From 91b033b387fa433a15cd1d01deb5d45b4a171516 Mon Sep 17 00:00:00 2001
From: Alex Rintt <alexrintt@gmail.com>
Date: Sat, 3 Dec 2022 01:05:46 -0300
Subject: [PATCH] (#25) Add autoscroll on drag bottom and top

---
 lib/widgets/packages_list.dart | 128 +++++++++++++++++++++------------
 1 file changed, 81 insertions(+), 47 deletions(-)

diff --git a/lib/widgets/packages_list.dart b/lib/widgets/packages_list.dart
index 9bf83e8..51d97b4 100644
--- a/lib/widgets/packages_list.dart
+++ b/lib/widgets/packages_list.dart
@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:math';
 import 'dart:ui';
 
@@ -115,6 +116,9 @@ class _PackagesListState extends State<PackagesList>
   void initState() {
     super.initState();
     _scrollController = ScrollController();
+    _scrollController.addListener(() {
+      if (menuStore.context.isSelection) _onSelectionGesture();
+    });
   }
 
   @override
@@ -152,10 +156,12 @@ class _PackagesListState extends State<PackagesList>
 
       if (_globalInitialDragPosition == null) return;
 
-      final dragStartGlobalPosition = _globalInitialDragPosition!;
+      final dragStartGlobalPosition =
+          _globalInitialDragPosition! + _scrollControllerOffset;
 
       final dragFinalGlobalPosition =
-          _globalFinalDragPosition ?? _globalInitialDragPosition!;
+          (_globalFinalDragPosition ?? _globalInitialDragPosition!) +
+              _scrollControllerOffset;
 
       final pointerRect =
           _rectFromPoints(dragStartGlobalPosition, dragFinalGlobalPosition);
@@ -201,68 +207,92 @@ class _PackagesListState extends State<PackagesList>
     }
   }
 
-  var _autoscrolling = false;
+  Offset get _scrollControllerOffset => Offset(0, _scrollController.offset);
 
-  void _endAutoscrollFeature() {
-    _autoscrolling = false;
-  }
+  double get _maxScrollExtent => _scrollController.position.maxScrollExtent;
+  double get _minScrollExtent => _scrollController.position.minScrollExtent;
 
-  Future<void> _startAutoscrollFeature() async {
-    var _autoscrolling = true;
+  // var _acceleration = 0.01;
+  var _velocity = 4.0;
+  // static const _kInitialAutoscrollVelocity = 2.0;
+
+  double get _pixelRatio => window.devicePixelRatio;
+  Size get _logicalScreenSize => window.physicalSize / _pixelRatio;
+  double get _logicalHeight => _logicalScreenSize.height;
 
-    Offset? pointer() => _globalFinalDragPosition ?? _globalInitialDragPosition;
-    bool hasPointer() => pointer() != null;
+  void _autoscrollListener() {
+    _velocity = _acceleration * _logicalHeight / 10;
 
-    if (pointer() == null) return;
+    final step =
+        _autoscrollDirection == AxisDirection.up ? -_velocity : _velocity;
 
-    final pixelRatio = window.devicePixelRatio;
+    final newOffset = (_scrollControllerOffset.dy + step)
+        .clamp(_minScrollExtent, _maxScrollExtent);
 
-    final logicalScreenSize = window.physicalSize / pixelRatio;
-    final logicalHeight = logicalScreenSize.height;
+    _scrollController.jumpTo(newOffset);
+  }
+
+  StreamSubscription<void>? _autoscrollStreamSubscription;
 
-    const kAutoscrollArea = kToolbarHeight * 3;
+  Future<void> _startAutoscrolling() async {
+    const kFps = 60;
+    const k1s = 1000;
 
-    bool shouldAutoscrollToTop() =>
-        hasPointer() ? pointer()!.dy <= kAutoscrollArea : false;
+    _autoscrollStreamSubscription =
+        Stream<void>.periodic(const Duration(milliseconds: k1s ~/ kFps))
+            .listen((_) => _autoscrollListener());
+  }
 
-    bool shouldAutoscrollToBottom() =>
-        hasPointer() ? pointer()!.dy >= logicalHeight - kAutoscrollArea : false;
+  Future<void> _stopAutoscroll() async {
+    _autoscrollDirection = null;
+    _autoscrollStreamSubscription?.cancel();
+  }
 
-    double topDiffInPixels() =>
-        hasPointer() ? (kAutoscrollArea - pointer()!.dy).abs() : 0;
+  void _endAutoscrollFeature() {
+    _calcAutoscrollDirectionAndForce();
+    _stopAutoscroll();
+  }
 
-    double bottomDiffInPixels() => hasPointer()
-        ? (pointer()!.dy - logicalHeight - kAutoscrollArea).abs()
-        : 0;
+  void _updateAutoscrollFeature() {
+    _calcAutoscrollDirectionAndForce();
+  }
 
-    double topDiff() => (topDiffInPixels() / kAutoscrollArea).clamp(0, 1);
-    double bottomDiff() => (bottomDiffInPixels() / kAutoscrollArea).clamp(0, 1);
+  Future<void> _startAutoscrollFeature() async {
+    _calcAutoscrollDirectionAndForce();
+    _startAutoscrolling();
+  }
 
-    if (shouldAutoscrollToTop() || shouldAutoscrollToBottom()) {
-      final autoscrollStep =
-          (shouldAutoscrollToTop() ? topDiff() : bottomDiff()) * 300 + 10;
+  AxisDirection? _autoscrollDirection;
+  var _acceleration = 0.0;
+  void _calcAutoscrollDirectionAndForce() {
+    final pointer = _globalFinalDragPosition ?? _globalInitialDragPosition;
+    final hasPointer = pointer != null;
 
-      final autoscrollDuration = Duration(milliseconds: autoscrollStep ~/ 1);
+    const kAutoscrollArea = kToolbarHeight * 2;
 
-      _autoscrolling = true;
+    final topDiff = hasPointer ? 1 - pointer!.dy / kAutoscrollArea : 0.0;
+    final bottomDiff = hasPointer
+        ? 1 - (pointer!.dy - _logicalHeight).abs() / kAutoscrollArea
+        : 0.0;
 
-      final current = _scrollControllerOffset.dy;
+    final shouldAutoscrollToTop =
+        hasPointer ? pointer!.dy <= kAutoscrollArea : false;
 
-      final newOffset = shouldAutoscrollToTop() ? current - 1 : current + 1;
+    final shouldAutoscrollToBottom =
+        hasPointer ? pointer!.dy >= _logicalHeight - kAutoscrollArea : false;
 
-      _scrollController.jumpTo(
-        newOffset.clamp(
-          _scrollController.position.minScrollExtent,
-          _scrollController.position.maxScrollExtent,
-        ),
-      );
-    } else if (!hasPointer()) {
-      _scrollController.jumpTo(_scrollControllerOffset.dy);
+    if (shouldAutoscrollToTop) {
+      _autoscrollDirection = AxisDirection.up;
+      _acceleration = topDiff;
+    } else if (shouldAutoscrollToBottom) {
+      _autoscrollDirection = AxisDirection.down;
+      _acceleration = bottomDiff;
+    } else {
+      _autoscrollDirection = null;
+      _acceleration = 0.0;
     }
   }
 
-  Offset get _scrollControllerOffset => Offset(0, _scrollController.offset);
-
   @override
   Widget build(BuildContext context) {
     return WillPopScope(
@@ -286,21 +316,25 @@ class _PackagesListState extends State<PackagesList>
         animations: [store, menuStore],
         builder: (context, child) => GestureDetector(
           onLongPressStart: (details) {
-            _globalInitialDragPosition =
-                details.globalPosition + _scrollControllerOffset;
+            _globalInitialDragPosition = details.globalPosition;
             _startAutoscrollFeature();
           },
           onLongPressMoveUpdate: (details) {
-            _globalFinalDragPosition =
-                details.globalPosition + _scrollControllerOffset;
+            _globalFinalDragPosition = details.globalPosition;
 
             _onSelectionGesture();
+            _updateAutoscrollFeature();
           },
           onLongPressEnd: (details) {
             _globalInitialDragPosition = null;
             _globalFinalDragPosition = null;
             _endAutoscrollFeature();
           },
+          onLongPressCancel: () {
+            _globalInitialDragPosition = null;
+            _globalFinalDragPosition = null;
+            _endAutoscrollFeature();
+          },
           onLongPress: () {
             _onSelectionGesture();
           },