Adjust library sublist scroll on changes

app/src/main/java/org/koitharu/kotatsu/library/ui/adapter/LibraryGroupAD.kt

@@ -48,6 +48,7 @@ fun libraryGroupAD(
 		MangaItemDiffCallback(),
 		mangaGridItemAD(coil, lifecycleOwner, listenerAdapter, sizeResolver),
 	)
+	adapter.registerAdapterDataObserver(ScrollKeepObserver(binding.recyclerView))
 	binding.recyclerView.setRecycledViewPool(sharedPool)
 	binding.recyclerView.adapter = adapter
 	val spacingDecoration = SpacingItemDecoration(context.resources.getDimensionPixelOffset(R.dimen.grid_spacing))

app/src/main/java/org/koitharu/kotatsu/library/ui/adapter/ScrollKeepObserver.kt

@@ -0,0 +1,31 @@
+package org.koitharu.kotatsu.library.ui.adapter
+
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
+
+class ScrollKeepObserver(
+	private val recyclerView: RecyclerView,
+) : RecyclerView.AdapterDataObserver() {
+
+	private val layoutManager: LinearLayoutManager
+		get() = recyclerView.layoutManager as LinearLayoutManager
+
+	override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
+		val position = minOf(toPosition, fromPosition) // if items are swapping positions may be swapped too
+		if (position < layoutManager.findFirstVisibleItemPosition()) {
+			postScroll(position)
+		}
+	}
+
+	override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
+		if (positionStart < layoutManager.findFirstVisibleItemPosition()) {
+			postScroll(positionStart)
+		}
+	}
+
+	private fun postScroll(targetPosition: Int) {
+		recyclerView.post {
+			layoutManager.scrollToPositionWithOffset(targetPosition, 0)
+		}
+	}
+}