actaully make sure the chapter exists

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/Chapter.kt

@@ -18,8 +18,10 @@ import org.jetbrains.exposed.sql.select
 import org.jetbrains.exposed.sql.transactions.transaction
 import org.jetbrains.exposed.sql.update
 import suwayomi.tachidesk.manga.impl.Manga.getManga
+import suwayomi.tachidesk.manga.impl.Page.getPageName
 import suwayomi.tachidesk.manga.impl.util.GetHttpSource.getHttpSource
 import suwayomi.tachidesk.manga.impl.util.lang.awaitSingle
+import suwayomi.tachidesk.manga.impl.util.storage.CachedImageResponse
 import suwayomi.tachidesk.manga.model.dataclass.ChapterDataClass
 import suwayomi.tachidesk.manga.model.table.ChapterMetaTable
 import suwayomi.tachidesk.manga.model.table.ChapterTable
@@ -143,7 +145,15 @@ object Chapter {
             }.first()
         }
 
-        return if (!chapterEntry[ChapterTable.isDownloaded]) {
+        val isReallyDownloaded =
+            chapterEntry[ChapterTable.isDownloaded] && firstPageExists(mangaId, chapterEntry[ChapterTable.id].value)
+        return if (!isReallyDownloaded) {
+            transaction {
+                ChapterTable.update({ (ChapterTable.chapterIndex eq chapterIndex) and (ChapterTable.manga eq mangaId) }) {
+                    it[isDownloaded] = false
+                }
+            }
+
             val mangaEntry = transaction { MangaTable.select { MangaTable.id eq mangaId }.first() }
             val source = getHttpSource(mangaEntry[MangaTable.sourceReference])
 
@@ -210,6 +220,12 @@ object Chapter {
         }
     }
 
+    private fun firstPageExists(mangaId: Int, chapterId: Int): Boolean =
+        CachedImageResponse.findFileNameStartingWith(
+            Page.getChapterDir(mangaId, chapterId),
+            getPageName(0)
+        ) != null
+
     fun modifyChapter(
         mangaId: Int,
         chapterIndex: Int,

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/Page.kt

@@ -51,14 +51,14 @@ object Page {
 
         val pageEntry = transaction { PageTable.select { (PageTable.chapter eq chapterId) and (PageTable.index eq index) }.first() }
 
-        val tachiPage = Page(
+        val tachiyomiPage = Page(
             pageEntry[PageTable.index],
             pageEntry[PageTable.url],
             pageEntry[PageTable.imageUrl]
         )
 
         if (pageEntry[PageTable.imageUrl] == null) {
-            val trueImageUrl = getTrueImageUrl(tachiPage, source)
+            val trueImageUrl = getTrueImageUrl(tachiyomiPage, source)
             transaction {
                 PageTable.update({ (PageTable.chapter eq chapterId) and (PageTable.index eq index) }) {
                     it[imageUrl] = trueImageUrl
@@ -68,15 +68,18 @@ object Page {
 
         val saveDir = getChapterDir(mangaId, chapterId)
         File(saveDir).mkdirs()
-        val fileName = String.format("%03d", index) // e.g. 001.jpeg
+        val fileName = getPageName(index) // e.g. 001
 
         return getCachedImageResponse(saveDir, fileName) {
-            source.fetchImage(tachiPage).awaitSingle()
+            source.fetchImage(tachiyomiPage).awaitSingle()
         }
     }
 
+    fun getPageName(index: Int): String = String.format("%03d", index)
+
     private val applicationDirs by DI.global.instance<ApplicationDirs>()
-    private fun getChapterDir(mangaId: Int, chapterId: Int): String {
+
+    fun getChapterDir(mangaId: Int, chapterId: Int): String {
         val mangaEntry = transaction { MangaTable.select { MangaTable.id eq mangaId }.first() }
         val source = getHttpSource(mangaEntry[MangaTable.sourceReference])
         val chapterEntry = transaction { ChapterTable.select { ChapterTable.id eq chapterId }.first() }

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/util/storage/CachedImageResponse.kt

@@ -18,7 +18,7 @@ object CachedImageResponse {
         return FileInputStream(path).buffered()
     }
 
-    private fun findFileNameStartingWith(directoryPath: String, fileName: String): String? {
+    fun findFileNameStartingWith(directoryPath: String, fileName: String): String? {
         val target = "$fileName."
         File(directoryPath).listFiles().orEmpty().forEach { file ->
             if (file.name.startsWith(target))