Cursor continuously fetches new pages as the user scrolls

Whenever the user gets more than half a page away from the center, the
cursor will fetch the next page in that direction.

Test: manual test with Share Test
Test: atest IntentResolver-tests-unit
BUG: 341923886
FIX: 341923886
Flag: android.service.chooser.chooser_payload_toggling
Change-Id: Ifc9f651ccf028f25af8adfb7bc359977803d540a

6 files changed, 60 insertions, 7 deletions

diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/CursorPreviewsInteractor.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/CursorPreviewsInteractor.kt
index a0fc11c3..fa600c86 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/CursorPreviewsInteractor.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/CursorPreviewsInteractor.kt
@@ -43,6 +43,8 @@ import dagger.hilt.components.SingletonComponent
 import java.util.concurrent.ConcurrentHashMap
 import javax.inject.Inject
 import javax.inject.Qualifier
+import kotlin.math.max
+import kotlin.math.min
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.filterNotNull
@@ -93,11 +95,14 @@ constructor(
         var state = initialState
         val startPageNum = state.firstLoadedPageNum
         while ((state.hasMoreLeft || state.hasMoreRight) && state.numLoadedPages < maxLoadedPages) {
+            val (leftTriggerIndex, rightTriggerIndex) = state.triggerIndices()
             interactor.setPreviews(
                 previews = state.merged.values.toList(),
                 startIndex = startPageNum,
                 hasMoreLeft = state.hasMoreLeft,
                 hasMoreRight = state.hasMoreRight,
+                leftTriggerIndex = leftTriggerIndex,
+                rightTriggerIndex = rightTriggerIndex,
             )
             val loadedLeft = startPageNum - state.firstLoadedPageNum
             val loadedRight = state.lastLoadedPageNum - startPageNum
@@ -120,6 +125,8 @@ constructor(
     ) {
         var state = initialState
         while (true) {
+            val (leftTriggerIndex, rightTriggerIndex) = state.triggerIndices()
+
             // Design note: in order to prevent load requests from the UI when it was displaying a
             // previously-published dataset being accidentally associated with a recently-published
             // one, we generate a new Flow of load requests for each dataset and only listen to
@@ -130,6 +137,8 @@ constructor(
                     startIndex = 0, // TODO: actually track this as the window changes?
                     hasMoreLeft = state.hasMoreLeft,
                     hasMoreRight = state.hasMoreRight,
+                    leftTriggerIndex = leftTriggerIndex,
+                    rightTriggerIndex = rightTriggerIndex,
                 )
             state = loadingState.handleOneLoadRequest(state, pagedCursor, unclaimedRecords)
         }
@@ -238,6 +247,13 @@ constructor(
         }
     }
 
+    private fun CursorWindow.triggerIndices(): Pair<Int, Int> {
+        val totalIndices = numLoadedPages * pageSize
+        val midIndex = totalIndices / 2
+        val halfPage = pageSize / 2
+        return max(midIndex - halfPage, 0) to min(midIndex + halfPage, totalIndices - 1)
+    }
+
     private suspend fun readPage(
         state: CursorWindow,
         pagedCursor: PagedCursor<CursorRow?>,
diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/FetchPreviewsInteractor.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/FetchPreviewsInteractor.kt
index 388cbc7e..c9c9a9b3 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/FetchPreviewsInteractor.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/FetchPreviewsInteractor.kt
@@ -51,6 +51,8 @@ constructor(
             startIndex = focusedItemIdx,
             hasMoreLeft = false,
             hasMoreRight = false,
+            leftTriggerIndex = initialPreviewMap.indices.first(),
+            rightTriggerIndex = initialPreviewMap.indices.last(),
         )
         cursorInteractor.launch(cursor.await() ?: return@coroutineScope, initialPreviewMap)
     }
diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/SetCursorPreviewsInteractor.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/SetCursorPreviewsInteractor.kt
index 437bc942..124e2a3d 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/SetCursorPreviewsInteractor.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/domain/interactor/SetCursorPreviewsInteractor.kt
@@ -35,6 +35,8 @@ constructor(private val previewsRepo: CursorPreviewsRepository) {
         startIndex: Int,
         hasMoreLeft: Boolean,
         hasMoreRight: Boolean,
+        leftTriggerIndex: Int,
+        rightTriggerIndex: Int
     ): Flow<LoadDirection?> {
         val loadingState = MutableStateFlow<LoadDirection?>(null)
         previewsRepo.previewsModel.value =
@@ -53,6 +55,8 @@ constructor(private val previewsRepo: CursorPreviewsRepository) {
                     } else {
                         null
                     },
+                leftTriggerIndex = leftTriggerIndex,
+                rightTriggerIndex = rightTriggerIndex,
             )
         return loadingState.asStateFlow()
     }
diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/shared/model/PreviewsModel.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/shared/model/PreviewsModel.kt
index 1d3eb4b4..ae8bd1eb 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/shared/model/PreviewsModel.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/shared/model/PreviewsModel.kt
@@ -32,4 +32,14 @@ data class PreviewsModel(
      * indicates that there is no more data to load in that direction.
      */
     val loadMoreRight: (() -> Unit)?,
+    /**
+     * Index into [previewModels] where any attempted access less than or equal to it should trigger
+     * a window shift left.
+     */
+    val leftTriggerIndex: Int,
+    /**
+     * Index into [previewModels] where any attempted access greater than or equal to it should
+     * trigger a window shift right.
+     */
+    val rightTriggerIndex: Int,
 )
diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ShareouselComposable.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ShareouselComposable.kt
index 02d997ae..8e2626bf 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ShareouselComposable.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ShareouselComposable.kt
@@ -41,7 +41,9 @@ import androidx.compose.material3.LocalContentColor
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
@@ -59,6 +61,7 @@ import com.android.intentresolver.contentpreview.payloadtoggle.shared.ContentTyp
 import com.android.intentresolver.contentpreview.payloadtoggle.shared.model.PreviewsModel
 import com.android.intentresolver.contentpreview.payloadtoggle.ui.viewmodel.ShareouselPreviewViewModel
 import com.android.intentresolver.contentpreview.payloadtoggle.ui.viewmodel.ShareouselViewModel
+import kotlin.math.abs
 import kotlinx.coroutines.launch
 
 @Composable
@@ -104,7 +107,24 @@ private fun PreviewCarousel(
                 .systemGestureExclusion()
     ) {
         itemsIndexed(previews.previewModels, key = { _, model -> model.uri }) { index, model ->
-            ShareouselCard(viewModel.preview(index, model))
+
+            // Index if this is the element in the center of the viewing area, otherwise null
+            val previewIndex by remember {
+                derivedStateOf {
+                    carouselState.layoutInfo.visibleItemsInfo
+                        .firstOrNull { it.index == index }
+                        ?.let {
+                            val viewportCenter = carouselState.layoutInfo.viewportEndOffset / 2
+                            val halfPreviewWidth = it.size / 2
+                            val previewCenter = it.offset + halfPreviewWidth
+                            val previewDistanceToViewportCenter =
+                                abs(previewCenter - viewportCenter)
+                            if (previewDistanceToViewportCenter <= halfPreviewWidth) index else null
+                        }
+                }
+            }
+
+            ShareouselCard(viewModel.preview(model, previewIndex))
         }
     }
 }
diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/viewmodel/ShareouselViewModel.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/viewmodel/ShareouselViewModel.kt
index 9d53b92a..c3ad7b6c 100644
--- a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/viewmodel/ShareouselViewModel.kt
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/viewmodel/ShareouselViewModel.kt
@@ -55,7 +55,7 @@ data class ShareouselViewModel(
     /** List of action chips presented underneath Shareousel. */
     val actions: Flow<List<ActionChipViewModel>>,
     /** Creates a [ShareouselPreviewViewModel] for a [PreviewModel] present in [previews]. */
-    val preview: (index: Int, key: PreviewModel) -> ShareouselPreviewViewModel,
+    val preview: (key: PreviewModel, index: Int?) -> ShareouselPreviewViewModel,
 )
 
 @Module
@@ -112,7 +112,7 @@ interface ShareouselViewModelModule {
                             }
                         }
                     },
-                preview = { index, key ->
+                preview = { key, index ->
                     keySet.value?.maybeLoad(index)
                     val previewInteractor = interactor.preview(key)
                     val contentType =
@@ -134,9 +134,10 @@ interface ShareouselViewModelModule {
     }
 }
 
-private fun PreviewsModel.maybeLoad(index: Int) {
-    when (index) {
-        previewModels.indices.firstOrNull() -> loadMoreLeft?.invoke()
-        previewModels.indices.lastOrNull() -> loadMoreRight?.invoke()
+private fun PreviewsModel.maybeLoad(index: Int?) {
+    when {
+        index == null -> {}
+        index <= leftTriggerIndex -> loadMoreLeft?.invoke()
+        index >= rightTriggerIndex -> loadMoreRight?.invoke()
     }
 }