Feature/Improve chapter download with valid existing download handling (#1553)

* Fix early exit on download for existing download for FolderProvider

The current check only worked for the "ArchiveProvider". The "FolderProvider" never moved the existing download to the cache folder.

In case the existing download is considered to be reusable, there is no need to proceed with the download logic.

* Fix "ArchiveProvider#extractExistingDownload"

The "ChaptersFilesProvider#extractExistingDownload" expects the download to be extracted into the final download folder.
However, the "ArchiveProvider" extracted the download into the chapter download cache folder.

* Add chapter download function call requirements

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

@@ -2,6 +2,7 @@ package suwayomi.tachidesk.manga.impl
 
 import kotlinx.coroutines.CoroutineScope
 import org.jetbrains.exposed.sql.transactions.transaction
+import suwayomi.tachidesk.manga.impl.chapter.getChapterDownloadReady
 import suwayomi.tachidesk.manga.impl.download.fileProvider.ChaptersFilesProvider
 import suwayomi.tachidesk.manga.impl.download.fileProvider.impl.ArchiveProvider
 import suwayomi.tachidesk.manga.impl.download.fileProvider.impl.FolderProvider
@@ -32,6 +33,9 @@ object ChapterDownloadHelper {
         chapterId: Int,
     ): Boolean = provider(mangaId, chapterId).delete()
 
+    /**
+     * This function should never be called without calling [getChapterDownloadReady] beforehand.
+     */
     suspend fun download(
         mangaId: Int,
         chapterId: Int,

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/chapter/ChapterForDownload.kt

@@ -99,7 +99,7 @@ private class ChapterForDownload(
         if (!doPageCountsMatch) {
             log.debug { "use page count of downloaded chapter" }
 
-            updatePageCount(ChapterDownloadHelper.getImageCount(mangaId, chapterId))
+            updatePageCount(downloadPageCount)
         }
 
         return asDataClass()

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/download/fileProvider/ChaptersFilesProvider.kt

@@ -13,8 +13,8 @@ import libcore.net.MimeUtils
 import org.apache.commons.compress.archivers.zip.ZipArchiveEntry
 import org.jetbrains.exposed.sql.selectAll
 import org.jetbrains.exposed.sql.transactions.transaction
-import org.jetbrains.exposed.sql.update
 import suwayomi.tachidesk.manga.impl.Page
+import suwayomi.tachidesk.manga.impl.chapter.getChapterDownloadReady
 import suwayomi.tachidesk.manga.impl.download.model.DownloadChapter
 import suwayomi.tachidesk.manga.impl.util.createComicInfoFile
 import suwayomi.tachidesk.manga.impl.util.getChapterCachePath
@@ -105,6 +105,27 @@ abstract class ChaptersFilesProvider<Type : FileType>(
         scope: CoroutineScope,
         step: suspend (DownloadChapter?, Boolean) -> Unit,
     ): Boolean {
+        val existingDownloadPageCount =
+            try {
+                getImageCount()
+            } catch (_: Exception) {
+                0
+            }
+        val pageCount = download.chapter.pageCount
+
+        check(pageCount > 0) { "pageCount must be greater than 0 - ChapterForDownload#getChapterDownloadReady not called" }
+        check(existingDownloadPageCount == 0 || existingDownloadPageCount == pageCount) {
+            "existingDownloadPageCount must be 0 or equal to pageCount - ChapterForDownload#getChapterDownloadReady not called"
+        }
+
+        val doesUnrecognizedDownloadExist = existingDownloadPageCount == pageCount
+        if (doesUnrecognizedDownloadExist) {
+            download.progress = 1f
+            step(download, false)
+
+            return true
+        }
+
         extractExistingDownload()
 
         val finalDownloadFolder = getChapterDownloadPath(mangaId, chapterId)
@@ -113,57 +134,45 @@ abstract class ChaptersFilesProvider<Type : FileType>(
         val downloadCacheFolder = File(cacheChapterDir)
         downloadCacheFolder.mkdirs()
 
-        val pageCount = download.chapter.pageCount
-        if (
-            downloadCacheFolder
-                .listFiles()
-                .orEmpty()
-                .filter { it.name != COMIC_INFO_FILE }
-                .size >= pageCount
-        ) {
-            download.progress = 1f
-            step(download, false)
-        } else {
-            for (pageNum in 0 until pageCount) {
-                var pageProgressJob: Job? = null
-                val fileName = Page.getPageName(pageNum, pageCount) // might have to change this to index stored in database
+        for (pageNum in 0 until pageCount) {
+            var pageProgressJob: Job? = null
+            val fileName = Page.getPageName(pageNum, pageCount) // might have to change this to index stored in database
 
-                val pageExistsInFinalDownloadFolder = ImageResponse.findFileNameStartingWith(finalDownloadFolder, fileName) != null
-                val pageExistsInCacheDownloadFolder = ImageResponse.findFileNameStartingWith(cacheChapterDir, fileName) != null
+            val pageExistsInFinalDownloadFolder = ImageResponse.findFileNameStartingWith(finalDownloadFolder, fileName) != null
+            val pageExistsInCacheDownloadFolder = ImageResponse.findFileNameStartingWith(cacheChapterDir, fileName) != null
 
-                val doesPageAlreadyExist = pageExistsInFinalDownloadFolder || pageExistsInCacheDownloadFolder
-                if (doesPageAlreadyExist) {
-                    continue
-                }
-
-                try {
-                    Page
-                        .getPageImage(
-                            mangaId = download.mangaId,
-                            chapterIndex = download.chapterIndex,
-                            index = pageNum,
-                        ) { flow ->
-                            pageProgressJob =
-                                flow
-                                    .sample(100)
-                                    .distinctUntilChanged()
-                                    .onEach {
-                                        download.progress = (pageNum.toFloat() + (it.toFloat() * 0.01f)) / pageCount
-                                        step(
-                                            null,
-                                            false,
-                                        ) // don't throw on canceled download here since we can't do anything
-                                    }.launchIn(scope)
-                        }.first
-                        .close()
-                } finally {
-                    // always cancel the page progress job even if it throws an exception to avoid memory leaks
-                    pageProgressJob?.cancel()
-                }
-                // TODO: retry on error with 2,4,8 seconds of wait
-                download.progress = ((pageNum + 1).toFloat()) / pageCount
-                step(download, false)
+            val doesPageAlreadyExist = pageExistsInFinalDownloadFolder || pageExistsInCacheDownloadFolder
+            if (doesPageAlreadyExist) {
+                continue
             }
+
+            try {
+                Page
+                    .getPageImage(
+                        mangaId = download.mangaId,
+                        chapterIndex = download.chapterIndex,
+                        index = pageNum,
+                    ) { flow ->
+                        pageProgressJob =
+                            flow
+                                .sample(100)
+                                .distinctUntilChanged()
+                                .onEach {
+                                    download.progress = (pageNum.toFloat() + (it.toFloat() * 0.01f)) / pageCount
+                                    step(
+                                        null,
+                                        false,
+                                    ) // don't throw on canceled download here since we can't do anything
+                                }.launchIn(scope)
+                    }.first
+                    .close()
+            } finally {
+                // always cancel the page progress job even if it throws an exception to avoid memory leaks
+                pageProgressJob?.cancel()
+            }
+            // TODO: retry on error with 2,4,8 seconds of wait
+            download.progress = ((pageNum + 1).toFloat()) / pageCount
+            step(download, false)
         }
 
         createComicInfoFile(
@@ -180,17 +189,14 @@ abstract class ChaptersFilesProvider<Type : FileType>(
 
         handleSuccessfulDownload()
 
-        transaction {
-            ChapterTable.update({ ChapterTable.id eq chapterId }) {
-                it[ChapterTable.pageCount] = getImageCount()
-            }
-        }
-
         File(cacheChapterDir).deleteRecursively()
 
         return true
     }
 
+    /**
+     * This function should never be called without calling [getChapterDownloadReady] beforehand.
+     */
     override fun download(): FileDownload3Args<DownloadChapter, CoroutineScope, suspend (DownloadChapter?, Boolean) -> Unit> =
         FileDownload3Args(::downloadImpl)
 

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/download/fileProvider/impl/ArchiveProvider.kt

@@ -10,6 +10,7 @@ import suwayomi.tachidesk.manga.impl.download.fileProvider.ChaptersFilesProvider
 import suwayomi.tachidesk.manga.impl.download.fileProvider.FileType
 import suwayomi.tachidesk.manga.impl.util.getChapterCachePath
 import suwayomi.tachidesk.manga.impl.util.getChapterCbzPath
+import suwayomi.tachidesk.manga.impl.util.getChapterDownloadPath
 import suwayomi.tachidesk.manga.impl.util.getMangaDownloadDir
 import suwayomi.tachidesk.manga.impl.util.storage.FileDeletionHelper
 import suwayomi.tachidesk.server.ApplicationDirs
@@ -37,13 +38,13 @@ class ArchiveProvider(
 
     override fun extractExistingDownload() {
         val outputFile = File(getChapterCbzPath(mangaId, chapterId))
-        val chapterCacheFolder = File(getChapterCachePath(mangaId, chapterId))
+        val chapterDownloadFolder = File(getChapterDownloadPath(mangaId, chapterId))
 
         if (!outputFile.exists()) {
             return
         }
 
-        extractCbzFile(outputFile, chapterCacheFolder)
+        extractCbzFile(outputFile, chapterDownloadFolder)
     }
 
     override suspend fun handleSuccessfulDownload() {