Fix bugs in dual-page split (#4983)

If more bugs appear probably better to go back to the main thread and process dual-pages every time a page is shown as it did before

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

@@ -17,6 +17,7 @@ import eu.kanade.tachiyomi.source.SourceManager
 import eu.kanade.tachiyomi.source.model.Page
 import eu.kanade.tachiyomi.ui.base.presenter.BasePresenter
 import eu.kanade.tachiyomi.ui.reader.loader.ChapterLoader
+import eu.kanade.tachiyomi.ui.reader.model.InsertPage
 import eu.kanade.tachiyomi.ui.reader.model.ReaderChapter
 import eu.kanade.tachiyomi.ui.reader.model.ReaderPage
 import eu.kanade.tachiyomi.ui.reader.model.ViewerChapters
@@ -367,6 +368,11 @@ class ReaderPresenter(
 
         val selectedChapter = page.chapter
 
+        // Insert page doesn't change page progress
+        if (page is InsertPage) {
+            return
+        }
+
         // Save last page read and mark as read if needed
         selectedChapter.chapter.last_page_read = page.index
         val shouldTrack = !preferences.incognitoMode().get() || hasTrackers

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

@@ -230,7 +230,7 @@ class PagerPageHolder(
         readImageHeaderSubscription = Observable
             .fromCallable {
                 val stream = streamFn().buffered(16)
-                openStream = process(stream)
+                openStream = process(item, stream)
 
                 ImageUtil.findImageType(stream) == ImageUtil.ImageType.GIF
             }
@@ -249,7 +249,7 @@ class PagerPageHolder(
             .subscribe({}, {})
     }
 
-    private fun process(imageStream: InputStream): InputStream {
+    private fun process(page: ReaderPage, imageStream: InputStream): InputStream {
         if (!viewer.config.dualPageSplit) {
             return imageStream
         }
@@ -263,7 +263,7 @@ class PagerPageHolder(
             return imageStream
         }
 
-        onPageSplit()
+        onPageSplit(page)
 
         return splitInHalf(imageStream)
     }
@@ -287,7 +287,7 @@ class PagerPageHolder(
         return ImageUtil.splitInHalf(imageStream, side)
     }
 
-    private fun onPageSplit() {
+    private fun onPageSplit(page: ReaderPage) {
         val newPage = InsertPage(page)
         viewer.onPageSplit(page, newPage)
     }

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

@@ -192,6 +192,11 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
         Timber.d("onReaderPageSelected: ${page.number}/${pages.size}")
         activity.onPageSelected(page)
 
+        // Skip preload on inserts it causes unwanted page jumping
+        if (page is InsertPage) {
+            return
+        }
+
         // Preload next chapter once we're within the last 5 pages of the current chapter
         val inPreloadRange = pages.size - page.number < 5
         if (inPreloadRange && allowPreload && page.chapter == adapter.currentChapter) {
@@ -387,7 +392,7 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
     fun onPageSplit(currentPage: ReaderPage, newPage: InsertPage) {
         activity.runOnUiThread {
             // Need to insert on UI thread else images will go blank
-            adapter.onPageSplit(currentPage, newPage, this::class.java)
+            adapter.onPageSplit(currentPage, newPage)
         }
     }
 

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

@@ -22,6 +22,11 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
     var items: MutableList<Any> = mutableListOf()
         private set
 
+    /**
+     * Holds preprocessed items so they don't get removed when changing chapter
+     */
+    private var preprocessed: MutableMap<Int, InsertPage> = mutableMapOf()
+
     var nextTransition: ChapterTransition.Next? = null
         private set
 
@@ -54,10 +59,25 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
             newItems.add(ChapterTransition.Prev(chapters.currChapter, chapters.prevChapter))
         }
 
+        var insertPageLastPage: InsertPage? = null
+
         // Add current chapter.
         val currPages = chapters.currChapter.pages
         if (currPages != null) {
-            newItems.addAll(currPages)
+            val pages = currPages.toMutableList()
+
+            val lastPage = pages.last()
+
+            // Insert preprocessed pages into current page list
+            preprocessed.keys.sortedDescending()
+                .forEach { key ->
+                    if (lastPage.index == key) {
+                        insertPageLastPage = preprocessed[key]
+                    }
+                    preprocessed[key]?.let { pages.add(key + 1, it) }
+                }
+
+            newItems.addAll(pages)
         }
 
         currentChapter = chapters.currChapter
@@ -88,8 +108,14 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
             newItems.reverse()
         }
 
+        preprocessed = mutableMapOf()
         items = newItems
         notifyDataSetChanged()
+
+        // Will skip insert page otherwise
+        if (insertPageLastPage != null) {
+            viewer.moveToPage(insertPageLastPage!!)
+        }
     }
 
     /**
@@ -125,20 +151,25 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
         return POSITION_NONE
     }
 
-    fun onPageSplit(current: Any?, newPage: InsertPage, clazz: Class<out PagerViewer>) {
-        if (current !is ReaderPage) return
+    fun onPageSplit(currentPage: Any?, newPage: InsertPage) {
+        if (currentPage !is ReaderPage) return
 
-        val currentIndex = items.indexOf(current)
+        val currentIndex = items.indexOf(currentPage)
 
-        val placeAtIndex = when {
-            clazz.isAssignableFrom(L2RPagerViewer::class.java) -> currentIndex + 1
-            clazz.isAssignableFrom(VerticalPagerViewer::class.java) -> currentIndex + 1
-            clazz.isAssignableFrom(R2LPagerViewer::class.java) -> currentIndex
+        // Put aside preprocessed pages for next chapter so they don't get removed when changing chapter
+        if (currentPage.chapter.chapter.id != currentChapter?.chapter?.id) {
+            preprocessed[newPage.index] = newPage
+            return
+        }
+
+        val placeAtIndex = when (viewer) {
+            is L2RPagerViewer,
+            is VerticalPagerViewer -> currentIndex + 1
             else -> currentIndex
         }
 
         // It will enter a endless cycle of insert pages
-        if (clazz.isAssignableFrom(R2LPagerViewer::class.java) && items[placeAtIndex - 1] is InsertPage) {
+        if (viewer is R2LPagerViewer && placeAtIndex - 1 >= 0 && items[placeAtIndex - 1] is InsertPage) {
             return
         }