feat(settings): optional "Calendar" launcher name (#44)

Add a Settings → Appearance toggle that switches the app's launcher label
between "Calendula" and "Calendar", for users on launchers that can't rename
apps themselves.

The launcher entry moves off MainActivity onto two <activity-alias> components
(DefaultNameAlias / CalendarNameAlias); exactly one is enabled at a time via
PackageManager.setComponentEnabledSetting. MainActivity keeps every other intent
filter; the android.app.shortcuts meta-data moves onto both aliases so the
long-press shortcut still publishes. Component-enabled state is the single source
of truth — no persisted preference.

The ComponentName uses the applicationId for the package (carrying the
.debug/.releasetest suffix) and the namespace for the class, since manifest
".Alias" names resolve against the namespace; switching to Calendar enables the
target alias before disabling the other to avoid a zero-entry launcher transient.

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

app/src/main/java/de/jeanlucmakiola/calendula/data/appname/LauncherNameManager.kt

@@ -0,0 +1,109 @@
+package de.jeanlucmakiola.calendula.data.appname
+
+import android.content.ComponentName
+import android.content.Context
+import android.content.pm.PackageManager
+import dagger.hilt.android.qualifiers.ApplicationContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/** The launcher label the app shows for itself (issue #44). */
+enum class LauncherName { CALENDULA, CALENDAR }
+
+/** The two launcher aliases declared in the manifest. */
+enum class LauncherAlias { DEFAULT, CALENDAR }
+
+/** One component-enable change in a [aliasWritePlan]. */
+data class AliasStateChange(val alias: LauncherAlias, val enabled: Boolean)
+
+/**
+ * Interpret the `CalendarNameAlias` component-enabled state as a [LauncherName].
+ * Only [PackageManager.COMPONENT_ENABLED_STATE_ENABLED] means the "Calendar"
+ * name is active; `DEFAULT` (never toggled) and `DISABLED` both resolve to the
+ * manifest default, "Calendula".
+ */
+fun launcherNameFor(calendarAliasState: Int): LauncherName =
+    if (calendarAliasState == PackageManager.COMPONENT_ENABLED_STATE_ENABLED) {
+        LauncherName.CALENDAR
+    } else {
+        LauncherName.CALENDULA
+    }
+
+/**
+ * The ordered enable/disable steps to switch the launcher name to [target].
+ * Always **enables the target alias first, then disables the other** — the two
+ * `setComponentEnabledSetting` calls are not atomic, and this ordering means the
+ * only transient the launcher can observe is a harmless two-entry state, never a
+ * zero-entry one (which would briefly drop the app from the launcher).
+ */
+fun aliasWritePlan(target: LauncherName): List<AliasStateChange> = when (target) {
+    LauncherName.CALENDAR -> listOf(
+        AliasStateChange(LauncherAlias.CALENDAR, enabled = true),
+        AliasStateChange(LauncherAlias.DEFAULT, enabled = false),
+    )
+    LauncherName.CALENDULA -> listOf(
+        AliasStateChange(LauncherAlias.DEFAULT, enabled = true),
+        AliasStateChange(LauncherAlias.CALENDAR, enabled = false),
+    )
+}
+
+/**
+ * Switches the app's launcher label between "Calendula" and "Calendar" by
+ * enabling/disabling the two `<activity-alias>` components (issue #44). The
+ * component-enabled state is the single source of truth — there is no persisted
+ * preference — so [current] reads it straight from [PackageManager] and the two
+ * always agree.
+ *
+ * The decision logic lives in the pure [launcherNameFor] / [aliasWritePlan]
+ * functions above (JVM-tested); this class is only the thin framework seam.
+ */
+@Singleton
+class LauncherNameManager @Inject constructor(
+    @ApplicationContext private val context: Context,
+) {
+    private val packageManager: PackageManager get() = context.packageManager
+
+    // The class portion is namespace-qualified (suffix-free), the package portion
+    // is the applicationId (which carries the .debug / .releasetest suffix). The
+    // manifest's ".CalendarNameAlias" resolves its class against the namespace, so
+    // the real component is <namespace>.CalendarNameAlias registered under the
+    // suffixed applicationId. Do NOT use ComponentName(context, ".CalendarNameAlias")
+    // — its leading-dot form prepends the applicationId to the class too, producing
+    // "<appId>.CalendarNameAlias" and failing on every debug / releaseTest build.
+    private fun component(alias: LauncherAlias): ComponentName {
+        val simpleName = when (alias) {
+            LauncherAlias.DEFAULT -> "DefaultNameAlias"
+            LauncherAlias.CALENDAR -> "CalendarNameAlias"
+        }
+        return ComponentName(context.packageName, "$NAMESPACE.$simpleName")
+    }
+
+    /** The launcher name currently in effect. */
+    fun current(): LauncherName =
+        launcherNameFor(packageManager.getComponentEnabledSetting(component(LauncherAlias.CALENDAR)))
+
+    /** Switch the launcher name to [name] (no-op cost if already active). */
+    fun set(name: LauncherName) {
+        for (change in aliasWritePlan(name)) {
+            val state = if (change.enabled) {
+                PackageManager.COMPONENT_ENABLED_STATE_ENABLED
+            } else {
+                PackageManager.COMPONENT_ENABLED_STATE_DISABLED
+            }
+            packageManager.setComponentEnabledSetting(
+                component(change.alias),
+                state,
+                PackageManager.DONT_KILL_APP,
+            )
+        }
+    }
+
+    private companion object {
+        /**
+         * The app's namespace (R-class package) — NOT `applicationId`, which
+         * carries the build-type suffix. Kept in sync with `namespace` in
+         * `app/build.gradle.kts`.
+         */
+        const val NAMESPACE = "de.jeanlucmakiola.calendula"
+    }
+}

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

@@ -93,6 +93,7 @@ import androidx.lifecycle.LifecycleEventObserver
 import androidx.lifecycle.compose.LocalLifecycleOwner
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
+import de.jeanlucmakiola.calendula.data.appname.LauncherName
 import de.jeanlucmakiola.calendula.data.contacts.hasContactsPermission
 import de.jeanlucmakiola.calendula.data.prefs.PastEventDisplay
 import de.jeanlucmakiola.floret.reminders.ReminderOverride
@@ -489,6 +490,7 @@ private fun AppearanceScreen(
     var showPlainFont by remember { mutableStateOf(false) }
 
     val fonts by viewModel.fontState.collectAsStateWithLifecycle()
+    val launcherName by viewModel.launcherName.collectAsStateWithLifecycle()
     // A picked file that didn't parse as a font: tell the user and keep the old choice.
     val context = LocalContext.current
     val importFailedMessage = stringResource(R.string.settings_font_import_failed)
@@ -679,6 +681,36 @@ private fun AppearanceScreen(
             },
             onClick = { viewModel.setAgendaShowRangeBar(!state.agendaShowRangeBar) },
         )
+
+        Spacer(Modifier.height(16.dp))
+
+        // App name — flips the launcher label between "Calendula" and "Calendar"
+        // (issue #44). Own group: it's a launcher/system concern, not calendar
+        // formatting.
+        GroupedRow(
+            title = stringResource(R.string.settings_app_name),
+            summary = stringResource(R.string.settings_app_name_summary),
+            position = Position.Alone,
+            trailing = {
+                Switch(
+                    checked = launcherName == LauncherName.CALENDAR,
+                    onCheckedChange = {
+                        viewModel.setLauncherName(
+                            if (it) LauncherName.CALENDAR else LauncherName.CALENDULA,
+                        )
+                    },
+                )
+            },
+            onClick = {
+                viewModel.setLauncherName(
+                    if (launcherName == LauncherName.CALENDAR) {
+                        LauncherName.CALENDULA
+                    } else {
+                        LauncherName.CALENDAR
+                    },
+                )
+            },
+        )
     }
 
     if (showTheme) {

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

@@ -10,6 +10,8 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.calendula.data.appname.LauncherName
+import de.jeanlucmakiola.calendula.data.appname.LauncherNameManager
 import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
 import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesCalendarSpec
 import de.jeanlucmakiola.calendula.data.contacts.SpecialDatesScheduler
@@ -43,7 +45,9 @@ import de.jeanlucmakiola.calendula.widget.month.MonthWidget
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharedFlow
+import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.catch
@@ -62,6 +66,7 @@ class SettingsViewModel @Inject constructor(
     repository: CalendarRepository,
     private val specialDatesEngine: SpecialDatesSyncEngine,
     specialDatesSpec: SpecialDatesCalendarSpec,
+    private val launcherNameManager: LauncherNameManager,
     @IoDispatcher private val io: CoroutineDispatcher,
     @ApplicationContext private val appContext: Context,
 ) : ViewModel() {
@@ -202,6 +207,16 @@ class SettingsViewModel @Inject constructor(
         initialValue = AppFontSettings(),
     )
 
+    /**
+     * The launcher-label choice (issue #44). Backed by the manifest aliases'
+     * component-enabled state rather than a stored preference, so it's read
+     * imperatively via [LauncherNameManager] and held here in its own flow — the
+     * main settings combine is already at its arity limit and this isn't a
+     * DataStore flow anyway.
+     */
+    private val _launcherName = MutableStateFlow(launcherNameManager.current())
+    val launcherName: StateFlow<LauncherName> = _launcherName.asStateFlow()
+
     // Emitted when a picked font file couldn't be read as a font; the screen
     // surfaces it and the previous selection stays put.
     private val _fontImportFailed = MutableSharedFlow<Unit>(extraBufferCapacity = 1)
@@ -469,6 +484,13 @@ class SettingsViewModel @Inject constructor(
         viewModelScope.launch { prefs.setTodayButtonInToolbar(enabled) }
     }
 
+    /** Switch the launcher label between "Calendula" and "Calendar" (issue #44). */
+    fun setLauncherName(name: LauncherName) {
+        launcherNameManager.set(name)
+        // Re-read so the UI reflects the actual component state, not an assumption.
+        _launcherName.value = launcherNameManager.current()
+    }
+
     fun setPastEventDisplay(mode: PastEventDisplay) {
         viewModelScope.launch {
             prefs.setPastEventDisplay(mode)