sliver_app_bars.dart

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';

import 'diagram_step.dart';
import 'fake_drag_scroll_activity.dart';
import 'utils.dart';

final Duration _kTotalDuration =
    _kScrollPauseDuration +
    _kScrollUpDuration +
    _kScrollPauseDuration +
    _kScrollDownDurationPartOne +
    _kScrollPauseDuration +
    _kScrollDownDurationPartTwo +
    _kScrollPauseDuration;
const Duration _kScrollUpDuration = Duration(seconds: 1, milliseconds: 500);
const Duration _kScrollDownDurationPartOne = Duration(milliseconds: 800);
const Duration _kScrollDownDurationPartTwo = Duration(seconds: 1);
const Duration _kScrollPauseDuration = Duration(milliseconds: 900);

class SliverAppBarDiagram extends StatefulWidget with DiagramMetadata {
  const SliverAppBarDiagram({
    this.pinned = false,
    this.floating = false,
    this.snap = false,
    this.repeatAnimation = false,
    super.key,
  });

  final bool pinned;
  final bool floating;
  final bool snap;
  final bool repeatAnimation;

  @override
  State<SliverAppBarDiagram> createState() => SliverAppBarDiagramState();

  @override
  String get name {
    String name = 'app_bar';
    if (pinned) {
      name += '_pinned';
    }
    if (floating) {
      name += '_floating';
    }
    if (snap) {
      name += '_snap';
    }
    return name;
  }

  @override
  Duration? get duration => _kTotalDuration;
}

class SliverAppBarDiagramState extends State<SliverAppBarDiagram>
    with TickerProviderStateMixin, LockstepStateMixin {
  final ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    SchedulerBinding.instance.scheduleFrameCallback((Duration _) {
      if (mounted) {
        _play();
      }
    });
  }

  Future<void> _play() async {
    await waitLockstep(_kScrollPauseDuration);
    if (!mounted) {
      return;
    }
    await _animate(to: 600.0, duration: _kScrollUpDuration);
    await waitLockstep(_kScrollPauseDuration);
    if (!mounted) {
      return;
    }
    await _animate(to: 490.0, duration: _kScrollDownDurationPartOne);
    await waitLockstep(_kScrollPauseDuration);
    if (!mounted) {
      return;
    }
    await _animate(to: 0.0, duration: _kScrollDownDurationPartTwo);
    if (widget.repeatAnimation && mounted) {
      _play();
    }
  }

  Future<void> _animate({required double to, required Duration duration}) {
    final ScrollPositionWithSingleContext position =
        _scrollController.position as ScrollPositionWithSingleContext;
    final FakeDragScrollActivity activity = FakeDragScrollActivity(
      position,
      from: _scrollController.offset,
      to: to,
      duration: duration,
      curve: Curves.easeInOut,
      vsync: this,
    );
    _scrollController.position.beginActivity(activity);
    return activity.done;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      height: 400.0,
      width: 376.0,
      child: CustomScrollView(
        controller: _scrollController,
        slivers: <Widget>[
          SliverAppBar(
            primary: false,
            pinned: widget.pinned,
            snap: widget.snap,
            floating: widget.floating,
            title: const Text('App Bar'),
            expandedHeight: 180.0,
            leading: const Icon(Icons.menu),
          ),
          SliverList(
            delegate: SliverChildListDelegate(
              List<Widget>.generate(20, (int i) {
                return Container(
                  color: i.isEven ? Colors.white : Colors.black12,
                  height: 100.0,
                  child: Center(
                    child: Text('$i', textScaler: const TextScaler.linear(5)),
                  ),
                );
              }),
            ),
          ),
        ],
      ),
    );
  }
}

class SliverAppBarDiagramStep extends DiagramStep {
  @override
  final String category = 'material';

  final List<SliverAppBarDiagram> _diagrams = <SliverAppBarDiagram>[
    for (final bool pinned in <bool>[false, true])
      for (final bool floating in <bool>[false, true])
        // snap is only a legal option if floating is true.
        for (final bool snap in floating ? <bool>[false, true] : <bool>[false])
          SliverAppBarDiagram(pinned: pinned, floating: floating, snap: snap),
  ];

  @override
  Future<List<SliverAppBarDiagram>> get diagrams async => _diagrams;
}