Taking paging preload logic from upstream

app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderPresenter.kt

@@ -371,12 +371,10 @@ class ReaderPresenter(
      * Saves this [chapter] progress (last read page and whether it's read).
      */
     private fun saveChapterProgress(chapter: ReaderChapter) {
-        val dbChapter = db.getChapter(chapter.chapter.id!!).executeAsBlocking()
+        db.getChapter(chapter.chapter.id!!).executeAsBlocking()?.let { dbChapter ->
-        chapter.chapter.bookmark = dbChapter!!.bookmark
+            chapter.chapter.bookmark = dbChapter.bookmark
-        db.updateChapterProgress(chapter.chapter).asRxCompletable()
+        }
-            .onErrorComplete()
+        db.updateChapterProgress(chapter.chapter).executeAsBlocking()
-            .subscribeOn(Schedulers.io())
-            .subscribe()
     }
 
     /**

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt

@@ -12,6 +12,8 @@ import eu.kanade.tachiyomi.ui.reader.model.ChapterTransition
 import eu.kanade.tachiyomi.ui.reader.model.ReaderPage
 import eu.kanade.tachiyomi.ui.reader.model.ViewerChapters
 import eu.kanade.tachiyomi.ui.reader.viewer.BaseViewer
+import eu.kanade.tachiyomi.util.view.gone
+import eu.kanade.tachiyomi.util.view.visible
 import timber.log.Timber
 
 /**
@@ -63,7 +65,7 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
         }
 
     init {
-        pager.visibility = View.GONE // Don't layout the pager yet
+        pager.gone() // Don't layout the pager yet
         pager.layoutParams = LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)
         pager.offscreenPageLimit = 1
         pager.id = R.id.reader_pager
@@ -80,8 +82,8 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
         pager.tapListener = { event ->
             val positionX = event.x
             when {
-                positionX < pager.width * 0.33f -> if (config.tappingEnabled) moveLeft()
+                positionX < pager.width * 0.33f -> if (config.tappingEnabled) moveLeft() else activity.toggleMenu()
-                positionX > pager.width * 0.66f -> if (config.tappingEnabled) moveRight()
+                positionX > pager.width * 0.66f -> if (config.tappingEnabled) moveRight() else activity.toggleMenu()
                 else -> activity.toggleMenu()
             }
         }
@@ -113,40 +115,52 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
         return pager
     }
 
-    /**
-     * Destroys this viewer. Called when leaving the reader or swapping viewers.
-     */
-    override fun destroy() {
-        super.destroy()
-        config.unsubscribe()
-    }
-
     /**
      * Called when a new page (either a [ReaderPage] or [ChapterTransition]) is marked as active
      */
     private fun onPageChange(position: Int) {
         val page = adapter.items.getOrNull(position)
         if (page != null && currentPage != page) {
+            val allowPreload = checkAllowPreload(page as? ReaderPage)
             currentPage = page
             when (page) {
-                is ReaderPage -> onReaderPageSelected(page)
+                is ReaderPage -> onReaderPageSelected(page, allowPreload)
                 is ChapterTransition -> onTransitionSelected(page)
             }
         }
     }
 
+    private fun checkAllowPreload(page: ReaderPage?): Boolean {
+        // Page is transition page - preload allowed
+        page ?: return true
+
+        // Initial opening - preload allowed
+        currentPage ?: return true
+
+        // Allow preload for
+        // 1. Going to next chapter from chapter transition
+        // 2. Going between pages of same chapter
+        // 3. Next chapter page
+        return when (page.chapter) {
+            (currentPage as? ChapterTransition.Next)?.to -> true
+            (currentPage as? ReaderPage)?.chapter -> true
+            adapter.nextTransition?.to -> true
+            else -> false
+        }
+    }
+
     /**
      * Called when a [ReaderPage] is marked as active. It notifies the
      * activity of the change and requests the preload of the next chapter if this is the last page.
      */
-    private fun onReaderPageSelected(page: ReaderPage) {
+    private fun onReaderPageSelected(page: ReaderPage, allowPreload: Boolean) {
         activity.onPageSelected(page)
 
         val pages = page.chapter.pages ?: return
         Timber.d("onReaderPageSelected: ${page.number}/${pages.size}")
-        // Preload next chapter once we're within the last 3 pages of the current chapter
+        // Preload next chapter once we're within the last 5 pages of the current chapter
-        val inPreloadRange = pages.size - page.number < 3
+        val inPreloadRange = pages.size - page.number < 5
-        if (inPreloadRange) {
+        if (inPreloadRange && allowPreload && page.chapter == adapter.currentChapter) {
             Timber.d("Request preload next chapter because we're at page ${page.number} of ${pages.size}")
             adapter.nextTransition?.to?.let {
                 activity.requestPreloadChapter(it)
@@ -196,7 +210,7 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
             Timber.d("Pager first layout")
             val pages = chapters.currChapter.pages ?: return
             moveToPage(pages[chapters.currChapter.requestedPage])
-            pager.visibility = View.VISIBLE
+            pager.visible()
         }
     }
 

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewerAdapter.kt

@@ -23,6 +23,7 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
     var nextTransition: ChapterTransition.Next? = null
         private set
 
+    var currentChapter: ReaderChapter? = null
     /**
      * Updates this adapter with the given [chapters]. It handles setting a few pages of the
      * next/previous chapter to allow seamless transitions and inverting the pages if the viewer
@@ -52,11 +53,14 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
             newItems.addAll(currPages)
         }
 
+        currentChapter = chapters.currChapter
+
         // Add next chapter transition and pages.
         nextTransition = ChapterTransition.Next(chapters.currChapter, chapters.nextChapter)
             .also {
                 if (forceTransition ||
-                            chapters.nextChapter?.state !is ReaderChapter.State.Loaded) {
+                    chapters.nextChapter?.state !is ReaderChapter.State.Loaded
+                ) {
                     newItems.add(it)
                 }
             }
@@ -89,8 +93,7 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
      * Creates a new view for the item at the given [position].
      */
     override fun createView(container: ViewGroup, position: Int): View {
-        val item = items[position]
+        return when (val item = items[position]) {
-        return when (item) {
             is ReaderPage -> PagerPageHolder(viewer, item)
             is ChapterTransition -> PagerTransitionHolder(viewer, item)
             else -> throw NotImplementedError("Holder for ${item.javaClass} not implemented")