feat: auto hide fab

lib/view/widget/auto_hide_fab.dart

@@ -0,0 +1,86 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+
+final class AutoHideFab extends StatefulWidget {
+  final Widget child;
+  final ScrollController controller;
+
+  const AutoHideFab({
+    super.key,
+    required this.child,
+    required this.controller,
+  });
+
+  @override
+  State<AutoHideFab> createState() => _AutoHideFabState();
+}
+
+final class _AutoHideFabState extends State<AutoHideFab> {
+  bool _visible = true;
+  bool _isScrolling = false;
+  Timer? _timer;
+
+  @override
+  void initState() {
+    super.initState();
+    widget.controller.addListener(_scrollListener);
+  }
+
+  @override
+  void dispose() {
+    widget.controller.removeListener(_scrollListener);
+    _timer?.cancel();
+    _timer = null;
+    super.dispose();
+  }
+
+  void _setupTimer() {
+    if (_timer != null) {
+      _timer!.cancel();
+      _timer = null;
+    }
+    _timer = Timer.periodic(const Duration(seconds: 3), (_) {
+      if (_isScrolling) return;
+      if (!_visible) return;
+      if (widget.controller.position.maxScrollExtent <= 0) return;
+      setState(() {
+        _visible = false;
+      });
+    });
+  }
+
+  void _scrollListener() {
+    if (_isScrolling) return;
+    _isScrolling = true;
+    if (widget.controller.position.userScrollDirection ==
+        ScrollDirection.reverse) {
+      if (_visible) {
+        setState(() {
+          _visible = false;
+        });
+        _timer?.cancel();
+        _timer = null;
+      }
+    } else {
+      if (!_visible) {
+        setState(() {
+          _visible = true;
+        });
+        _setupTimer();
+      }
+    }
+    _isScrolling = false;
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedContainer(
+      duration: Durations.medium1,
+      curve: Curves.easeInOutCubic,
+      transform: Matrix4.translationValues(_visible ? 0.0 : 55, 0.0, 0.0),
+      child: widget.child,
+    );
+  }
+}