musikr: bundle cleanup into api

Prevents as much footguns.

app/src/main/java/org/oxycblt/auxio/music/MusicRepository.kt

@@ -391,7 +391,7 @@ constructor(
         val storage = Storage(cache, covers, storedPlaylists)
         val interpretation = Interpretation(nameFactory, separators)
 
-        val newLibrary =
+        val result =
             Musikr.new(context, storage, interpretation).run(locations, ::emitIndexingProgress)
         // Music loading completed, update the revision right now so we re-use this work
         // later.
@@ -399,11 +399,9 @@ constructor(
         // Deliver the library to the rest of the app
         // This will more or less block until all required item translation and
         // cleanup finishes.
-        emitLibrary(newLibrary)
-        // Old cover revisions may be lying around, even during a normal refresh due
-        // to really lucky cancellations. Now that it is impossible for the rest of
-        // the app to possible be using them, clean them up.
-        covers.cleanup(newLibrary.songs.mapNotNull { it.cover })
+        emitLibrary(result.library)
+        // Clean up old data that is now impossible for the app to be using.
+        result.cleanup()
         // Finish up loading.
         emitIndexingCompletion(null)
     }

musikr/src/main/java/org/oxycblt/musikr/Musikr.kt

@@ -34,17 +34,24 @@ interface Musikr {
     suspend fun run(
         locations: List<MusicLocation>,
         onProgress: suspend (IndexingProgress) -> Unit = {}
-    ): MutableLibrary
+    ): LibraryResult
 
     companion object {
         fun new(context: Context, storage: Storage, interpretation: Interpretation): Musikr =
             MusikrImpl(
+                storage,
                 ExploreStep.from(context, storage),
                 ExtractStep.from(context, storage),
                 EvaluateStep.new(storage, interpretation))
     }
 }
 
+interface LibraryResult {
+    val library: MutableLibrary
+
+    suspend fun cleanup()
+}
+
 /**
  * Represents the current progress of music loading.
  *
@@ -57,6 +64,7 @@ sealed interface IndexingProgress {
 }
 
 private class MusikrImpl(
+    private val storage: Storage,
     private val exploreStep: ExploreStep,
     private val extractStep: ExtractStep,
     private val evaluateStep: EvaluateStep
@@ -79,6 +87,16 @@ private class MusikrImpl(
                 .buffer(Channel.UNLIMITED)
                 .onEach { onProgress(IndexingProgress.Songs(++extractedCount, exploredCount)) }
                 .onCompletion { onProgress(IndexingProgress.Indeterminate) }
-        evaluateStep.evaluate(extracted)
+        val library = evaluateStep.evaluate(extracted)
+        LibraryResultImpl(storage, library)
+    }
+}
+
+private class LibraryResultImpl(
+    private val storage: Storage,
+    override val library: MutableLibrary) : LibraryResult {
+
+    override suspend fun cleanup() {
+        storage.storedCovers.cleanup(library.songs.mapNotNull { it.cover })
     }
 }

musikr/src/main/java/org/oxycblt/musikr/tag/interpret/Interpretation.kt

@@ -0,0 +1 @@
+package org.oxycblt.musikr.tag.interpret