Give Backup & restore its loading and failure states (#304 )

The screen derived its rows straight from the calendar list, which starts empty, catches to empty on a provider error, and can legitimately load with nothing exportable and nothing importable. All three rendered as a blank page with no way to import anything. Adds BackupUiState (Loading / Failure / Ready) and keeps the restore row on screen whenever the screen has anything at all to show: when no calendar can receive events it says so and routes to the calendar manager instead of disappearing. New FailureReason.NoImportTarget covers the case the list itself can't explain -- calendars exist and are visible, but every one is read-only, managed or not synced. Export stays available on an all-hidden device: it reads the provider directly, so calling that a failure would hide a working action. Also adds an import test against a Google Calendar export dialect (VTIMEZONE, TZID-qualified DTSTART/EXDATE, folded lines, RECURRENCE-ID overrides) -- the parser already handles all of it.
2026-09-20 21:49:31 +02:00
11 changed files with 530 additions and 85 deletions
@@ -253,6 +253,13 @@ enum class FailureReason {
    PermissionRevoked,
    NoCalendarsConfigured,
    AllCalendarsHidden,
+
+    /**
+     * Calendars exist and are switched on, but none can receive an event: every
+     * one is read-only, app-managed, or not synced to this device. Distinct from
+     * [AllCalendarsHidden], which a visibility switch fixes.
+     */
+    NoImportTarget,
    ProviderUnavailable,
    EventNotFound,
    Unknown,
@@ -549,12 +549,17 @@ fun CalendarHost(
            visible = showBackup,
            enter = slideInHorizontally(slideSpec) { it } + fadeIn(),
            exit = slideOutHorizontally(slideSpec) { it } + fadeOut(),
+        ) {
+            // The manager sits directly under this screen, so its failure states'
+            // "Manage calendars" way out is simply popping back to it (#304).
+            CompositionLocalProvider(
+                LocalManageCalendars provides { showBackup = false },
            ) {
                BackupScreen(
                    onBack = { showBackup = false },
-                // Restore runs the normal .ics import, and both this screen and
-                // the manager that can have opened it are declared above the
-                // import overlays — so both have to step aside.
+                    // Restore runs the normal .ics import, and both this screen
+                    // and the manager that can have opened it are declared above
+                    // the import overlays — so both have to step aside.
                    onImport = {
                        importUri = it
                        importForceMany = true
@@ -564,6 +569,7 @@ fun CalendarHost(
                )
            }
        }
+    }
 }

 /** Persists the view back stack across config change / process death by ordinal. */
@@ -4,6 +4,7 @@ import android.net.Uri
 import android.text.format.DateUtils
 import androidx.activity.compose.rememberLauncherForActivityResult
 import androidx.activity.result.contract.ActivityResultContracts
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
@@ -18,6 +19,7 @@ import androidx.compose.material.icons.filled.Schedule
 import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.Button
 import androidx.compose.material3.Checkbox
+import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
@@ -47,9 +49,10 @@ 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.domain.isEventTarget
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
+import de.jeanlucmakiola.calendula.ui.common.CalendarFailure
 import de.jeanlucmakiola.calendula.ui.common.LeadingAvatar
+import de.jeanlucmakiola.calendula.ui.common.LocalManageCalendars
 import de.jeanlucmakiola.floret.components.CollapsingScaffold
 import de.jeanlucmakiola.floret.components.DialogAmountField
 import de.jeanlucmakiola.floret.components.DialogUnitDropdown
@@ -80,18 +83,13 @@ fun BackupScreen(
    onImport: (Uri) -> Unit,
    viewModel: CalendarsViewModel = hiltViewModel(),
 ) {
-    val calendars by viewModel.calendars.collectAsStateWithLifecycle()
+    val state by viewModel.backupState.collectAsStateWithLifecycle()
    val backupResult by viewModel.backupResult.collectAsStateWithLifecycle()
    val autoBackup by viewModel.autoBackup.collectAsStateWithLifecycle()

    val context = LocalContext.current
    val snackbarHostState = remember { SnackbarHostState() }

-    // Export covers local calendars only; managed special-dates mirrors are
-    // rebuilt from contacts. Restore can target anything the import picker offers.
-    val exportable = calendars.filter { it.isLocal && it.canModifyContents && !it.isManaged }
-    val canImport = calendars.any { it.isEventTarget }
-
    // Exports everything eligible (null); the per-calendar selector owns its
    // own launcher.
    val createBackup = rememberLauncherForActivityResult(
@@ -135,28 +133,115 @@ fun BackupScreen(
        snackbarHost = { SnackbarHost(snackbarHostState) },
        predictiveBack = true,
    ) {
-        HintText(stringResource(R.string.calendars_backup_hint))
+        when (val s = state) {
+            BackupUiState.Loading -> BackupLoading()
+            is BackupUiState.Failure -> CalendarFailure(reason = s.reason, onRetry = onBack)
+            is BackupUiState.Ready -> BackupContent(
+                exportable = s.exportable,
+                canImport = s.canImport,
+                autoBackup = autoBackup,
+                viewModel = viewModel,
+                onRestore = { runCatching { openBackup.launch(RESTORE_MIME_TYPES) } },
+                onPickFolder = { runCatching { pickFolder.launch(null) } },
+                onExportAll = {
+                    runCatching { createBackup.launch(defaultBackupName()) }
+                },
+                onExportPick = { showExportPicker = true },
+                onEditInterval = { showInterval = true },
+            )
+        }
+    }

-        if (exportable.isNotEmpty()) {
+    // Gated on Ready rather than resetting the flag when the state leaves it:
+    // flipping it here would be a write during composition.
+    (state as? BackupUiState.Ready)?.let { ready ->
+        if (showExportPicker) {
+            ExportCalendarPicker(
+                calendars = ready.exportable,
+                onExport = viewModel::exportBackup,
+                onDismiss = { showExportPicker = false },
+            )
+        }
+    }
+    if (showInterval) {
+        BackupIntervalDialog(
+            currentMinutes = autoBackup.intervalMinutes,
+            onConfirm = viewModel::setAutoBackupIntervalMinutes,
+            onDismiss = { showInterval = false },
+        )
+    }
+}
+
+/** The screen's one-line loading state, in the scaffold's content column. */
+@Composable
+private fun BackupLoading() {
+    Box(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(vertical = 48.dp),
+        contentAlignment = Alignment.Center,
+    ) {
+        CircularProgressIndicator()
+    }
+}
+
+/** Default file name for a one-shot export. */
+private fun defaultBackupName(): String = "calendula-backup-${LocalDate.now()}.ics"
+
+/**
+ * The working screen: export (when there are local calendars to export), restore,
+ * and the automatic-backup block. Restore is always on screen — when nothing can
+ * receive the events it says so and routes to the calendar manager rather than
+ * disappearing, which is what #304 reported as an invisible button.
+ */
+@Composable
+private fun BackupContent(
+    exportable: List<CalendarSource>,
+    canImport: Boolean,
+    autoBackup: AutoBackupUiState,
+    viewModel: CalendarsViewModel,
+    onRestore: () -> Unit,
+    onPickFolder: () -> Unit,
+    onExportAll: () -> Unit,
+    onExportPick: () -> Unit,
+    onEditInterval: () -> Unit,
+) {
+    val manageCalendars = LocalManageCalendars.current
+    // Restore never depends on export eligibility, and never disappears: when no
+    // calendar can receive events it explains that and offers the way to fix it.
+    val restoreSummary = if (canImport) {
+        stringResource(R.string.calendars_restore_hint)
+    } else {
+        stringResource(R.string.calendars_restore_unavailable)
+    }
+    val onRestoreClick = if (canImport) onRestore else (manageCalendars ?: onRestore)
+
+    if (exportable.isEmpty()) {
+        SectionHeader(stringResource(R.string.calendars_restore_header))
+        HintText(restoreSummary)
+        GroupedRow(
+            title = stringResource(R.string.calendars_restore_action),
+            position = Position.Alone,
+            leading = { LeadingAvatar(Icons.Default.FileUpload) },
+            onClick = onRestoreClick,
+        )
+        return
+    }
+
+    HintText(stringResource(R.string.calendars_backup_hint))
    GroupedRow(
        title = stringResource(R.string.calendars_backup_action),
        position = Position.Top,
        leading = { LeadingAvatar(Icons.Default.FileDownload) },
-                onClick = {
        // A single exportable calendar skips the selector.
-                    if (exportable.size == 1) {
-                        runCatching { createBackup.launch("calendula-backup-${LocalDate.now()}.ics") }
-                    } else {
-                        showExportPicker = true
-                    }
-                },
+        onClick = if (exportable.size == 1) onExportAll else onExportPick,
    )
    GroupedRow(
        title = stringResource(R.string.calendars_restore_action),
-                summary = stringResource(R.string.calendars_restore_hint),
+        summary = restoreSummary,
        position = Position.Middle,
        leading = { LeadingAvatar(Icons.Default.FileUpload) },
-                onClick = { runCatching { openBackup.launch(RESTORE_MIME_TYPES) } },
+        onClick = onRestoreClick,
    )
    GroupedRow(
        title = stringResource(R.string.calendars_auto_backup),
@@ -174,44 +259,16 @@ fun BackupScreen(
            summary = rememberFolderName(autoBackup.folderUri)
                ?: stringResource(R.string.calendars_auto_backup_folder_unset),
            position = Position.Middle,
-                    onClick = { runCatching { pickFolder.launch(null) } },
+            onClick = onPickFolder,
        )
        GroupedRow(
            title = stringResource(R.string.calendars_auto_backup_interval),
            summary = backupIntervalLabel(autoBackup.intervalMinutes),
            position = Position.Bottom,
-                    onClick = { showInterval = true },
+            onClick = onEditInterval,
        )
        HintText(backupStatusText(autoBackup.status))
    }
-        } else if (canImport) {
-            // Nothing to back up, but restore is still possible — don't hide
-            // it behind export eligibility.
-            SectionHeader(stringResource(R.string.calendars_restore_header))
-            HintText(stringResource(R.string.calendars_restore_hint))
-            GroupedRow(
-                title = stringResource(R.string.calendars_restore_action),
-                position = Position.Alone,
-                leading = { LeadingAvatar(Icons.Default.FileUpload) },
-                onClick = { runCatching { openBackup.launch(RESTORE_MIME_TYPES) } },
-            )
-        }
-    }
-
-    if (showExportPicker) {
-        ExportCalendarPicker(
-            calendars = exportable,
-            onExport = viewModel::exportBackup,
-            onDismiss = { showExportPicker = false },
-        )
-    }
-    if (showInterval) {
-        BackupIntervalDialog(
-            currentMinutes = autoBackup.intervalMinutes,
-            onConfirm = viewModel::setAutoBackupIntervalMinutes,
-            onDismiss = { showInterval = false },
-        )
-    }
 }

 /**
@@ -0,0 +1,53 @@
+package de.jeanlucmakiola.calendula.ui.calendars
+
+import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.FailureReason
+import de.jeanlucmakiola.calendula.domain.calendarListFailure
+import de.jeanlucmakiola.calendula.domain.isEventTarget
+
+/**
+ * State of the Backup & restore screen (#69). Three states, because the calendar
+ * list it is derived from has all three: it arrives empty, it can throw, and
+ * "loaded but nothing to offer" is a real outcome the screen used to render as a
+ * blank page (#304).
+ */
+sealed interface BackupUiState {
+    data object Loading : BackupUiState
+    data class Failure(val reason: FailureReason) : BackupUiState
+
+    /**
+     * At least one half of the screen works. [exportable] may be empty (restore
+     * only) and [canImport] may be false (export only), but never both — that is
+     * a [Failure].
+     */
+    data class Ready(
+        val exportable: List<CalendarSource>,
+        val canImport: Boolean,
+    ) : BackupUiState
+}
+
+/**
+ * What the screen can offer for this calendar list.
+ *
+ * Export covers the app's own local calendars; managed special-dates mirrors are
+ * rebuilt from contacts, so they are excluded. Restore can target anything the
+ * import picker offers ([isEventTarget]).
+ *
+ * A failure is raised only when *neither* is possible — deliberately not
+ * [calendarListFailure] on its own, which would call an all-hidden device a
+ * failure while its local calendars are still perfectly exportable. When both
+ * halves are dead the list itself usually says why (no calendars, everything
+ * switched off); [FailureReason.NoImportTarget] covers the remaining case, where
+ * calendars exist and are visible but every one of them is read-only, managed or
+ * not synced to the device.
+ */
+fun backupUiState(calendars: List<CalendarSource>): BackupUiState {
+    val exportable = calendars.filter { it.isLocal && it.canModifyContents && !it.isManaged }
+    val canImport = calendars.any { it.isEventTarget }
+    if (exportable.isEmpty() && !canImport) {
+        return BackupUiState.Failure(
+            calendarListFailure(calendars) ?: FailureReason.NoImportTarget,
+        )
+    }
+    return BackupUiState.Ready(exportable = exportable, canImport = canImport)
+}
@@ -14,6 +14,7 @@ import de.jeanlucmakiola.calendula.data.ics.IcsExporter
 import de.jeanlucmakiola.calendula.data.prefs.BackupStatus
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.FailureReason
 import de.jeanlucmakiola.calendula.domain.ics.IcsWriter
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -24,6 +25,7 @@ import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flowOn
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
@@ -56,6 +58,22 @@ class CalendarsViewModel @Inject constructor(
                initialValue = emptyList(),
            )

+    /**
+     * The Backup & restore screen's own view of that list, with the loading and
+     * failure states [calendars] flattens away — it starts empty and catches to
+     * empty, which that screen used to render as a blank page (#304).
+     */
+    val backupState: StateFlow<BackupUiState> =
+        repository.calendars()
+            .map { backupUiState(it) }
+            .catch { emit(BackupUiState.Failure(FailureReason.ProviderUnavailable)) }
+            .flowOn(io)
+            .stateIn(
+                scope = viewModelScope,
+                started = SharingStarted.WhileSubscribed(5_000L),
+                initialValue = BackupUiState.Loading,
+            )
+
    /** Automatic-backup settings + last-run status, for the Backup section UI. */
    val autoBackup: StateFlow<AutoBackupUiState> = combine(
        settingsPrefs.autoBackupEnabled,
@@ -36,6 +36,7 @@ fun CalendarFailure(reason: FailureReason, onRetry: () -> Unit) {
        FailureReason.PermissionRevoked -> R.string.state_failure_permission
        FailureReason.NoCalendarsConfigured -> R.string.state_failure_no_calendars
        FailureReason.AllCalendarsHidden -> R.string.state_failure_all_hidden
+        FailureReason.NoImportTarget -> R.string.state_failure_no_import_target
        FailureReason.ProviderUnavailable -> R.string.state_failure_provider
        FailureReason.Unknown,
        FailureReason.EventNotFound -> R.string.state_failure_unknown
@@ -43,6 +44,7 @@ fun CalendarFailure(reason: FailureReason, onRetry: () -> Unit) {
    val actionRes = when (reason) {
        FailureReason.NoCalendarsConfigured -> R.string.state_failure_no_calendars_action
        FailureReason.AllCalendarsHidden -> R.string.state_failure_all_hidden_action
+        FailureReason.NoImportTarget -> R.string.state_failure_all_hidden_action
        FailureReason.PermissionRevoked -> R.string.state_failure_permission_action
        else -> R.string.state_retry
    }
@@ -50,7 +52,9 @@ fun CalendarFailure(reason: FailureReason, onRetry: () -> Unit) {
        FailureReason.NoCalendarsConfigured -> {
            { context.startCalendarSetup() }
        }
-        FailureReason.AllCalendarsHidden -> manageCalendars ?: onRetry
+        FailureReason.AllCalendarsHidden,
+        FailureReason.NoImportTarget,
+        -> manageCalendars ?: onRetry
        else -> onRetry
    }
    Column(
@@ -16,6 +16,7 @@
    <string name="state_failure_no_calendars_action">Open system calendar settings</string>
    <string name="state_failure_all_hidden">All your calendars are switched off.</string>
    <string name="state_failure_all_hidden_action">Manage calendars</string>
+    <string name="state_failure_no_import_target">None of your calendars can take new events. They are read-only, managed by another app, or not synced to this device.</string>
    <string name="state_failure_provider">Could not read the calendar.</string>

    <!-- Long-press a field to copy it (#195) -->
@@ -679,6 +680,7 @@
    <string name="calendars_restore_header">Restore</string>
    <string name="calendars_restore_action">Restore from .ics file</string>
    <string name="calendars_restore_hint">Import events from a backup or another calendar app.</string>
+    <string name="calendars_restore_unavailable">No calendar can take the imported events yet.</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>
@@ -36,12 +36,13 @@ class ModelsTest {
    }

    @Test
-    fun `FailureReason enum has all six variants`() {
+    fun `FailureReason enum has all seven variants`() {
        assertThat(FailureReason.values().toSet()).isEqualTo(
            setOf(
                FailureReason.PermissionRevoked,
                FailureReason.NoCalendarsConfigured,
                FailureReason.AllCalendarsHidden,
+                FailureReason.NoImportTarget,
                FailureReason.ProviderUnavailable,
                FailureReason.EventNotFound,
                FailureReason.Unknown,
@@ -0,0 +1,116 @@
+package de.jeanlucmakiola.calendula.domain.ics
+
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.calendula.domain.Availability
+import kotlinx.datetime.TimeZone
+import org.junit.jupiter.api.Test
+
+/**
+ * Reading a Google Calendar export (Codeberg #304), whose dialect the parser had
+ * never been held to: `VTIMEZONE` blocks with `X-LIC-LOCATION`, `TZID`-qualified
+ * `DTSTART`/`EXDATE`, folded `DESCRIPTION` and `ATTENDEE` lines, `RECURRENCE-ID`
+ * overrides written as separate `VEVENT`s, and `@google.com` UIDs.
+ *
+ * The fixture is a trimmed copy of what "Settings → Import & export → Export"
+ * produces, CRLF and all. Note that Google hands that export out as a **zip**
+ * containing one `.ics` per calendar — the file here is one member of it.
+ */
+class IcsGoogleImportTest {
+
+    private val parser = IcsParser(TimeZone.of("Europe/Berlin"))
+
+    private val result: IcsParseResult = parser.parse(
+        checkNotNull(
+            javaClass.classLoader?.getResourceAsStream("ics/google-calendar-export.ics"),
+        ).use { it.readBytes().toString(Charsets.UTF_8) },
+    )
+
+    private fun event(summary: String) = result.events.single { it.summary == summary }
+
+    @Test
+    fun `every master event imports and the VTIMEZONE block is not mistaken for one`() {
+        assertThat(result.events.map { it.summary })
+            .containsExactly("Team standup", "Day off", "Christmas break")
+    }
+
+    @Test
+    fun `X-WR-CALNAME names the calendar for all of them`() {
+        assertThat(result.events.map { it.calendarName }.distinct())
+            .containsExactly("jane@example.com")
+    }
+
+    @Test
+    fun `a TZID-qualified start resolves against the device tz database`() {
+        val standup = event("Team standup")
+        assertThat(standup.isAllDay).isFalse()
+        assertThat(standup.zoneId).isEqualTo("Europe/Berlin")
+        // 10:00 CEST is 08:00 UTC.
+        assertThat(standup.start.toString()).isEqualTo("2026-09-15T08:00:00Z")
+        assertThat((standup.end - standup.start).inWholeMinutes).isEqualTo(90)
+    }
+
+    @Test
+    fun `the recurrence rule and its TZID-qualified EXDATE survive`() {
+        val standup = event("Team standup")
+        assertThat(standup.recurrenceRule).isEqualTo("FREQ=WEEKLY;BYDAY=TU")
+        assertThat(standup.exDates).containsExactly("20260929T080000Z")
+    }
+
+    @Test
+    fun `the moved occurrence is skipped rather than imported as a duplicate`() {
+        // Google writes a RECURRENCE-ID override as its own VEVENT carrying the
+        // master's UID. Importing it would put a second "standup" in the
+        // calendar; Calendula models no overrides, so it is reported instead.
+        assertThat(result.events.map { it.summary }).doesNotContain("Team standup (moved)")
+        assertThat(result.warnings).contains(IcsParseWarning.ModifiedOccurrenceSkipped)
+    }
+
+    @Test
+    fun `a folded DESCRIPTION is unfolded and unescaped`() {
+        assertThat(event("Team standup").description).isEqualTo(
+            "Weekly sync with the team.\nAgenda lives in the shared doc, see the link below.",
+        )
+    }
+
+    @Test
+    fun `an escaped comma in LOCATION comes back as a comma`() {
+        assertThat(event("Team standup").location).isEqualTo("Meeting room 2, 3rd floor")
+    }
+
+    @Test
+    fun `attendees are reported rather than silently dropped`() {
+        assertThat(result.warnings).contains(IcsParseWarning.AttendeesIgnored)
+    }
+
+    @Test
+    fun `a timed VALARM becomes its lead time in minutes`() {
+        assertThat(event("Team standup").semanticReminderMinutes()).containsExactly(30)
+    }
+
+    @Test
+    fun `an all-day event keeps the single day the file gives it`() {
+        val dayOff = event("Day off")
+        assertThat(dayOff.isAllDay).isTrue()
+        assertThat((dayOff.end - dayOff.start).inWholeDays).isEqualTo(1)
+        assertThat(dayOff.availability).isEqualTo(Availability.Free)
+    }
+
+    @Test
+    fun `an all-day alarm comes back as whole days before`() {
+        // Google writes an all-day reminder as a whole-day offset from the
+        // event's UTC midnight; a day has to survive as a day.
+        assertThat(event("Day off").semanticReminderMinutes()).containsExactly(1440)
+    }
+
+    @Test
+    fun `a multi-day all-day event keeps its exclusive DTEND span`() {
+        val christmas = event("Christmas break")
+        assertThat(christmas.isAllDay).isTrue()
+        assertThat((christmas.end - christmas.start).inWholeDays).isEqualTo(3)
+    }
+
+    @Test
+    fun `no recurrence rule is repaired - Google writes them well-formed`() {
+        assertThat(result.warnings).doesNotContain(IcsParseWarning.RecurrenceRuleRepaired)
+    }
+}
@@ -0,0 +1,90 @@
+package de.jeanlucmakiola.calendula.ui.calendars
+
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.FailureReason
+import org.junit.jupiter.api.Test
+
+/** What the Backup & restore screen offers for a given calendar list (#304). */
+class BackupUiStateTest {
+
+    private fun cal(
+        id: Long,
+        local: Boolean = false,
+        writable: Boolean = true,
+        visible: Boolean = true,
+        managed: Boolean = false,
+        syncs: Boolean = true,
+    ) = CalendarSource(
+        id = id,
+        displayName = "Calendar $id",
+        accountName = "acc@example.com",
+        accountType = if (local) "LOCAL" else "com.google",
+        color = 0,
+        isVisibleInSystem = visible,
+        canModifyContents = writable,
+        isLocal = local,
+        isManaged = managed,
+        syncsEvents = syncs,
+    )
+
+    private fun failure(state: BackupUiState) = (state as BackupUiState.Failure).reason
+
+    private fun ready(state: BackupUiState) = state as BackupUiState.Ready
+
+    @Test
+    fun `no calendars at all reports the empty device`() {
+        assertThat(failure(backupUiState(emptyList())))
+            .isEqualTo(FailureReason.NoCalendarsConfigured)
+    }
+
+    @Test
+    fun `a synced writable calendar can receive a restore`() {
+        val state = ready(backupUiState(listOf(cal(1L))))
+        assertThat(state.canImport).isTrue()
+        assertThat(state.exportable).isEmpty()
+    }
+
+    @Test
+    fun `the reported case - only a calendar that cannot take events`() {
+        // #304: a Google account with calendar sync switched off leaves nothing
+        // exportable and nothing importable, which used to render a blank screen.
+        assertThat(failure(backupUiState(listOf(cal(1L, syncs = false)))))
+            .isEqualTo(FailureReason.NoImportTarget)
+    }
+
+    @Test
+    fun `a read-only subscription is no import target either`() {
+        assertThat(failure(backupUiState(listOf(cal(1L, writable = false)))))
+            .isEqualTo(FailureReason.NoImportTarget)
+    }
+
+    @Test
+    fun `everything switched off is reported as hidden, not as a missing target`() {
+        // The remedy differs: a visibility switch fixes this one.
+        assertThat(failure(backupUiState(listOf(cal(1L, visible = false)))))
+            .isEqualTo(FailureReason.AllCalendarsHidden)
+    }
+
+    @Test
+    fun `a hidden local calendar still exports`() {
+        // Export reads the provider directly, so system visibility is irrelevant
+        // to it — calling this a failure would hide a working action.
+        val state = ready(backupUiState(listOf(cal(1L, local = true, visible = false))))
+        assertThat(state.exportable).hasSize(1)
+        assertThat(state.canImport).isFalse()
+    }
+
+    @Test
+    fun `a managed special-dates mirror is neither exportable nor a target`() {
+        assertThat(failure(backupUiState(listOf(cal(1L, local = true, managed = true)))))
+            .isEqualTo(FailureReason.NoImportTarget)
+    }
+
+    @Test
+    fun `a local calendar alongside a synced one offers both halves`() {
+        val state = ready(backupUiState(listOf(cal(1L, local = true), cal(2L))))
+        assertThat(state.exportable.map { it.id }).containsExactly(1L)
+        assertThat(state.canImport).isTrue()
+    }
+}
@@ -0,0 +1,91 @@
+BEGIN:VCALENDAR
+PRODID:-//Google Inc//Google Calendar 70.9054//EN
+VERSION:2.0
+CALSCALE:GREGORIAN
+METHOD:PUBLISH
+X-WR-CALNAME:jane@example.com
+X-WR-TIMEZONE:Europe/Berlin
+BEGIN:VTIMEZONE
+TZID:Europe/Berlin
+X-LIC-LOCATION:Europe/Berlin
+BEGIN:DAYLIGHT
+TZOFFSETFROM:+0100
+TZOFFSETTO:+0200
+TZNAME:CEST
+DTSTART:19700329T020000
+RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
+END:DAYLIGHT
+BEGIN:STANDARD
+TZOFFSETFROM:+0200
+TZOFFSETTO:+0100
+TZNAME:CET
+DTSTART:19701025T030000
+RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
+END:STANDARD
+END:VTIMEZONE
+BEGIN:VEVENT
+DTSTART;TZID=Europe/Berlin:20260915T100000
+DTEND;TZID=Europe/Berlin:20260915T113000
+RRULE:FREQ=WEEKLY;BYDAY=TU
+EXDATE;TZID=Europe/Berlin:20260929T100000
+DTSTAMP:20260912T183000Z
+UID:0abcdef1234567890abcdef12345@google.com
+CREATED:20260901T120000Z
+DESCRIPTION:Weekly sync with the team.\nAgenda lives in the shared doc\, see
+  the link below.
+LAST-MODIFIED:20260902T081500Z
+LOCATION:Meeting room 2\, 3rd floor
+SEQUENCE:0
+STATUS:CONFIRMED
+SUMMARY:Team standup
+TRANSP:OPAQUE
+ORGANIZER;CN=Jane Doe:mailto:jane@example.com
+ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;CN=John:m
+ ailto:john@example.com
+BEGIN:VALARM
+ACTION:DISPLAY
+DESCRIPTION:This is an event reminder
+TRIGGER:-PT30M
+END:VALARM
+END:VEVENT
+BEGIN:VEVENT
+DTSTART;TZID=Europe/Berlin:20260929T140000
+DTEND;TZID=Europe/Berlin:20260929T153000
+DTSTAMP:20260912T183000Z
+UID:0abcdef1234567890abcdef12345@google.com
+RECURRENCE-ID;TZID=Europe/Berlin:20260929T100000
+CREATED:20260901T120000Z
+LAST-MODIFIED:20260910T091500Z
+SEQUENCE:1
+STATUS:CONFIRMED
+SUMMARY:Team standup (moved)
+TRANSP:OPAQUE
+END:VEVENT
+BEGIN:VEVENT
+DTSTART;VALUE=DATE:20261024
+DTEND;VALUE=DATE:20261025
+DTSTAMP:20260912T183000Z
+UID:1bcdef01234567890abcdef23456@google.com
+CREATED:20260820T101500Z
+LAST-MODIFIED:20260820T101500Z
+SEQUENCE:0
+STATUS:CONFIRMED
+SUMMARY:Day off
+TRANSP:TRANSPARENT
+BEGIN:VALARM
+ACTION:DISPLAY
+DESCRIPTION:This is an event reminder
+TRIGGER:-P1D
+END:VALARM
+END:VEVENT
+BEGIN:VEVENT
+DTSTART;VALUE=DATE:20261224
+DTEND;VALUE=DATE:20261227
+DTSTAMP:20260912T183000Z
+UID:2cdef012345678901abcdef34567@google.com
+SEQUENCE:0
+STATUS:CONFIRMED
+SUMMARY:Christmas break
+TRANSP:TRANSPARENT
+END:VEVENT
+END:VCALENDAR