musikr: introduce cover cleanup

Helps reduce overall memory use.

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

@@ -432,7 +432,7 @@ constructor(
         // Old cover revisions may be lying around, even during a normal refresh due
         // to really lucky cancellations. Clean those up now that it's impossible for
         // the rest of the app to be using them.
-        covers.cleanup(context)
+        covers.cleanup(newLibrary)
     }
 
     private suspend fun emitIndexingProgress(progress: IndexingProgress) {

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

@@ -19,9 +19,11 @@
 package org.oxycblt.auxio.music
 
 import android.content.Context
+import java.io.File
 import java.util.UUID
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
+import org.oxycblt.musikr.Library
 import org.oxycblt.musikr.cover.Cover
 import org.oxycblt.musikr.cover.CoverFiles
 import org.oxycblt.musikr.cover.CoverFormat
@@ -29,8 +31,11 @@ import org.oxycblt.musikr.cover.CoverParams
 import org.oxycblt.musikr.cover.MutableStoredCovers
 import org.oxycblt.musikr.cover.StoredCovers
 
-class RevisionedCovers(private val revision: UUID, private val inner: MutableStoredCovers) :
-    MutableStoredCovers {
+class RevisionedCovers(
+    private val rootDir: File,
+    private val revision: UUID,
+    private val inner: MutableStoredCovers
+) : MutableStoredCovers {
     override suspend fun obtain(id: String): RevisionedCover? {
         val (coverId, coverRevision) = parse(id) ?: return null
         if (coverRevision != revision) return null
@@ -41,24 +46,27 @@ class RevisionedCovers(private val revision: UUID, private val inner: MutableSto
         return inner.write(data)?.let { RevisionedCover(revision, it) }
     }
 
-    suspend fun cleanup(context: Context) =
+    override suspend fun cleanup(assuming: Library) {
+        inner.cleanup(assuming)
+
+        // Destroy old revisions no longer being used.
         withContext(Dispatchers.IO) {
             val exclude = revision.toString()
-            context.filesDir
-                .resolve("covers")
-                .listFiles { file -> file.name != exclude }
-                ?.forEach { it.deleteRecursively() }
+            rootDir.listFiles { file -> file.name != exclude }?.forEach { it.deleteRecursively() }
+        }
     }
 
     companion object {
         suspend fun at(context: Context, revision: UUID): RevisionedCovers {
-            val dir =
+            val rootDir: File
+            val revisionDir: File
             withContext(Dispatchers.IO) {
-                    context.filesDir.resolve("covers/${revision}").apply { mkdirs() }
+                rootDir = context.filesDir.resolve("covers").apply { mkdirs() }
+                revisionDir = rootDir.resolve(revision.toString()).apply { mkdirs() }
             }
-            return RevisionedCovers(
-                revision,
-                StoredCovers.from(CoverFiles.at(dir), CoverFormat.jpeg(CoverParams.of(750, 80))))
+            val files = CoverFiles.at(revisionDir)
+            val format = CoverFormat.jpeg(CoverParams.of(750, 80))
+            return RevisionedCovers(rootDir, revision, StoredCovers.from(files, format))
         }
 
         private fun parse(id: String): Pair<String, UUID>? {

musikr/src/main/java/org/oxycblt/musikr/cover/CoverFiles.kt

@@ -32,6 +32,8 @@ interface CoverFiles {
 
     suspend fun write(name: String, block: suspend (OutputStream) -> Unit): CoverFile?
 
+    suspend fun deleteWhere(block: (String) -> Boolean)
+
     companion object {
         suspend fun at(dir: File): CoverFiles {
             withContext(Dispatchers.IO) { check(dir.exists() && dir.isDirectory) }
@@ -83,6 +85,12 @@ private class CoverFilesImpl(private val dir: File) : CoverFiles {
             }
         }
     }
+
+    override suspend fun deleteWhere(block: (String) -> Boolean) {
+        withContext(Dispatchers.IO) {
+            dir.listFiles { file -> block(file.name) }?.forEach { it.deleteRecursively() }
+        }
+    }
 }
 
 private class CoverFileImpl(private val file: File) : CoverFile {

musikr/src/main/java/org/oxycblt/musikr/cover/StoredCovers.kt

@@ -18,6 +18,8 @@
  
 package org.oxycblt.musikr.cover
 
+import org.oxycblt.musikr.Library
+
 interface StoredCovers {
     suspend fun obtain(id: String): Cover?
 
@@ -32,6 +34,8 @@ interface StoredCovers {
 
 interface MutableStoredCovers : StoredCovers {
     suspend fun write(data: ByteArray): Cover?
+
+    suspend fun cleanup(assuming: Library)
 }
 
 private class FileStoredCovers(
@@ -49,6 +53,11 @@ private class FileStoredCovers(
             ?.let { FileCover(id, it) }
     }
 
+    override suspend fun cleanup(assuming: Library) {
+        val used = assuming.songs.mapNotNullTo(mutableSetOf()) { it.cover?.id?.let(::getFileName) }
+        coverFiles.deleteWhere { it !in used }
+    }
+
     private fun getFileName(id: String) = "$id.${coverFormat.extension}"
 }