smart_page_view.dart

import 'dart:collection';

import 'package:flutter/gestures.dart';
import 'package:flutter/widgets.dart';

const smartPageSwitcherCurve = Curves.easeInOut;

class SmartPageViewController {
  _SmartPageSwitcherImplState? _state;

  double get _height => _state!.widget.constraints.maxHeight;

  double get _width => _state!.widget.constraints.maxWidth;

  PageController get _pageController => _state!._controller;

  bool get isAnimating => _state!.ignorePointer;

  Future<void> go(int page) async {
    final currentPageIndex = _pageController.page!;
    final toRight = page > currentPageIndex;
    final toLeft = !toRight;

    if (_state!._ignorePointer ||
        page == currentPageIndex ||
        page > _state!.widget.children.length - 1) {
      return;
    }

    int rangeBegin;
    int rangeEnd;

    if (toRight) {
      rangeBegin = currentPageIndex.ceil() + 1;
      rangeEnd = page;
    } else {
      rangeBegin = page + 1;
      rangeEnd = currentPageIndex.ceil();
    }

    final indexes = [..._state!.indexes];
    final removedIndexes = <int>[];

    for (var i = rangeEnd - 1; i >= rangeBegin; i--) {
      removedIndexes.add(indexes.removeAt(i));
    }

    _state!.indexes = [...indexes, ...removedIndexes];
    _state!.ignorePointer = true;

    try {
      if (toLeft) {
        _pageController.jumpToPage(rangeBegin);
        await _animateToPage(rangeBegin - 1);
      } else {
        await _animateToPage(rangeBegin);
      }
    } catch (e, s) {
      debugPrintStack(stackTrace: s, label: '$s');
    } finally {
      _pageController.jumpToPage(page);
      _state!.ignorePointer = false;
      _state!._resetIndexes();
    }
  }

  Future<void> _animateToPage(int page) => _pageController.animateToPage(
    page,
    duration: _state!.widget.duration,
    curve: _state!.widget.curve,
  );
}

class SmartPageSwitcher extends StatelessWidget {
  const SmartPageSwitcher({
    super.key,
    required this.controller,
    this.initialPage = 0,
    required this.children,
    required this.duration,
    this.curve = smartPageSwitcherCurve,
    this.onPageChanged,
    // page view
    this.scrollDirection = Axis.horizontal,
    this.reverse = false,
    this.physics,
    this.pageSnapping = true,
    this.dragStartBehavior = DragStartBehavior.start,
    this.allowImplicitScrolling = false,
    this.restorationId,
    this.clipBehavior = Clip.hardEdge,
    this.hitTestBehavior = HitTestBehavior.opaque,
    this.scrollBehavior,
    this.padEnds = true,
  });

  final SmartPageViewController controller;
  final int initialPage;
  final List<Widget> children;
  final Duration duration;
  final Curve curve;
  final ValueChanged<int>? onPageChanged;

  // page view
  final Axis scrollDirection;
  final bool reverse;
  final ScrollPhysics? physics;
  final bool pageSnapping;
  final bool padEnds;
  final ScrollBehavior? scrollBehavior;
  final Clip clipBehavior;
  final HitTestBehavior hitTestBehavior;
  final String? restorationId;
  final bool allowImplicitScrolling;
  final DragStartBehavior dragStartBehavior;

  @override
  Widget build(BuildContext context) => LayoutBuilder(
    builder: (context, constraints) => _SmartPageSwitcherImpl(
      controller: controller,
      initialPage: initialPage,
      constraints: constraints,
      duration: duration,
      curve: curve,
      onPageChanged: onPageChanged,
      // page view
      scrollDirection: scrollDirection,
      reverse: reverse,
      physics: physics,
      pageSnapping: pageSnapping,
      dragStartBehavior: dragStartBehavior,
      allowImplicitScrolling: allowImplicitScrolling,
      restorationId: restorationId,
      clipBehavior: clipBehavior,
      hitTestBehavior: hitTestBehavior,
      scrollBehavior: scrollBehavior,
      padEnds: padEnds,
      // page view end
      children: children,
    ),
  );
}

class _SmartPageSwitcherImpl extends StatefulWidget {
  const _SmartPageSwitcherImpl({
    super.key,
    required this.controller,
    required this.constraints,
    required this.duration,
    this.initialPage = 0,
    this.curve = smartPageSwitcherCurve,
    this.onPageChanged,
    required this.children,
    // page view
    this.scrollDirection = Axis.horizontal,
    this.reverse = false,
    this.physics,
    this.pageSnapping = true,
    this.dragStartBehavior = DragStartBehavior.start,
    this.allowImplicitScrolling = false,
    this.restorationId,
    this.clipBehavior = Clip.hardEdge,
    this.hitTestBehavior = HitTestBehavior.opaque,
    this.scrollBehavior,
    this.padEnds = true,
  }) : assert(children.length > 0);

  final SmartPageViewController controller;
  final int initialPage;
  final Curve curve;
  final Duration duration;
  final BoxConstraints constraints;
  final ValueChanged<int>? onPageChanged;
  final List<Widget> children;

  // page view
  final Axis scrollDirection;
  final bool reverse;
  final ScrollPhysics? physics;
  final bool pageSnapping;
  final bool padEnds;
  final ScrollBehavior? scrollBehavior;
  final Clip clipBehavior;
  final HitTestBehavior hitTestBehavior;
  final String? restorationId;
  final bool allowImplicitScrolling;
  final DragStartBehavior dragStartBehavior;

  @override
  State<_SmartPageSwitcherImpl> createState() => _SmartPageSwitcherImplState();
}

class _SmartPageSwitcherImplState extends State<_SmartPageSwitcherImpl> {
  late final _controller = PageController(initialPage: widget.initialPage);

  UnmodifiableListView<int> get indexes => UnmodifiableListView(_indexes);

  final _indexes = <int>[];

  set indexes(List<int> value) => setState(
    () => _indexes
      ..clear()
      ..addAll(value),
  );

  bool get ignorePointer => _ignorePointer;

  @protected
  var _ignorePointer = false;

  set ignorePointer(bool value) {
    if (_ignorePointer != value) {
      setState(() => _ignorePointer = value);
    }
  }

  @override
  void initState() {
    super.initState();

    _indexes.addAll(List.generate(widget.children.length, (i) => i));

    widget.controller._state = this;
  }

  @override
  void dispose() {
    widget.controller._state = null;

    super.dispose();
  }

  @override
  void didUpdateWidget(covariant _SmartPageSwitcherImpl oldWidget) {
    super.didUpdateWidget(oldWidget);

    _resetIndexes();
  }

  void _resetIndexes() {
    if (!_ignorePointer) {
      indexes = List.generate(widget.children.length, (i) => i);
    }
  }

  @override
  Widget build(BuildContext context) => AbsorbPointer(
    absorbing: _ignorePointer,
    child: PageView(
      scrollDirection: widget.scrollDirection,
      reverse: widget.reverse,
      controller: _controller,
      physics: widget.physics,
      pageSnapping: widget.pageSnapping,
      onPageChanged: (p) {
        if (!_ignorePointer) {
          widget.onPageChanged?.call(p);
        }
      },
      dragStartBehavior: widget.dragStartBehavior,
      allowImplicitScrolling: widget.allowImplicitScrolling,
      restorationId: widget.restorationId,
      clipBehavior: widget.clipBehavior,
      hitTestBehavior: widget.hitTestBehavior,
      scrollBehavior: widget.scrollBehavior,
      padEnds: widget.padEnds,
      children: [for (final index in _indexes) widget.children[index]],
    ),
  );
}