car audio: explain a blocked microphone permission instead of failing silently

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

@@ -8,8 +8,10 @@ import android.hardware.usb.UsbAccessory
 import android.hardware.usb.UsbManager
 import android.media.projection.MediaProjection
 import android.media.projection.MediaProjectionManager
+import android.net.Uri
 import android.os.Bundle
 import android.os.ParcelFileDescriptor
+import android.provider.Settings
 import android.view.MotionEvent
 import android.view.Surface
 import android.view.WindowManager
@@ -74,7 +76,13 @@ class GearslipActivity : ComponentActivity(), Projection {
     private val audioPermission = registerForActivityResult(
         androidx.activity.result.contract.ActivityResultContracts.RequestPermission(),
     ) { granted ->
-        if (granted) askAudioCapture() else {
+        if (granted) askAudioCapture()
+        else if (!shouldShowRequestPermissionRationale(android.Manifest.permission.RECORD_AUDIO)) {
+            // Refused twice: Android now says no without showing anything, so the phone must.
+            GearslipLog.w("audio: record permission blocked - Android no longer asks")
+            CarAudio.micBlocked()
+            micBlockedNotice.value = true
+        } else {
             GearslipLog.w("audio: record permission declined")
             CarAudio.denied()
         }
@@ -91,6 +99,9 @@ class GearslipActivity : ComponentActivity(), Projection {
         }
     }
 
+    /** Raised when the microphone permission is blocked; see [MicBlockedDialog]. */
+    private val micBlockedNotice = kotlinx.coroutines.flow.MutableStateFlow(false)
+
     /** Raised once, after the first "no" to the capture dialog; see [AudioChoiceDialog]. */
     private val offerBluetooth = kotlinx.coroutines.flow.MutableStateFlow(false)
 
@@ -148,6 +159,18 @@ class GearslipActivity : ComponentActivity(), Projection {
                         onKeepAsking = ::close,
                     )
                 }
+                val micNotice by micBlockedNotice.collectAsState()
+                if (micNotice) {
+                    app.seb3thehacker.gearslip.ui.MicBlockedDialog(
+                        onOpenSettings = {
+                            micBlockedNotice.value = false
+                            startActivity(
+                                Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS, Uri.fromParts("package", packageName, null)),
+                            )
+                        },
+                        onDismiss = { micBlockedNotice.value = false },
+                    )
+                }
             }
         }
 
@@ -173,6 +196,10 @@ class GearslipActivity : ComponentActivity(), Projection {
         Prefetch.warm(this)
         UsageStats.onAppOpened(this)
         app.seb3thehacker.gearslip.update.UpdateChecker.onAppOpened(this)
+        // Back from the app's settings with the microphone turned on: try car audio again.
+        if (checkSelfPermission(android.Manifest.permission.RECORD_AUDIO) == android.content.pm.PackageManager.PERMISSION_GRANTED) {
+            CarAudio.micAllowed()
+        }
     }
 
     override fun onNewIntent(intent: Intent) {

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

@@ -100,6 +100,26 @@ object CarAudio {
         _capture.value = Capture.DENIED
     }
 
+    private val _micBlocked = MutableStateFlow(false)
+
+    /** The microphone permission is off for good: Android refuses without asking, so say why. */
+    val micBlocked: StateFlow<Boolean> = _micBlocked.asStateFlow()
+
+    fun micBlocked() {
+        _micBlocked.value = true
+        denied()
+    }
+
+    /** The driver turned the permission back on mid-drive: ask for capture again. */
+    fun micAllowed() {
+        if (!_micBlocked.value) return
+        _micBlocked.value = false
+        if (_capture.value == Capture.DENIED) {
+            _capture.value = Capture.OFF
+            if (wanted) request()
+        }
+    }
+
     internal fun captureStarted() {
         _capture.value = Capture.ON
         link?.start()

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

@@ -449,10 +449,13 @@ private sealed interface LyricsState {
 
 @Composable
 private fun AudioBadge(capture: CarAudio.Capture) {
+    val micBlocked by CarAudio.micBlocked.collectAsStateWithLifecycle()
     val text = when (capture) {
         CarAudio.Capture.ON -> "Audio to car"
         CarAudio.Capture.ASKING -> "Allow audio capture on the phone"
-        CarAudio.Capture.DENIED -> "Audio stays on the phone"
+        CarAudio.Capture.DENIED ->
+            if (micBlocked) "Audio stays on the phone: turn on Gearslip's microphone permission"
+            else "Audio stays on the phone"
         CarAudio.Capture.OFF -> return
     }
     Text(text, style = MaterialTheme.typography.labelLarge, color = MaterialTheme.colorScheme.onSurfaceVariant)

gearslip/src/main/java/app/seb3thehacker/gearslip/ui/AudioChoiceDialog.kt

@@ -47,3 +47,25 @@ fun AudioChoiceDialog(onUseBluetooth: () -> Unit, onKeepAsking: () -> Unit) {
         dismissButton = { TextButton(onClick = onKeepAsking) { Text("Keep asking") } },
     )
 }
+
+/**
+ * Android lets an app capture other apps' audio only while it holds the microphone permission.
+ * Once the driver has refused that twice, Android stops asking, and music silently stays on the
+ * phone; this says why and where to turn it back on.
+ */
+@Composable
+fun MicBlockedDialog(onOpenSettings: () -> Unit, onDismiss: () -> Unit) {
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text("Car audio needs the microphone permission") },
+        text = {
+            Text(
+                "Android lets an app send other apps' sound to the car only if it has the " +
+                    "microphone permission. It's turned off for Gearslip, so music plays on the " +
+                    "phone. Turn it on under Permissions, then Microphone.",
+            )
+        },
+        confirmButton = { TextButton(onClick = onOpenSettings) { Text("Open app settings") } },
+        dismissButton = { TextButton(onClick = onDismiss) { Text("Not now") } },
+    )
+}