Fix/downloader manager persisting queue (#639)

* Extract reorder logic into function

* Save download queue everytime a download was finished

The download queue was never saved after a download was finished.
This caused finished download to be restored on a server start, which caused unnecessary "downloads" which most of the time would just finish immediately since the pages were still in the cache

* Wait for download queue save process to be finished

Since multiple downloaders could be finished at the same time, the download queue should be saved synchronously

* Remove unnecessary download queue save trigger

This gets called everytime a downloader finished downloading all chapters of its source.
Since the queue is now saved everytime a download is finished, this is trigger is not needed anymore

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

@@ -20,7 +20,9 @@ import kotlinx.coroutines.channels.BufferOverflow
 import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.launchIn
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.sample
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
@@ -70,6 +72,10 @@ object DownloadManager {
             .apply()
     }
 
+    private fun triggerSaveDownloadQueue() {
+        scope.launch { saveQueueFlow.emit(Unit) }
+    }
+
     fun restoreAndResumeDownloads() {
         scope.launch {
             logger.debug { "restoreAndResumeDownloads: Restore download queue..." }
@@ -126,6 +132,11 @@ object DownloadManager {
         }
     }
 
+    private val saveQueueFlow = MutableSharedFlow<Unit>(extraBufferCapacity = 1, onBufferOverflow = BufferOverflow.DROP_OLDEST)
+    init {
+        saveQueueFlow.onEach { saveDownloadQueue() }.launchIn(scope)
+    }
+
     private fun sendStatusToAllClients() {
         val status = getStatus()
         clients.forEach {
@@ -186,7 +197,6 @@ object DownloadManager {
     private fun refreshDownloaders() {
         scope.launch {
             downloaderWatch.emit(Unit)
-            saveDownloadQueue()
         }
     }
 
@@ -196,7 +206,8 @@ object DownloadManager {
             sourceId = sourceId,
             downloadQueue = downloadQueue,
             notifier = ::notifyAllClients,
-            onComplete = ::refreshDownloaders
+            onComplete = ::refreshDownloaders,
+            onDownloadFinished = ::triggerSaveDownloadQueue
         )
     }
 
@@ -276,7 +287,7 @@ object DownloadManager {
                 manga
             )
             downloadQueue.add(newDownloadChapter)
-            saveDownloadQueue()
+            triggerSaveDownloadQueue()
             logger.debug { "Added chapter ${chapter.id} to download queue ($newDownloadChapter)" }
             return newDownloadChapter
         }
@@ -308,30 +319,33 @@ object DownloadManager {
         logger.debug { "dequeue ${chapterDownloads.size} chapters [${chapterDownloads.joinToString(separator = ", ") { "$it" }}]" }
 
         downloadQueue.removeAll(chapterDownloads)
-        saveDownloadQueue()
+        triggerSaveDownloadQueue()
 
         notifyAllClients()
     }
 
     fun reorder(chapterIndex: Int, mangaId: Int, to: Int) {
-        require(to >= 0) { "'to' must be over or equal to 0" }
         val download = downloadQueue.find { it.mangaId == mangaId && it.chapterIndex == chapterIndex }
             ?: return
 
+        reorder(download, to)
+    }
+
+    fun reorder(chapterId: Int, to: Int) {
+        val download = downloadQueue.find { it.chapter.id == chapterId }
+            ?: return
+
+        reorder(download, to)
+    }
+
+    private fun reorder(download: DownloadChapter, to: Int) {
+        require(to >= 0) { "'to' must be over or equal to 0" }
+
         logger.debug { "reorder download $download from ${downloadQueue.indexOf(download)} to $to" }
 
         downloadQueue -= download
         downloadQueue.add(to, download)
-        saveDownloadQueue()
-    }
-
-    fun reorder(chapterId: Int, to: Int) {
-        require(to >= 0) { "'to' must be over or equal to 0" }
-        val download = downloadQueue.find { it.chapter.id == chapterId }
-            ?: return
-        downloadQueue -= download
-        downloadQueue.add(to, download)
-        saveDownloadQueue()
+        triggerSaveDownloadQueue()
     }
 
     fun start() {
@@ -360,7 +374,7 @@ object DownloadManager {
 
         stop()
         downloadQueue.clear()
-        saveDownloadQueue()
+        triggerSaveDownloadQueue()
         notifyAllClients()
     }
 }

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

@@ -34,7 +34,8 @@ class Downloader(
     val sourceId: String,
     private val downloadQueue: CopyOnWriteArrayList<DownloadChapter>,
     private val notifier: (immediate: Boolean) -> Unit,
-    private val onComplete: () -> Unit
+    private val onComplete: () -> Unit,
+    private val onDownloadFinished: () -> Unit
 ) {
     private val logger = KotlinLogging.logger("${Downloader::class.java.name} source($sourceId)")
 
@@ -112,6 +113,7 @@ class Downloader(
                 downloadQueue.removeIf { it.mangaId == download.mangaId && it.chapterIndex == download.chapterIndex }
                 step(null, false)
                 downloadLogger.debug { "finished" }
+                onDownloadFinished()
             } catch (e: CancellationException) {
                 logger.debug("Downloader was stopped")
                 availableSourceDownloads.filter { it.state == Downloading }.forEach { it.state = Queued }