Hide manga title in toolbar when at top

(cherry picked from commit bdc441a5be2503ff35c783d37e44ebd74b87a2b1)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/manga/MangaController.kt

app/src/main/java/eu/kanade/tachiyomi/ui/base/controller/BaseController.kt

@@ -74,7 +74,7 @@ abstract class BaseController<VB : ViewBinding>(bundle: Bundle? = null) :
         return null
     }
 
-    fun setTitle() {
+    fun setTitle(title: String? = null) {
         var parentController = parentController
         while (parentController != null) {
             if (parentController is BaseController<*> && parentController.getTitle() != null) {
@@ -83,7 +83,7 @@ abstract class BaseController<VB : ViewBinding>(bundle: Bundle? = null) :
             parentController = parentController.parentController
         }
 
-        (activity as? AppCompatActivity)?.supportActionBar?.title = getTitle()
+        (activity as? AppCompatActivity)?.supportActionBar?.title = title ?: getTitle()
     }
 
     private fun Controller.instance(): String {

app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryController.kt

@@ -156,7 +156,7 @@ class LibraryController(
         retainViewMode = RetainViewMode.RETAIN_DETACH
     }
 
-    private var title: String? = null
+    private var currentTitle: String? = null
         set(value) {
             if (field != value) {
                 field = value
@@ -165,15 +165,15 @@ class LibraryController(
         }
 
     override fun getTitle(): String? {
-        return title ?: resources?.getString(R.string.label_library)
+        return currentTitle ?: resources?.getString(R.string.label_library)
     }
 
     private fun updateTitle() {
         if (preferences.categoryTabs().get()) {
-            title = resources?.getString(R.string.label_library)
+            currentTitle = resources?.getString(R.string.label_library)
         } else {
             adapter?.categories?.get(binding.libraryPager.currentItem)?.let {
-                title = it.name
+                currentTitle = it.name
             }
         }
     }

app/src/main/java/eu/kanade/tachiyomi/ui/manga/MangaController.kt

@@ -4,6 +4,7 @@ import android.animation.Animator
 import android.animation.AnimatorListenerAdapter
 import android.app.Activity
 import android.content.Intent
+import android.graphics.Color
 import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.Menu
@@ -65,6 +66,7 @@ import eu.kanade.tachiyomi.ui.recent.history.HistoryController
 import eu.kanade.tachiyomi.ui.recent.updates.UpdatesController
 import eu.kanade.tachiyomi.ui.webview.WebViewActivity
 import eu.kanade.tachiyomi.util.hasCustomCover
+import eu.kanade.tachiyomi.util.system.getResourceColor
 import eu.kanade.tachiyomi.util.system.toast
 import eu.kanade.tachiyomi.util.view.getCoordinates
 import eu.kanade.tachiyomi.util.view.gone
@@ -74,7 +76,9 @@ import eu.kanade.tachiyomi.util.view.visible
 import exh.metadata.metadata.base.FlatMetadata
 import exh.metadata.metadata.base.RaisedSearchMetadata
 import java.io.IOException
+import kotlin.math.min
 import kotlinx.android.synthetic.main.main_activity.root_coordinator
+import kotlinx.android.synthetic.main.main_activity.toolbar
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.NonCancellable
@@ -82,6 +86,7 @@ import kotlinx.coroutines.flow.launchIn
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.withContext
 import reactivecircus.flowbinding.android.view.clicks
+import reactivecircus.flowbinding.recyclerview.scrollEvents
 import reactivecircus.flowbinding.swiperefreshlayout.refreshes
 import timber.log.Timber
 import uy.kohesive.injekt.Injekt
@@ -133,6 +138,9 @@ class MangaController :
     private val preferences: PreferencesHelper by injectLazy()
     private val coverCache: CoverCache by injectLazy()
 
+    private val toolbarTextColor by lazy { view!!.context.getResourceColor(R.attr.colorOnPrimary) }
+    private var toolbarTextAlpha = 255
+
     private var mangaInfoAdapter: MangaInfoHeaderAdapter? = null
     private var mangaInfoItemAdapter: MangaInfoItemAdapter? = null
     private var mangaInfoButtonsAdapter: MangaInfoButtonsAdapter? = null
@@ -177,10 +185,6 @@ class MangaController :
         setHasOptionsMenu(true)
     }
 
-    override fun getTitle(): String? {
-        return manga?.title
-    }
-
     override fun onChangeEnded(handler: ControllerChangeHandler, type: ControllerChangeType) {
         super.onChangeEnded(handler, type)
         if (manga == null || source == null) {
@@ -246,8 +250,18 @@ class MangaController :
             if (!fromSource && preferences.jumpToChapters()) {
                 (binding.recycler.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(1, 0)
             }
+
+            // Delayed in case we need to jump to chapters
+            binding.recycler.post {
+                updateToolbarTitleAlpha()
+                setTitle(manga?.title)
+            }
         }
 
+        binding.recycler.scrollEvents()
+            .onEach { updateToolbarTitleAlpha() }
+            .launchIn(scope)
+
         binding.swipeRefresh.refreshes()
             .onEach {
                 fetchMangaInfoFromSource(manualFetch = true)
@@ -267,6 +281,32 @@ class MangaController :
         updateFilterIconState()
     }
 
+    private fun updateToolbarTitleAlpha(alpha: Int? = null) {
+        val calculatedAlpha = when {
+            // Specific alpha provided
+            alpha != null -> alpha
+
+            // First item isn't in view, full opacity
+            ((binding.recycler.layoutManager as LinearLayoutManager).findFirstVisibleItemPosition() > 0) -> 255
+
+            // Based on scroll amount when first item is in view
+            else -> min(binding.recycler.computeVerticalScrollOffset(), 255)
+        }
+
+        if (calculatedAlpha != toolbarTextAlpha) {
+            toolbarTextAlpha = calculatedAlpha
+
+            activity?.toolbar?.setTitleTextColor(
+                Color.argb(
+                    toolbarTextAlpha,
+                    Color.red(toolbarTextColor),
+                    Color.green(toolbarTextColor),
+                    Color.blue(toolbarTextColor)
+                )
+            )
+        }
+    }
+
     private fun updateFilterIconState() {
         chaptersHeaderAdapter?.setHasActiveFilters(settingsSheet?.filters?.hasActiveFilters() == true)
     }
@@ -316,6 +356,7 @@ class MangaController :
         chaptersHeaderAdapter = null
         chaptersAdapter = null
         settingsSheet = null
+        updateToolbarTitleAlpha(255)
         super.onDestroyView(view)
     }