Music comes back after a call when it plays through Gearslip

When the car took the speakers for a moment, for a call or its own voice, Gearslip
paused the music and gave up its claim, so the car never handed the sound back.
It now keeps the claim and plays the music again once the car is done.

gearslip/src/main/java/app/seb3thehacker/gearslip/GearslipRunner.kt

@@ -589,6 +589,8 @@ class GearslipRunner(
             // The driver picked the radio or another source on the car: pause the phone's music
             // as Android Auto does, instead of letting it play on to no one.
             onTakenBack = { CarServices.pausePhoneMedia("the car switched to another source") },
+            onPausedForNow = { CarServices.pausePhoneMediaForNow() },
+            onGivenBack = { CarServices.resumePhoneMedia() },
         )
         if (CarSettings.pipeAudio.value) {
             openChannel(media.serviceId)

gearslip/src/main/java/app/seb3thehacker/gearslip/audio/AudioLink.kt

@@ -36,6 +36,9 @@ class AudioLink(
     private val onClose: (AudioLink) -> Unit = { CarAudio.detach(it) },
     /** The car took the sound back after giving it, as when the driver switches to the radio. */
     private val onTakenBack: () -> Unit = {},
+    /** The car wants the speakers for a moment (a call, its own voice), and then [onGivenBack]. */
+    private val onPausedForNow: () -> Unit = {},
+    private val onGivenBack: () -> Unit = {},
 ) : CarAudio.Link {
 
     private var configIndex = 0
@@ -43,6 +46,8 @@ class AudioLink(
     @Volatile private var started = false
     @Volatile private var focusGranted = false
     @Volatile private var focusRequested = false
+    /** The car took the speakers for a moment, and we paused the phone's music until it's done. */
+    @Volatile private var pausedForNow = false
     @Volatile private var inFlight = 0
     // The Uconnect asks for 4 on its video channel; assume the same until its Config says otherwise.
     @Volatile private var maxUnacked = 4
@@ -222,9 +227,32 @@ class AudioLink(
         val had = focusGranted
         focusGranted = state == FOCUS_STATE_GAIN || state == FOCUS_STATE_GAIN_TRANSIENT ||
             state == FOCUS_STATE_GAIN_MEDIA_ONLY
-        if (focusGranted) startStream() else stop()
-        // A ducking request leaves the music playing; a loss means another source has the speakers.
-        if (had && (state == FOCUS_STATE_LOSS || state == FOCUS_STATE_LOSS_TRANSIENT)) onTakenBack()
+        when {
+            focusGranted -> {
+                startStream()
+                if (pausedForNow) {
+                    pausedForNow = false
+                    onGivenBack()
+                }
+            }
+            // A call or the car's own voice. Releasing focus here meant the car never handed it
+            // back, so the music stayed paused after the call: keep the claim and wait for GAIN.
+            state == FOCUS_STATE_LOSS_TRANSIENT -> {
+                synchronized(startLock) { stopLocked(release = false) }
+                if (had) {
+                    pausedForNow = true
+                    onPausedForNow()
+                }
+            }
+            else -> {
+                stop()
+                // A ducking request leaves the music playing; a loss means another source has the speakers.
+                if (state == FOCUS_STATE_LOSS && (had || pausedForNow)) {
+                    pausedForNow = false
+                    onTakenBack()
+                }
+            }
+        }
     }
 
     /**
@@ -299,19 +327,20 @@ class AudioLink(
         synchronized(startLock) { stopLocked() }
     }
 
-    private fun stopLocked() {
+    /** [release] false keeps our claim on the speakers, so the car hands them back on its own. */
+    private fun stopLocked(release: Boolean = true) {
         if (!started) return
         started = false
         synchronized(ackLock) { ackLock.notifyAll() }
         runCatching {
             sendOnChannel(MSG_STOP, Protobuf.varintField(1, sessionId.toLong()))
-            if (focusRequested) sendControl(MSG_FOCUS_REQUEST, Protobuf.varintField(1, FOCUS_RELEASE.toLong()))
+            if (release && focusRequested) sendControl(MSG_FOCUS_REQUEST, Protobuf.varintField(1, FOCUS_RELEASE.toLong()))
         }
-        focusRequested = false
+        if (release) focusRequested = false
         focusGranted = false
         aac?.release()
         aac = null
-        GearslipLog.i("$tag: -> Stop, AudioFocusRequest(RELEASE) after $chunks chunks / $bytes bytes")
+        GearslipLog.i("$tag: -> Stop${if (release) ", AudioFocusRequest(RELEASE)" else ""} after $chunks chunks / $bytes bytes")
         chunks = 0
         bytes = 0
         // A new stream starts with the car's buffer empty again: earn the lead back if it's needed.

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarServices.kt

@@ -2,6 +2,7 @@ package app.seb3thehacker.gearslip.car
 
 import android.content.ComponentName
 import android.content.Context
+import android.media.session.MediaController
 import android.media.session.MediaSessionManager
 import android.media.session.PlaybackState
 import app.seb3thehacker.gearslip.audio.CarAudio
@@ -254,7 +255,41 @@ object CarServices {
      * just the one Gearslip opened: anything the car was playing was going through the car.
      */
     fun pausePhoneMedia(why: String = "the car left") {
-        val ctx = context ?: return
+        pausedForNow = null
+        pausedOwnForNow = false
+        pause(why)
+    }
+
+    /** What [pausePhoneMediaForNow] paused, for [resumePhoneMedia] to play again. */
+    @Volatile private var pausedForNow: List<MediaController>? = null
+    /** Without notification access, whether it paused the app Gearslip drives itself. */
+    @Volatile private var pausedOwnForNow = false
+
+    /** The car wants the speakers for a moment: pause, and remember what to play after. */
+    fun pausePhoneMediaForNow() {
+        pausedOwnForNow = false
+        pausedForNow = pause("the car needs the speakers for a moment")
+    }
+
+    /** The car handed the speakers back: play what it paused, unless the driver has since. */
+    fun resumePhoneMedia() {
+        val paused = pausedForNow ?: return
+        pausedForNow = null
+        if (pausedOwnForNow) {
+            pausedOwnForNow = false
+            mediaOrNull()?.let { if (!it.now.value.playing) it.togglePlay() }
+            return
+        }
+        val waiting = paused.filter { it.playbackState?.state == PlaybackState.STATE_PAUSED }
+        waiting.forEach { runCatching { it.transportControls.play() } }
+        if (waiting.isNotEmpty()) {
+            app.seb3thehacker.gearslip.GearslipLog.i("media: playing ${waiting.joinToString { it.packageName }} again: the car gave the speakers back")
+        }
+    }
+
+    /** What it paused. Without notification access it can only reach the app Gearslip drives itself. */
+    private fun pause(why: String): List<MediaController> {
+        val ctx = context ?: return emptyList()
         val manager = ctx.getSystemService(MediaSessionManager::class.java)
         val listener = ComponentName(ctx, GearslipNotificationListener::class.java)
         val playing = try {
@@ -264,13 +299,19 @@ object CarServices {
         }
         if (playing == null) {
             // No notification access: the app Gearslip itself is driving is all it can reach.
-            mediaOrNull()?.let { if (it.now.value.playing) it.togglePlay() }
-            return
+            mediaOrNull()?.let {
+                if (it.now.value.playing) {
+                    it.togglePlay()
+                    pausedOwnForNow = true
+                }
+            }
+            return emptyList()
         }
         playing.forEach { runCatching { it.transportControls.pause() } }
         if (playing.isNotEmpty()) {
             app.seb3thehacker.gearslip.GearslipLog.i("media: paused ${playing.joinToString { it.packageName }}: $why")
         }
+        return playing
     }
 
     /** The car went away: nothing should keep running for a screen that no longer exists. */