kamino_intro.dart

import 'dart:convert';
import 'dart:io';
import 'dart:math' as math;
import 'dart:ui';

import 'package:async/async.dart';
import 'package:auto_size_text/auto_size_text.dart';
import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:flutter_material_color_picker/flutter_material_color_picker.dart';
import 'package:flutter_svg/svg.dart';
import 'package:kamino/api/realdebrid.dart';
import 'package:kamino/api/tmdb.dart';
import 'package:kamino/api/trakt.dart';
import 'package:kamino/generated/i18n.dart';
import 'package:kamino/interface/settings/page_appearance.dart';
import 'package:kamino/interface/settings/page_playback.dart';
import 'package:kamino/main.dart';
import 'package:kamino/models/content.dart';
import 'package:kamino/models/list.dart';
import 'package:dots_indicator/dots_indicator.dart';
import 'package:kamino/ui/elements.dart';
import 'package:kamino/ui/interface.dart';
import 'package:kamino/util/settings.dart';

class KaminoIntro extends StatefulWidget {

  final bool skipAnimation;
  final Function then;

  KaminoIntro({ this.then, this.skipAnimation = false });

  @override
  State<StatefulWidget> createState() => KaminoIntroState();

}

class KaminoIntroState extends State<KaminoIntro> with SingleTickerProviderStateMixin {

  KaminoAppState appState;

  Map<String, bool> _selectedCategories = {};

  bool traktConnected;
  bool rdConnected;
  PlayerSettings playerSettings;

  final Map<String, AsyncMemoizer> _categoryMemoizers = {};
  final _fadeInTween = Tween<double>(begin: 0, end: 1);
  AnimationController _animationController;
  Animation<double> _fadeInAnimation;

  PageController _controller;
  bool _detailedLayoutType;

  bool _handleKeyEvent(FocusNode node, RawKeyEvent event){
    const KEY_ENTER = 1108101562391;

    if(event.logicalKey != null && event.logicalKey.keyId == KEY_ENTER){
      final renderObject = context.findRenderObject();
      if(renderObject is RenderBox){
        // Get the currently focused node.
        FocusNode focusedNode = node.enclosingScope.children.first.children.where((node) => node.hasFocus).first;

        // Get a list of elements at the focused node's coordinates
        BoxHitTestResult result = BoxHitTestResult();
        renderObject.hitTest(result, position: focusedNode.rect.center);

        // Call handleEvent on that pointer event.
        result.path.forEach((entry){
          print(entry.target.runtimeType);

          if(entry.target is RenderSemanticsGestureHandler){
            var target = entry.target as RenderSemanticsGestureHandler;
            if(event is RawKeyDownEvent) target.onTap();
          }
        });

      }
      return true;
    }

    if(event is RawKeyDownEvent){
      if(event.logicalKey == LogicalKeyboardKey.arrowUp){
        node.focusInDirection(TraversalDirection.up);
        return true;
      }

      if(event.logicalKey == LogicalKeyboardKey.arrowDown){
        node.focusInDirection(TraversalDirection.down);
        return true;
      }

      if(event.logicalKey == LogicalKeyboardKey.arrowLeft){
        node.focusInDirection(TraversalDirection.left);
        return true;
      }

      if(event.logicalKey == LogicalKeyboardKey.arrowRight){
        node.focusInDirection(TraversalDirection.right);
        return true;
      }
    }

    return false;
  }

  @override
  void initState() {
    // Load default settings for layout type
    (Settings.detailedContentInfoEnabled as Future).then(
      (result) => setState(() => _detailedLayoutType = result)
    );

    (Settings.homepageCategories as Future).then(
      (result) => setState(() => _selectedCategories = jsonDecode(result).cast<String, bool>())
    );

    traktConnected = false;
    rdConnected = false;
    playerSettings = PlayerSettings.defaultPlayer();

    (() async {
      traktConnected = await Trakt.isAuthenticated();
      rdConnected = await RealDebrid.isAuthenticated();
      playerSettings = await Settings.playerInfo;
    })();

    // Initialize controller.
    _controller = PageController();
    _controller.addListener(() => setState((){}));

    // Initialize animation controller.
    _animationController = AnimationController(
      duration: const Duration(milliseconds: 2000),
      vsync: this
    );
    _animationController.addStatusListener((AnimationStatus status) => setState((){}));

    _fadeInAnimation = CurvedAnimation(
        parent: _animationController,
        curve: Interval(0.9, 1.0, curve: Curves.easeIn)
    );

    // Wait a second for the application to catch up.
    if(!widget.skipAnimation) Future.delayed(Duration(milliseconds: 500), () => _animationController.forward());
    else _animationController.value = 1.0;

    super.initState();
  }

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

  @override
  Widget build(BuildContext context){
    appState = context.ancestorStateOfType(const TypeMatcher<KaminoAppState>());

    final _pages = <Page>[
      Page(
        child: Builder(builder: (BuildContext context){
          const double size = 130;
          const double foregroundPadding = 30;

          final _rocketMotionTween = Tween<double>(begin: 0, end: ((MediaQuery.of(context).size.width / 2) + size));
          final _backgroundSizeTween = Tween<double>(begin: size, end: 0);
          final _rocketSizeTween = Tween<double>(begin: size - foregroundPadding, end: 0);

          final _rocketAnimation = CurvedAnimation(
              parent: _animationController,
              curve: Interval(0.2, 0.9, curve: ApolloRocketCurve())
          );

          // This animation is basically just used to clean up
          // the area after the rocket has animated away.
          final _rocketSizeAnimation = CurvedAnimation(
              parent: _animationController,
              curve: Interval(0.7, 0.9, curve: Curves.easeOut)
          );

          final _backgroundAnimation = CurvedAnimation(
            parent: _animationController,
            curve: Interval(0.7, 0.9, curve: Curves.easeOut),
          );

          return AnimatedBuilder(
              child: Padding(
                padding: EdgeInsets.symmetric(horizontal: 30),
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    TitleText(S.of(context).welcome_to_appname(appName), fontSize: 32, textAlign: TextAlign.center, allowOverflow: true),
                    Text(S.of(context).app_tagline, textAlign: TextAlign.center),

                    Container(padding: EdgeInsets.symmetric(vertical: 20)),

                    FlatButton.icon(
                      shape: Border(
                        top: BorderSide(color: Colors.white24),
                        bottom: BorderSide(color: Colors.white24),
                      ),
                      onPressed: () => Interface.showLanguageSelectionDialog(context),
                      icon: Icon(Icons.language, size: 24),
                      //label: Text(/*S.of(context).select_language*/),
                      label: Row(
                        mainAxisSize: MainAxisSize.min,
                        mainAxisAlignment: MainAxisAlignment.spaceBetween,
                        children: <Widget>[
                          Text(S.of(context).$_language_name, style: TextStyle(
                              fontSize: 16
                          ), textAlign: TextAlign.left),
                          Icon(Icons.arrow_drop_down)
                        ],
                      )
                    )
                  ],
                )
              ),
              animation: _animationController,
              builder: (BuildContext context, Widget child){
                var translateOffset = _rocketMotionTween.evaluate(_rocketAnimation);

                return Column(
                  children: <Widget>[
                    Stack(
                      alignment: Alignment.center,
                      children: <Widget>[
                        ClipRRect(
                          borderRadius: BorderRadius.circular(100),
                          child: Image.asset(
                            "assets/images/logo_background.png",
                            height: _backgroundSizeTween.evaluate(_backgroundAnimation),
                            width: _backgroundSizeTween.evaluate(_backgroundAnimation),
                          ),
                        ),

                        Transform.translate(
                          offset: Offset(translateOffset, -translateOffset),
                          child: Transform.rotate(
                            angle: math.pi / -15,
                            child: Image.asset(
                                "assets/images/logo_foreground_lg.png",
                                height: _rocketSizeTween.evaluate(_rocketSizeAnimation),
                                width: _rocketSizeTween.evaluate(_rocketSizeAnimation),
                                fit: BoxFit.cover
                            ),
                          ),
                        )
                      ],
                    ),

                    Offstage(offstage: _fadeInTween.evaluate(_fadeInAnimation) == 0, child: Opacity(
                      opacity: _fadeInTween.evaluate(_fadeInAnimation),
                      child: child,
                    ))
                  ],
                );
              }
          );
        }),
      ),

      Page(
        child: Builder(builder: (_) => Expanded(
          child: Scrollbar(
            child: Container(
              padding: EdgeInsets.all(20).copyWith(bottom: 0),
              width: MediaQuery.of(context).size.width,
              child: ListView(
                children: <Widget>[
                  TitleText(S.of(context).customize_appearance, fontSize: 32, allowOverflow: true),
                  Container(padding: EdgeInsets.symmetric(vertical: 10)),
                  Text(S.of(context).customize_appearance_description(appName), style: Theme.of(context).textTheme.caption.copyWith(fontSize: 14)),

                  Container(
                    margin: EdgeInsets.symmetric(vertical: 20),
                  ),

                  Form(
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: <Widget>[
                        Material(
                          elevation: 3,
                          borderRadius: BorderRadius.circular(5),
                          color: Theme.of(context).cardColor,
                          child: ListTile(
                            onTap: () => showThemeChoice(context, appState),
                            leading: Icon(Icons.style),
                            isThreeLine: true,
                            title: TitleText(S.of(context).choose_a_theme),
                            subtitle: Text(S.of(context).choose_a_theme_description),
                          ),
                        ),

                        Container(margin: EdgeInsets.symmetric(vertical: 5)),

                        Material(
                          elevation: 3,
                          borderRadius: BorderRadius.circular(5),
                          color: Theme.of(context).cardColor,
                          child: ListTile(
                            onTap: () => setPrimaryColor(context, appState),
                            leading: CircleColor(
                              circleSize: 32,
                              color: Theme.of(context).primaryColor,
                            ),
                            isThreeLine: true,
                            title: TitleText(S.of(context).whats_your_favorite_color),
                            subtitle: Text(S.of(context).whats_your_favorite_color_description),
                          ),
                        ),

                        Container(
                          padding: EdgeInsets.only(top: 30, left: 15, right: 15),
                          child: Column(
                            mainAxisSize: MainAxisSize.min,
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: <Widget>[
                              TitleText(
                                  S.of(context).which_do_you_prefer
                              ),
                              Padding(
                                padding: EdgeInsets.symmetric(vertical: 5),
                                child: Text(
                                    S.of(context).layout_preferences_subtitle,
                                    style: Theme.of(context).textTheme.caption.copyWith(fontSize: 14)
                                ),
                              ),
                              LayoutBuilder(builder: (BuildContext context, BoxConstraints constraints){
                                var _buttonElements = <Widget>[
                                  VerticalIconButton(
                                    backgroundColor: _detailedLayoutType ? Theme.of(context).primaryColor : null,
                                    onTap: () async {
                                      await (Settings.detailedContentInfoEnabled = true);
                                      _detailedLayoutType = await Settings.detailedContentInfoEnabled;
                                      setState(() {});
                                    },
                                    title: TitleText(S.of(context).card_layout),
                                    icon: Icon(Icons.view_agenda),
                                  ),
                                  VerticalIconButton(
                                    backgroundColor: !_detailedLayoutType ? Theme.of(context).primaryColor : null,
                                    onTap: () async {
                                      await (Settings.detailedContentInfoEnabled = false);
                                      _detailedLayoutType = await Settings.detailedContentInfoEnabled;
                                      setState(() {});
                                    },
                                    title: TitleText(S.of(context).grid_layout),
                                    icon: Icon(Icons.grid_on),
                                  )
                                ];

                                if(constraints.maxWidth < 300){
                                  return Column(
                                    crossAxisAlignment: CrossAxisAlignment.stretch,
                                    children: _buttonElements
                                        + [Container(padding: EdgeInsets.symmetric(vertical: 10))],
                                  );
                                }else{
                                  return ButtonBar(
                                    alignment: MainAxisAlignment.spaceBetween,
                                    children: _buttonElements,
                                  );
                                }
                              })
                            ],
                          ),
                        )
                      ],
                    ),
                  )
                ],
              ),
            )
          )
        )),
      ),

      Page(
        child: Builder(builder: (_) => Expanded(
            child: Scrollbar(
              child: Container(
                padding: EdgeInsets.all(20).copyWith(bottom: 0),
                width: MediaQuery.of(context).size.width,
                child: ListView(
                  children: <Widget>[
                    TitleText(S.of(context).general_settings, fontSize: 32),
                    Container(padding: EdgeInsets.symmetric(vertical: 10)),
                    Text(S.of(context).general_settings_description, style: Theme.of(context).textTheme.caption.copyWith(fontSize: 14)),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 20),
                    ),

                    (Platform.isAndroid) ? Material(
                      elevation: 3,
                      borderRadius: BorderRadius.circular(5),
                      color: Theme.of(context).cardColor,
                      child: ListTile(
                        onTap: () => PlaybackSettingsPage.showPlayerSelectDialog(context, onSelect: () async {
                          playerSettings = await Settings.playerInfo;
                          setState(() {});
                        }),
                        leading: Icon(Icons.play_circle_filled),
                        isThreeLine: false,
                        title: TitleText(S.of(context).choose_player),
                        subtitle: Text(
                            playerSettings.isValid() ? playerSettings.name : "${PlaybackSettingsPage.BUILT_IN_PLAYER_NAME} (${S.of(context).default_})"
                        ),
                      ),
                    ) : Container(child: Text("External players are not currently supported on iOS.", textAlign: TextAlign.center,)),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 30),
                    ),

                    TitleText(S.of(context).extensions, fontSize: 32),
                    Text(S.of(context).extensions_description(appName), style: Theme.of(context).textTheme.caption.copyWith(fontSize: 14)),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 20),
                    ),

                    Form(
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: <Widget>[
                          Material(
                            elevation: 3,
                            borderRadius: BorderRadius.circular(5),
                            color: Theme.of(context).cardColor,
                            child: ListTile(
                                onTap: () async {
                                  if(!traktConnected){
                                    if(await Trakt.authenticate(context)){
                                      Trakt.synchronize(context, silent: false);
                                      traktConnected = await Trakt.isAuthenticated();
                                      appState.setState(() {});
                                    }
                                  }else{
                                    await Trakt.deauthenticate(context);
                                    traktConnected = await Trakt.isAuthenticated();
                                    appState.setState(() {});
                                  }
                                },
                                leading: SvgPicture.asset("assets/icons/trakt.svg", height: 36, width: 36, color: const Color(0xFFED1C24)),
                                isThreeLine: true,
                                title: TitleText(traktConnected ? S.of(context).disconnect_your_trakt_account : S.of(context).connect_your_trakt_account),
                                subtitle: Text(S.of(context).appname_can_synchronise_your_watch_history_and_favorites_from_trakttv(appName))
                            ),
                          ),

                          Container(
                            margin: EdgeInsets.symmetric(vertical: 10),
                          ),

                          Material(
                            elevation: 3,
                            borderRadius: BorderRadius.circular(5),
                            color: Theme.of(context).cardColor,
                            child: ListTile(
                                onTap: () async {
                                  if(!rdConnected){
                                    await RealDebrid.authenticate(context);
                                    rdConnected = await RealDebrid.isAuthenticated();
                                    setState(() {});
                                  }else{
                                    await RealDebrid.deauthenticate(context);
                                    rdConnected = await RealDebrid.isAuthenticated();
                                    setState(() {});
                                  }
                                },
                                leading: SvgPicture.asset("assets/icons/realdebrid.svg", height: 36, width: 36, color: const Color(0xFF78BB6F)),
                                isThreeLine: true,
                                title: TitleText(rdConnected ? S.of(context).disconnect_your_realdebrid_account : S.of(context).connect_your_realdebrid_account),
                                subtitle: Text(S.of(context).realdebrid_service_info)
                            ),
                          )
                        ],
                      ),
                    ),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 20),
                    )
                  ],
                ),
              ),
            )
        )),
      ),

      Page(
        canProceedFunction: (){
          return _selectedCategories.length >= 3;
        },
        child: Builder(builder: (_) => Expanded(
            child: Scrollbar(
              child: Container(
                padding: EdgeInsets.all(20),
                width: MediaQuery.of(context).size.width,
                child: ListView(
                  children: <Widget>[
                    TitleText(S.of(context).choose_n_categories((3 - _selectedCategories.length < 0 ? 0 : 3 - _selectedCategories.length).toString()), fontSize: 32, allowOverflow: true),
                    Container(padding: EdgeInsets.symmetric(vertical: 10)),
                    Text(S.of(context).choose_n_categories_description, style: Theme.of(context).textTheme.caption.copyWith(fontSize: 14)),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 20),
                    ),

                    LayoutBuilder(
                      builder: (BuildContext context, BoxConstraints constraints){
                        double idealWidth = 200;
                        double spacing = 10.0;

                        List<String> curatedTMDBLists = [];
                        TMDB.curatedTMDBLists.forEach((ContentType type, List<String> typeCuratedLists){
                          typeCuratedLists.forEach((String entry){
                            curatedTMDBLists.add("$entry|${getPrettyContentType(type, plural: true)}");
                          });
                        });

                        return GridView.builder(
                          shrinkWrap: true,
                          physics: NeverScrollableScrollPhysics(),
                          gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                              crossAxisCount: (constraints.maxWidth / idealWidth).round(),
                              childAspectRatio: 2,
                              mainAxisSpacing: spacing,
                              crossAxisSpacing: spacing
                          ),
                          itemCount: curatedTMDBLists.length,
                          itemBuilder: (BuildContext context, int index){
                            if(!_categoryMemoizers.containsKey(curatedTMDBLists[index]))
                              _categoryMemoizers[curatedTMDBLists[index]] = new AsyncMemoizer();

                            return FutureBuilder(
                                future: _categoryMemoizers[curatedTMDBLists[index]].runOnce(
                                        () async => { "list": await TMDB.getList(context, int.parse(curatedTMDBLists[index].split("|")[0])), "type": curatedTMDBLists[index].split("|")[1] }
                                ),
                                builder: (BuildContext context, AsyncSnapshot snapshot){
                                  if(snapshot.hasError){
                                    print("Error loading list: ${curatedTMDBLists[index]}");
                                    return Container();
                                  }

                                  switch(snapshot.connectionState){
                                    case ConnectionState.none:
                                    case ConnectionState.waiting:
                                    case ConnectionState.active:
                                      return Center(
                                        child: CircularProgressIndicator(),
                                      );

                                    case ConnectionState.done:
                                      ContentListModel list = snapshot.data['list'];
                                      String type = snapshot.data['type'];

                                      return Material(
                                        type: MaterialType.card,
                                        borderRadius: BorderRadius.circular(5),
                                        clipBehavior: Clip.antiAlias,
                                        child: Stack(
                                          fit: StackFit.expand,
                                          alignment: Alignment.center,
                                          children: <Widget>[
                                            CachedNetworkImage(
                                              imageUrl: TMDB.IMAGE_CDN_LOWRES + list.backdrop,
                                              fit: BoxFit.cover,
                                            ),

                                            Container(
                                              color: const Color(0x7F000000),
                                              child: Center(child: Padding(
                                                padding: EdgeInsets.symmetric(horizontal: 5),
                                                child: Column(
                                                  mainAxisSize: MainAxisSize.min,
                                                  children: <Widget>[
                                                    AutoSizeText(
                                                      list.name,
                                                      style: TextStyle(
                                                          fontSize: 18,
                                                          fontFamily: 'GlacialIndifference'
                                                      ),
                                                      softWrap: true,
                                                      maxLines: 1,
                                                      maxFontSize: 18,
                                                      textAlign: TextAlign.center,
                                                    ),

                                                    Text(type)
                                                  ],
                                                ),
                                              )),
                                            ),

                                            AnimatedOpacity(child: Container(
                                              color: const Color(0x9F000000),
                                              child: Center(
                                                child: Icon(Icons.check),
                                              ),
                                            ), opacity: _selectedCategories.containsKey(list.id.toString()) ? 1 : 0,
                                                duration: Duration(milliseconds: 300)),

                                            Material(
                                              color: Colors.transparent,
                                              child: InkWell(
                                                onTap: () => setState((){
                                                  _selectedCategories.containsKey(list.id.toString())
                                                      ? _selectedCategories.remove(list.id.toString())
                                                      : _selectedCategories[list.id.toString()] = true;
                                                }),
                                              ),
                                            )
                                          ],
                                        ),
                                      );
                                  }
                                }
                            );
                          },
                        );
                      },
                    ),

                    Container(
                      margin: EdgeInsets.symmetric(vertical: 20),
                    )
                  ],
                ),
              ),
            )
        )),
      )
    ];

    bool onFirstPage(){
      return _controller.hasClients && _controller.page.round() == 0;
    }

    bool onLastPage(){
      return _controller.hasClients && _controller.page.round() == (_pages.length - 1);
    }

    return DefaultFocusTraversal(
        policy: ReadingOrderTraversalPolicy(),
        child: FocusScope(
            onKey: _handleKeyEvent,
            autofocus: true,
            child: Scaffold(
              appBar: AppBar(
                leading: new Container(),
                backgroundColor: Theme.of(context).backgroundColor,
                elevation: 0,

                centerTitle: true,
                title: Interface.generateHeaderLogo(context),
              ),

              backgroundColor: Theme.of(context).backgroundColor,

              body: NotificationListener<OverscrollIndicatorNotification>(
                  onNotification: (notification){
                    notification.disallowGlow();
                    return true;
                  },
                  child: IgnorePointer(
                    ignoring: !_animationController.isCompleted,
                    child: PageView.builder(
                      controller: _controller,
                      itemCount: _pages.length,
                      itemBuilder: (BuildContext context, int index){
                        return _pages[index];
                      },
                    ),
                  )
              ),

              bottomNavigationBar: AnimatedBuilder(
                animation: _animationController,
                builder: (BuildContext context, Widget child) => IgnorePointer(
                  ignoring: !_fadeInAnimation.isCompleted,
                  child: Opacity(
                      opacity: _fadeInTween.evaluate(_fadeInAnimation),
                      child: Container(
                        child: child,
                      )
                  ),
                ),

                child: Container(
                  padding: EdgeInsets.symmetric(horizontal: 10, vertical: 10),
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: <Widget>[
                      FlatButton(
                        onPressed: (){
                          if(onFirstPage()){
                            Navigator.of(context).pop();
                            Settings.initialSetupComplete = true;

                            // Perform OTA check now.
                            if(widget.then != null) widget.then();
                          }
                          else _controller.previousPage(duration: Duration(milliseconds: 300), curve: Curves.easeInOut);
                        },
                        highlightColor: Colors.transparent,
                        child: Text(onFirstPage() ? S.of(context).skip : S.of(context).back, style: TextStyle(
                            fontSize: 16
                        )),
                        padding: EdgeInsets.symmetric(vertical: 15),
                        materialTapTargetSize: MaterialTapTargetSize.padded,
                      ),

                      DotsIndicator(
                          position: _controller.hasClients ? _controller.page.round() : _controller.initialPage,
                          decorator: DotsDecorator(
                            activeShape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(5.0)),
                            activeColor: Theme.of(context).primaryColor,
                            activeSize: const Size(18.0, 9.0),
                          ),
                          dotsCount: _pages.length
                      ),

                      new FlatButton(
                        onPressed: _pages[_controller.hasClients ? _controller.page.round() : _controller.initialPage]._canProceed() ? (){
                          // DONE BUTTON?: onLastPage
                          if(onLastPage()){
                            // Write settings.
                            Settings.homepageCategories = jsonEncode(_selectedCategories);
                            Settings.initialSetupComplete = true;

                            Navigator.of(context).pop();

                            // Perform OTA check now.
                            if(widget.then != null) widget.then();

                            return;
                          }

                          _controller.nextPage(duration: Duration(milliseconds: 300), curve: Curves.easeInOut);
                        } : null,
                        highlightColor: Colors.transparent,
                        child: Text(onLastPage() ? S.of(context).lets_go : S.of(context).next, style: TextStyle(
                            fontSize: 16
                        )),
                        padding: EdgeInsets.symmetric(vertical: 15),
                        materialTapTargetSize: MaterialTapTargetSize.padded,
                      )
                    ],
                  ),
                ),
              ),
            )
        )
    );
  }

}

class Page extends StatelessWidget {

  final Builder child;
  final Function canProceedFunction;

  get _canProceed => (){
    if(canProceedFunction != null) return canProceedFunction();
    return true;
  };

  Page({
    @required this.child,
    this.canProceedFunction
  });

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        child.build(context)
      ]
    );
  }

}

class ApolloRocketCurve extends ElasticInCurve {

  @override
  double transformInternal(double t) {
    final double s = period / 4.0;
    t = t - 1.0;
    return -math.pow(2.0, 10.0 * t) * math.sin((t - s) * (math.pi * 1.0) / period);
  }

}