One rollover-following today flow for the view models

app/src/main/java/de/jeanlucmakiola/calendula/data/time/TodaySource.kt

@@ -4,10 +4,14 @@ import android.content.Context
 import android.content.Intent
 import dagger.hilt.android.qualifiers.ApplicationContext
 import de.jeanlucmakiola.floret.android.broadcastTicks
+import de.jeanlucmakiola.floret.android.stateWhileSubscribed
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.transformLatest
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.TimeZone
@@ -43,3 +47,21 @@ class AndroidTodaySource @Inject constructor(
 private const val MINUTE_MILLIS = 60_000L
 
 fun currentDate(): LocalDate = Clock.System.now().toLocalDateTime(TimeZone.currentSystemDefault()).date
+
+/**
+ * Today as a hot flow seeded with [initial]. [onRollover] runs with the previous
+ * and the new date each time the day changes while collected, so a screen left
+ * open over midnight can move off yesterday (#373).
+ */
+fun Flow<LocalDate>.stateFollowingDays(
+    scope: CoroutineScope,
+    initial: LocalDate,
+    onRollover: (old: LocalDate, new: LocalDate) -> Unit,
+): StateFlow<LocalDate> {
+    var last = initial
+    return onEach { date ->
+        val old = last
+        last = date
+        if (old != date) onRollover(old, date)
+    }.stateWhileSubscribed(scope, initial)
+}

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

@@ -10,6 +10,7 @@ import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.data.time.TodaySource
 import de.jeanlucmakiola.calendula.data.time.currentDate
+import de.jeanlucmakiola.calendula.data.time.stateFollowingDays
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.FailureReason
@@ -26,7 +27,6 @@ import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
@@ -98,21 +98,14 @@ class AgendaViewModel @Inject constructor(
     var lastTopDate: LocalDate? = null
         private set
 
-    private var lastToday = todayDate
-
     /**
      * Today, kept current across midnight (#373). An agenda still starting on
      * yesterday moves on to the new day; one jumped elsewhere stays put.
      */
-    private val today: StateFlow<LocalDate> = todaySource.today
-        .onEach { date ->
-            val old = lastToday
-            lastToday = date
-            if (old != date && _window.value.anchor == old) {
-                _window.value = _window.value.copy(anchor = date)
-            }
+    private val today: StateFlow<LocalDate> =
+        todaySource.today.stateFollowingDays(viewModelScope, todayDate) { old, date ->
+            if (_window.value.anchor == old) _window.value = _window.value.copy(anchor = date)
         }
-        .stateWhileSubscribed(viewModelScope, todayDate)
 
     // A transient, in-view override of the saved agenda range. Held in memory
     // (not persisted), so it survives view switches and rotation within the

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

@@ -10,6 +10,7 @@ import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.data.prefs.firstDayOfWeek
 import de.jeanlucmakiola.calendula.data.time.TodaySource
 import de.jeanlucmakiola.calendula.data.time.currentDate
+import de.jeanlucmakiola.calendula.data.time.stateFollowingDays
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.FailureReason
@@ -90,16 +91,9 @@ class MonthViewModel @Inject constructor(
     private val todayDate: LocalDate
         get() = currentDate()
 
-    private var lastToday = todayDate
-
     /** Today, kept current across midnight so a grid left open doesn't mark yesterday (#373). */
-    val today: StateFlow<LocalDate> = todaySource.today
-        .onEach { date ->
-            val old = lastToday
-            lastToday = date
-            if (old != date) followToday(old, date)
-        }
-        .stateWhileSubscribed(viewModelScope, todayDate)
+    val today: StateFlow<LocalDate> =
+        todaySource.today.stateFollowingDays(viewModelScope, todayDate, ::followToday)
 
     private val _month = MutableStateFlow(todayDate.yearMonth)
     val month: StateFlow<YearMonth> = _month

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

@@ -10,6 +10,7 @@ import de.jeanlucmakiola.calendula.data.prefs.resolveFirstDay
 import de.jeanlucmakiola.calendula.data.time.TodaySource
 import de.jeanlucmakiola.calendula.data.time.ZoneSource
 import de.jeanlucmakiola.calendula.data.time.currentDate
+import de.jeanlucmakiola.calendula.data.time.stateFollowingDays
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.displayPriority
@@ -32,7 +33,6 @@ import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.DayOfWeek
@@ -124,16 +124,9 @@ abstract class PagedTimelineViewModel(
     val rule: StateFlow<(LocalDate) -> PageGrid> =
         gridRule.stateIn(viewModelScope, SharingStarted.Eagerly, initialRule)
 
-    private var lastToday = todayDate
-
     /** Today, kept current across midnight so a page left open doesn't mark yesterday (#373). */
-    private val today: StateFlow<LocalDate> = todaySource.today
-        .onEach { date ->
-            val old = lastToday
-            lastToday = date
-            if (old != date) followToday(old, date)
-        }
-        .stateWhileSubscribed(viewModelScope, todayDate)
+    private val today: StateFlow<LocalDate> =
+        todaySource.today.stateFollowingDays(viewModelScope, todayDate, ::followToday)
 
     private val position: StateFlow<PagerPosition> =
         combine(_anchor, rule) { anchor, rule -> positionOf(anchor, rule) }