Manga cover updates (#3101)

* cover caching overhaul

* add ui for removing custom cover

* skip some loading work

* minor cleanup

* allow refresh library metadata to refresh local manga

* rename metadata_date to cover_last_modified

* rearrange removeMangaFromLibrary

* change custom cover directory
add setting for updating cover when refreshing library

* remove toggle and explicit action for updating covers

app/src/main/java/eu/kanade/tachiyomi/util/MangaExtensions.kt

@@ -0,0 +1,32 @@
+package eu.kanade.tachiyomi.util
+
+import eu.kanade.tachiyomi.data.cache.CoverCache
+import eu.kanade.tachiyomi.data.database.DatabaseHelper
+import eu.kanade.tachiyomi.data.database.models.Manga
+import eu.kanade.tachiyomi.source.LocalSource
+import java.util.Date
+
+fun Manga.isLocal() = source == LocalSource.ID
+
+/**
+ * Call before updating [Manga.thumbnail_url] to ensure old cover can be cleared from cache
+ */
+fun Manga.prepUpdateCover(coverCache: CoverCache) {
+    cover_last_modified = Date().time
+
+    if (!isLocal()) {
+        coverCache.deleteFromCache(this, false)
+    }
+}
+
+fun Manga.removeCovers(coverCache: CoverCache) {
+    if (isLocal()) return
+
+    cover_last_modified = Date().time
+    coverCache.deleteFromCache(this, true)
+}
+
+fun Manga.updateCoverLastModified(db: DatabaseHelper) {
+    cover_last_modified = Date().time
+    db.updateMangaCoverLastModified(this).executeAsBlocking()
+}