feat(app,android,ios): end an episode without chapters as well as one with them

The up-next countdown only ran over a credits chapter, so a file with no
chapters - most that are not anime - cut straight into the next episode
with no warning and no way to stay. Such a file now shows the same card
over its last ten seconds, counted on the file's own clock so it reaches
zero at the end of file, and its second button is Cancel rather than
Watch till the end.

On the phones, an episode that ends with nothing after it - the last one,
autoplay off, or cancelled - left a black screen. It now says so, with
Play next or Watch again, and Close.

Android also:
- saves the resume position from PlaybackService rather than the player
  screen. With background audio on the service outlives the activity, and
  a position only the screen kept stopped being saved when it went. A swipe
  from Recents saves and stops instead of playing on with nothing to
  return to.
- shows "Opening <episode>..." while the stream opens, where there was a
  black screen for as long as the share session and block list took.

android/app/src/main/java/io/narl/protonstream/playback/PlaybackService.kt

@@ -19,9 +19,11 @@ import android.media.session.MediaSession
 import android.media.session.PlaybackState
 import android.os.Binder
 import android.os.IBinder
+import android.os.SystemClock
 import androidx.core.content.ContextCompat
 import io.narl.protonstream.MainActivity
 import io.narl.protonstream.R
+import io.narl.protonstream.native.NativeRuntime
 import io.narl.protonstream.settings.SettingsStore
 import io.narl.protonstream.ui.loadArtwork
 import io.narl.protonstream.ui.loadThumbnail
@@ -33,6 +35,8 @@ import kotlinx.coroutines.cancel
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withContext
 import kotlinx.coroutines.withTimeoutOrNull
 
 /** Owns libmpv so audio survives Activity recreation and rotation. */
@@ -81,6 +85,9 @@ class PlaybackService : Service() {
     private var notified: NotificationShape? = null
     /** The pending teardown, held so an episode transition can call it off. */
     private var retire: Job? = null
+    /** The open episode's latest reading, which [track] saves. */
+    private var lastReading: MpvPlaybackState? = null
+    private var lastSave = 0L
     /** The episode's artwork, and the source key it was fetched for. */
     private var artwork: Pair<String, Bitmap>? = null
     private val binder = PlaybackBinder()
@@ -115,7 +122,7 @@ class PlaybackService : Service() {
                 }
                 mediaSession.isActive = true
             }
-            onStateChanged = { updateSession(it) }
+            onStateChanged = { updateSession(it); track(it) }
             onExplicitStop = { retirePlayback() }
         }
         mediaSession = MediaSession(this, "proton-stream").apply {
@@ -164,6 +171,22 @@ class PlaybackService : Service() {
         return START_NOT_STICKY
     }
 
+    /**
+     * Swiped away from Recents. With background audio on, this service would
+     * otherwise play on with no screen to return to and no autoplay, so it
+     * saves where the episode got to and stops.
+     */
+    override fun onTaskRemoved(rootIntent: Intent?) {
+        lastReading?.let { reading ->
+            // Bounded and on this thread: the process may go as soon as the
+            // service stops, and a save launched into its scope would go with it.
+            runBlocking { withTimeoutOrNull(SAVE_ON_EXIT_MS) { withContext(Dispatchers.IO) { save(reading) } } }
+        }
+        host?.stop()
+        retirePlayback()
+        super.onTaskRemoved(rootIntent)
+    }
+
     override fun onDestroy() {
         scope.cancel()
         runCatching { unregisterReceiver(becomingNoisy) }
@@ -225,6 +248,52 @@ class PlaybackService : Service() {
         return audioManager.requestAudioFocus(request) == AudioManager.AUDIOFOCUS_REQUEST_GRANTED
     }
 
+    /**
+     * Keep the resume position from here rather than from the player screen.
+     *
+     * This service outlives the activity whenever background audio is on, and a
+     * position the screen alone kept stopped being saved the moment the screen
+     * went. Readings are attributed by [MpvPlaybackState.media], so an episode
+     * change saves the outgoing episode's last reading before the new one's.
+     */
+    private fun track(state: MpvPlaybackState) {
+        val media = state.media ?: return
+        if (state.duration <= 0.0) return
+        val previous = lastReading
+        lastReading = state
+        val now = SystemClock.elapsedRealtime()
+        val due = when {
+            previous != null && previous.media != media -> {
+                scope.launch(Dispatchers.IO) { save(previous) }
+                true
+            }
+            state.ended -> previous?.ended != true
+            state.paused -> previous?.paused != true
+            else -> now - lastSave >= SAVE_EVERY_MS
+        }
+        if (due) {
+            lastSave = now
+            scope.launch(Dispatchers.IO) { save(state) }
+        }
+    }
+
+    private suspend fun save(state: MpvPlaybackState) {
+        val media = state.media ?: return
+        // Played to the end, or near enough that what is left is credits. A
+        // failure or a stop also "ends", and recording either as watched would
+        // retire an episode nobody saw.
+        val watched = state.endReason == EndReason.Eof || state.position >= state.duration * WATCHED_FRACTION
+        runCatching {
+            NativeRuntime.engine().saveWatchState(
+                media.substringBeforeLast(':'),
+                media.substringAfterLast(':'),
+                state.position.coerceIn(0.0, state.duration),
+                state.duration,
+                watched,
+            )
+        }
+    }
+
     private fun updateSession(state: MpvPlaybackState) {
         refreshSession(state, host?.nowPlaying?.value)
         if (state.ended) scheduleRetire() else cancelRetire()
@@ -419,6 +488,9 @@ class PlaybackService : Service() {
         private const val TRANSITION_GRACE_MS = 30_000L
         /** How far the volume drops for a navigation prompt or a notification. */
         private const val DUCK_FACTOR = 0.3
+        private const val SAVE_EVERY_MS = 5_000L
+        /** How long a swipe from Recents may hold the main thread to save. */
+        private const val SAVE_ON_EXIT_MS = 2_000L
 
         /** Catppuccin Mocha mauve, the accent the app is themed with. */
         private const val ACCENT = 0xFFCBA6F7.toInt()

android/app/src/main/java/io/narl/protonstream/playback/PlayerScreen.kt

@@ -19,6 +19,7 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.layout.widthIn
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.heightIn
 import androidx.compose.foundation.layout.padding
@@ -71,6 +72,7 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.platform.LocalWindowInfo
+import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.viewinterop.AndroidView
@@ -107,6 +109,7 @@ import uniffi.pstr_android.EpisodeRecord
 import uniffi.pstr_android.TitleRecord
 import uniffi.pstr_android.TrackPreferencesRecord
 import uniffi.pstr_android.skipOffer
+import kotlin.math.ceil
 import kotlin.math.roundToInt
 
 /** How long the controls stay up after a tap. */
@@ -116,7 +119,7 @@ private const val CONTROLS_SECONDS = 4L
 private const val UP_NEXT_SECONDS = 10
 
 /** Past this much of an episode it counts as watched. */
-private const val WATCHED_FRACTION = 0.9
+internal const val WATCHED_FRACTION = 0.9
 
 /** The loudest this app plays. Matches `pstr_core::prefs`, which stores it. */
 private const val MAX_VOLUME = 100f
@@ -191,6 +194,10 @@ fun PlayerScreen(
     var retryFrom by remember(key) { mutableStateOf<Double?>(null) }
     val session = remember(key, attempt) { RustStreamSession(episode) }
     var playbackError by remember(key) { mutableStateOf<String?>(null) }
+    // From the click until mpv has the file: the share session, the revision
+    // and its block list all come first, and on a slow link that is seconds of
+    // black screen unless something says so.
+    var opening by remember(key, attempt) { mutableStateOf(true) }
 
     LaunchedEffect(session, host) {
         runCatching {
@@ -229,6 +236,7 @@ fun PlayerScreen(
             nativeHost.setSpeed(startup.speed)
             session.transferToPlayer()
         }.onFailure { playbackError = it.message ?: "Playback failed" }
+        opening = false
     }
 
     // Per episode: the stream Rust holds open. The surface is the screen's, not
@@ -266,12 +274,8 @@ fun PlayerScreen(
             )
         }
     }
-    LaunchedEffect(key) {
-        while (true) {
-            delay(5_000)
-            save()
-        }
-    }
+    // The five-second save is PlaybackService's, which outlives this screen;
+    // these are the moments only the screen sees.
     DisposableEffect(key) { onDispose { save() } }
 
     val next = episodes.getOrNull(index + 1)
@@ -323,8 +327,10 @@ fun PlayerScreen(
 
     // Autoplay fires on a clean end of file only, and only for this episode's
     // own reading — never on a failure, and never on the outgoing file's.
+    // Cancelled from the end-of-file card: the viewer chose to stay.
+    var stay by remember(key) { mutableStateOf(false) }
     LaunchedEffect(state.endReason, state.media) {
-        if (state.endReason == EndReason.Eof && state.media == key && autoplay && next != null) advance()
+        if (state.endReason == EndReason.Eof && state.media == key && autoplay && !stay && next != null) advance()
     }
     // A file mpv could not play ends like any other. Saying so is the whole
     // difference between a broken episode and an app that silently skipped one.
@@ -491,21 +497,45 @@ fun PlayerScreen(
             ) { Text(skip.label) }
         }
 
+        // A file with no chapters has no credits to count over, so the card
+        // takes its last seconds instead: without it the next episode cut in
+        // with no warning and no way to stay. Counted on the file's own clock,
+        // so it reaches zero at the end of file, which is what advances.
+        val tailLeft = (state.duration - state.position).takeIf {
+            chapters.creditsStart == null && state.duration > UP_NEXT_SECONDS * 6 && it <= UP_NEXT_SECONDS
+        }
         UpNextCard(
             next = next,
-            visible = autoplay && !state.paused && playingThis &&
-                chapters.creditsStart?.let { state.position >= it } == true,
+            visible = autoplay && !stay && !state.paused && !state.ended && playingThis &&
+                (tailLeft != null || chapters.creditsStart?.let { state.position >= it } == true),
+            secondsLeft = tailLeft?.let { ceil(it).toInt() },
             onPlayNow = { advance() },
+            onStay = { stay = true },
             modifier = Modifier
                 .align(Alignment.BottomEnd)
                 .windowInsetsPadding(WindowInsets.safeDrawing)
                 .padding(end = 16.dp, bottom = if (showControls) 132.dp else 24.dp),
         )
 
+        // Played to the end with nothing starting after it: the last episode,
+        // autoplay off, or the viewer stayed. A black screen said none of that.
+        if (playingThis && state.endReason == EndReason.Eof && (next == null || !autoplay || stay)) {
+            EndCard(
+                finished = episode.label,
+                show = title.displayName,
+                next = next,
+                onPlayNext = { advance() },
+                // mpv unloads a file at its end, so this opens it again.
+                onReplay = { retryFrom = 0.0; attempt++ },
+                onClose = onClose,
+                modifier = Modifier.align(Alignment.Center),
+            )
+        }
+
         // Only while nothing else explains the still picture: an error is the
         // more useful thing to say, and a spinner over it reads as "still
         // trying".
-        if (state.stalled && playbackError == null) {
+        if ((opening || state.stalled) && playbackError == null) {
             Column(
                 Modifier
                     .align(Alignment.Center)
@@ -517,10 +547,13 @@ fun PlayerScreen(
                     color = MaterialTheme.colorScheme.primary,
                     modifier = Modifier.size(36.dp),
                 )
-                if (state.buffering) {
+                if (opening || state.buffering) {
                     Text(
-                        state.cachePercent.takeIf { it > 0.0 }
-                            ?.let { "Buffering… ${it.roundToInt()}%" } ?: "Buffering…",
+                        when {
+                            opening -> "Opening ${episode.label}…"
+                            state.cachePercent > 0.0 -> "Buffering… ${state.cachePercent.roundToInt()}%"
+                            else -> "Buffering…"
+                        },
                         color = MaterialTheme.colorScheme.onSurface,
                         style = MaterialTheme.typography.labelMedium,
                         modifier = Modifier.padding(top = 12.dp),
@@ -1016,24 +1049,31 @@ private fun EpisodeChooser(
  *
  * "Watch till the end" holds for the rest of the file: someone who wants the
  * post-credits scene should have to say so once, not once every ten seconds.
+ *
+ * With [secondsLeft] the card counts down the end of a file that has no credits
+ * chapter, on the file's own clock; the end of file is what advances, and the
+ * second button is "Cancel", since there are no credits to watch.
  */
 @Composable
 private fun UpNextCard(
     next: EpisodeRecord?,
     visible: Boolean,
+    secondsLeft: Int?,
     onPlayNow: () -> Unit,
+    onStay: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
     var held by remember(next?.linkId) { mutableStateOf(false) }
-    var remaining by remember(next?.linkId) { mutableStateOf(UP_NEXT_SECONDS) }
+    var counted by remember(next?.linkId) { mutableStateOf(UP_NEXT_SECONDS) }
+    val remaining = secondsLeft ?: counted
     val upNext = next
     val showing = visible && upNext != null && !held
-    LaunchedEffect(showing) {
-        if (!showing) return@LaunchedEffect
-        remaining = UP_NEXT_SECONDS
-        while (remaining > 0) {
+    LaunchedEffect(showing, secondsLeft == null) {
+        if (!showing || secondsLeft != null) return@LaunchedEffect
+        counted = UP_NEXT_SECONDS
+        while (counted > 0) {
             delay(1_000)
-            remaining -= 1
+            counted -= 1
         }
         onPlayNow()
     }
@@ -1096,8 +1136,49 @@ private fun UpNextCard(
                 )
             }
         }
-        QuietButton(onClick = { held = true }, modifier = Modifier.padding(top = 4.dp)) {
-            Text("Watch till the end")
+        if (secondsLeft != null) {
+            QuietButton(onClick = { held = true; onStay() }, modifier = Modifier.padding(top = 4.dp)) {
+                Text("Cancel")
+            }
+        } else {
+            QuietButton(onClick = { held = true }, modifier = Modifier.padding(top = 4.dp)) {
+                Text("Watch till the end")
+            }
+        }
+    }
+}
+
+/** What the player says once an episode ends and nothing starts after it. */
+@Composable
+private fun EndCard(
+    finished: String,
+    show: String,
+    next: EpisodeRecord?,
+    onPlayNext: () -> Unit,
+    onReplay: () -> Unit,
+    onClose: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    Column(
+        modifier
+            .widthIn(max = 360.dp)
+            .background(MaterialTheme.colorScheme.surfaceContainerHighest, MaterialTheme.shapes.medium)
+            .padding(20.dp),
+        horizontalAlignment = Alignment.CenterHorizontally,
+    ) {
+        Text(
+            if (next == null) "That was the last episode of $show" else "Finished $finished",
+            color = MaterialTheme.colorScheme.onSurface,
+            style = MaterialTheme.typography.titleMedium,
+            textAlign = TextAlign.Center,
+        )
+        Row(Modifier.padding(top = 12.dp), verticalAlignment = Alignment.CenterVertically) {
+            if (next != null) {
+                AccentButton(onClick = onPlayNext) { Text("Play next") }
+            } else {
+                QuietButton(onClick = onReplay) { Text("Watch again") }
+            }
+            QuietButton(onClick = onClose, modifier = Modifier.padding(start = 8.dp)) { Text("Close") }
         }
     }
 }