Fix concurrent chapters loading in reader

app/src/main/java/org/koitharu/kotatsu/base/ui/list/BoundsScrollListener.kt

@@ -8,19 +8,22 @@ abstract class BoundsScrollListener(private val offsetTop: Int, private val offs
 
 	override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
 		super.onScrolled(recyclerView, dx, dy)
+		if (recyclerView.hasPendingAdapterUpdates()) {
+			return
+		}
 		val layoutManager = (recyclerView.layoutManager as? LinearLayoutManager) ?: return
 		val firstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition()
 		if (firstVisibleItemPosition == RecyclerView.NO_POSITION) {
 			return
 		}
-		if (firstVisibleItemPosition <= offsetTop) {
-			onScrolledToStart(recyclerView)
-		}
 		val visibleItemCount = layoutManager.childCount
 		val totalItemCount = layoutManager.itemCount
 		if (visibleItemCount + firstVisibleItemPosition >= totalItemCount - offsetBottom) {
 			onScrolledToEnd(recyclerView)
 		}
+		if (firstVisibleItemPosition <= offsetTop) {
+			onScrolledToStart(recyclerView)
+		}
 	}
 
 	abstract fun onScrolledToStart(recyclerView: RecyclerView)

app/src/main/java/org/koitharu/kotatsu/base/ui/list/ScrollListenerInvalidationObserver.kt

@@ -0,0 +1,30 @@
+package org.koitharu.kotatsu.base.ui.list
+
+import androidx.recyclerview.widget.RecyclerView
+
+class ScrollListenerInvalidationObserver(
+	private val recyclerView: RecyclerView,
+	private val scrollListener: RecyclerView.OnScrollListener,
+) : RecyclerView.AdapterDataObserver() {
+
+	override fun onChanged() {
+		super.onChanged()
+		invalidateScroll()
+	}
+
+	override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
+		super.onItemRangeInserted(positionStart, itemCount)
+		invalidateScroll()
+	}
+
+	override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
+		super.onItemRangeRemoved(positionStart, itemCount)
+		invalidateScroll()
+	}
+
+	private fun invalidateScroll() {
+		recyclerView.post {
+			scrollListener.onScrolled(recyclerView, 0, 0)
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/reader/ui/ReaderViewModel.kt

@@ -252,6 +252,7 @@ class ReaderViewModel @Inject constructor(
 		val prevJob = stateChangeJob
 		stateChangeJob = launchJob(Dispatchers.Default) {
 			prevJob?.cancelAndJoin()
+			loadingJob?.join()
 			val pages = content.value?.pages ?: return@launchJob
 			pages.getOrNull(position)?.let { page ->
 				currentState.update { cs ->
@@ -263,12 +264,12 @@ class ReaderViewModel @Inject constructor(
 				return@launchJob
 			}
 			ensureActive()
-			if (position <= BOUNDS_PAGE_OFFSET) {
-				loadPrevNextChapter(pages.first().chapterId, isNext = false)
-			}
 			if (position >= pages.lastIndex - BOUNDS_PAGE_OFFSET) {
 				loadPrevNextChapter(pages.last().chapterId, isNext = true)
 			}
+			if (position <= BOUNDS_PAGE_OFFSET) {
+				loadPrevNextChapter(pages.first().chapterId, isNext = false)
+			}
 			if (pageLoader.isPrefetchApplicable()) {
 				pageLoader.prefetch(pages.trySublist(position + 1, position + PREFETCH_LIMIT))
 			}
@@ -348,7 +349,9 @@ class ReaderViewModel @Inject constructor(
 
 	@AnyThread
 	private fun loadPrevNextChapter(currentId: Long, isNext: Boolean) {
+		val prevJob = loadingJob
 		loadingJob = launchLoadingJob(Dispatchers.Default) {
+			prevJob?.join()
 			chaptersLoader.loadPrevNextChapter(mangaData.requireValue(), currentId, isNext)
 			content.emitValue(ReaderContent(chaptersLoader.snapshot(), null))
 		}

app/src/main/java/org/koitharu/kotatsu/utils/ext/ViewExt.kt

@@ -54,6 +54,11 @@ var RecyclerView.firstVisibleItemPosition: Int
 		}
 	}
 
+val RecyclerView.visibleItemCount: Int
+	get() = (layoutManager as? LinearLayoutManager)?.run {
+		findLastVisibleItemPosition() - findFirstVisibleItemPosition()
+	} ?: 0
+
 fun View.hasGlobalPoint(x: Int, y: Int): Boolean {
 	if (visibility != View.VISIBLE) {
 		return false