freezer/lib/ui/fancy_scaffold.dart

import 'package:flutter/material.dart';

class FancyScaffold extends StatefulWidget {
  final Widget bottomPanel;
  final double bottomPanelHeight;
  final Widget expandedPanel;
  final Widget? bottomNavigationBar;
  final Widget? drawer;
  final Widget? navigationRail;
  final Widget body;
  final void Function(AnimationStatus)? onAnimationStatusChange;

  const FancyScaffold({
    required this.bottomPanel,
    required this.bottomPanelHeight,
    required this.expandedPanel,
    required this.body,
    this.onAnimationStatusChange,
    this.bottomNavigationBar,
    this.navigationRail,
    this.drawer,
    super.key,
  });

  static FancyScaffoldState? of(BuildContext context) =>
      context.findAncestorStateOfType<FancyScaffoldState>();

  @override
  FancyScaffoldState createState() => FancyScaffoldState();
}

class FancyScaffoldState extends State<FancyScaffold>
    with TickerProviderStateMixin {
  // goes from 0 to 1 (double)
  // 0 = preview, 1 = expanded
  late final AnimationController dragController;
  final statusNotifier =
      ValueNotifier<AnimationStatus>(AnimationStatus.dismissed);

  @override
  void initState() {
    dragController = AnimationController(
        vsync: this, duration: const Duration(milliseconds: 500));
    dragController.addStatusListener((status) => statusNotifier.value = status);
    statusNotifier.addListener(
        () => widget.onAnimationStatusChange?.call(statusNotifier.value));
    super.initState();
  }

  @override
  void dispose() {
    dragController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final systemPadding = MediaQuery.of(context).viewPadding;
    final defaultBottomPadding =
        (widget.bottomNavigationBar == null ? 0 : 80.0) + systemPadding.bottom;
    final screenHeight = MediaQuery.of(context).size.height;
    final sizeAnimation = Tween<double>(
      begin: widget.bottomPanelHeight / MediaQuery.of(context).size.height,
      end: 1.0,
    ).animate(dragController);
    return WillPopScope(
      onWillPop: () {
        if (statusNotifier.value == AnimationStatus.completed ||
            statusNotifier.value == AnimationStatus.reverse) {
          dragController.fling(velocity: -1.0);
          return Future.value(false);
        }

        return Future.value(true);
      },
      child: Stack(
        children: [
          Positioned.fill(
            child: Scaffold(
              body: widget.navigationRail != null
                  ? Row(children: [
                      widget.navigationRail!,
                      const VerticalDivider(
                        indent: 0.0,
                        endIndent: 0.0,
                        width: 2.0,
                      ),
                      Expanded(child: widget.body)
                    ])
                  : widget.body,
              drawer: widget.drawer,
              bottomNavigationBar: Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  SizedBox(height: widget.bottomPanelHeight),
                  if (widget.bottomNavigationBar != null)
                    SizeTransition(
                      axisAlignment: -1.0,
                      sizeFactor:
                          Tween(begin: 1.0, end: 0.0).animate(sizeAnimation),
                      child: widget.bottomNavigationBar,
                    ),
                ],
              ),
            ),
          ),
          Positioned(
            bottom: 0,
            left: 0,
            right: 0,
            child: AnimatedBuilder(
              animation: sizeAnimation,
              builder: (context, child) {
                final x = 1.0 - sizeAnimation.value;
                return Padding(
                  padding: EdgeInsets.only(
                    bottom: (defaultBottomPadding /*+ 8.0*/) * x,
                    //right: 8.0 * x,
                    //left: 8.0 * x,
                  ),
                  child: child,
                );
              },
              child: ValueListenableBuilder(
                valueListenable: statusNotifier,
                builder: (context, state, child) {
                  return GestureDetector(
                    onVerticalDragEnd: _onVerticalDragEnd,
                    onVerticalDragUpdate: _onVerticalDragUpdate,
                    child: child,
                  );
                },
                child: SizeTransition(
                    sizeFactor: sizeAnimation,
                    axisAlignment: -1.0,
                    axis: Axis.vertical,
                    child: SizedBox(
                      height: screenHeight,
                      width: MediaQuery.of(context).size.width,
                      child: ValueListenableBuilder(
                        valueListenable: statusNotifier,
                        builder: (context, state, _) => Stack(
                          children: [
                            if (state != AnimationStatus.dismissed)
                              Positioned.fill(
                                key: const Key('player_screen'),
                                child: widget.expandedPanel,
                              ),
                            if (state != AnimationStatus.completed)
                              Positioned(
                                top: 0,
                                right: 0,
                                left: 0,
                                key: const Key('player_bar'),
                                child: FadeTransition(
                                  opacity: Tween(begin: 1.0, end: 0.0)
                                      .animate(dragController),
                                  child: SizedBox(
                                      height: widget.bottomPanelHeight,
                                      child: widget.bottomPanel),
                                ),
                              ),
                          ],
                        ),
                      ),
                    )),
              ),
            ),
          ),
        ],
      ),
    );
  }

  void _onVerticalDragUpdate(DragUpdateDetails details) {
    dragController.value -=
        details.delta.dy / MediaQuery.of(context).size.height;
  }

  void _onVerticalDragEnd(DragEndDetails details) {
    // snap widget to size
    // this should be also handled by drag velocity and not only with bare size.

    const double minFlingVelocity = 365.0;

    if (details.velocity.pixelsPerSecond.dy.abs() > minFlingVelocity) {
      dragController.fling(
          velocity: -details.velocity.pixelsPerSecond.dy /
              MediaQuery.of(context).size.height);
      return;
    }

    dragController.fling(velocity: dragController.value > 0.5 ? 1.0 : -1.0);
  }
}