feat: auto-sync the library on a timer while the app is open

While the app is in the foreground a timer checks the auto-sync setting and
syncs when due (default every 24h; the interval is selectable from 15 minutes
to 24 hours). It stops when the app is backgrounded. "Sync automatically"
is one setting: Off, Wi-Fi only (default) or Always.

A running sync is shown by a silent, dismissible notification and a small
spinner on the library tab bar's settings button. A manual pull-to-refresh
still holds the pull spinner; only an automatic sync does not. The library
and Home sync actions no-op while a sync is running, and SyncManager
coalesces a request that arrives mid-run into a single follow-up, so repeated
pull-to-refresh cannot pile up runs while adding a server still syncs it.

The time of the last sync attempt is recorded, so a failing server is retried
once per interval rather than every poll. The sync consumer and the auto-sync
loop both survive an unexpected failure instead of silently disabling syncing
for the rest of the process.

The poll sleeps for the interval (capped at 15 minutes) instead of a fixed
minute, the network mode is collected once rather than re-registering a
connectivity callback each poll, and the decision is logged at DEBUG (visible
with Verbose logging) rather than writing to the log file every poll.

app/src/test/kotlin/com/subtracks/data/sync/AutoSyncTest.kt

@@ -0,0 +1,146 @@
+package com.subtracks.data.sync
+
+import com.subtracks.awaitUntil
+import com.subtracks.cancelAndJoinBlocking
+import com.subtracks.data.net.NetworkMode
+import com.subtracks.data.prefs.DEFAULT_SYNC_INTERVAL_MINUTES
+import com.subtracks.data.prefs.SyncMode
+import com.subtracks.data.prefs.UserPreferences
+import com.subtracks.data.prefs.fakeUserPreferences
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.runBlocking
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import java.util.concurrent.atomic.AtomicBoolean
+import java.util.concurrent.atomic.AtomicInteger
+
+class AutoSyncTest {
+    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
+
+    @After
+    fun tearDown() {
+        cancelAndJoinBlocking(scope)
+    }
+
+    @Test
+    fun decidesWhetherASyncIsDue() {
+        assertTrue(shouldSync())
+        assertTrue(shouldSync(mode = SyncMode.WifiOnly))
+        assertTrue(shouldSync(mode = SyncMode.Always, network = NetworkMode.Mobile))
+        assertTrue(shouldSync(lastSyncAt = INTERVAL_MS * 2, now = INTERVAL_MS))
+
+        assertFalse(shouldSync(mode = SyncMode.Off))
+        assertFalse(shouldSync(mode = SyncMode.WifiOnly, network = NetworkMode.Mobile))
+        assertFalse(shouldSync(lastSyncAt = INTERVAL_MS - 1, now = INTERVAL_MS))
+        assertFalse(shouldSync(offline = true))
+        assertFalse(shouldSync(hasSource = false))
+    }
+
+    @Test
+    fun syncsWhenTheAppIsActiveAndDue() {
+        val preferences = fakeUserPreferences()
+        runBlocking {
+            preferences.setSyncMode(SyncMode.WifiOnly)
+            preferences.setLastSyncAt(0L)
+        }
+        val requested = AtomicBoolean(false)
+        val autoSync = autoSync(preferences, requestSync = { requested.set(true) })
+
+        autoSync.setForeground(true)
+
+        awaitUntil("auto sync requested") { requested.get() }
+        autoSync.setForeground(false)
+    }
+
+    @Test
+    fun doesNotSyncWhenOff() {
+        val preferences = fakeUserPreferences()
+        runBlocking {
+            preferences.setSyncMode(SyncMode.Off)
+            preferences.setLastSyncAt(0L)
+        }
+        val requested = AtomicBoolean(false)
+        val autoSync = autoSync(preferences, requestSync = { requested.set(true) })
+
+        autoSync.setForeground(true)
+        runBlocking { delay(300) }
+        autoSync.setForeground(false)
+
+        assertFalse(requested.get())
+    }
+
+    @Test
+    fun stopsSyncingWhenBackgrounded() {
+        val preferences = fakeUserPreferences()
+        runBlocking {
+            preferences.setSyncMode(SyncMode.Always)
+            preferences.setLastSyncAt(0L)
+        }
+        val count = AtomicInteger(0)
+        val autoSync =
+            AutoSync(
+                preferences = preferences,
+                networkMode = flowOf(NetworkMode.Wifi),
+                hasSource = { true },
+                requestSync = { count.incrementAndGet() },
+                scope = scope,
+                now = { INTERVAL_MS + 1 },
+                maxPollMs = 50L,
+            )
+
+        autoSync.setForeground(true)
+        awaitUntil("first sync") { count.get() >= 1 }
+        autoSync.setForeground(false)
+
+        runBlocking { delay(200) }
+        val afterStop = count.get()
+        runBlocking { delay(300) }
+
+        assertEquals(afterStop, count.get())
+    }
+
+    private fun autoSync(
+        preferences: UserPreferences,
+        requestSync: () -> Unit,
+        now: () -> Long = { INTERVAL_MS + 1 },
+    ): AutoSync =
+        AutoSync(
+            preferences = preferences,
+            networkMode = flowOf(NetworkMode.Wifi),
+            hasSource = { true },
+            requestSync = requestSync,
+            scope = scope,
+            now = now,
+            maxPollMs = 10_000L,
+        )
+
+    private fun shouldSync(
+        mode: SyncMode = SyncMode.WifiOnly,
+        network: NetworkMode = NetworkMode.Wifi,
+        offline: Boolean = false,
+        hasSource: Boolean = true,
+        lastSyncAt: Long = 0L,
+        now: Long = INTERVAL_MS,
+        intervalMs: Long = INTERVAL_MS,
+    ): Boolean =
+        shouldAutoSync(
+            mode = mode,
+            network = network,
+            offline = offline,
+            hasSource = hasSource,
+            lastSyncAt = lastSyncAt,
+            now = now,
+            intervalMs = intervalMs,
+        )
+
+    private companion object {
+        val INTERVAL_MS = DEFAULT_SYNC_INTERVAL_MINUTES * 60_000L
+    }
+}

app/src/test/kotlin/com/subtracks/data/sync/SyncManagerTest.kt

@@ -10,6 +10,7 @@ import com.subtracks.TEST_TIMEOUT_MS
 import com.subtracks.cancelAndJoinBlocking
 import com.subtracks.data.db.SubtracksDatabase
 import com.subtracks.data.download.ArtworkStore
+import com.subtracks.data.prefs.UserPreferences
 import com.subtracks.data.prefs.fakeUserPreferences
 import com.subtracks.data.repo.NetworkServerActionSink
 import com.subtracks.data.repo.QueueRepository
@@ -44,6 +45,7 @@ class SyncManagerTest {
     private lateinit var sourceRepository: SourceRepository
     private lateinit var queueRepository: QueueRepository
     private lateinit var manager: SyncManager
+    private lateinit var preferences: UserPreferences
     private lateinit var scope: CoroutineScope
     private val messages = CopyOnWriteArrayList<String>()
     private lateinit var server: MockWebServer
@@ -62,12 +64,14 @@ class SyncManagerTest {
         sourceRepository =
             SourceRepository(db, OkHttpClient(), fakeUserPreferences(), ArtworkStore(File(context.cacheDir, "art")), scope = scope)
         queueRepository = QueueRepository(db)
+        preferences = fakeUserPreferences()
         manager =
             SyncManager(
                 db,
                 sourceRepository,
                 queueRepository,
                 NetworkServerActionSink(sourceRepository),
+                preferences = preferences,
                 showMessage = { messages += it.resolve(resources) },
                 scope = scope,
             )
@@ -89,6 +93,16 @@ class SyncManagerTest {
             withTimeout(TEST_TIMEOUT_MS) { manager.status.first { it is SyncStatus.Failed } }
 
             assertEquals(listOf("No server configured"), messages)
+            assertTrue(preferences.lastSyncAt().first() > 0)
+        }
+
+    @Test
+    fun aSilentSyncDoesNotTellTheUser() =
+        runBlocking {
+            manager.requestSync(silent = true)
+            withTimeout(TEST_TIMEOUT_MS) { manager.status.first { it is SyncStatus.Failed } }
+
+            assertTrue(messages.isEmpty())
         }
 
     @Test
@@ -114,6 +128,7 @@ class SyncManagerTest {
 
             assertEquals(listOf("ar1"), db.libraryDao().artistIds(1))
             assertEquals(listOf("al1"), db.libraryDao().albumIds(1))
+            assertTrue(preferences.lastSyncAt().first() > 0)
         }
 
     @Test

app/src/test/kotlin/com/subtracks/ui/settings/AddSourceViewModelTest.kt

@@ -156,7 +156,14 @@ class AddSourceViewModelTest {
 
     private fun viewModel(sourceId: Long? = null): AddSourceViewModel {
         val syncManager =
-            SyncManager(db, sourceRepository, QueueRepository(db), NetworkServerActionSink(sourceRepository), scope = repoScope)
+            SyncManager(
+                db,
+                sourceRepository,
+                QueueRepository(db),
+                NetworkServerActionSink(sourceRepository),
+                preferences = fakeUserPreferences(),
+                scope = repoScope,
+            )
         val resources = ApplicationProvider.getApplicationContext<Context>().resources
         return AddSourceViewModel(sourceRepository, syncManager, downloadRepository, sourceId, resources).also { createdViewModels += it }
     }