Add auto scroll to discover featured carousal

base.gradle

@@ -31,6 +31,7 @@ android {
         // Feature Flags
         buildConfigField "boolean", "END_OF_YEAR_ENABLED", "false"
         buildConfigField "boolean", "SINGLE_SIGN_ON_ENABLED", "false"
+        buildConfigField "boolean", "DISCOVER_FEATURED_AUTO_SCROLL", "false"
 
         testInstrumentationRunner project.testInstrumentationRunner
         testApplicationId "au.com.shiftyjelly.pocketcasts.test" + project.name.replace("-", "_")

modules/features/discover/src/main/java/au/com/shiftyjelly/pocketcasts/discover/util/AutoScrollHelper.kt

@@ -0,0 +1,36 @@
+package au.com.shiftyjelly.pocketcasts.discover.util
+
+import java.util.Timer
+import java.util.TimerTask
+
+private const val AUTO_SCROLL_INTERVAL = 3000L
+
+class AutoScrollHelper(private val onAutoScrollCompleted: () -> Unit) {
+    private var autoScrollTimer: Timer? = null
+    private var autoScrollTimerTask: TimerTask? = null
+    private var skipAutoScroll = false
+
+    fun startAutoScrollTimer() {
+        if (autoScrollTimerTask != null) return
+        autoScrollTimerTask = object : TimerTask() {
+            override fun run() {
+                if (!skipAutoScroll) onAutoScrollCompleted()
+                skipAutoScroll = false
+            }
+        }
+        autoScrollTimer = Timer().apply {
+            schedule(autoScrollTimerTask, 0, AUTO_SCROLL_INTERVAL)
+        }
+    }
+
+    fun stopAutoScrollTimer() {
+        autoScrollTimer?.cancel()
+        autoScrollTimerTask?.cancel()
+        autoScrollTimer = null
+        autoScrollTimerTask = null
+    }
+
+    fun skipAutoScroll() {
+        skipAutoScroll = true
+    }
+}

modules/features/discover/src/main/java/au/com/shiftyjelly/pocketcasts/discover/view/DiscoverAdapter.kt

@@ -13,6 +13,7 @@ import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.ListAdapter
 import androidx.recyclerview.widget.RecyclerView
+import androidx.recyclerview.widget.RecyclerView.OnScrollListener
 import au.com.shiftyjelly.pocketcasts.analytics.AnalyticsEvent
 import au.com.shiftyjelly.pocketcasts.analytics.AnalyticsTrackerWrapper
 import au.com.shiftyjelly.pocketcasts.analytics.FirebaseAnalyticsTracker
@@ -27,13 +28,15 @@ import au.com.shiftyjelly.pocketcasts.discover.databinding.RowPodcastSmallListBi
 import au.com.shiftyjelly.pocketcasts.discover.databinding.RowSingleEpisodeBinding
 import au.com.shiftyjelly.pocketcasts.discover.databinding.RowSinglePodcastBinding
 import au.com.shiftyjelly.pocketcasts.discover.extensions.updateSubscribeButtonIcon
+import au.com.shiftyjelly.pocketcasts.discover.util.AutoScrollHelper
 import au.com.shiftyjelly.pocketcasts.discover.view.DiscoverFragment.Companion.EPISODE_UUID_KEY
 import au.com.shiftyjelly.pocketcasts.discover.view.DiscoverFragment.Companion.LIST_ID_KEY
 import au.com.shiftyjelly.pocketcasts.discover.view.DiscoverFragment.Companion.PODCAST_UUID_KEY
 import au.com.shiftyjelly.pocketcasts.discover.viewmodel.PodcastList
 import au.com.shiftyjelly.pocketcasts.localization.helper.TimeHelper
 import au.com.shiftyjelly.pocketcasts.localization.helper.tryToLocalise
 import au.com.shiftyjelly.pocketcasts.models.entity.Episode
+import au.com.shiftyjelly.pocketcasts.preferences.BuildConfig
 import au.com.shiftyjelly.pocketcasts.repositories.images.into
 import au.com.shiftyjelly.pocketcasts.servers.cdn.ArtworkColors
 import au.com.shiftyjelly.pocketcasts.servers.cdn.StaticServerManagerImpl
@@ -163,6 +166,28 @@ internal class DiscoverAdapter(
     }
 
     inner class CarouselListViewHolder(var binding: RowCarouselListBinding) : NetworkLoadableViewHolder(binding.root) {
+        private var autoScrollHelper: AutoScrollHelper? = null
+        private val scrollListener = object : OnScrollListener() {
+            private var draggingStarted: Boolean = false
+
+            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
+                super.onScrollStateChanged(recyclerView, newState)
+                when (newState) {
+                    RecyclerView.SCROLL_STATE_SETTLING -> Unit // Do nothing
+                    RecyclerView.SCROLL_STATE_DRAGGING -> {
+                        draggingStarted = true
+                        autoScrollHelper?.stopAutoScrollTimer()
+                    }
+                    RecyclerView.SCROLL_STATE_IDLE -> {
+                        if (draggingStarted) {
+                            autoScrollHelper?.startAutoScrollTimer()
+                            draggingStarted = false
+                        }
+                    }
+                }
+            }
+        }
+
         val adapter = CarouselListRowAdapter(null, theme, listener::onPodcastClicked, listener::onPodcastSubscribe, analyticsTracker)
 
         private val linearLayoutManager =
@@ -173,23 +198,61 @@ internal class DiscoverAdapter(
         init {
             recyclerView?.layoutManager = linearLayoutManager
             recyclerView?.itemAnimator = null
+            recyclerView?.addOnScrollListener(scrollListener)
+
+            if (BuildConfig.DISCOVER_FEATURED_AUTO_SCROLL) {
+                autoScrollHelper = AutoScrollHelper {
+                    if (adapter.itemCount == 0) return@AutoScrollHelper
+                    val nextPosition = (binding.pageIndicatorView.position + 1)
+                        .takeIf { it < adapter.itemCount } ?: 0
+                    recyclerView?.smoothScrollToPosition(nextPosition)
+                    binding.pageIndicatorView.position = nextPosition
+                    trackPageChanged(nextPosition)
+                }
+            }
+
             val snapHelper = HorizontalPeekSnapHelper(0)
             snapHelper.attachToRecyclerView(recyclerView)
             snapHelper.onSnapPositionChanged = { position ->
+                /* Page just snapped, skip auto scroll */
+                autoScrollHelper?.skipAutoScroll()
                 binding.pageIndicatorView.position = position
-                analyticsTracker.track(AnalyticsEvent.DISCOVER_FEATURED_PAGE_CHANGED, mapOf(CURRENT_PAGE to position, TOTAL_PAGES to adapter.itemCount))
+                trackPageChanged(position)
             }
 
             recyclerView?.adapter = adapter
             adapter.submitList(listOf(LoadingItem()))
+
+            itemView.viewTreeObserver?.apply {
+                /* Stop auto scroll when app is backgrounded */
+                addOnWindowFocusChangeListener { hasFocus ->
+                    if (!hasFocus) autoScrollHelper?.stopAutoScrollTimer()
+                }
+                /* Manage auto scroll when itemView's visibility changes on going to next screen */
+                addOnGlobalLayoutListener {
+                    if (itemView.isShown) {
+                        autoScrollHelper?.startAutoScrollTimer()
+                    } else {
+                        autoScrollHelper?.stopAutoScrollTimer()
+                    }
+                }
+            }
         }
 
         override fun onRestoreInstanceState(state: Parcelable?) {
             super.onRestoreInstanceState(state)
             recyclerView?.post {
                 binding.pageIndicatorView.position = linearLayoutManager.findFirstVisibleItemPosition()
+                recyclerView.scrollToPosition(binding.pageIndicatorView.position)
             }
         }
+
+        private fun trackPageChanged(position: Int) {
+            analyticsTracker.track(
+                AnalyticsEvent.DISCOVER_FEATURED_PAGE_CHANGED,
+                mapOf(CURRENT_PAGE to position, TOTAL_PAGES to adapter.itemCount)
+            )
+        }
     }
 
     inner class SmallListViewHolder(val binding: RowPodcastSmallListBinding) : NetworkLoadableViewHolder(binding.root), ShowAllRow {