aves/lib/widgets/viewer/entry_vertical_pager.dart

import 'dart:async';
import 'dart:math';

import 'package:aves/model/entry.dart';
import 'package:aves/model/source/collection_lens.dart';
import 'package:aves/theme/durations.dart';
import 'package:aves/widgets/common/magnifier/pan/scroll_physics.dart';
import 'package:aves/widgets/viewer/entry_horizontal_pager.dart';
import 'package:aves/widgets/viewer/info/info_page.dart';
import 'package:aves/widgets/viewer/info/notifications.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';

class ViewerVerticalPageView extends StatefulWidget {
  final CollectionLens? collection;
  final ValueNotifier<AvesEntry?> entryNotifier;
  final PageController horizontalPager, verticalPager;
  final void Function(int page) onVerticalPageChanged, onHorizontalPageChanged;
  final VoidCallback onImagePageRequested;
  final void Function(AvesEntry mainEntry, AvesEntry? pageEntry) onViewDisposed;

  const ViewerVerticalPageView({
    Key? key,
    required this.collection,
    required this.entryNotifier,
    required this.verticalPager,
    required this.horizontalPager,
    required this.onVerticalPageChanged,
    required this.onHorizontalPageChanged,
    required this.onImagePageRequested,
    required this.onViewDisposed,
  }) : super(key: key);

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

class _ViewerVerticalPageViewState extends State<ViewerVerticalPageView> {
  final ValueNotifier<Color> _backgroundColorNotifier = ValueNotifier(Colors.black);
  final ValueNotifier<bool> _isVerticallyScrollingNotifier = ValueNotifier(false);
  Timer? _verticalScrollMonitoringTimer;
  AvesEntry? _oldEntry;

  CollectionLens? get collection => widget.collection;

  bool get hasCollection => collection != null;

  AvesEntry? get entry => widget.entryNotifier.value;

  @override
  void initState() {
    super.initState();
    _registerWidget(widget);
  }

  @override
  void didUpdateWidget(covariant ViewerVerticalPageView oldWidget) {
    super.didUpdateWidget(oldWidget);
    _unregisterWidget(oldWidget);
    _registerWidget(widget);
  }

  @override
  void dispose() {
    _unregisterWidget(widget);
    _stopScrollMonitoringTimer();
    super.dispose();
  }

  void _registerWidget(ViewerVerticalPageView widget) {
    widget.verticalPager.addListener(_onVerticalPageControllerChanged);
    widget.entryNotifier.addListener(_onEntryChanged);
    if (_oldEntry != entry) _onEntryChanged();
  }

  void _unregisterWidget(ViewerVerticalPageView widget) {
    widget.verticalPager.removeListener(_onVerticalPageControllerChanged);
    widget.entryNotifier.removeListener(_onEntryChanged);
    _oldEntry?.imageChangeNotifier.removeListener(_onImageChanged);
  }

  @override
  Widget build(BuildContext context) {
    // fake page for opacity transition between collection and viewer
    const transitionPage = SizedBox();

    final imagePage = hasCollection
        ? MultiEntryScroller(
            collection: collection!,
            pageController: widget.horizontalPager,
            onPageChanged: widget.onHorizontalPageChanged,
            onViewDisposed: widget.onViewDisposed,
          )
        : entry != null
            ? SingleEntryScroller(
                entry: entry!,
              )
            : const SizedBox();

    final infoPage = NotificationListener<ShowImageNotification>(
      onNotification: (notification) {
        widget.onImagePageRequested();
        return true;
      },
      child: AnimatedBuilder(
        animation: widget.verticalPager,
        builder: (context, child) {
          return Visibility(
            visible: widget.verticalPager.page! > 1,
            child: child!,
          );
        },
        child: InfoPage(
          collection: collection,
          entryNotifier: widget.entryNotifier,
          isScrollingNotifier: _isVerticallyScrollingNotifier,
        ),
      ),
    );

    final pages = [
      transitionPage,
      imagePage,
      infoPage,
    ];
    return ValueListenableBuilder<Color>(
      valueListenable: _backgroundColorNotifier,
      builder: (context, backgroundColor, child) => Container(
        color: backgroundColor,
        child: child,
      ),
      child: PageView(
        // key is expected by test driver
        key: const Key('vertical-pageview'),
        scrollDirection: Axis.vertical,
        controller: widget.verticalPager,
        physics: const MagnifierScrollerPhysics(parent: PageScrollPhysics()),
        onPageChanged: widget.onVerticalPageChanged,
        children: pages,
      ),
    );
  }

  void _onVerticalPageControllerChanged() {
    final opacity = min(1.0, widget.verticalPager.page!);
    _backgroundColorNotifier.value = _backgroundColorNotifier.value.withOpacity(opacity * opacity);

    _isVerticallyScrollingNotifier.value = true;
    _stopScrollMonitoringTimer();
    _verticalScrollMonitoringTimer = Timer(Durations.infoScrollMonitoringTimerDelay, () {
      _isVerticallyScrollingNotifier.value = false;
    });
  }

  void _stopScrollMonitoringTimer() {
    _verticalScrollMonitoringTimer?.cancel();
  }

  // when the entry changed (e.g. by scrolling through the PageView, or if the entry got deleted)
  Future<void> _onEntryChanged() async {
    _oldEntry?.imageChangeNotifier.removeListener(_onImageChanged);
    _oldEntry = entry;

    final _entry = entry;
    if (_entry != null) {
      _entry.imageChangeNotifier.addListener(_onImageChanged);
      // make sure to locate the entry,
      // so that we can display the address instead of coordinates
      // even when initial collection locating has not reached this entry yet
      await _entry.catalog(background: false, persist: true, force: false);
      await _entry.locate(background: false, force: false);
    } else {
      Navigator.pop(context);
    }

    // needed to refresh when entry changes but the page does not (e.g. on page deletion)
    setState(() {});
  }

  // when the entry image itself changed (e.g. after rotation)
  void _onImageChanged() async {
    // rebuild to refresh the Image inside ImagePage
    setState(() {});
  }
}