Manage title visibility on DetailsActivity

app/src/main/kotlin/org/koitharu/kotatsu/details/ui/DetailsFragment.kt

@@ -83,6 +83,7 @@ class DetailsFragment :
 		binding.infoLayout.textViewSource.setOnClickListener(this)
 		binding.textViewDescription.movementMethod = LinkMovementMethod.getInstance()
 		binding.chipsTags.onChipClickListener = this
+		TitleScrollCoordinator(binding.textViewTitle).attach(binding.scrollView)
 		viewModel.manga.filterNotNull().observe(viewLifecycleOwner, ::onMangaUpdated)
 		viewModel.isLoading.observe(viewLifecycleOwner, ::onLoadingStateChanged)
 		viewModel.historyInfo.observe(viewLifecycleOwner, ::onHistoryChanged)

app/src/main/kotlin/org/koitharu/kotatsu/details/ui/TitleScrollCoordinator.kt

@@ -0,0 +1,45 @@
+package org.koitharu.kotatsu.details.ui
+
+import android.content.Context
+import android.widget.TextView
+import androidx.appcompat.app.AppCompatActivity
+import androidx.core.view.doOnLayout
+import androidx.core.widget.NestedScrollView
+import org.koitharu.kotatsu.core.util.ext.findActivity
+import java.lang.ref.WeakReference
+
+class TitleScrollCoordinator(
+	private val titleView: TextView,
+) : NestedScrollView.OnScrollChangeListener {
+
+	private val location = IntArray(2)
+	private var activityRef: WeakReference<AppCompatActivity>? = null
+
+	override fun onScrollChange(v: NestedScrollView, scrollX: Int, scrollY: Int, oldScrollX: Int, oldScrollY: Int) {
+		val actionBar = getActivity(v.context)?.supportActionBar ?: return
+		titleView.getLocationOnScreen(location)
+		var top = location[1] + titleView.height
+		v.getLocationOnScreen(location)
+		top -= location[1]
+		actionBar.setDisplayShowTitleEnabled(top < 0)
+	}
+
+	fun attach(scrollView: NestedScrollView) {
+		scrollView.setOnScrollChangeListener(this)
+		scrollView.doOnLayout {
+			onScrollChange(scrollView, 0, 0, 0, 0)
+		}
+	}
+
+	private fun getActivity(context: Context): AppCompatActivity? {
+		activityRef?.get()?.let {
+			if (!it.isDestroyed) return it
+		}
+		val activity = context.findActivity() as? AppCompatActivity
+		if (activity == null || activity.isDestroyed) {
+			return null
+		}
+		activityRef = WeakReference(activity)
+		return activity
+	}
+}