fix(detail): clamp a backwards DTEND instead of dropping the event (#34)

toEventDetailCore returned null when a present DTEND preceded DTSTART, the
only remaining false-drop that surfaces as the generic "Something went
wrong." error screen — the same un-openable trap as the pre-1970 DTSTART
bug, and worse because the user can't even open the malformed event to fix
it. Clamp the end to DTSTART (a zero-length event) instead, matching how
SearchMapper already coerces its end. After this the detail mapper drops a
row only when DTSTART is genuinely absent (unrenderable).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -23,26 +23,29 @@ internal fun ColumnReader.toEventDetailCore(
     attendees: List<Attendee>,
     reminders: List<Reminder>,
 ): EventDetail? {
-    val begin = getLong(EventDetailProjection.IDX_DTSTART)
-
-    if (begin < 0L) {
-        Log.w(TAG, "Dropping event with negative dtstart=$begin")
+    // DTSTART is epoch millis in UTC, so a series anchored before 1970 (common
+    // for yearly birthdays/anniversaries synced over CalDAV) is legitimately
+    // negative — only an *absent* DTSTART marks a malformed row worth dropping.
+    // Dropping negatives made every occurrence of such a series un-openable
+    // (the detail loads the ancient series-master DTSTART), see issue #34.
+    if (isNull(EventDetailProjection.IDX_DTSTART)) {
+        Log.w(TAG, "Dropping event with missing dtstart")
         return null
     }
+    val begin = getLong(EventDetailProjection.IDX_DTSTART)
 
     // Recurring events store DURATION instead of DTEND, so the series row's
     // DTEND is null. Keep the event (end == begin); callers that opened a
     // specific occurrence supply the real per-occurrence times from
-    // CalendarContract.Instances. Only a present-but-backwards DTEND is malformed.
+    // CalendarContract.Instances. A present-but-backwards DTEND is malformed,
+    // but dropping the row would make the event un-openable — the same trap as
+    // the pre-1970 DTSTART bug above (issue #34): it would surface as the
+    // generic error screen with no way to open the event and fix it. Clamp to a
+    // zero-length event instead (matching SearchMapper's coerceAtLeast).
     val end = if (isNull(EventDetailProjection.IDX_DTEND)) {
         begin
     } else {
-        val rawEnd = getLong(EventDetailProjection.IDX_DTEND)
-        if (rawEnd < begin) {
-            Log.w(TAG, "Dropping event with dtend=$rawEnd < dtstart=$begin")
-            return null
-        }
-        rawEnd
+        getLong(EventDetailProjection.IDX_DTEND).coerceAtLeast(begin)
     }
 
     // Kept raw (no untitled fallback): the detail screen substitutes its own

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

@@ -10,8 +10,11 @@ import de.jeanlucmakiola.calendula.domain.ics.parseRfc2445DurationMillis
  * of DTEND — reconstruct the end the same way the `.ics` export does.
  */
 internal fun ColumnReader.toSearchResult(): EventInstance? {
+    // A pre-1970 series anchor is a legitimately negative epoch-millis DTSTART
+    // (see EventDetailMapper / issue #34); drop only a genuinely absent one, so
+    // long-running birthdays/anniversaries still surface in search.
+    if (isNull(SearchProjection.IDX_DTSTART)) return null
     val dtStart = getLong(SearchProjection.IDX_DTSTART)
-    if (dtStart < 0L) return null
     val end = when {
         !isNull(SearchProjection.IDX_DTEND) -> getLong(SearchProjection.IDX_DTEND)
         else -> dtStart + parseRfc2445DurationMillis(getString(SearchProjection.IDX_DURATION))

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/TimePickerAlert.kt

@@ -4,14 +4,9 @@ import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
-import android.content.Context
-import android.content.res.Resources
-import android.provider.Settings
-import android.text.format.DateFormat
 import androidx.compose.material3.TimePicker
 import androidx.compose.material3.rememberTimePickerState
 import androidx.compose.runtime.Composable
-import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.stringResource
 import de.jeanlucmakiola.calendula.R
 import kotlinx.datetime.LocalTime
@@ -27,10 +22,13 @@ fun TimePickerAlert(
     onConfirm: (LocalTime) -> Unit,
     onDismiss: () -> Unit,
 ) {
+    // Honour the app's own time-format preference (the value every time label
+    // reads), not the system/locale clock — otherwise an explicit 24h setting
+    // still showed an AM/PM dial (issue #27).
     val state = rememberTimePickerState(
         initialHour = initial.hour,
         initialMinute = initial.minute,
-        is24Hour = deviceUses24HourClock(LocalContext.current),
+        is24Hour = LocalUse24HourFormat.current,
     )
     AlertDialog(
         onDismissRequest = onDismiss,
@@ -45,24 +43,3 @@ fun TimePickerAlert(
         text = { TimePicker(state = state) },
     )
 }
-
-/**
- * Whether the clock should read 24-hour, matching the rest of the device.
- *
- * [DateFormat.is24HourFormat] resolves a "locale default" system setting against
- * the *app's* context locale — and this app applies a per-app language
- * (AppCompatDelegate), so an English UI on a German-region phone would wrongly
- * read 12-hour while the system clock shows 24-hour. So we honour an explicit
- * system 12/24 override, and otherwise fall back to the **device** locale
- * (Resources.getSystem), not the app's.
- */
-private fun deviceUses24HourClock(context: Context): Boolean =
-    when (Settings.System.getString(context.contentResolver, Settings.System.TIME_12_24)) {
-        "24" -> true
-        "12" -> false
-        // 'a' is the AM/PM marker; a best-fit pattern without it is 24-hour.
-        else -> {
-            val deviceLocale = Resources.getSystem().configuration.locales[0]
-            !DateFormat.getBestDateTimePattern(deviceLocale, "jm").contains('a')
-        }
-    }

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

@@ -22,8 +22,8 @@ class EventDetailMapperTest {
         eventColor: Any? = null,
         eventColorKey: String? = null,
         calendarColor: Int = 0xFFAABBCC.toInt(),
-        dtstart: Long = 1_000_000_000L,
-        dtend: Long = 1_000_003_600L,
+        dtstart: Long? = 1_000_000_000L,
+        dtend: Long? = 1_000_003_600L,
         allDay: Int = 0,
         location: String? = "Berlin",
         calendarId: Long = 7L,
@@ -120,9 +120,31 @@ class EventDetailMapperTest {
     }
 
     @Test
-    fun `dtend before dtstart drops detail`() {
+    fun `dtend before dtstart is clamped to a zero-length event, not dropped`() {
+        // A backwards DTEND is malformed, but dropping it would make the event
+        // un-openable (the "Something went wrong" trap, same as issue #34); keep
+        // it as a zero-length event so the user can still open and fix it.
         val detail = detailReader(dtstart = 2000L, dtend = 1000L).toDetail()
-        assertThat(detail).isNull()
+        assertThat(detail).isNotNull()
+        assertThat(detail!!.instance.start.toEpochMilliseconds()).isEqualTo(2000L)
+        assertThat(detail.instance.end.toEpochMilliseconds()).isEqualTo(2000L)
+    }
+
+    @Test
+    fun `pre-1970 negative dtstart is kept, not dropped (issue #34)`() {
+        // A yearly birthday/anniversary anchored before the epoch has a
+        // legitimately negative UTC epoch-millis DTSTART; recurring rows carry
+        // no DTEND (they use DURATION), so it stays end == begin.
+        val begin = -157_766_400_000L // 1965-01-01T00:00:00Z
+        val detail = detailReader(dtstart = begin, dtend = null).toDetail()
+        assertThat(detail).isNotNull()
+        assertThat(detail!!.instance.start.toEpochMilliseconds()).isEqualTo(begin)
+        assertThat(detail.instance.end.toEpochMilliseconds()).isEqualTo(begin)
+    }
+
+    @Test
+    fun `absent dtstart drops detail`() {
+        assertThat(detailReader(dtstart = null).toDetail()).isNull()
     }
 
     @Test

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

@@ -0,0 +1,45 @@
+package de.jeanlucmakiola.calendula.data.calendar
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class SearchMapperTest {
+
+    private fun searchReader(
+        id: Long = 1L,
+        calendarId: Long = 7L,
+        title: String? = "Birthday",
+        dtstart: Long? = 1_000_000_000L,
+        dtend: Long? = null,
+        duration: String? = "P1D",
+        allDay: Int = 1,
+        eventColor: Any? = null,
+        calendarColor: Int = 0xFFAABBCC.toInt(),
+        location: String? = null,
+    ): MapColumnReader = MapColumnReader(
+        SearchProjection.IDX_ID to id,
+        SearchProjection.IDX_CALENDAR_ID to calendarId,
+        SearchProjection.IDX_TITLE to title,
+        SearchProjection.IDX_DTSTART to dtstart,
+        SearchProjection.IDX_DTEND to dtend,
+        SearchProjection.IDX_DURATION to duration,
+        SearchProjection.IDX_ALL_DAY to allDay,
+        SearchProjection.IDX_EVENT_COLOR to eventColor,
+        SearchProjection.IDX_CALENDAR_COLOR to calendarColor,
+        SearchProjection.IDX_LOCATION to location,
+    )
+
+    @Test
+    fun `pre-1970 negative dtstart still surfaces in search (issue #34)`() {
+        val begin = -157_766_400_000L // 1965-01-01T00:00:00Z
+        val result = searchReader(dtstart = begin, dtend = null, duration = "P1D").toSearchResult()
+        assertThat(result).isNotNull()
+        assertThat(result!!.start.toEpochMilliseconds()).isEqualTo(begin)
+        assertThat(result.title).isEqualTo("Birthday")
+    }
+
+    @Test
+    fun `absent dtstart drops the search hit`() {
+        assertThat(searchReader(dtstart = null).toSearchResult()).isNull()
+    }
+}