Implement a download cache

app/src/main/java/eu/kanade/tachiyomi/ui/manga/chapter/ChaptersPresenter.kt

@@ -128,13 +128,11 @@ class ChaptersPresenter(
      * @param chapters the list of chapter from the database.
      */
     private fun setDownloadedChapters(chapters: List<ChapterItem>) {
-        val files = downloadManager.findMangaDir(source, manga)?.listFiles() ?: return
-        val cached = mutableMapOf<Chapter, String>()
-        files.mapNotNull { it.name }
-                .mapNotNull { name -> chapters.find {
-                    name == cached.getOrPut(it) { downloadManager.getChapterDirName(it) }
-                } }
-                .forEach { it.status = Download.DOWNLOADED }
+        for (chapter in chapters) {
+            if (downloadManager.isChapterDownloaded(chapter, manga)) {
+                chapter.status = Download.DOWNLOADED
+            }
+        }
     }
 
     /**
@@ -283,7 +281,7 @@ class ChaptersPresenter(
      */
     private fun deleteChapter(chapter: ChapterItem) {
         downloadManager.queue.remove(chapter)
-        downloadManager.deleteChapter(source, manga, chapter)
+        downloadManager.deleteChapter(chapter, manga, source)
         chapter.status = Download.NOT_DOWNLOADED
         chapter.download = null
     }

app/src/main/java/eu/kanade/tachiyomi/ui/manga/info/MangaInfoPresenter.kt

@@ -115,14 +115,14 @@ class MangaInfoPresenter(
      * Returns true if the manga has any downloads.
      */
     fun hasDownloads(): Boolean {
-        return downloadManager.findMangaDir(source, manga) != null
+        return downloadManager.getDownloadCount(manga) > 0
     }
 
     /**
      * Deletes all the downloads for the manga.
      */
     fun deleteDownloads() {
-        downloadManager.findMangaDir(source, manga)?.delete()
+        downloadManager.deleteManga(manga, source)
     }
 
     /**