home: temporarily re-add no music case

I actually have no idea how to go about decoupling the other music
loading errors from the "No Music" case without a very jarring user
experience, so I'm not doing it for now.

app/src/main/java/org/oxycblt/auxio/home/HomeFragment.kt

@@ -338,28 +338,43 @@ class HomeFragment :
             val throwable = unlikelyToBeNull(result.exceptionOrNull())
             binding.homeIndexingContainer.visibility = View.VISIBLE
             binding.homeIndexingProgress.visibility = View.INVISIBLE
-            if (throwable is Indexer.NoPermissionException) {
-                logD("Updating UI to permission request state")
-                binding.homeIndexingStatus.text = context.getString(R.string.err_no_perms)
-                // Configure the action to act as a permission launcher.
-                binding.homeIndexingAction.apply {
-                    visibility = View.VISIBLE
-                    text = context.getString(R.string.lbl_grant)
-                    setOnClickListener {
-                        requireNotNull(storagePermissionLauncher) {
-                                "Permission launcher was not available"
-                            }
-                            .launch(Indexer.PERMISSION_READ_AUDIO)
+            when (throwable) {
+                is Indexer.NoPermissionException -> {
+                    logD("Updating UI to permission request state")
+                    binding.homeIndexingStatus.text = context.getString(R.string.err_no_perms)
+                    // Configure the action to act as a permission launcher.
+                    binding.homeIndexingAction.apply {
+                        visibility = View.VISIBLE
+                        text = context.getString(R.string.lbl_grant)
+                        setOnClickListener {
+                            requireNotNull(storagePermissionLauncher) {
+                                    "Permission launcher was not available"
+                                }
+                                .launch(Indexer.PERMISSION_READ_AUDIO)
+                        }
                     }
                 }
-            } else {
-                logD("Updating UI to error state")
-                binding.homeIndexingStatus.text = context.getString(R.string.err_index_failed)
-                // Configure the action to act as a reload trigger.
-                binding.homeIndexingAction.apply {
-                    visibility = View.VISIBLE
-                    text = context.getString(R.string.lbl_retry)
-                    setOnClickListener { musicModel.refresh() }
+                is Indexer.NoMusicException -> {
+                    logD("Updating UI to no music state")
+                    // TODO: Rework how empty libraries are treated to feel less jarring if
+                    //  there was a previously loaded library
+                    binding.homeIndexingStatus.text = context.getString(R.string.err_no_music)
+                    // Configure the action to act as a reload trigger.
+                    binding.homeIndexingAction.apply {
+                        visibility = View.VISIBLE
+                        text = context.getString(R.string.lbl_retry)
+                        setOnClickListener { musicModel.refresh() }
+                    }
+                }
+                else -> {
+                    logD("Updating UI to error state")
+                    binding.homeIndexingStatus.text = context.getString(R.string.err_index_failed)
+                    // Configure the action to act as a reload trigger.
+                    binding.homeIndexingAction.apply {
+                        visibility = View.VISIBLE
+                        text = context.getString(R.string.lbl_retry)
+                        setOnClickListener { musicModel.rescan() }
+                    }
                 }
             }
         }
@@ -420,10 +435,9 @@ class HomeFragment :
         val binding = requireBinding()
         if (binding.homeSelectionToolbar.updateSelectionAmount(selected.size) &&
             selected.isNotEmpty()) {
+            // New selection started, show the AppBarLayout to indicate the new state.
             logD("Significant selection occurred, expanding AppBar")
-            // Significant enough change where we want to expand the RecyclerView
-            binding.homeAppbar.expandWithRecycler(
-                binding.homePager.findViewById(getTabRecyclerId(homeModel.currentTabMode.value)))
+            binding.homeAppbar.expandWithScrollingRecycler()
         }
     }
 

app/src/main/java/org/oxycblt/auxio/music/system/Indexer.kt

@@ -197,7 +197,9 @@ class Indexer private constructor() {
      * @param context [Context] required to load music.
      * @param withCache Whether to use the cache or not when loading. If false, the cache will still
      * be written, but no cache entries will be loaded into the new library.
-     * @return A newly-loaded [MusicStore.Library]. May be empty.
+     * @return A newly-loaded [MusicStore.Library].
+     * @throws NoPermissionException If [PERMISSION_READ_AUDIO] was not granted.
+     * @throws NoMusicException If no music was found on the device.
      */
     private suspend fun indexImpl(context: Context, withCache: Boolean): MusicStore.Library {
         if (ContextCompat.checkSelfPermission(context, PERMISSION_READ_AUDIO) ==
@@ -227,7 +229,8 @@ class Indexer private constructor() {
 
         val metadataExtractor = MetadataExtractor(context, mediaStoreExtractor)
 
-        val songs = buildSongs(metadataExtractor, Settings(context))
+        val songs =
+            buildSongs(metadataExtractor, Settings(context)).ifEmpty { throw NoMusicException() }
         // Build the rest of the music library from the song list. This is much more powerful
         // and reliable compared to using MediaStore to obtain grouping information.
         val buildStart = System.currentTimeMillis()
@@ -380,7 +383,7 @@ class Indexer private constructor() {
      * Emit a new [State.Complete] state. This can be used to signal the completion of the music
      * loading process to external code. Will check if the callee has not been canceled and thus has
      * the ability to emit a new state
-     * @param result The new [Response] to emit, representing the outcome of the music loading
+     * @param result The new [Result] to emit, representing the outcome of the music loading
      * process.
      */
     private suspend fun emitCompletion(result: Result<MusicStore.Library>) {
@@ -442,6 +445,12 @@ class Indexer private constructor() {
             get() = "Not granted permissions to load music library"
     }
 
+    /** Thrown when no music was found on the device. */
+    class NoMusicException : Exception() {
+        override val message: String
+            get() = "Unable to find any music"
+    }
+
     /**
      * A listener for rapid-fire changes in the music loading state.
      *

app/src/main/java/org/oxycblt/auxio/ui/CoordinatorAppBarLayout.kt

@@ -68,14 +68,14 @@ constructor(context: Context, attrs: AttributeSet? = null, @AttrRes defStyleAttr
     }
 
     /**
-     * Expand this [AppBarLayout] with respect to the given [RecyclerView], preventing it from
-     * jumping around.
-     * @param recycler [RecyclerView] to expand with, or null if one is currently unavailable.
+     * Expand this [AppBarLayout] with respect to the current [RecyclerView] at
+     * [liftOnScrollTargetViewId], preventing it from jumping around.
      */
-    fun expandWithRecycler(recycler: RecyclerView?) {
-        // TODO: Is it possible to use liftOnScrollTargetViewId to avoid the RecyclerView arg?
+    fun expandWithScrollingRecycler() {
         setExpanded(true)
-        recycler?.let { addOnOffsetChangedListener(ExpansionHackListener(it)) }
+        (findScrollingChild() as? RecyclerView)?.let {
+            addOnOffsetChangedListener(ExpansionHackListener(it))
+        }
     }
 
     override fun onDetachedFromWindow() {