feat(android): notify when a show gains episodes

NewEpisodesWorker runs crawl_for_news every six hours on a network with
the battery not low, and posts one notification per show, grouped. A
setting under Playback turns it off and cancels the schedule.

android/app/src/main/java/io/narl/protonstream/MainActivity.kt

@@ -21,6 +21,7 @@ import io.narl.protonstream.native.NativeRuntime
 import io.narl.protonstream.playback.NativeMpvHost
 import io.narl.protonstream.playback.PlaybackService
 import io.narl.protonstream.settings.SettingsStore
+import io.narl.protonstream.sync.NewEpisodesWorker
 import io.narl.protonstream.sync.WatchSyncWorker
 import io.narl.protonstream.ui.ProtonStreamApp
 import io.narl.protonstream.ui.theme.AppearanceState
@@ -79,6 +80,7 @@ class MainActivity : ComponentActivity() {
             playbackConnection,
             Context.BIND_AUTO_CREATE,
         )
+        NewEpisodesWorker.schedule(this)
         if (
             Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU &&
             checkSelfPermission(Manifest.permission.POST_NOTIFICATIONS) != PackageManager.PERMISSION_GRANTED

android/app/src/main/java/io/narl/protonstream/settings/SettingsStore.kt

@@ -56,6 +56,11 @@ class SettingsStore(context: Context) {
         get() = preferences.getBoolean(KEY_LIBRARY_GROUPED, true)
         set(value) { preferences.edit { putBoolean(KEY_LIBRARY_GROUPED, value) } }
 
+    /** Whether a background crawl may say that a show gained episodes. */
+    var newEpisodeNotifications: Boolean
+        get() = preferences.getBoolean(KEY_NEW_EPISODE_NOTIFICATIONS, true)
+        set(value) { preferences.edit { putBoolean(KEY_NEW_EPISODE_NOTIFICATIONS, value) } }
+
     companion object {
         /** The desktop's range, in the steps a phone's storage is bought in. */
         val CACHE_BUDGET_CHOICES = listOf(1, 2, 4, 8, 16)
@@ -78,6 +83,7 @@ class SettingsStore(context: Context) {
         private const val KEY_LIBRARY_SORT = "library_sort"
         private const val KEY_LIBRARY_GROUPED = "library_grouped"
         private const val KEY_LIBRARY_FILTER = "library_filter"
+        private const val KEY_NEW_EPISODE_NOTIFICATIONS = "new_episode_notifications"
         private const val KEY_METADATA_OFFER_DISMISSED = "metadata_offer_dismissed"
     }
 }

android/app/src/main/java/io/narl/protonstream/sync/NewEpisodesWorker.kt

@@ -0,0 +1,136 @@
+package io.narl.protonstream.sync
+
+import android.Manifest
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.PendingIntent
+import android.content.Context
+import android.content.Intent
+import android.content.pm.PackageManager
+import android.os.Build
+import androidx.core.app.NotificationCompat
+import androidx.core.app.NotificationManagerCompat
+import androidx.work.Constraints
+import androidx.work.CoroutineWorker
+import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.NetworkType
+import androidx.work.PeriodicWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import io.narl.protonstream.MainActivity
+import io.narl.protonstream.R
+import io.narl.protonstream.native.NativeRuntime
+import io.narl.protonstream.settings.SettingsStore
+import uniffi.pstr_android.NewEpisodesRecord
+import java.util.concurrent.TimeUnit
+
+/**
+ * Look at the shares while the app is away, and say when a show gained episodes.
+ *
+ * The app crawls a share it has not looked at for six hours whenever it opens,
+ * which finds a new episode only once someone opens it to look. This runs the
+ * same crawl on WorkManager's schedule instead. It only reports files the
+ * crawl itself found, so a share the app crawled since says nothing twice.
+ */
+class NewEpisodesWorker(
+    appContext: Context,
+    parameters: WorkerParameters,
+) : CoroutineWorker(appContext, parameters) {
+    override suspend fun doWork(): Result {
+        if (!SettingsStore(applicationContext).newEpisodeNotifications) return Result.success()
+        val news = runCatching { NativeRuntime.engine().crawlForNews() }.getOrElse { return Result.retry() }
+        if (news.isNotEmpty()) post(news)
+        return Result.success()
+    }
+
+    private fun post(news: List<NewEpisodesRecord>) {
+        if (
+            Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU &&
+            applicationContext.checkSelfPermission(Manifest.permission.POST_NOTIFICATIONS) !=
+            PackageManager.PERMISSION_GRANTED
+        ) {
+            return
+        }
+        val manager = applicationContext.getSystemService(NotificationManager::class.java)
+        manager.createNotificationChannel(
+            NotificationChannel(CHANNEL_ID, "New episodes", NotificationManager.IMPORTANCE_DEFAULT).apply {
+                description = "A show in your library gained episodes"
+            },
+        )
+        val open = PendingIntent.getActivity(
+            applicationContext,
+            0,
+            Intent(applicationContext, MainActivity::class.java),
+            PendingIntent.FLAG_IMMUTABLE or PendingIntent.FLAG_UPDATE_CURRENT,
+        )
+        val compat = NotificationManagerCompat.from(applicationContext)
+        // One per show, keyed by it, so a second crawl's news for the same show
+        // replaces the first rather than stacking under it.
+        news.forEach { item ->
+            val notification = NotificationCompat.Builder(applicationContext, CHANNEL_ID)
+                .setSmallIcon(R.drawable.ic_notification_stream)
+                .setContentTitle(item.title)
+                .setContentText(describe(item))
+                .setContentIntent(open)
+                .setGroup(GROUP)
+                .setAutoCancel(true)
+                .build()
+            compat.notify(item.titleKey, NOTIFICATION_ID, notification)
+        }
+        if (news.size > 1) {
+            val summary = NotificationCompat.Builder(applicationContext, CHANNEL_ID)
+                .setSmallIcon(R.drawable.ic_notification_stream)
+                .setContentTitle("New episodes")
+                .setContentText(news.joinToString { it.title })
+                .setContentIntent(open)
+                .setGroup(GROUP)
+                .setGroupSummary(true)
+                .setAutoCancel(true)
+                .build()
+            compat.notify(SUMMARY_TAG, NOTIFICATION_ID, summary)
+        }
+    }
+
+    companion object {
+        private const val WORK_NAME = "new-episodes"
+        private const val CHANNEL_ID = "new-episodes"
+        private const val GROUP = "io.narl.protonstream.NEW_EPISODES"
+        private const val SUMMARY_TAG = "new-episodes-summary"
+        private const val NOTIFICATION_ID = 7
+        private const val INTERVAL_HOURS = 6L
+
+        /** What one show's notification says: "S01E04 and 2 more". */
+        fun describe(news: NewEpisodesRecord): String {
+            val more = news.count.toInt() - 1
+            val first = news.first
+            return when {
+                first == null -> if (news.count == 1u) "1 new episode" else "${news.count} new episodes"
+                more == 0 -> "$first is new"
+                more == 1 -> "$first and 1 more are new"
+                else -> "$first and $more more are new"
+            }
+        }
+
+        /**
+         * Keep the periodic look scheduled, or cancel it when the viewer
+         * turned it off. Called on every launch; keeping an existing schedule
+         * means a launch does not push the next look back.
+         */
+        fun schedule(context: Context) {
+            val work = WorkManager.getInstance(context.applicationContext)
+            if (!SettingsStore(context).newEpisodeNotifications) {
+                work.cancelUniqueWork(WORK_NAME)
+                return
+            }
+            val request = PeriodicWorkRequestBuilder<NewEpisodesWorker>(INTERVAL_HOURS, TimeUnit.HOURS)
+                .setConstraints(
+                    Constraints.Builder()
+                        .setRequiredNetworkType(NetworkType.CONNECTED)
+                        .setRequiresBatteryNotLow(true)
+                        .build(),
+                )
+                .build()
+            work.enqueueUniquePeriodicWork(WORK_NAME, ExistingPeriodicWorkPolicy.KEEP, request)
+        }
+    }
+}

android/app/src/main/java/io/narl/protonstream/ui/SettingsScreen.kt

@@ -59,6 +59,7 @@ import androidx.compose.ui.window.DialogProperties
 import androidx.compose.ui.window.SecureFlagPolicy
 import androidx.compose.ui.unit.dp
 import io.narl.protonstream.settings.SettingsStore
+import io.narl.protonstream.sync.NewEpisodesWorker
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
@@ -104,6 +105,7 @@ internal fun SettingsScreen(
     val settings = remember { SettingsStore(context) }
     var wifiOnly by remember { mutableStateOf(settings.wifiOnly) }
     var backgroundAudio by remember { mutableStateOf(settings.backgroundAudio) }
+    var newEpisodes by remember { mutableStateOf(settings.newEpisodeNotifications) }
     var hardwareDecoding by remember { mutableStateOf(settings.hardwareDecoding) }
     var cacheBudgetGib by remember { mutableStateOf(settings.cacheBudgetGib) }
     // Playback preferences are the shared store's, not this app's: they are the
@@ -207,6 +209,15 @@ internal fun SettingsScreen(
                 backgroundAudio = it
                 settings.backgroundAudio = it
             }
+            SettingSwitch(
+                "New episode notifications",
+                "Looks at your shares every few hours and says when a show gains episodes",
+                newEpisodes,
+            ) {
+                newEpisodes = it
+                settings.newEpisodeNotifications = it
+                NewEpisodesWorker.schedule(context)
+            }
         }
         SettingsPage.Storage -> SettingsSubPage(SettingsPage.Storage, padding, back) {
             SettingSwitch("Download on Wi-Fi only", "Mobile data is never used for downloads", wifiOnly) {