reorg ui into app

lib/app/util/custom_scroll_fix.dart

@@ -0,0 +1,175 @@
+import 'package:flutter/material.dart';
+
+// Fixes scroll postion being reset in a tab when scrolling up inside a
+// NestedScrollView.
+//
+// https://dartpad.dev/?id=5d1a0c7c4b55281ccff377fc8ea90b60
+// https://github.com/flutter/flutter/issues/159123#issuecomment-2614343654
+
+class CustomScrollProvider extends StatefulWidget {
+  const CustomScrollProvider({
+    super.key,
+    required this.tabController,
+    required this.parent,
+    required this.child,
+  });
+
+  final TabController tabController;
+  final ScrollController parent;
+  final Widget child;
+
+  @override
+  State<CustomScrollProvider> createState() => _CustomScrollProviderState();
+}
+
+class _CustomScrollProviderState extends State<CustomScrollProvider> {
+  late final List<CustomScrollController> scrollControllers;
+
+  @override
+  void initState() {
+    super.initState();
+
+    final activeIndex = widget.tabController.index;
+
+    scrollControllers = List.generate(
+      widget.tabController.length,
+      (index) => CustomScrollController(
+        isActive: index == activeIndex,
+        parent: widget.parent,
+        debugLabel: 'CustomScrollController/$index',
+      ),
+    );
+
+    widget.tabController.addListener(() {
+      changeActiveIndex(widget.tabController.index);
+    });
+  }
+
+  @override
+  void dispose() {
+    for (final scrollController in scrollControllers) {
+      scrollController.dispose();
+    }
+
+    super.dispose();
+  }
+
+  void changeActiveIndex(int value) {
+    for (var i = 0; i < scrollControllers.length; i++) {
+      final scrollController = scrollControllers[i];
+      final isActive = i == value;
+      scrollController.isActive = isActive;
+
+      if (isActive) {
+        scrollController.forceAttach();
+      } else {
+        scrollController.forceDetach();
+      }
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return CustomScrollProviderData(
+      scrollControllers: scrollControllers,
+      child: widget.child,
+    );
+  }
+}
+
+class CustomScrollProviderData extends InheritedWidget {
+  const CustomScrollProviderData({
+    super.key,
+    required super.child,
+    required this.scrollControllers,
+  });
+
+  static CustomScrollProviderData of(BuildContext context) {
+    return context
+        .dependOnInheritedWidgetOfExactType<CustomScrollProviderData>()!;
+  }
+
+  final List<CustomScrollController> scrollControllers;
+
+  @override
+  bool updateShouldNotify(CustomScrollProviderData oldWidget) {
+    return scrollControllers != oldWidget.scrollControllers;
+  }
+}
+
+class CustomScrollController extends ScrollController {
+  CustomScrollController({
+    required this.isActive,
+    required this.parent,
+    String debugLabel = 'CustomScrollController',
+  }) : super(
+         debugLabel: parent.debugLabel == null
+             ? null
+             : '${parent.debugLabel}/$debugLabel',
+         initialScrollOffset: parent.initialScrollOffset,
+         keepScrollOffset: parent.keepScrollOffset,
+       );
+
+  bool isActive;
+  final ScrollController parent;
+
+  @override
+  ScrollPosition createScrollPosition(
+    ScrollPhysics physics,
+    ScrollContext context,
+    ScrollPosition? oldPosition,
+  ) {
+    debugPrint('$debugLabel-createScrollPosition: $isActive');
+
+    return parent.createScrollPosition(physics, context, oldPosition);
+  }
+
+  @override
+  void attach(ScrollPosition position) {
+    debugPrint('$debugLabel-attach: $isActive');
+
+    super.attach(position);
+    if (isActive && !parent.positions.contains(position)) {
+      parent.attach(position);
+    }
+  }
+
+  @override
+  void detach(ScrollPosition position) {
+    debugPrint('$debugLabel-detach: $isActive');
+
+    if (parent.positions.contains(position)) {
+      parent.detach(position);
+    }
+
+    super.detach(position);
+  }
+
+  void forceDetach() {
+    debugPrint('$debugLabel-forceDetach: $isActive');
+
+    for (final position in positions) {
+      if (parent.positions.contains(position)) {
+        parent.detach(position);
+      }
+    }
+  }
+
+  void forceAttach() {
+    debugPrint('$debugLabel-forceAttach: $isActive');
+
+    for (final position in positions) {
+      if (!parent.positions.contains(position)) {
+        parent.attach(position);
+      }
+    }
+  }
+
+  @override
+  void dispose() {
+    debugPrint('$debugLabel-dispose: $isActive');
+
+    forceDetach();
+    super.dispose();
+  }
+}