Improve tap to scroll support to be ready for rollout

- Moves tap to scroll detection to the scrollable container instead of
  the children of the container, reducing the amount of jank from
  calculations required for each tap, as well as the code complexity.
- Encapsulates the behavior in a single Modifier extension for ease of
  code readability and usability.
- Generifies the solution to work with any arbitrary scrollable
  container.

Test: Manual test with Share Test
BUG: 384656926
Flag: com.android.intentresolver.shareousel_tap_to_scroll_support
Change-Id: Ic40e040068b2a8ce6038d2e9d7d2bca6f0a88670

2 files changed, 125 insertions, 72 deletions

diff --git a/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ModifierExt.kt b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ModifierExt.kt
new file mode 100644
index 00000000..a9d8b9dc
--- /dev/null
+++ b/java/src/com/android/intentresolver/contentpreview/payloadtoggle/ui/composable/ModifierExt.kt
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.intentresolver.contentpreview.payloadtoggle.ui.composable
+
+import androidx.compose.foundation.gestures.ScrollableState
+import androidx.compose.foundation.gestures.animateScrollBy
+import androidx.compose.foundation.gestures.awaitEachGesture
+import androidx.compose.foundation.gestures.awaitFirstDown
+import androidx.compose.foundation.gestures.waitForUpOrCancellation
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.input.pointer.PointerEventPass
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.layout.onGloballyPositioned
+import androidx.compose.ui.platform.LocalLayoutDirection
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.LayoutDirection
+import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.launch
+
+/** Calls [whenTrue] on this [Modifier] if [condition] is true. */
+@Composable
+inline fun Modifier.conditional(
+    condition: Boolean,
+    crossinline whenTrue: @Composable Modifier.() -> Modifier,
+): Modifier = if (condition) this.whenTrue() else this
+
+/**
+ * Overlays tap regions at the beginning and end of the scrollable region.
+ *
+ * When tap regions are tapped, [scrollableState] will be scrolled by the size of the modified
+ * scrollable multiplied by the [scrollRatio].
+ *
+ * Note: [scrollableState] must be shared with the scrollable being modified and [vertical] must be
+ * true only if the modified scrollable scrolls vertically.
+ */
+@Composable
+fun Modifier.tapToScroll(
+    scrollableState: ScrollableState,
+    vertical: Boolean = false,
+    tapRegionSize: Dp = 48.dp,
+    scrollRatio: Float = 0.5f,
+): Modifier {
+    val scope = rememberCoroutineScope()
+    var viewSize by remember { mutableStateOf(0) }
+    val isLtrLayoutDirection = LocalLayoutDirection.current == LayoutDirection.Ltr
+    val normalizedScrollVector = remember {
+        derivedStateOf {
+            if (vertical || isLtrLayoutDirection) {
+                viewSize * scrollRatio
+            } else {
+                -viewSize * scrollRatio
+            }
+        }
+    }
+    return onGloballyPositioned { viewSize = if (vertical) it.size.height else it.size.width }
+        .pointerInput(Unit) {
+            val tapRegionSizePx = tapRegionSize.roundToPx()
+
+            awaitEachGesture {
+                // Tap to scroll is disabled if the modified composable is not large enough to fit
+                // both tap regions.
+                if (viewSize < tapRegionSizePx * 2) return@awaitEachGesture
+
+                val down = awaitFirstDown(pass = PointerEventPass.Initial)
+                if (down.isConsumed) return@awaitEachGesture
+
+                val downPosition = if (vertical) down.position.y else down.position.x
+                val scrollVector =
+                    when {
+                        // Start taps scroll toward start
+                        downPosition <= tapRegionSizePx -> -normalizedScrollVector.value
+
+                        // End taps scroll toward end
+                        downPosition >= viewSize - tapRegionSizePx -> normalizedScrollVector.value
+
+                        // Middle taps are ignored
+                        else -> return@awaitEachGesture
+                    }
+
+                val up =
+                    waitForUpOrCancellation(pass = PointerEventPass.Initial)
+                        ?: return@awaitEachGesture
+
+                // Long presses are ignored
+                if (up.uptimeMillis - down.uptimeMillis >= viewConfiguration.longPressTimeoutMillis)
+                    return@awaitEachGesture
+
+                // Swipes are ignored
+                if ((up.position - down.position).getDistance() >= viewConfiguration.touchSlop)
+                    return@awaitEachGesture
+
+                down.consume()
+                up.consume()
+                scope.launch { scrollableState.animateScrollBy(scrollVector) }
+            }
+        }
+}
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 9a9a0821..015a0490 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
@@ -22,8 +22,7 @@ import androidx.compose.foundation.ExperimentalFoundationApi
 import androidx.compose.foundation.Image
 import androidx.compose.foundation.background
 import androidx.compose.foundation.border
-import androidx.compose.foundation.gestures.animateScrollBy
-import androidx.compose.foundation.gestures.detectTapGestures
+import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -61,7 +60,6 @@ import androidx.compose.ui.draw.clip
 import androidx.compose.ui.draw.scale
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.graphics.asImageBitmap
-import androidx.compose.ui.input.pointer.pointerInput
 import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.layout.MeasureScope
 import androidx.compose.ui.layout.Placeable
@@ -77,7 +75,7 @@ import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.android.intentresolver.Flags.announceShareouselItemListPosition
 import com.android.intentresolver.Flags.shareouselScrollOffscreenSelections
 import com.android.intentresolver.Flags.shareouselSelectionShrink
-import com.android.intentresolver.Flags.shareouselTapToScroll
+import com.android.intentresolver.Flags.shareouselTapToScrollSupport
 import com.android.intentresolver.Flags.unselectFinalItem
 import com.android.intentresolver.R
 import com.android.intentresolver.contentpreview.payloadtoggle.domain.model.ValueUpdate
@@ -178,7 +176,10 @@ private fun PreviewCarouselItems(
                 start = measurements.horizontalPaddingDp,
                 end = measurements.horizontalPaddingDp,
             ),
-        modifier = Modifier.fillMaxSize(),
+        modifier =
+            Modifier.fillMaxSize().conditional(shareouselTapToScrollSupport()) {
+                tapToScroll(scrollableState = state)
+            },
     ) {
         itemsIndexed(
             items = previews.previewModels,
@@ -226,9 +227,6 @@ private fun PreviewCarouselItems(
             }
 
             ShareouselCard(
-                carouselState = state,
-                measurements = measurements,
-                index = index,
                 viewModel = previewModel,
                 aspectRatio = measurements.coerceAspectRatio(previewModel.aspectRatio),
                 annotateWithPosition = previews.previewModels.size > 1,
@@ -285,9 +283,6 @@ private fun ScrollOffscreenSelectionsEffect(
 
 @Composable
 private fun ShareouselCard(
-    carouselState: LazyListState,
-    measurements: PreviewCarouselMeasurements,
-    index: Int,
     viewModel: ShareouselPreviewViewModel,
     aspectRatio: Float,
     annotateWithPosition: Boolean,
@@ -307,13 +302,7 @@ private fun ShareouselCard(
             modifier =
                 Modifier.semantics { this.contentDescription = contentDescription }
                     .testTag(viewModel.testTag)
-                    .clickableWithTapToScrollSupport(
-                        state = carouselState,
-                        index = index,
-                        measurements = measurements,
-                    ) {
-                        scope.launch { viewModel.setSelected(!selected) }
-                    }
+                    .clickable { scope.launch { viewModel.setSelected(!selected) } }
                     .conditional(shareouselSelectionShrink()) {
                         val selectionScale by animateFloatAsState(if (selected) 0.95f else 1f)
                         scale(selectionScale)
@@ -335,50 +324,6 @@ private fun ShareouselCard(
 }
 
 @Composable
-private fun Modifier.clickableWithTapToScrollSupport(
-    state: LazyListState,
-    index: Int,
-    measurements: PreviewCarouselMeasurements,
-    onClick: () -> Unit,
-): Modifier {
-    val scope = rememberCoroutineScope()
-    return pointerInput(Unit) {
-        detectTapGestures { offset ->
-            with(state.layoutInfo) {
-                val item = visibleItemsInfo.firstOrNull { it.index == index }
-                when {
-                    // If the item is not visible, then this was likely an accidental click event
-                    // while flinging so ignore it.
-                    item == null -> {}
-
-                    // If tap to scroll flag is off, do a normal click
-                    !shareouselTapToScroll() -> onClick()
-
-                    // If click is in the start tap to scroll region
-                    (item.offset + offset.x) - viewportStartOffset <
-                        measurements.scrollByTapWidthPx ->
-                        // Scroll towards the start
-                        scope.launch {
-                            state.animateScrollBy(-measurements.viewportCenterPx.toFloat())
-                        }
-
-                    // If click is in the end tap to scroll region
-                    viewportEndOffset - (item.offset + offset.x) <
-                        measurements.scrollByTapWidthPx ->
-                        // Scroll towards the end
-                        scope.launch {
-                            state.animateScrollBy(measurements.viewportCenterPx.toFloat())
-                        }
-
-                    // If click is between the tap to scroll regions, do a normal click
-                    else -> onClick()
-                }
-            }
-        }
-    }
-}
-
-@Composable
 private fun buildContentDescription(
     annotateWithPosition: Boolean,
     viewModel: ShareouselPreviewViewModel,
@@ -520,12 +465,6 @@ private fun ShareouselAction(
     )
 }
 
-@Composable
-private inline fun Modifier.conditional(
-    condition: Boolean,
-    crossinline whenTrue: @Composable Modifier.() -> Modifier,
-): Modifier = if (condition) this.whenTrue() else this
-
 private data class PreviewCarouselMeasurements(
     val viewportHeightPx: Int,
     val viewportWidthPx: Int,
@@ -533,7 +472,6 @@ private data class PreviewCarouselMeasurements(
     val maxAspectRatio: Float,
     val horizontalPaddingPx: Int,
     val horizontalPaddingDp: Dp,
-    val scrollByTapWidthPx: Int,
 ) {
     constructor(
         placeable: Placeable,
@@ -551,7 +489,6 @@ private data class PreviewCarouselMeasurements(
             },
         horizontalPaddingPx = horizontalPadding.roundToInt(),
         horizontalPaddingDp = with(measureScope) { horizontalPadding.toDp() },
-        scrollByTapWidthPx = with(measureScope) { SCROLL_BY_TAP_WIDTH.roundToPx() },
     )
 
     fun coerceAspectRatio(ratio: Float): Float = ratio.coerceIn(MIN_ASPECT_RATIO, maxAspectRatio)
@@ -572,7 +509,6 @@ private data class PreviewCarouselMeasurements(
         private const val MIN_ASPECT_RATIO = 0.4f
         private const val MAX_ASPECT_RATIO = 2.5f
 
-        val SCROLL_BY_TAP_WIDTH = 48.dp
         val UNMEASURED =
             PreviewCarouselMeasurements(
                 viewportHeightPx = 0,
@@ -580,7 +516,6 @@ private data class PreviewCarouselMeasurements(
                 maxAspectRatio = 0f,
                 horizontalPaddingPx = 0,
                 horizontalPaddingDp = 0.dp,
-                scrollByTapWidthPx = 0,
             )
     }
 }