Fix webtoon page gravity

app/src/main/java/org/koitharu/kotatsu/ui/common/list/BaseRecyclerAdapter.kt

@@ -10,7 +10,7 @@ abstract class BaseRecyclerAdapter<T, E>(private val onItemClickListener: OnRecy
 	RecyclerView.Adapter<BaseViewHolder<T, E>>(),
 	KoinComponent {
 
-	protected val dataSet = ArrayList<T>()
+	protected val dataSet = ArrayList<T>() //TODO make private
 
 	val items get() = dataSet.toImmutableList()
 

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

@@ -9,21 +9,12 @@ import org.koitharu.kotatsu.ui.reader.PageLoader
 
 class WebtoonAdapter(private val loader: PageLoader) : BaseRecyclerAdapter<MangaPage, Int>() {
 
-	private var lastBound = -1
+	var pageGravity: Int = Gravity.TOP
 
 	override fun onCreateViewHolder(parent: ViewGroup) =
 		WebtoonHolder(parent, loader)
 
 	override fun onGetItemId(item: MangaPage) = item.id
 
-	override fun onBindViewHolder(holder: BaseViewHolder<MangaPage, Int>, position: Int) {
-		super.onBindViewHolder(holder, position)
-		lastBound = position
-	}
-
-	override fun getExtra(item: MangaPage, position: Int) = if (position >= lastBound) {
-		Gravity.TOP
-	} else {
-		Gravity.BOTTOM
-	}
+	override fun getExtra(item: MangaPage, position: Int) = pageGravity
 }

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

@@ -2,14 +2,18 @@ package org.koitharu.kotatsu.ui.reader.wetoon
 
 import android.content.Context
 import android.util.AttributeSet
+import android.view.Gravity
 import android.view.View
 import androidx.core.view.children
 import androidx.recyclerview.widget.RecyclerView
+import kotlin.math.sign
 
 class WebtoonRecyclerView @JvmOverloads constructor(
 	context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
 ) : RecyclerView(context, attrs, defStyleAttr) {
 
+	private var lastScrollDirection = 0
+
 	override fun dispatchNestedPreScroll(
 		dx: Int,
 		dy: Int,
@@ -42,7 +46,21 @@ class WebtoonRecyclerView @JvmOverloads constructor(
 			else -> null
 		} ?: return 0
 		var scrollY = dy
-		scrollY -= (child as WebtoonFrameLayout) .dispatchVerticalScroll(scrollY)
+		scrollY -= (child as WebtoonFrameLayout).dispatchVerticalScroll(scrollY)
 		return dy - scrollY
 	}
+
+	override fun onScrolled(dx: Int, dy: Int) {
+		val direction = dy.sign
+		if (direction != lastScrollDirection) {
+			(adapter as? WebtoonAdapter)?.let {
+				it.pageGravity = if (dy < 0) {
+					Gravity.BOTTOM
+				} else {
+					Gravity.TOP
+				}
+				lastScrollDirection = direction
+			}
+		}
+	}
 }

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

@@ -23,6 +23,7 @@ import androidx.viewpager2.widget.ViewPager2
 import com.google.android.material.chip.Chip
 import com.google.android.material.chip.ChipGroup
 import org.koitharu.kotatsu.ui.common.ChipsFactory
+import kotlin.math.roundToInt
 
 fun View.hideKeyboard() {
 	val imm = context.getSystemService(Activity.INPUT_METHOD_SERVICE) as InputMethodManager
@@ -182,7 +183,7 @@ fun RecyclerView.doOnCurrentItemChanged(callback: (Int) -> Unit) {
 		override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
 			super.onScrolled(recyclerView, dx, dy)
 			val item = (recyclerView.layoutManager as? LinearLayoutManager)
-				?.findFirstVisibleItemPosition()
+				?.findMiddleVisibleItemPosition()
 			if (item != null && item != RecyclerView.NO_POSITION && item != lastItem) {
 				lastItem = item
 				callback(item)
@@ -219,4 +220,8 @@ fun ViewPager2.callOnPageChaneListeners() {
 	} catch (e: Throwable) {
 		Log.e(null, "ViewPager2.callOnPageChaneListeners() failed", e)
 	}
+}
+
+fun LinearLayoutManager.findMiddleVisibleItemPosition(): Int {
+	return ((findFirstVisibleItemPosition() + findLastVisibleItemPosition()) / 2.0).roundToInt()
 }