Merge pull request #3088 from vitorpamplona/claude/intelligent-fermat-8y2or

Auto-stick feeds to top on prepend with StickToTopOnPrepend

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/feeds/FeedContentStateView.kt

@@ -63,6 +63,7 @@ fun SaveableFeedContentState(
         }
 
     WatchScrollToTop(feedContentState, listState)
+    StickToTopOnPrepend(feedContentState, listState)
 
     content(listState)
 }
@@ -81,6 +82,7 @@ fun SaveableGridFeedContentState(
         }
 
     WatchScrollToTop(feedContentState, gridState)
+    StickToTopOnPrepend(feedContentState, gridState)
 
     content(gridState)
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/feeds/WatchScrollToTop.kt

@@ -26,8 +26,16 @@ import androidx.compose.foundation.pager.PagerState
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.snapshotFlow
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import com.vitorpamplona.amethyst.commons.ui.feeds.FeedState
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.notifications.CardFeedContentState
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.map
 
 @Composable
 fun WatchScrollToTop(
@@ -88,3 +96,141 @@ fun WatchScrollToTop(
         }
     }
 }
+
+/**
+ * Keeps the user pinned to index 0 when new items prepend to a feed, but
+ * only if they were already at the very top right before the update.
+ *
+ * Why this is non-trivial: every feed uses stable `key = item.idHex` in
+ * its lazy list, which makes Compose preserve the visual anchor across
+ * data changes. When N items prepend, the user's previously-visible
+ * top item is still on screen but its index is now N — so
+ * `firstVisibleItemIndex` shifts from 0 to N without any user gesture.
+ * A naive `if (firstVisibleItemIndex <= 1) scrollToItem(0)` check inside
+ * `LaunchedEffect(items.firstOrNull())` therefore fails as soon as more
+ * than one item arrives in the same batch.
+ *
+ * The trick: track "was at top" continuously via [snapshotFlow], but
+ * only flip it from true → false when [LazyListState.isScrollInProgress]
+ * is true (i.e. the user is actively scrolling). Compose's keyed-item
+ * shift after a data update does not set that flag — only real touch
+ * gestures and `animate*` calls do — so data-driven index shifts can
+ * never poison the cached value. When [firstItemKey] changes (head of
+ * the list moved), if the cached value is still true, snap back to 0
+ * with an instant (non-animated) scroll so the prepend appears as
+ * in-place growth rather than a visible jump-then-scroll.
+ *
+ * Most callers should not invoke this directly: [SaveableFeedContentState],
+ * [SaveableGridFeedContentState], and the analogous wrappers in
+ * `ui/screen/FeedView.kt` already apply auto-stick to every feed they
+ * own. Invoke the explicit overload only when the listState is
+ * constructed outside one of those wrappers, or when the key that
+ * should trigger the snap is not the default `items.list[0].idHex`
+ * (e.g. notifications, chats, or feeds keyed on something other than a
+ * Note's hex id).
+ */
+@Composable
+fun StickToTopOnPrepend(
+    listState: LazyListState,
+    firstItemKey: Any?,
+) {
+    stickToTopOnPrepend(
+        stateKey = listState,
+        firstItemKey = firstItemKey,
+        sampler = {
+            snapshotFlow {
+                listState.firstVisibleItemIndex == 0 && listState.firstVisibleItemScrollOffset == 0
+            }
+        },
+        isScrollInProgress = { listState.isScrollInProgress },
+        firstVisibleItemIndex = { listState.firstVisibleItemIndex },
+        scrollToTop = { listState.scrollToItem(0) },
+    )
+}
+
+@Composable
+fun StickToTopOnPrepend(
+    gridState: LazyGridState,
+    firstItemKey: Any?,
+) {
+    stickToTopOnPrepend(
+        stateKey = gridState,
+        firstItemKey = firstItemKey,
+        sampler = {
+            snapshotFlow {
+                gridState.firstVisibleItemIndex == 0 && gridState.firstVisibleItemScrollOffset == 0
+            }
+        },
+        isScrollInProgress = { gridState.isScrollInProgress },
+        firstVisibleItemIndex = { gridState.firstVisibleItemIndex },
+        scrollToTop = { gridState.scrollToItem(0) },
+    )
+}
+
+/**
+ * Auto-stick wired straight to a [FeedContentState]: derives the head
+ * key from `feedContent → Loaded.feed → list.firstOrNull()?.idHex` so
+ * callers don't have to collect the inner feed flow themselves. Used
+ * by the Saveable* wrappers; suitable for any Note-keyed feed.
+ */
+@Composable
+fun StickToTopOnPrepend(
+    feedContentState: FeedContentState,
+    listState: LazyListState,
+) {
+    StickToTopOnPrepend(listState, rememberFirstItemIdHex(feedContentState))
+}
+
+@Composable
+fun StickToTopOnPrepend(
+    feedContentState: FeedContentState,
+    gridState: LazyGridState,
+) {
+    StickToTopOnPrepend(gridState, rememberFirstItemIdHex(feedContentState))
+}
+
+@OptIn(ExperimentalCoroutinesApi::class)
+@Composable
+private fun rememberFirstItemIdHex(feedContentState: FeedContentState): String? {
+    val flow =
+        remember(feedContentState) {
+            feedContentState.feedContent.flatMapLatest { state ->
+                when (state) {
+                    is FeedState.Loaded -> state.feed.map { it.list.firstOrNull()?.idHex }
+                    else -> flowOf(null)
+                }
+            }
+        }
+    val key by flow.collectAsStateWithLifecycle(initialValue = null)
+    return key
+}
+
+@Composable
+private fun stickToTopOnPrepend(
+    stateKey: Any,
+    firstItemKey: Any?,
+    sampler: () -> Flow<Boolean>,
+    isScrollInProgress: () -> Boolean,
+    firstVisibleItemIndex: () -> Int,
+    scrollToTop: suspend () -> Unit,
+) {
+    // Plain holder instead of mutableStateOf — we only read this inside
+    // effects, never in composition, so we don't need snapshot tracking.
+    val wasAtTop = remember { booleanArrayOf(true) }
+
+    LaunchedEffect(stateKey) {
+        sampler().collect { atTop ->
+            if (atTop) {
+                wasAtTop[0] = true
+            } else if (isScrollInProgress()) {
+                wasAtTop[0] = false
+            }
+        }
+    }
+
+    LaunchedEffect(firstItemKey) {
+        if (firstItemKey != null && wasAtTop[0] && firstVisibleItemIndex() > 0) {
+            scrollToTop()
+        }
+    }
+}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/FeedView.kt

@@ -36,6 +36,7 @@ import com.vitorpamplona.amethyst.ui.feeds.FeedError
 import com.vitorpamplona.amethyst.ui.feeds.FeedLoaded
 import com.vitorpamplona.amethyst.ui.feeds.LoadingFeed
 import com.vitorpamplona.amethyst.ui.feeds.RefresheableBox
+import com.vitorpamplona.amethyst.ui.feeds.StickToTopOnPrepend
 import com.vitorpamplona.amethyst.ui.feeds.WatchScrollToTop
 import com.vitorpamplona.amethyst.ui.feeds.rememberForeverLazyGridState
 import com.vitorpamplona.amethyst.ui.feeds.rememberForeverLazyListState
@@ -72,6 +73,7 @@ fun SaveableFeedState(
         }
 
     WatchScrollToTop(feedContentState, listState)
+    StickToTopOnPrepend(feedContentState, listState)
 
     content(listState)
 }
@@ -90,6 +92,7 @@ fun SaveableGridFeedState(
         }
 
     WatchScrollToTop(viewModel.feedState, gridState)
+    StickToTopOnPrepend(viewModel.feedState, gridState)
 
     content(gridState)
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/UserFeedView.kt

@@ -35,6 +35,7 @@ import com.vitorpamplona.amethyst.ui.feeds.FeedEmpty
 import com.vitorpamplona.amethyst.ui.feeds.FeedError
 import com.vitorpamplona.amethyst.ui.feeds.LoadingFeed
 import com.vitorpamplona.amethyst.ui.feeds.RefresheableBox
+import com.vitorpamplona.amethyst.ui.feeds.StickToTopOnPrepend
 import com.vitorpamplona.amethyst.ui.layouts.rememberFeedContentPadding
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.note.UserCompose
@@ -90,6 +91,8 @@ private fun FeedLoaded(
     val items by state.feed.collectAsStateWithLifecycle()
     val listState = rememberLazyListState()
 
+    StickToTopOnPrepend(listState, items.firstOrNull()?.pubkeyHex)
+
     LazyColumn(
         modifier = Modifier.fillMaxSize(),
         contentPadding = rememberFeedContentPadding(FeedPadding),

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/emojipacks/browse/BrowseEmojiSetsScreen.kt

@@ -44,6 +44,7 @@ import com.vitorpamplona.amethyst.ui.feeds.FeedError
 import com.vitorpamplona.amethyst.ui.feeds.LoadingFeed
 import com.vitorpamplona.amethyst.ui.feeds.RefresheableBox
 import com.vitorpamplona.amethyst.ui.feeds.ScrollStateKeys
+import com.vitorpamplona.amethyst.ui.feeds.StickToTopOnPrepend
 import com.vitorpamplona.amethyst.ui.feeds.WatchLifecycleAndUpdateModel
 import com.vitorpamplona.amethyst.ui.feeds.WatchScrollToTop
 import com.vitorpamplona.amethyst.ui.feeds.rememberForeverLazyGridState
@@ -157,6 +158,8 @@ private fun BrowseEmojiSetsGridLoaded(
 ) {
     val items by loaded.feed.collectAsStateWithLifecycle()
 
+    StickToTopOnPrepend(gridState, items.list.firstOrNull()?.idHex)
+
     LazyVerticalGrid(
         columns = GridCells.Adaptive(minSize = 160.dp),
         state = gridState,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/CardFeedView.kt

@@ -58,6 +58,7 @@ import com.vitorpamplona.amethyst.commons.ui.notifications.CardFeedState
 import com.vitorpamplona.amethyst.logTime
 import com.vitorpamplona.amethyst.ui.feeds.FeedError
 import com.vitorpamplona.amethyst.ui.feeds.LoadingFeed
+import com.vitorpamplona.amethyst.ui.feeds.StickToTopOnPrepend
 import com.vitorpamplona.amethyst.ui.layouts.rememberFeedContentPadding
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.note.BadgeCompose
@@ -151,6 +152,8 @@ private fun FeedLoaded(
     val items by loaded.feed.collectAsStateWithLifecycle()
     val openPolls by polls.flow.collectAsStateWithLifecycle()
 
+    StickToTopOnPrepend(listState, items.list.firstOrNull()?.id())
+
     // Track which card is highlighted (will auto-clear after animation)
     var highlightedCardId by remember { mutableStateOf<String?>(null) }
 

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/profile/newthreads/TabNotesNewThreads.kt

@@ -40,6 +40,7 @@ import com.vitorpamplona.amethyst.ui.feeds.FeedEmpty
 import com.vitorpamplona.amethyst.ui.feeds.FeedError
 import com.vitorpamplona.amethyst.ui.feeds.LoadingFeed
 import com.vitorpamplona.amethyst.ui.feeds.RefresheableBox
+import com.vitorpamplona.amethyst.ui.feeds.StickToTopOnPrepend
 import com.vitorpamplona.amethyst.ui.feeds.WatchScrollToTop
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.note.NoteCompose
@@ -133,6 +134,11 @@ private fun FeedLoadedWithPinnedNotes(
             state
         }
 
+    StickToTopOnPrepend(
+        listState,
+        pinnedItems?.list?.firstOrNull()?.idHex ?: feedItems?.list?.firstOrNull()?.idHex,
+    )
+
     LazyColumn(
         contentPadding = FeedPadding,
         state = listState,