvent(null), // no UID → always inserted
+        )
+
+        val summary = repo.importEvents(targetCalendarId = 3L, events = events)
+
+        assertThat(summary.imported).isEqualTo(2)
+        assertThat(summary.skippedDuplicate).isEqualTo(1)
+        assertThat(fake.importedEvents.map { it.first.uid }).containsExactly("new@x", null)
+        assertThat(fake.importedEvents.map { it.second }).containsExactly(3L, 3L)
+    }
+
+    private fun parsedEvent(uid: String?) = de.jeanlucmakiola.calendula.domain.ics.ParsedIcsEvent(
+        uid = uid,
+        summary = "E",
+        start = Instant.fromEpochMilliseconds(1_000_000_000L),
+        end = Instant.fromEpochMilliseconds(1_000_003_600L),
+        isAllDay = false,
+        zoneId = "UTC",
+    )
 }

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

@@ -6,6 +6,7 @@ import de.jeanlucmakiola.calendula.domain.EventDetail
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.ics.IcsEvent
+import de.jeanlucmakiola.calendula.domain.ics.ParsedIcsEvent
 
 /**
  * Test-only fake. Tunable via the three `var` properties; `tick()` simulates
@@ -18,6 +19,8 @@ internal class FakeCalendarDataSource : CalendarDataSource {
     var eventDetailResult: (Long) -> EventDetail? = { null }
     var eventColorPaletteResult: (Long) -> List<EventColorOption> = { emptyList() }
     var exportableEventsResult: List<IcsEvent> = emptyList()
+    /** UIDs the target calendar already holds, for import dedup. */
+    var existingUidsResult: Set<String> = emptySet()
     /** Set to make the next write call throw. */
     var writeError: Exception? = null
     /** Id returned by the next [insertEvent]. */
@@ -53,6 +56,17 @@ internal class FakeCalendarDataSource : CalendarDataSource {
         eventColorPaletteResult(calendarId)
     override fun exportableEvents(): List<IcsEvent> = exportableEventsResult
 
+    override fun existingUids(calendarId: Long): Set<String> = existingUidsResult
+
+    /** (event, targetCalendarId) pairs passed to [insertImportedEvent]. */
+    val importedEvents = mutableListOf<Pair<ParsedIcsEvent, Long>>()
+
+    override fun insertImportedEvent(event: ParsedIcsEvent, calendarId: Long): Long {
+        writeError?.let { throw it }
+        importedEvents += event to calendarId
+        return nextInsertId
+    }
+
     override fun createLocalCalendar(displayName: String, color: Int, description: String?): Long {
         writeError?.let { throw it }
         createdCalendars += CreatedCalendar(displayName, color, description)

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

@@ -7,16 +7,6 @@ import org.junit.jupiter.api.Test
 
 class IcsExportMapperTest {
 
-    @Test
-    fun `parses the duration forms Calendula writes plus general ones`() {
-        assertThat(parseRfc2445DurationMillis("P1D")).isEqualTo(86_400_000L)
-        assertThat(parseRfc2445DurationMillis("P3600S")).isEqualTo(3_600_000L)
-        assertThat(parseRfc2445DurationMillis("PT1H30M")).isEqualTo(5_400_000L)
-        assertThat(parseRfc2445DurationMillis("P1W")).isEqualTo(604_800_000L)
-        assertThat(parseRfc2445DurationMillis(null)).isEqualTo(0L)
-        assertThat(parseRfc2445DurationMillis("nonsense")).isEqualTo(0L)
-    }
-
     @Test
     fun `timed one-off row maps with its DTEND and kept UID`() {
         val reader = MapColumnReader(

app/src/test/java/de/jeanlucmakiola/calendula/domain/ics/IcsDurationTest.kt

@@ -0,0 +1,28 @@
+package de.jeanlucmakiola.calendula.domain.ics
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class IcsDurationTest {
+
+    @Test
+    fun `parses the single-unit forms Calendula writes plus general ones`() {
+        assertThat(parseRfc2445DurationMillis("P1D")).isEqualTo(86_400_000L)
+        assertThat(parseRfc2445DurationMillis("P3600S")).isEqualTo(3_600_000L)
+        assertThat(parseRfc2445DurationMillis("PT1H30M")).isEqualTo(5_400_000L)
+        assertThat(parseRfc2445DurationMillis("P1W")).isEqualTo(604_800_000L)
+    }
+
+    @Test
+    fun `is sign-aware for before-start VALARM triggers`() {
+        assertThat(parseRfc2445DurationMillis("-PT15M")).isEqualTo(-900_000L)
+        assertThat(parseRfc2445DurationMillis("PT0M")).isEqualTo(0L)
+    }
+
+    @Test
+    fun `unparseable input is zero`() {
+        assertThat(parseRfc2445DurationMillis(null)).isEqualTo(0L)
+        assertThat(parseRfc2445DurationMillis("")).isEqualTo(0L)
+        assertThat(parseRfc2445DurationMillis("nonsense")).isEqualTo(0L)
+    }
+}

app/src/test/java/de/jeanlucmakiola/calendula/domain/ics/IcsParserTest.kt

@@ -0,0 +1,168 @@
+package de.jeanlucmakiola.calendula.domain.ics
+
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.calendula.domain.Availability
+import de.jeanlucmakiola.calendula.domain.EventStatus
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.atStartOfDayIn
+import kotlinx.datetime.toInstant
+import org.junit.jupiter.api.Test
+import kotlin.time.Instant
+
+class IcsParserTest {
+
+    private val parser = IcsParser(deviceZone = TimeZone.of("Europe/Berlin"))
+    private val writer = IcsWriter()
+    private val stamp = LocalDateTime(2026, 6, 18, 9, 30, 0).toInstant(TimeZone.UTC)
+
+    private fun roundTrip(event: IcsEvent): ParsedIcsEvent {
+        val text = writer.writeCalendar(listOf(event), stamp)
+        val result = parser.parse(text)
+        assertThat(result.events).hasSize(1)
+        return result.events.single()
+    }
+
+    private fun instantUtc(y: Int, mo: Int, d: Int, h: Int, mi: Int): Instant =
+        LocalDateTime(y, mo, d, h, mi, 0).toInstant(TimeZone.UTC)
+
+    @Test
+    fun `round-trips a timed one-off event`() {
+        val event = IcsEvent(
+            uid = "u1@calendula",
+            summary = "Lunch; with, friends",
+            start = instantUtc(2026, 6, 18, 11, 0),
+            end = instantUtc(2026, 6, 18, 12, 0),
+            isAllDay = false,
+            zoneId = "Europe/Berlin",
+            location = "Café",
+            availability = Availability.Free,
+            status = EventStatus.Tentative,
+        )
+        val parsed = roundTrip(event)
+        assertThat(parsed.uid).isEqualTo("u1@calendula")
+        assertThat(parsed.summary).isEqualTo("Lunch; with, friends")
+        assertThat(parsed.start).isEqualTo(event.start)
+        assertThat(parsed.end).isEqualTo(event.end)
+        assertThat(parsed.isAllDay).isFalse()
+        assertThat(parsed.location).isEqualTo("Café")
+        assertThat(parsed.availability).isEqualTo(Availability.Free)
+        assertThat(parsed.status).isEqualTo(EventStatus.Tentative)
+    }
+
+    @Test
+    fun `round-trips a recurring TZID event to the same instant`() {
+        val event = IcsEvent(
+            uid = "u2@calendula",
+            summary = "Weekly",
+            start = instantUtc(2026, 6, 18, 13, 0),
+            end = instantUtc(2026, 6, 18, 14, 0),
+            isAllDay = false,
+            zoneId = "Europe/Berlin",
+            recurrenceRule = "FREQ=WEEKLY",
+        )
+        val parsed = roundTrip(event)
+        assertThat(parsed.start).isEqualTo(event.start)
+        assertThat(parsed.end).isEqualTo(event.end)
+        assertThat(parsed.zoneId).isEqualTo("Europe/Berlin")
+        assertThat(parsed.recurrenceRule).isEqualTo("FREQ=WEEKLY")
+    }
+
+    @Test
+    fun `round-trips an all-day event`() {
+        val event = IcsEvent(
+            uid = "u3@calendula",
+            summary = "Holiday",
+            start = LocalDate(2026, 6, 18).atStartOfDayIn(TimeZone.UTC),
+            end = LocalDate(2026, 6, 19).atStartOfDayIn(TimeZone.UTC),
+            isAllDay = true,
+            zoneId = "UTC",
+        )
+        val parsed = roundTrip(event)
+        assertThat(parsed.isAllDay).isTrue()
+        assertThat(parsed.start).isEqualTo(event.start)
+        assertThat(parsed.end).isEqualTo(event.end)
+    }
+
+    @Test
+    fun `round-trips reminders as before-start lead minutes`() {
+        val event = IcsEvent(
+            uid = "u4@calendula",
+            summary = "Meeting",
+            start = instantUtc(2026, 6, 18, 13, 0),
+            end = instantUtc(2026, 6, 18, 14, 0),
+            isAllDay = false,
+            zoneId = "UTC",
+            reminderMinutes = listOf(15, 0),
+        )
+        val parsed = roundTrip(event)
+        assertThat(parsed.reminderMinutes).containsExactly(15, 0)
+    }
+
+    @Test
+    fun `tolerates folded lines and a missing UID`() {
+        val ics = buildString {
+            append("BEGIN:VCALENDAR\r\n")
+            append("VERSION:2.0\r\n")
+            append("BEGIN:VEVENT\r\n")
+            // Folded DESCRIPTION (continuation line begins with a space).
+            append("DESCRIPTION:This is a long descriptio\r\n n that was folded\r\n")
+            append("SUMMARY:No UID here\r\n")
+            append("DTSTART:20260618T090000Z\r\n")
+            append("DTEND:20260618T100000Z\r\n")
+            append("END:VEVENT\r\n")
+            append("END:VCALENDAR\r\n")
+        }
+        val parsed = parser.parse(ics).events.single()
+        assertThat(parsed.uid).isNull()
+        assertThat(parsed.description).isEqualTo("This is a long description that was folded")
+        assertThat(parsed.summary).isEqualTo("No UID here")
+    }
+
+    @Test
+    fun `skips a RECURRENCE-ID override and reports it`() {
+        val ics = "BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nUID:x\r\n" +
+            "RECURRENCE-ID:20260618T090000Z\r\nDTSTART:20260618T090000Z\r\n" +
+            "SUMMARY:Override\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n"
+        val result = parser.parse(ics)
+        assertThat(result.events).isEmpty()
+        assertThat(result.warnings).contains(IcsParseWarning.ModifiedOccurrenceSkipped)
+    }
+
+    @Test
+    fun `reports ignored attendees but still imports the event`() {
+        val ics = "BEGIN:VCALENDAR\r\nBEGIN:VEVENT\r\nUID:y\r\n" +
+            "DTSTART:20260618T090000Z\r\nSUMMARY:Has guests\r\n" +
+            "ATTENDEE;CN=Bob:mailto:bob@example.com\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n"
+        val result = parser.parse(ics)
+        assertThat(result.events).hasSize(1)
+        assertThat(result.warnings).contains(IcsParseWarning.AttendeesIgnored)
+    }
+
+    @Test
+    fun `parses multiple events and carries the calendar name`() {
+        val events = listOf(
+            IcsEvent("a@c", "One", instantUtc(2026, 6, 18, 9, 0), instantUtc(2026, 6, 18, 10, 0),
+                false, "UTC", calendarName = "Personal"),
+            IcsEvent("b@c", "Two", instantUtc(2026, 6, 19, 9, 0), instantUtc(2026, 6, 19, 10, 0),
+                false, "UTC", calendarName = "Personal"),
+        )
+        val text = writer.writeCalendar(events, stamp)
+        val result = parser.parse(text)
+        assertThat(result.events).hasSize(2)
+        assertThat(result.events.map { it.calendarName }).containsExactly("Personal", "Personal")
+    }
+
+    @Test
+    fun `a malformed event does not sink the rest of the file`() {
+        // First VEVENT has no DTSTART (skipped); second is valid.
+        val ics = "BEGIN:VCALENDAR\r\n" +
+            "BEGIN:VEVENT\r\nUID:bad\r\nSUMMARY:No start\r\nEND:VEVENT\r\n" +
+            "BEGIN:VEVENT\r\nUID:good\r\nDTSTART:20260618T090000Z\r\nSUMMARY:Fine\r\nEND:VEVENT\r\n" +
+            "END:VCALENDAR\r\n"
+        val result = parser.parse(ics)
+        assertThat(result.events.map { it.uid }).containsExactly("good")
+        assertThat(result.warnings).contains(IcsParseWarning.EventWithoutStartSkipped)
+    }
+}

app/src/test/java/de/jeanlucmakiola/calendula/domain/ics/ParsedIcsFormTest.kt

@@ -0,0 +1,54 @@
+package de.jeanlucmakiola.calendula.domain.ics
+
+import com.google.common.truth.Truth.assertThat
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.LocalDateTime
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.atStartOfDayIn
+import kotlinx.datetime.toInstant
+import org.junit.jupiter.api.Test
+
+class ParsedIcsFormTest {
+
+    private val berlin = TimeZone.of("Europe/Berlin")
+
+    @Test
+    fun `timed event maps to wall-clock form times in the device zone`() {
+        val event = ParsedIcsEvent(
+            uid = "u@x",
+            summary = "Call",
+            start = LocalDateTime(2026, 6, 18, 13, 0, 0).toInstant(TimeZone.UTC),
+            end = LocalDateTime(2026, 6, 18, 14, 0, 0).toInstant(TimeZone.UTC),
+            isAllDay = false,
+            zoneId = "UTC",
+            reminderMinutes = listOf(10, 10, 5),
+            recurrenceRule = "FREQ=WEEKLY",
+        )
+        val form = event.toEventForm(berlin)
+
+        assertThat(form.calendarId).isNull()
+        assertThat(form.title).isEqualTo("Call")
+        // 13:00 UTC == 15:00 Berlin (summer).
+        assertThat(form.start).isEqualTo(LocalDateTime(2026, 6, 18, 15, 0, 0))
+        assertThat(form.end).isEqualTo(LocalDateTime(2026, 6, 18, 16, 0, 0))
+        assertThat(form.reminders).containsExactly(5, 10).inOrder()
+        assertThat(form.rrule).isEqualTo("FREQ=WEEKLY")
+    }
+
+    @Test
+    fun `all-day event shows the last covered day, not the exclusive end`() {
+        val event = ParsedIcsEvent(
+            uid = null,
+            summary = "Trip",
+            start = LocalDate(2026, 6, 18).atStartOfDayIn(TimeZone.UTC),
+            end = LocalDate(2026, 6, 20).atStartOfDayIn(TimeZone.UTC), // exclusive
+            isAllDay = true,
+            zoneId = "UTC",
+        )
+        val form = event.toEventForm(berlin)
+
+        assertThat(form.isAllDay).isTrue()
+        assertThat(form.start.date).isEqualTo(LocalDate(2026, 6, 18))
+        assertThat(form.end.date).isEqualTo(LocalDate(2026, 6, 19)) // last covered day
+    }
+}