Use kotlinx-datetime's YearMonth and java.time converters

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaRange.kt

@@ -3,8 +3,9 @@ package de.jeanlucmakiola.calendula.ui.agenda
 import de.jeanlucmakiola.floret.locale.localizedDateFormatter
 import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
-import java.time.YearMonth
 import java.util.Locale
+import kotlinx.datetime.toJavaLocalDate
+import kotlinx.datetime.yearMonth
 
 /**
  * How far ahead the agenda (screen or widget) shows events, starting at today.
@@ -50,7 +51,7 @@ fun AgendaRange.dayCount(anchor: LocalDate, weekStart: DayOfWeek): Int = when (t
         DAYS_PER_WEEK - sinceWeekStart
     }
     AgendaRange.ThisMonth -> {
-        val daysInMonth = YearMonth.of(anchor.year, anchor.month.ordinal + 1).lengthOfMonth()
+        val daysInMonth = anchor.yearMonth.numberOfDays
         daysInMonth - anchor.day + 1
     }
     is AgendaRange.Custom -> days.coerceIn(AgendaRange.MIN_CUSTOM_DAYS, AgendaRange.MAX_CUSTOM_DAYS)
@@ -105,8 +106,8 @@ fun agendaRangeWindowSummary(
     locale: Locale,
     monthAsSpan: Boolean = false,
 ): String {
-    val javaStart = java.time.LocalDate.of(start.year, start.month.ordinal + 1, start.day)
-    val javaEnd = java.time.LocalDate.of(end.year, end.month.ordinal + 1, end.day)
+    val javaStart = start.toJavaLocalDate()
+    val javaEnd = end.toJavaLocalDate()
     val dayMonth = localizedDateFormatter(locale, "dMMM")
     val dayMonthYear = localizedDateFormatter(locale, "dMMMy")
     return when {

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaRows.kt

@@ -52,6 +52,7 @@ import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
 import kotlinx.datetime.plus
+import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
 import java.util.Locale
@@ -210,7 +211,7 @@ private fun formatTime(
 
 private fun formatAgendaDate(date: LocalDate): String {
     val locale = Locale.getDefault()
-    val java = java.time.LocalDate.of(date.year, date.month.ordinal + 1, date.day)
+    val java = date.toJavaLocalDate()
     // Weekday + date in the locale's own field order (e.g. "Wed, Jun 17, 2026"
     // vs "Mi., 17. Juni 2026") rather than a hardcoded day-month-year layout.
     return localizedDateFormatter(locale, "EEEdMMMy").format(java)

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthScreen.kt

@@ -192,10 +192,13 @@ import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
 import kotlinx.datetime.plus
 import kotlinx.datetime.YearMonth
+import kotlinx.datetime.toJavaDayOfWeek
 import kotlinx.datetime.toJavaLocalDate
 import kotlin.time.Instant
 import java.time.format.TextStyle as JavaTextStyle
 import java.util.Locale
+import kotlinx.datetime.toJavaMonth
+import kotlinx.datetime.yearMonth
 
 private val LocalTodayPulse = staticCompositionLocalOf { 0 }
 
@@ -344,7 +347,7 @@ fun MonthScreen(
             if (dense) {
                 val midweek = weekStartForIndex(listState.firstVisibleItemIndex + 1, weekStart)
                     .plus(3, DateTimeUnit.DAY)
-                YearMonth(midweek.year, midweek.month)
+                midweek.yearMonth
             } else {
                 yearMonthForIndex(monthIndexForItem(listState.firstVisibleItemIndex))
             }
@@ -393,7 +396,7 @@ fun MonthScreen(
             }
     }
 
-    val isOnCurrentMonth = titleMonth == YearMonth(today.year, today.month)
+    val isOnCurrentMonth = titleMonth == today.yearMonth
     var splitExpanded by rememberSaveable(viewStyle) {
         mutableStateOf(viewStyle == MonthViewStyle.Paged)
     }
@@ -422,7 +425,7 @@ fun MonthScreen(
     val jumpToToday: () -> Unit = {
         todayPulse++
         if (scrolling) {
-            val targetMonth = YearMonth(today.year, today.month)
+            val targetMonth = today.yearMonth
             pendingScrollMonth = targetMonth
             val requestId = ++scrollRequestId
             viewModel.goToToday()
@@ -440,13 +443,13 @@ fun MonthScreen(
             }
         } else {
             viewModel.goToToday()
-            jumpToMonth(YearMonth(today.year, today.month))
+            jumpToMonth(today.yearMonth)
         }
     }
     // Drawer jump-to-date.
     val jumpToDate: (LocalDate) -> Unit = { target ->
         if (scrolling) {
-            val targetMonth = YearMonth(target.year, target.month)
+            val targetMonth = target.yearMonth
             pendingScrollMonth = targetMonth
             val requestId = ++scrollRequestId
             viewModel.goToDate(target)
@@ -464,7 +467,7 @@ fun MonthScreen(
             }
         } else {
             viewModel.goToDate(target)
-            jumpToMonth(YearMonth(target.year, target.month))
+            jumpToMonth(target.yearMonth)
         }
     }
 
@@ -548,7 +551,7 @@ fun MonthScreen(
                         // still settling would land and take the tap back.
                         onSelectDay = { date ->
                             viewModel.selectDate(date)
-                            jumpToMonth(YearMonth(date.year, date.month))
+                            jumpToMonth(date.yearMonth)
                         },
                         onOpenDay = onOpenDay,
                         onEventClick = onEventClick,
@@ -721,7 +724,7 @@ internal fun WeekdayHeader(weekStart: DayOfWeek, showWeekNumbers: Boolean) {
         if (showWeekNumbers) Spacer(Modifier.width(rememberWeekNumberGutter()))
         days.forEach { dow ->
             val isWeekend = dow == DayOfWeek.SATURDAY || dow == DayOfWeek.SUNDAY
-            val javaDow = java.time.DayOfWeek.of(dow.ordinal + 1)
+            val javaDow = dow.toJavaDayOfWeek()
             Text(
                 text = javaDow.getDisplayName(JavaTextStyle.SHORT, locale),
                 style = MaterialTheme.typography.labelMedium,
@@ -940,7 +943,7 @@ internal fun ContinuousMonthGrid(
     modifier: Modifier = Modifier,
 ) {
     val monthCount = remember { continuousMonthCount() }
-    val todayMonth = remember(state.today) { YearMonth(state.today.year, state.today.month) }
+    val todayMonth = remember(state.today) { state.today.yearMonth }
     val timeChipWidth = rememberMonthTimeChipWidth()
     LazyColumn(
         state = listState,
@@ -2698,7 +2701,7 @@ private fun DayNumberCell(
 private fun shortMonthName(date: LocalDate): String {
     val locale = currentLocale()
     return remember(date.month, locale) {
-        java.time.Month.of(date.month.ordinal + 1)
+        date.month.toJavaMonth()
             .getDisplayName(JavaTextStyle.SHORT, locale)
     }
 }
@@ -2861,7 +2864,7 @@ private fun formatMonthTitle(
     abbreviated: Boolean = false,
 ): String =
     formatCalendarTitle(
-        date = java.time.LocalDate.of(ym.year, ym.month.ordinal + 1, 1),
+        date = ym.firstDay.toJavaLocalDate(),
         locale = locale,
         currentYear = currentYear,
         skeleton = if (abbreviated) "LLL" else "LLLL",

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthStylePreview.kt

@@ -14,10 +14,10 @@ import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
-import kotlinx.datetime.YearMonth
 import kotlinx.datetime.plus
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Clock
+import kotlinx.datetime.yearMonth
 
 /**
  * A live, scaled-down Month view in a given [MonthViewStyle], for the settings
@@ -51,7 +51,7 @@ internal fun MonthStylePreview(
                 state = sample.continuous,
                 listState = rememberLazyListState(
                     initialFirstVisibleItemIndex = itemIndexForMonth(
-                        monthIndexOf(YearMonth(today.year, today.month)),
+                        monthIndexOf(today.yearMonth),
                     ),
                 ),
                 showWeekNumbers = false,
@@ -109,7 +109,7 @@ private fun sampleMonthState(
     weekStart: DayOfWeek,
     zone: TimeZone,
 ): SampleMonth {
-    val ym = YearMonth(today.year, today.month)
+    val ym = today.yearMonth
     val first = LocalDate(ym.year, ym.month, 1)
     val events = sampleMonthEvents(first, today, zone)
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthViewModel.kt

@@ -47,6 +47,7 @@ import kotlinx.datetime.plus
 import kotlinx.datetime.toLocalDateTime
 import kotlin.time.Instant
 import javax.inject.Inject
+import kotlinx.datetime.yearMonth
 
 /** How many months either side of the requested one [MonthViewModel.month] keeps cached. */
 private const val MONTH_CACHE_SPAN = 2
@@ -100,7 +101,7 @@ class MonthViewModel @Inject constructor(
         }
         .stateWhileSubscribed(viewModelScope, todayDate)
 
-    private val _month = MutableStateFlow(YearMonth(todayDate.year, todayDate.month))
+    private val _month = MutableStateFlow(todayDate.yearMonth)
     val month: StateFlow<YearMonth> = _month
 
     /**
@@ -181,11 +182,11 @@ class MonthViewModel @Inject constructor(
 
     /** Last reported visible range, so a widening step can re-centre on it. */
     @Volatile
-    private var visibleMonths = monthIndexOf(YearMonth(todayDate.year, todayDate.month))
+    private var visibleMonths = monthIndexOf(todayDate.yearMonth)
         .let { it..it }
 
     private val _loadedMonths = MutableStateFlow(
-        monthIndexOf(YearMonth(todayDate.year, todayDate.month))
+        monthIndexOf(todayDate.yearMonth)
             .let { clampMonthWindow(it - INITIAL_PAD..it + INITIAL_PAD) },
     )
 
@@ -201,10 +202,8 @@ class MonthViewModel @Inject constructor(
                 // Widened to whole grid weeks at both ends: a month block still
                 // has to know about an event that starts in the boundary week's
                 // clipped-off days, or a bar running into the block would vanish.
-                val first = firstOfMonth(yearMonthForIndex(window.first)).startOfWeek(ws)
-                val last = firstOfMonth(yearMonthForIndex(window.last))
-                    .plus(1, DateTimeUnit.MONTH)
-                    .minus(1, DateTimeUnit.DAY)
+                val first = yearMonthForIndex(window.first).firstDay.startOfWeek(ws)
+                val last = yearMonthForIndex(window.last).lastDay
                     .startOfWeek(ws)
                     .plus(6, DateTimeUnit.DAY)
                 val range = dayRange(first, last, zone)
@@ -305,7 +304,7 @@ class MonthViewModel @Inject constructor(
      * silently list a date the grid isn't pointing at.
      */
     fun selectDate(date: LocalDate) {
-        val target = YearMonth(date.year, date.month)
+        val target = date.yearMonth
         _selectedDate.value = if (target == _month.value && _selectedDate.value == date) null else date
         if (target != _month.value) _month.value = target
     }
@@ -320,12 +319,12 @@ class MonthViewModel @Inject constructor(
         } else {
             val next = selected.plus(days, DateTimeUnit.DAY)
             _selectedDate.value = next
-            _month.value = YearMonth(next.year, next.month)
+            _month.value = next.yearMonth
         }
     }
 
     fun goToToday() {
-        _month.value = YearMonth(todayDate.year, todayDate.month)
+        _month.value = todayDate.yearMonth
         _selectedDate.value = null
     }
 
@@ -336,8 +335,8 @@ class MonthViewModel @Inject constructor(
      */
     private fun followToday(old: LocalDate, new: LocalDate) {
         if (viewStyle.value.isScrolling) return
-        if (_month.value != YearMonth(old.year, old.month)) return
-        _month.value = YearMonth(new.year, new.month)
+        if (_month.value != old.yearMonth) return
+        _month.value = new.yearMonth
         _selectedDate.value = null
     }
 
@@ -357,7 +356,7 @@ class MonthViewModel @Inject constructor(
 
     /** Jump to the month containing [date] (drawer jump-to-date). */
     fun goToDate(date: LocalDate) {
-        _month.value = YearMonth(date.year, date.month)
+        _month.value = date.yearMonth
         _selectedDate.value = date
     }
 
@@ -407,7 +406,7 @@ internal fun layoutMonthWeeks(
     byDay: DayIndex,
     zone: TimeZone,
 ): List<MonthWeek> {
-    val gridStart = firstOfMonth(ym).startOfWeek(weekStart)
+    val gridStart = ym.firstDay.startOfWeek(weekStart)
     val weekCount = weekRowsInMonth(ym, weekStart)
 
     return (0 until weekCount).map { row ->
@@ -528,8 +527,7 @@ internal fun monthGridRange(
     weekStart: DayOfWeek,
     zone: TimeZone,
 ): ClosedRange<Instant> {
-    val firstOfMonth = LocalDate(ym.year, ym.month, 1)
-    val gridStart = firstOfMonth.startOfWeek(weekStart)
+    val gridStart = ym.firstDay.startOfWeek(weekStart)
     return dayRange(gridStart, gridStart.plus(41, DateTimeUnit.DAY), zone)
 }
 
@@ -558,7 +556,7 @@ internal fun edgeForPad(pad: Int): Int = minOf(WINDOW_EDGE, pad - 1).coerceAtLea
  * the first of the visible month.
  */
 internal fun agendaStartForMonth(month: YearMonth, today: LocalDate): LocalDate =
-    if (YearMonth(today.year, today.month) == month) {
+    if (today.yearMonth == month) {
         today
     } else {
         LocalDate(month.year, month.month, 1)
@@ -626,8 +624,6 @@ internal fun clampMonthWindow(window: IntRange): IntRange {
     return window.first.coerceIn(0, last)..window.last.coerceIn(0, last)
 }
 
-internal fun firstOfMonth(ym: YearMonth): LocalDate = LocalDate(ym.year, ym.month, 1)
-
 /**
  * The Dense style addresses *weeks* by absolute index instead: it has no month
  * blocks to key by, and a row's identity has to survive the months around it
@@ -658,7 +654,7 @@ internal fun monthIndexForWeek(weekIndex: Int, weekStart: DayOfWeek): Int {
     // The row's midweek day: a boundary week is reported as whichever month owns
     // most of it, the same rule the title uses.
     val midweek = weekStartForIndex(weekIndex, weekStart).plus(3, DateTimeUnit.DAY)
-    return monthIndexOf(YearMonth(midweek.year, midweek.month))
+    return monthIndexOf(midweek.yearMonth)
 }
 
 /**
@@ -667,19 +663,16 @@ internal fun monthIndexForWeek(weekIndex: Int, weekStart: DayOfWeek): Int {
  * laid out too, rather than flickering as placeholders.
  */
 internal fun weekWindowFor(window: IntRange, weekStart: DayOfWeek): IntRange {
-    val first = weekIndexOf(firstOfMonth(yearMonthForIndex(window.first)), weekStart) - 1
-    val lastMonthEnd = firstOfMonth(yearMonthForIndex(window.last))
-        .plus(1, DateTimeUnit.MONTH)
-        .minus(1, DateTimeUnit.DAY)
+    val first = weekIndexOf(yearMonthForIndex(window.first).firstDay, weekStart) - 1
+    val lastMonthEnd = yearMonthForIndex(window.last).lastDay
     return first..(weekIndexOf(lastMonthEnd, weekStart) + 1)
 }
 
 /** How many week rows [ym] needs under [weekStart] — 4 (a non-leap February), 5 or 6. */
 internal fun weekRowsInMonth(ym: YearMonth, weekStart: DayOfWeek): Int {
-    val first = firstOfMonth(ym)
+    val first = ym.firstDay
     val leadOffset = ((first.dayOfWeek.ordinal - weekStart.ordinal) + 7) % 7
-    val daysInMonth = java.time.YearMonth.of(ym.year, ym.month.ordinal + 1).lengthOfMonth()
-    return (leadOffset + daysInMonth + 6) / 7
+    return (leadOffset + ym.numberOfDays + 6) / 7
 }
 
 /**

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/ViewsSettings.kt

@@ -56,6 +56,7 @@ import de.jeanlucmakiola.floret.components.ReorderableRowHeight
 import de.jeanlucmakiola.floret.locale.currentLocale
 import kotlinx.datetime.DayOfWeek
 import java.time.format.TextStyle as JavaTextStyle
+import kotlinx.datetime.toJavaDayOfWeek
 
 /**
  * Views: everything that changes how a calendar view reads, grouped by the view
@@ -504,7 +505,7 @@ private val WEEK_START_OPTIONS: List<WeekStartPref> =
 internal fun weekStartLabel(pref: WeekStartPref): String = when (pref) {
     WeekStartPref.Auto -> stringResource(R.string.settings_week_start_auto)
     // Localised weekday name, so no per-day string resource is needed.
-    is WeekStartPref.Day -> java.time.DayOfWeek.of(pref.day.ordinal + 1)
+    is WeekStartPref.Day -> pref.day.toJavaDayOfWeek()
         .getDisplayName(JavaTextStyle.FULL, currentLocale())
 }
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -202,10 +202,12 @@ import kotlinx.coroutines.launch
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
 import kotlinx.datetime.plus
+import kotlinx.datetime.toJavaDayOfWeek
 import kotlinx.datetime.toJavaLocalDate
 import kotlinx.datetime.toLocalDateTime
 import java.time.format.TextStyle as JavaTextStyle
 import java.util.Locale
+import kotlinx.datetime.yearMonth
 
 /** One lane of the all-day strip, sized to a trimmed bar line (#190). */
 private val ALL_DAY_ROW_HEIGHT = 20.dp
@@ -1084,7 +1086,7 @@ private fun WeekDayHeader(
             .fillMaxWidth()
             .padding(top = HEADER_TOP_PADDING, bottom = HEADER_BOTTOM_PADDING, end = TIMELINE_CONTENT_END_INSET),
     ) { date ->
-        val javaDow = java.time.DayOfWeek.of(date.dayOfWeek.ordinal + 1)
+        val javaDow = date.dayOfWeek.toJavaDayOfWeek()
         val isToday = date == today
         Column(
             modifier = Modifier
@@ -1958,7 +1960,7 @@ private fun formatWeekTitle(
     abbreviated: Boolean = false,
 ): String {
     return formatCalendarTitle(
-        date = java.time.LocalDate.of(weekStart.year, weekStart.month.ordinal + 1, 1),
+        date = weekStart.yearMonth.firstDay.toJavaLocalDate(),
         locale = locale,
         currentYear = currentYear,
         skeleton = if (abbreviated) "LLL" else "LLLL",
@@ -1974,7 +1976,7 @@ private fun formatDayTitle(
     abbreviated: Boolean = false,
 ): String =
     formatCalendarTitle(
-        date = java.time.LocalDate.of(date.year, date.month.ordinal + 1, date.day),
+        date = date.toJavaLocalDate(),
         locale = locale,
         currentYear = currentYear,
         skeleton = if (abbreviated) "dMMM" else "EEEdMMM",

app/src/test/java/de/jeanlucmakiola/calendula/ui/month/ContinuousMonthIndexTest.kt

@@ -121,8 +121,8 @@ class ContinuousMonthIndexTest {
             val weeks = weekWindowFor(window, ws)
             window.forEach { index ->
                 val ym = yearMonthForIndex(index)
-                val first = weekIndexOf(firstOfMonth(ym), ws)
-                val last = weekIndexOf(firstOfMonth(yearMonthForIndex(index + 1)).minus(1, DateTimeUnit.DAY), ws)
+                val first = weekIndexOf(ym.firstDay, ws)
+                val last = weekIndexOf(yearMonthForIndex(index + 1).firstDay.minus(1, DateTimeUnit.DAY), ws)
                 assertThat(weeks.contains(first)).isTrue()
                 assertThat(weeks.contains(last)).isTrue()
             }
@@ -162,8 +162,8 @@ class ContinuousMonthIndexTest {
     }
 
     @Test
-    fun `firstOfMonth is the 1st`() {
-        assertThat(firstOfMonth(jun26)).isEqualTo(LocalDate(2026, 6, 1))
+    fun `firstDay is the 1st`() {
+        assertThat(jun26.firstDay).isEqualTo(LocalDate(2026, 6, 1))
     }
 
     @Test