extract scroll helpers into their own hook

lib/helpers/hooks/chat_scroll.dart

@@ -0,0 +1,131 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:flutter_hooks/flutter_hooks.dart";
+import "package:hooks_riverpod/hooks_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:super_sliver_list/super_sliver_list.dart";
+
+final class ChatScroll({
+  required final ListController listController,
+  required final ScrollController scrollController,
+  required final bool hasMore,
+  required final Future<void> Function() loadOlder,
+  required final Future<void> Function(String id) jumpToId,
+}) {
+  static ChatScroll use<T>({
+    required AsyncValue<IList<T>?> controllerData,
+    required String Function(T item) id,
+    required Future<bool> Function() loadOlder,
+    required bool Function() shouldLoadOlder,
+    required Future<void> Function() onReachedBottom,
+  }) {
+    final listController = useRef(ListController());
+    final scrollController = useScrollController();
+
+    final hasMore = useState(true);
+    final topItemBeforeLoad = useState<String?>(null);
+    final loadingOlder = useRef(false);
+    final initialized = useRef(false);
+
+    Future<void> loadOlderItems() async {
+      if (loadingOlder.value || !hasMore.value) return;
+
+      if (controllerData case AsyncData(:final value?)) {
+        loadingOlder.value = true;
+        topItemBeforeLoad.value = value.firstOrNull == null
+            ? null
+            : id(value.first);
+
+        try {
+          hasMore.value = await loadOlder();
+        } finally {
+          loadingOlder.value = false;
+        }
+      }
+    }
+
+    Future<void> jumpToId(String itemId) async {
+      final index =
+          controllerData.value?.indexWhere((item) => id(item) == itemId) ?? -1;
+
+      if (index == -1) return;
+
+      listController.value.animateToItem(
+        index: index,
+        scrollController: scrollController,
+        alignment: 0.5,
+        duration: (_) => .new(milliseconds: 700),
+        curve: (_) => Curves.easeInOut,
+      );
+    }
+
+    useEffect(() {
+      if (controllerData case AsyncData(:final value?)) {
+        WidgetsBinding.instance.addPostFrameCallback((_) {
+          if (!scrollController.hasClients) return;
+
+          if (!initialized.value) {
+            initialized.value = true;
+
+            if (value.isNotEmpty) {
+              listController.value.jumpToItem(
+                index: value.length - 1,
+                scrollController: scrollController,
+                alignment: 1,
+              );
+            }
+            return;
+          }
+
+          final topItem = topItemBeforeLoad.value;
+
+          if (topItem != null) {
+            final index = value.indexWhere((item) => id(item) == topItem);
+
+            if (index != -1) {
+              listController.value.jumpToItem(
+                index: index,
+                scrollController: scrollController,
+                alignment: 0,
+              );
+            }
+
+            topItemBeforeLoad.value = null;
+          } else if (scrollController.position.atEdge &&
+              scrollController.position.pixels != 0) {
+            scrollController.jumpTo(scrollController.position.maxScrollExtent);
+          }
+        });
+      }
+
+      return null;
+    }, [controllerData]);
+
+    useEffect(() {
+      Future<void> listener() async {
+        if (!scrollController.hasClients || !scrollController.position.atEdge) {
+          return;
+        }
+
+        if (scrollController.position.pixels == 0) {
+          if (shouldLoadOlder()) {
+            await loadOlderItems();
+          }
+        } else {
+          await onReachedBottom();
+        }
+      }
+
+      scrollController.addListener(listener);
+
+      return () => scrollController.removeListener(listener);
+    }, [controllerData]);
+
+    return .new(
+      listController: listController.value,
+      scrollController: scrollController,
+      hasMore: hasMore.value,
+      loadOlder: loadOlderItems,
+      jumpToId: jumpToId,
+    );
+  }
+}