fix(screensaver): fade only on a move, survive dock and theme changes

The in-app screen saver also handles uiMode, density, font scale and
locale changes in place, so docking it or the dark-theme schedule no
longer recreates it at night brightness. Only a move crossfades; a new
next alarm or a settings change redraws in place, and the outgoing copy
keeps its own minute. The AM/PM split skips quoted pattern text, and
rememberLocalTimeFormatter reads the same currentLocale() as the screen
saver.

app/src/main/AndroidManifest.xml

@@ -308,12 +308,13 @@
 
         <!-- The same screen saver on demand, from the tabs' overflow menu: an
              app cannot start the system's dream itself. Not exported; it
-             finishes itself once no longer shown. Rotating into a dock or a
-             stand re-lays it out rather than recreating it, which would
-             flash black and reset its brightness. -->
+             finishes itself once no longer shown. Rotating it into a stand,
+             docking it, or the dark-theme schedule firing re-lays it out
+             rather than recreating it, which would flash black and reset its
+             brightness. -->
         <activity
             android:name=".ui.screensaver.ScreenSaverActivity"
-            android:configChanges="orientation|screenSize|smallestScreenSize|screenLayout|keyboardHidden"
+            android:configChanges="orientation|screenSize|smallestScreenSize|screenLayout|keyboardHidden|uiMode|density|fontScale|locale|layoutDirection"
             android:exported="false"
             android:theme="@style/Theme.Clockula.ScreenSaver" />
 

app/src/main/java/de/jeanlucmakiola/clockula/ui/common/AlarmTimeFormatter.kt

@@ -6,6 +6,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.ui.platform.LocalConfiguration
 import androidx.compose.ui.platform.LocalContext
 import de.jeanlucmakiola.clockula.domain.TimeOfDay
+import de.jeanlucmakiola.floret.locale.currentLocale
 import java.time.LocalTime
 import java.time.chrono.IsoChronology
 import java.time.format.DateTimeFormatter
@@ -26,8 +27,8 @@ internal fun rememberLocalTimeFormatter(): (LocalTime) -> String {
     // The locale can change under a running activity, and the 12/24-hour
     // choice rides the same configuration, so both are re-read with it.
     val configuration = LocalConfiguration.current
-    val formatter = remember(configuration) {
-        val locale = Locale.getDefault(Locale.Category.FORMAT)
+    val locale = currentLocale()
+    val formatter = remember(configuration, locale) {
         DateTimeFormatter.ofPattern(localTimePattern(DateFormat.is24HourFormat(context), locale), locale)
     }
     return remember(formatter) {

app/src/main/java/de/jeanlucmakiola/clockula/ui/screensaver/ScreenSaverContent.kt

@@ -61,7 +61,8 @@ import kotlin.math.roundToInt
  * moves once a minute ([ScreenSaverDrift]) so nothing stays lit in one place.
  * The move is a slow crossfade rather than a slide, as DeskClock's is, and
  * a cut under reduce motion: the old minute fades out where it was as the
- * new one fades in at its new spot.
+ * new one fades in at its new spot. Only a move fades: a new next alarm or
+ * a settings change redraws in place.
  */
 @Composable
 internal fun ScreenSaverContent(state: ScreenSaverUiState, modifier: Modifier = Modifier) {
@@ -76,19 +77,31 @@ internal fun ScreenSaverContent(state: ScreenSaverUiState, modifier: Modifier =
         // Sized from the screen's shorter side, so the clock is as large in
         // landscape on a bedside dock as it is upright in the hand.
         val side = minOf(maxWidth, maxHeight)
+        // The last frame drawn at each spot, so the outgoing copy keeps its
+        // own minute while it fades. Two are all a crossfade ever shows.
+        val frames = remember { RecentFrames() }
+        frames[state.position] = state
         Crossfade(
-            targetState = state,
+            targetState = state.position,
             animationSpec = if (reduceMotion) snap() else tween(ScreenSaverDefaults.MOVE_MILLIS),
             label = "drift",
-        ) { shown ->
+        ) { position ->
+            val current = position == state.position
+            val shown = if (current) state else frames[position] ?: state
             // The outgoing minute is only a picture while it fades: a screen
             // reader finds one time on screen, never two.
-            val semantics = if (shown == state) Modifier else Modifier.clearAndSetSemantics {}
-            Drifting(shown.position, semantics) { Clock(shown, side) }
+            val semantics = if (current) Modifier else Modifier.clearAndSetSemantics {}
+            Drifting(position, semantics) { Clock(shown, side) }
         }
     }
 }
 
+/** The newest two frames by position; older ones have finished fading. */
+private class RecentFrames : LinkedHashMap<ScreenSaverDrift.Position, ScreenSaverUiState>() {
+    override fun removeEldestEntry(eldest: MutableMap.MutableEntry<ScreenSaverDrift.Position, ScreenSaverUiState>?): Boolean =
+        size > 2
+}
+
 /** Places its one child at [position]'s fractions of the space the child leaves free. */
 @Composable
 private fun Drifting(position: ScreenSaverDrift.Position, modifier: Modifier, content: @Composable () -> Unit) {
@@ -221,7 +234,7 @@ private data class TimeParts(val before: String, val marker: String, val after:
 
 private fun timeParts(time: LocalTime, use24Hour: Boolean, locale: Locale): TimeParts {
     val pattern = localTimePattern(use24Hour, locale)
-    val markerAt = pattern.indexOf('a')
+    val markerAt = markerIndex(pattern)
     if (markerAt < 0) return TimeParts(format(time, pattern, locale), "", "")
     return runCatching {
         TimeParts(
@@ -232,6 +245,18 @@ private fun timeParts(time: LocalTime, use24Hour: Boolean, locale: Locale): Time
     }.getOrElse { TimeParts(format(time, pattern, locale), "", "") }
 }
 
+/** Where the pattern's AM/PM field is, skipping quoted literal text; -1 when it has none. */
+private fun markerIndex(pattern: String): Int {
+    var quoted = false
+    pattern.forEachIndexed { index, char ->
+        when {
+            char == '\'' -> quoted = !quoted
+            !quoted && char == 'a' -> return index
+        }
+    }
+    return -1
+}
+
 private fun format(time: LocalTime, pattern: String, locale: Locale): String =
     if (pattern.isBlank()) pattern else DateTimeFormatter.ofPattern(pattern, locale).format(time)