feat(backup): automatic periodic .ics export of local calendars (#8)

Scheduled one-way export of local calendars to a user-chosen folder, overwriting calendula-backup.ics each run — the manual backup, automated. Not a sync; stays INTERNET-free (provider reads + local file write). - WorkManager periodic job (deps: work-runtime-ktx, documentfile); worker pulls collaborators via a Hilt @EntryPoint, so no custom WorkerFactory wiring. First periodic run is delayed one interval so it can't race the immediate "run now" feedback run; the writer also overwrites the canonical file and cleans up any "(1)" duplicates from earlier races. - SettingsPrefs: enabled, interval (minutes, floored at 30), folder Uri, last-run status; persisted SAF write grant. - UI in Calendars > Backup: toggle, folder picker, amount+unit interval dialog, last-run status line. Notifies after repeated failures. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-06-27 22:13:55 +02:00
parent a6ae4d7e1d
commit 548e581554
8 changed files with 531 additions and 0 deletions
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -152,6 +152,9 @@ dependencies {

    implementation(libs.androidx.datastore.preferences)

+    implementation(libs.androidx.work.runtime.ktx)
+    implementation(libs.androidx.documentfile)
+
    implementation(libs.androidx.glance.appwidget)
    implementation(libs.androidx.glance.material3)

--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/backup/AutoBackup.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/backup/AutoBackup.kt
@@ -0,0 +1,170 @@
+package de.jeanlucmakiola.calendula.data.backup
+
+import android.Manifest
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.PendingIntent
+import android.content.Context
+import android.content.pm.PackageManager
+import android.os.Build
+import android.util.Log
+import androidx.core.app.NotificationCompat
+import androidx.core.app.NotificationManagerCompat
+import androidx.core.content.ContextCompat
+import androidx.core.net.toUri
+import androidx.work.CoroutineWorker
+import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.ExistingWorkPolicy
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.PeriodicWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import dagger.hilt.EntryPoint
+import dagger.hilt.InstallIn
+import dagger.hilt.android.EntryPointAccessors
+import dagger.hilt.components.SingletonComponent
+import de.jeanlucmakiola.calendula.R
+import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
+import de.jeanlucmakiola.calendula.data.ics.IcsExporter
+import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
+import de.jeanlucmakiola.calendula.domain.ics.IcsWriter
+import kotlinx.coroutines.flow.first
+import java.util.concurrent.TimeUnit
+import kotlin.time.Clock
+
+/**
+ * Schedules and runs the automatic periodic `.ics` backup of local calendars
+ * (issue #8). One-way export only — it mirrors the manual "Back up" into a
+ * user-chosen folder on an interval; it is not a sync. Stays INTERNET-free:
+ * everything is local provider reads + a local file write.
+ */
+object BackupScheduler {
+
+    private const val WORK_NAME = "auto-backup"
+    private const val WORK_NAME_NOW = "auto-backup-now"
+
+    /**
+     * Reconcile the scheduled work with the current settings: enqueue a unique
+     * periodic request when backup is on and a folder is set, otherwise cancel
+     * it. WorkManager persists the request across reboots on its own.
+     *
+     * The first run is delayed by one interval so it never overlaps an immediate
+     * [runNow] (two simultaneous writes would race and leave a "(1)" duplicate).
+     */
+    fun apply(context: Context, enabled: Boolean, intervalMinutes: Long, hasFolder: Boolean) {
+        val workManager = WorkManager.getInstance(context)
+        if (!enabled || !hasFolder) {
+            workManager.cancelUniqueWork(WORK_NAME)
+            return
+        }
+        // WorkManager's own floor is 15 min; the UI floors the user choice at 30.
+        val interval = intervalMinutes.coerceAtLeast(15L)
+        val request = PeriodicWorkRequestBuilder<BackupWorker>(interval, TimeUnit.MINUTES)
+            .setInitialDelay(interval, TimeUnit.MINUTES)
+            .build()
+        workManager.enqueueUniquePeriodicWork(
+            WORK_NAME,
+            ExistingPeriodicWorkPolicy.UPDATE,
+            request,
+        )
+    }
+
+    /**
+     * Run one export immediately (e.g. right after enabling or changing the
+     * folder) for instant feedback. Unique + REPLACE so rapid taps coalesce into
+     * a single run rather than racing each other.
+     */
+    fun runNow(context: Context) {
+        WorkManager.getInstance(context).enqueueUniqueWork(
+            WORK_NAME_NOW,
+            ExistingWorkPolicy.REPLACE,
+            OneTimeWorkRequestBuilder<BackupWorker>().build(),
+        )
+    }
+}
+
+/**
+ * Exports the local calendars to `calendula-backup.ics` in the configured folder,
+ * overwriting the previous file. Pulls its collaborators through a Hilt
+ * [EntryPoint] so it works under WorkManager's default (no-arg) worker factory —
+ * no custom factory / Application wiring needed. Records the outcome for the
+ * settings status line, and notifies after repeated failures.
+ */
+class BackupWorker(
+    appContext: Context,
+    params: WorkerParameters,
+) : CoroutineWorker(appContext, params) {
+
+    @EntryPoint
+    @InstallIn(SingletonComponent::class)
+    interface Deps {
+        fun settingsPrefs(): SettingsPrefs
+        fun repository(): CalendarRepository
+        fun exporter(): IcsExporter
+    }
+
+    override suspend fun doWork(): Result {
+        val deps = EntryPointAccessors.fromApplication(applicationContext, Deps::class.java)
+        val prefs = deps.settingsPrefs()
+        val folder = prefs.autoBackupFolderUri.first()
+            ?: return Result.failure() // nothing to write to — leave scheduling to settings
+        val now = System.currentTimeMillis()
+        return try {
+            val events = deps.repository().exportEvents()
+            val content = IcsWriter().writeCalendar(events, Clock.System.now())
+            deps.exporter().writeToFolder(folder.toUri(), BACKUP_FILE_NAME, content)
+            prefs.recordAutoBackupRun(success = true, atMillis = now)
+            Result.success()
+        } catch (e: Exception) {
+            prefs.recordAutoBackupRun(success = false, atMillis = now)
+            if (prefs.autoBackupStatus.first().consecutiveFailures >= FAILURE_NOTIFY_THRESHOLD) {
+                notifyFailure(applicationContext)
+            }
+            Log.w(TAG, "Automatic backup failed", e)
+            Result.retry()
+        }
+    }
+
+    private fun notifyFailure(context: Context) {
+        val canPost = Build.VERSION.SDK_INT < Build.VERSION_CODES.TIRAMISU ||
+            ContextCompat.checkSelfPermission(context, Manifest.permission.POST_NOTIFICATIONS) ==
+            PackageManager.PERMISSION_GRANTED
+        if (!canPost) return
+        val manager = NotificationManagerCompat.from(context)
+        manager.createNotificationChannel(
+            NotificationChannel(
+                CHANNEL_ID,
+                context.getString(R.string.backup_channel_name),
+                NotificationManager.IMPORTANCE_LOW,
+            ).apply { description = context.getString(R.string.backup_channel_description) },
+        )
+        val launch = context.packageManager.getLaunchIntentForPackage(context.packageName)
+        val tap = launch?.let {
+            PendingIntent.getActivity(
+                context, 0, it,
+                PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE,
+            )
+        }
+        val notification = NotificationCompat.Builder(context, CHANNEL_ID)
+            .setSmallIcon(R.drawable.ic_notification)
+            .setContentTitle(context.getString(R.string.backup_failed_title))
+            .setContentText(context.getString(R.string.backup_failed_text))
+            .setCategory(NotificationCompat.CATEGORY_ERROR)
+            .setAutoCancel(true)
+            .apply { tap?.let(::setContentIntent) }
+            .build()
+        try {
+            manager.notify(NOTIFICATION_ID, notification)
+        } catch (e: SecurityException) {
+            Log.w(TAG, "Could not post backup-failure notification", e)
+        }
+    }
+
+    companion object {
+        const val BACKUP_FILE_NAME = "calendula-backup.ics"
+        private const val FAILURE_NOTIFY_THRESHOLD = 2
+        private const val CHANNEL_ID = "backup"
+        private const val NOTIFICATION_ID = 2
+        private const val TAG = "BackupWorker"
+    }
+}
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/ics/IcsExporter.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/ics/IcsExporter.kt
@@ -3,6 +3,7 @@ package de.jeanlucmakiola.calendula.data.ics
 import android.content.Context
 import android.net.Uri
 import androidx.core.content.FileProvider
+import androidx.documentfile.provider.DocumentFile
 import dagger.hilt.android.qualifiers.ApplicationContext
 import java.io.File
 import java.io.IOException
@@ -28,6 +29,36 @@ class IcsExporter @Inject constructor(
        } ?: throw IOException("Could not open output stream for export (scheme=${uri.scheme})")
    }

+    /**
+     * Write [content] to [fileName] inside the persisted SAF tree [folder],
+     * overwriting it if it already exists (the automatic-backup destination).
+     * Requires a persisted write grant on [folder]. Throws on failure.
+     */
+    fun writeToFolder(folder: Uri, fileName: String, content: String) {
+        val dir = DocumentFile.fromTreeUri(context, folder)
+            ?: throw IOException("Backup folder is not accessible")
+        if (!dir.exists() || !dir.canWrite()) {
+            throw IOException("Backup folder is missing or not writable")
+        }
+        // Reuse the canonical file if present and clean up any "name (1).ics"
+        // duplicates SAF may have created if two runs ever raced — so we always
+        // converge on a single overwritten file.
+        val base = fileName.substringBeforeLast('.')
+        val ext = fileName.substringAfterLast('.', "")
+        var target: DocumentFile? = null
+        for (child in dir.listFiles()) {
+            val name = child.name ?: continue
+            when {
+                name == fileName -> target = child
+                name.startsWith("$base (") && name.endsWith(".$ext") -> child.delete()
+            }
+        }
+        val file = target
+            ?: dir.createFile(MIME_CALENDAR, fileName)
+            ?: throw IOException("Could not create backup file in the chosen folder")
+        writeDocument(file.uri, content)
+    }
+
    /**
     * Stage [content] in a private cache file and return a shareable content
     * Uri for an `ACTION_SEND`. [fileName] is the suggested `.ics` name shown to
@@ -42,5 +73,6 @@ class IcsExporter @Inject constructor(

    private companion object {
        const val SHARE_DIR = "shared_ics"
+        const val MIME_CALENDAR = "text/calendar"
    }
 }
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/prefs/SettingsPrefs.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/prefs/SettingsPrefs.kt
@@ -5,6 +5,7 @@ import androidx.datastore.preferences.core.Preferences
 import androidx.datastore.preferences.core.booleanPreferencesKey
 import androidx.datastore.preferences.core.edit
 import androidx.datastore.preferences.core.intPreferencesKey
+import androidx.datastore.preferences.core.longPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.ui.agenda.AgendaRange
@@ -327,6 +328,52 @@ class SettingsPrefs @Inject constructor(
        }
    }

+    // --- Automatic backup (issue #8) ------------------------------------
+
+    /** Whether periodic automatic `.ics` export of local calendars is on. Default OFF. */
+    val autoBackupEnabled: Flow<Boolean> = store.data.map { it[AUTO_BACKUP_ENABLED_KEY] ?: false }
+
+    suspend fun setAutoBackupEnabled(enabled: Boolean) {
+        store.edit { it[AUTO_BACKUP_ENABLED_KEY] = enabled }
+    }
+
+    /** Export interval in minutes. Default daily; floored at [MIN_BACKUP_INTERVAL]. */
+    val autoBackupIntervalMinutes: Flow<Long> = store.data.map { prefs ->
+        (prefs[AUTO_BACKUP_INTERVAL_KEY] ?: DEFAULT_BACKUP_INTERVAL).coerceAtLeast(MIN_BACKUP_INTERVAL)
+    }
+
+    suspend fun setAutoBackupIntervalMinutes(minutes: Long) {
+        store.edit { it[AUTO_BACKUP_INTERVAL_KEY] = minutes.coerceAtLeast(MIN_BACKUP_INTERVAL) }
+    }
+
+    /** Persisted SAF tree Uri of the destination folder, or null if unset. */
+    val autoBackupFolderUri: Flow<String?> = store.data.map { it[AUTO_BACKUP_FOLDER_KEY] }
+
+    suspend fun setAutoBackupFolderUri(uri: String?) {
+        store.edit { prefs ->
+            if (uri == null) prefs.remove(AUTO_BACKUP_FOLDER_KEY) else prefs[AUTO_BACKUP_FOLDER_KEY] = uri
+        }
+    }
+
+    /** Outcome of the last automatic run, for the settings status line. */
+    val autoBackupStatus: Flow<BackupStatus> = store.data.map { prefs ->
+        BackupStatus(
+            lastRun = prefs[AUTO_BACKUP_LAST_RUN_KEY] ?: 0L,
+            lastSuccess = prefs[AUTO_BACKUP_LAST_SUCCESS_KEY] ?: true,
+            consecutiveFailures = prefs[AUTO_BACKUP_FAILURES_KEY] ?: 0,
+        )
+    }
+
+    /** Record an automatic run's outcome; resets the failure streak on success. */
+    suspend fun recordAutoBackupRun(success: Boolean, atMillis: Long) {
+        store.edit { prefs ->
+            prefs[AUTO_BACKUP_LAST_RUN_KEY] = atMillis
+            prefs[AUTO_BACKUP_LAST_SUCCESS_KEY] = success
+            val failures = prefs[AUTO_BACKUP_FAILURES_KEY] ?: 0
+            prefs[AUTO_BACKUP_FAILURES_KEY] = if (success) 0 else failures + 1
+        }
+    }
+
    private fun parseFormFields(stored: String?): Set<EventFormField> = when (stored) {
        null -> DEFAULT_FORM_FIELDS
        else -> stored.split(',')
@@ -366,9 +413,27 @@ class SettingsPrefs @Inject constructor(
            stringPreferencesKey("per_calendar_allday_reminder_override")
        internal val DEFAULT_FORM_FIELDS =
            setOf(EventFormField.Location, EventFormField.Description)
+        internal val AUTO_BACKUP_ENABLED_KEY = booleanPreferencesKey("auto_backup_enabled")
+        internal val AUTO_BACKUP_INTERVAL_KEY = longPreferencesKey("auto_backup_interval_minutes")
+        internal val AUTO_BACKUP_FOLDER_KEY = stringPreferencesKey("auto_backup_folder_uri")
+        internal val AUTO_BACKUP_LAST_RUN_KEY = longPreferencesKey("auto_backup_last_run")
+        internal val AUTO_BACKUP_LAST_SUCCESS_KEY = booleanPreferencesKey("auto_backup_last_success")
+        internal val AUTO_BACKUP_FAILURES_KEY = intPreferencesKey("auto_backup_failures")
+        /** Default automatic-backup interval: daily. */
+        const val DEFAULT_BACKUP_INTERVAL = 1_440L
+        /** Floor for the automatic-backup interval (also above WorkManager's 15-min limit). */
+        const val MIN_BACKUP_INTERVAL = 30L
    }
 }

+/** Snapshot of the automatic backup's last outcome (see [SettingsPrefs.autoBackupStatus]). */
+data class BackupStatus(
+    /** Epoch millis of the last run, or 0 if it has never run. */
+    val lastRun: Long,
+    val lastSuccess: Boolean,
+    val consecutiveFailures: Int,
+)
+
 /** A calendar's reminder-default override (see [SettingsPrefs.perCalendarReminderOverride]). */
 sealed interface CalendarReminderOverride {
    /** No override — the calendar uses the global default. */
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsScreen.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsScreen.kt
@@ -4,6 +4,7 @@ import android.accounts.AccountManager
 import android.content.Context
 import android.content.Intent
 import android.provider.Settings
+import android.text.format.DateUtils
 import androidx.activity.compose.rememberLauncherForActivityResult
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.compose.animation.AnimatedVisibility
@@ -39,6 +40,7 @@ import androidx.compose.material.icons.filled.FileDownload
 import androidx.compose.material.icons.filled.MoreVert
 import androidx.compose.material.icons.filled.Palette
 import androidx.compose.material.icons.filled.PhoneAndroid
+import androidx.compose.material.icons.filled.Schedule
 import androidx.compose.material.icons.filled.Visibility
 import androidx.compose.material.icons.filled.VisibilityOff
 import androidx.compose.material3.AlertDialog
@@ -76,18 +78,26 @@ import androidx.compose.ui.graphics.asImageBitmap
 import androidx.compose.ui.graphics.vector.ImageVector
 import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.pluralStringResource
+import androidx.compose.ui.res.stringArrayResource
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.input.KeyboardCapitalization
 import androidx.compose.ui.unit.dp
 import androidx.core.graphics.drawable.toBitmap
+import androidx.core.net.toUri
+import androidx.documentfile.provider.DocumentFile
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
+import de.jeanlucmakiola.calendula.data.prefs.BackupStatus
+import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.ui.common.CALENDAR_COLOR_PALETTE
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
+import de.jeanlucmakiola.calendula.ui.common.DialogAmountField
+import de.jeanlucmakiola.calendula.ui.common.DialogUnitDropdown
 import de.jeanlucmakiola.calendula.ui.common.calendarCollapseExit
 import de.jeanlucmakiola.calendula.ui.common.calendarExpandEnter
 import de.jeanlucmakiola.calendula.ui.common.predictiveBack
@@ -118,6 +128,7 @@ fun CalendarsScreen(
    val disabledIds by viewModel.disabledCalendarIds.collectAsStateWithLifecycle()
    val error by viewModel.error.collectAsStateWithLifecycle()
    val backupResult by viewModel.backupResult.collectAsStateWithLifecycle()
+    val autoBackup by viewModel.autoBackup.collectAsStateWithLifecycle()

    // null = list; NEW_CALENDAR_ID = create; any other id = edit that calendar.
    // [editorSession] bumps on every open so the editor's field state resets for
@@ -158,6 +169,10 @@ fun CalendarsScreen(
            backupResult = backupResult,
            onExportBackup = viewModel::exportBackup,
            onConsumeBackupResult = viewModel::consumeBackupResult,
+            autoBackup = autoBackup,
+            onSetAutoBackupEnabled = viewModel::setAutoBackupEnabled,
+            onSetAutoBackupInterval = viewModel::setAutoBackupIntervalMinutes,
+            onSetAutoBackupFolder = viewModel::setAutoBackupFolder,
            onBack = onBack,
            onAdd = { editorSession++; editorId = NEW_CALENDAR_ID },
            onEdit = { calendar -> editorSession++; editorId = calendar.id },
@@ -177,6 +192,10 @@ private fun CalendarsList(
    backupResult: BackupResult?,
    onExportBackup: (android.net.Uri) -> Unit,
    onConsumeBackupResult: () -> Unit,
+    autoBackup: AutoBackupUiState,
+    onSetAutoBackupEnabled: (Boolean) -> Unit,
+    onSetAutoBackupInterval: (Long) -> Unit,
+    onSetAutoBackupFolder: (android.net.Uri) -> Unit,
    onBack: () -> Unit,
    onAdd: () -> Unit,
    onEdit: (CalendarSource) -> Unit,
@@ -204,6 +223,13 @@ private fun CalendarsList(
        contract = ActivityResultContracts.CreateDocument("text/calendar"),
    ) { uri -> uri?.let(onExportBackup) }

+    // SAF folder picker for the automatic-backup destination; the VM persists the
+    // write grant so background runs can keep writing to it.
+    val pickFolder = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.OpenDocumentTree(),
+    ) { uri -> uri?.let(onSetAutoBackupFolder) }
+    var showInterval by remember { mutableStateOf(false) }
+
    val backupFailedText = stringResource(R.string.calendars_backup_failed)
    LaunchedEffect(backupResult) {
        when (val r = backupResult) {
@@ -288,6 +314,35 @@ private fun CalendarsList(
                    runCatching { createBackup.launch("calendula-backup-${LocalDate.now()}.ics") }
                },
            )
+
+            // Automatic periodic export to a chosen folder (issue #8).
+            Spacer(Modifier.height(16.dp))
+            GroupedRow(
+                title = stringResource(R.string.calendars_auto_backup),
+                summary = stringResource(R.string.calendars_auto_backup_hint),
+                position = if (autoBackup.enabled) Position.Top else Position.Alone,
+                leading = { LeadingAvatar(Icons.Default.Schedule) },
+                trailing = {
+                    Switch(checked = autoBackup.enabled, onCheckedChange = onSetAutoBackupEnabled)
+                },
+                onClick = { onSetAutoBackupEnabled(!autoBackup.enabled) },
+            )
+            if (autoBackup.enabled) {
+                GroupedRow(
+                    title = stringResource(R.string.calendars_auto_backup_folder),
+                    summary = rememberFolderName(autoBackup.folderUri)
+                        ?: stringResource(R.string.calendars_auto_backup_folder_unset),
+                    position = Position.Middle,
+                    onClick = { runCatching { pickFolder.launch(null) } },
+                )
+                GroupedRow(
+                    title = stringResource(R.string.calendars_auto_backup_interval),
+                    summary = backupIntervalLabel(autoBackup.intervalMinutes),
+                    position = Position.Bottom,
+                    onClick = { showInterval = true },
+                )
+                HintText(backupStatusText(autoBackup.status))
+            }
        }

        Spacer(Modifier.height(16.dp))
@@ -346,6 +401,14 @@ private fun CalendarsList(
                }
            }
    }
+
+    if (showInterval) {
+        BackupIntervalDialog(
+            currentMinutes = autoBackup.intervalMinutes,
+            onConfirm = onSetAutoBackupInterval,
+            onDismiss = { showInterval = false },
+        )
+    }
 }

@OptIn(ExperimentalMaterial3Api::class)
@@ -760,6 +823,95 @@ private fun HintText(text: String) {
    )
 }

+/** Readable name of the persisted backup folder, resolved from its tree Uri. */
+@Composable
+private fun rememberFolderName(uriString: String?): String? {
+    val context = LocalContext.current
+    return remember(uriString) {
+        uriString?.let {
+            runCatching { DocumentFile.fromTreeUri(context, it.toUri())?.name }.getOrNull()
+        }
+    }
+}
+
+/** "Every 30 minutes" / "Every 2 hours" / "Every day" — the interval in its largest whole unit. */
+@Composable
+private fun backupIntervalLabel(minutes: Long): String {
+    val duration = when {
+        minutes % MINUTES_PER_WEEK == 0L ->
+            pluralStringResource(R.plurals.duration_weeks, (minutes / MINUTES_PER_WEEK).toInt(), (minutes / MINUTES_PER_WEEK).toInt())
+        minutes % MINUTES_PER_DAY == 0L ->
+            pluralStringResource(R.plurals.duration_days, (minutes / MINUTES_PER_DAY).toInt(), (minutes / MINUTES_PER_DAY).toInt())
+        minutes % 60L == 0L ->
+            pluralStringResource(R.plurals.duration_hours, (minutes / 60L).toInt(), (minutes / 60L).toInt())
+        else ->
+            pluralStringResource(R.plurals.duration_minutes, minutes.toInt(), minutes.toInt())
+    }
+    return stringResource(R.string.calendars_auto_backup_every, duration)
+}
+
+/** "Last backup: 5 minutes ago" / "… failed" / "No automatic backup yet". */
+@Composable
+private fun backupStatusText(status: BackupStatus): String {
+    if (status.lastRun == 0L) return stringResource(R.string.calendars_auto_backup_status_never)
+    val relative = DateUtils.getRelativeTimeSpanString(
+        status.lastRun, System.currentTimeMillis(), DateUtils.MINUTE_IN_MILLIS,
+    ).toString()
+    return if (status.lastSuccess) {
+        stringResource(R.string.calendars_auto_backup_status_ok, relative)
+    } else {
+        stringResource(R.string.calendars_auto_backup_status_failed, relative)
+    }
+}
+
+/** Amount + unit picker for the backup interval (floored at 30 minutes). */
+@Composable
+private fun BackupIntervalDialog(
+    currentMinutes: Long,
+    onConfirm: (Long) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    // minutes-per-unit for each entry; pick the largest unit the current value divides into.
+    val unitMinutes = remember { listOf(1L, 60L, MINUTES_PER_DAY, MINUTES_PER_WEEK) }
+    val units = stringArrayResource(R.array.backup_interval_units).toList()
+    val initialUnit = unitMinutes.indexOfLast { currentMinutes % it == 0L }.coerceAtLeast(0)
+    var amount by rememberSaveable { mutableStateOf((currentMinutes / unitMinutes[initialUnit]).toString()) }
+    var unitIndex by rememberSaveable { mutableStateOf(initialUnit) }
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.calendars_auto_backup_interval)) },
+        text = {
+            Column {
+                Row(verticalAlignment = Alignment.CenterVertically) {
+                    DialogAmountField(value = amount, onValueChange = { amount = it }, placeholder = "1")
+                    Spacer(Modifier.width(12.dp))
+                    DialogUnitDropdown(label = units[unitIndex], entries = units) { unitIndex = it }
+                }
+                Spacer(Modifier.height(8.dp))
+                Text(
+                    text = stringResource(R.string.calendars_auto_backup_interval_min),
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+        },
+        confirmButton = {
+            TextButton(onClick = {
+                val value = amount.toLongOrNull()?.coerceAtLeast(1L) ?: 1L
+                onConfirm((value * unitMinutes[unitIndex]).coerceAtLeast(SettingsPrefs.MIN_BACKUP_INTERVAL))
+                onDismiss()
+            }) { Text(stringResource(R.string.reminder_custom_set)) }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.dialog_cancel)) }
+        },
+    )
+}
+
+private const val MINUTES_PER_DAY = 1_440L
+private const val MINUTES_PER_WEEK = 10_080L
+
 /**
 * Pick the app to open for managing a synced calendar's account. The account's
 * own authenticator package (resolved from [AccountManager], no permission
--- a/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsViewModel.kt
@@ -1,13 +1,19 @@
 package de.jeanlucmakiola.calendula.ui.calendars

+import android.content.Context
+import android.content.Intent
 import android.net.Uri
 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.backup.BackupScheduler
 import de.jeanlucmakiola.calendula.data.calendar.CalendarRepository
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.ics.IcsExporter
+import de.jeanlucmakiola.calendula.data.prefs.BackupStatus
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
+import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.ics.IcsWriter
 import kotlinx.coroutines.CoroutineDispatcher
@@ -16,6 +22,7 @@ import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.stateIn
@@ -33,9 +40,11 @@ import javax.inject.Inject
 */
@HiltViewModel
 class CalendarsViewModel @Inject constructor(
+    @ApplicationContext private val context: Context,
    private val repository: CalendarRepository,
    private val icsExporter: IcsExporter,
    private val prefs: CalendarPrefs,
+    private val settingsPrefs: SettingsPrefs,
    @IoDispatcher private val io: CoroutineDispatcher,
 ) : ViewModel() {

@@ -63,6 +72,22 @@ class CalendarsViewModel @Inject constructor(
                initialValue = emptySet(),
            )

+    /** Automatic-backup settings + last-run status, for the Backup section UI. */
+    val autoBackup: StateFlow<AutoBackupUiState> = combine(
+        settingsPrefs.autoBackupEnabled,
+        settingsPrefs.autoBackupIntervalMinutes,
+        settingsPrefs.autoBackupFolderUri,
+        settingsPrefs.autoBackupStatus,
+    ) { enabled, interval, folder, status ->
+        AutoBackupUiState(enabled, interval, folder, status)
+    }
+        .flowOn(io)
+        .stateIn(
+            scope = viewModelScope,
+            started = SharingStarted.WhileSubscribed(5_000L),
+            initialValue = AutoBackupUiState(),
+        )
+
    private val _error = MutableStateFlow(false)
    val error: StateFlow<Boolean> = _error.asStateFlow()

@@ -136,6 +161,50 @@ class CalendarsViewModel @Inject constructor(
        }
    }

+    // --- Automatic backup (issue #8) ------------------------------------
+
+    fun setAutoBackupEnabled(enabled: Boolean) {
+        viewModelScope.launch {
+            settingsPrefs.setAutoBackupEnabled(enabled)
+            reschedule()
+            // Give immediate feedback when turning it on with a folder already set.
+            if (enabled && settingsPrefs.autoBackupFolderUri.first() != null) {
+                BackupScheduler.runNow(context)
+            }
+        }
+    }
+
+    fun setAutoBackupIntervalMinutes(minutes: Long) {
+        viewModelScope.launch {
+            settingsPrefs.setAutoBackupIntervalMinutes(minutes)
+            reschedule()
+        }
+    }
+
+    /** Persist the chosen destination folder (taking a durable write grant) and run once. */
+    fun setAutoBackupFolder(uri: Uri) {
+        viewModelScope.launch {
+            runCatching {
+                context.contentResolver.takePersistableUriPermission(
+                    uri,
+                    Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION,
+                )
+            }
+            settingsPrefs.setAutoBackupFolderUri(uri.toString())
+            reschedule()
+            if (settingsPrefs.autoBackupEnabled.first()) BackupScheduler.runNow(context)
+        }
+    }
+
+    private suspend fun reschedule() {
+        BackupScheduler.apply(
+            context = context,
+            enabled = settingsPrefs.autoBackupEnabled.first(),
+            intervalMinutes = settingsPrefs.autoBackupIntervalMinutes.first(),
+            hasFolder = settingsPrefs.autoBackupFolderUri.first() != null,
+        )
+    }
+
    private inline fun write(crossinline block: suspend () -> Unit) {
        viewModelScope.launch {
            try {
@@ -149,6 +218,14 @@ class CalendarsViewModel @Inject constructor(
    }
 }

+/** Automatic-backup settings + last-run status for the Backup section. */
+data class AutoBackupUiState(
+    val enabled: Boolean = false,
+    val intervalMinutes: Long = SettingsPrefs.DEFAULT_BACKUP_INTERVAL,
+    val folderUri: String? = null,
+    val status: BackupStatus = BackupStatus(lastRun = 0L, lastSuccess = true, consecutiveFailures = 0),
+)
+
 /** Outcome of a whole-calendar backup, surfaced once to the screen. */
 sealed interface BackupResult {
    data class Success(val eventCount: Int) : BackupResult
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -197,6 +197,14 @@
        <item quantity="one">%d hour</item>
        <item quantity="other">%d hours</item>
    </plurals>
+    <plurals name="duration_days">
+        <item quantity="one">%d day</item>
+        <item quantity="other">%d days</item>
+    </plurals>
+    <plurals name="duration_weeks">
+        <item quantity="one">%d week</item>
+        <item quantity="other">%d weeks</item>
+    </plurals>

    <!-- Shared event strings -->
    <string name="event_untitled">(No title)</string>
@@ -363,6 +371,26 @@
    <string name="calendars_backup_header">Backup</string>
    <string name="calendars_backup_hint">Local calendars aren\'t synced anywhere, so export them to an .ics file to keep a copy.</string>
    <string name="calendars_backup_action">Export as .ics file</string>
+    <string name="calendars_auto_backup">Automatic backup</string>
+    <string name="calendars_auto_backup_hint">Periodically export your local calendars to a folder as an .ics file.</string>
+    <string name="calendars_auto_backup_folder">Backup folder</string>
+    <string name="calendars_auto_backup_folder_unset">Tap to choose a folder</string>
+    <string name="calendars_auto_backup_interval">Interval</string>
+    <string name="calendars_auto_backup_every">Every %1$s</string>
+    <string name="calendars_auto_backup_interval_min">Minimum 30 minutes.</string>
+    <string name="calendars_auto_backup_status_never">No automatic backup yet</string>
+    <string name="calendars_auto_backup_status_ok">Last backup: %1$s</string>
+    <string name="calendars_auto_backup_status_failed">Last backup failed: %1$s</string>
+    <string name="backup_channel_name">Backup</string>
+    <string name="backup_channel_description">Warns if automatic backups fail repeatedly.</string>
+    <string name="backup_failed_title">Automatic backup failed</string>
+    <string name="backup_failed_text">Calendula couldn\'t write the backup file. Check the backup folder in Settings.</string>
+    <string-array name="backup_interval_units">
+        <item>Minutes</item>
+        <item>Hours</item>
+        <item>Days</item>
+        <item>Weeks</item>
+    </string-array>
    <string name="calendars_backup_failed">Couldn\'t export the backup.</string>
    <plurals name="calendars_backup_done">
        <item quantity="one">Exported %d event.</item>