com.unity.uiwidgets/com.unity.uiwidgets/Runtime/widgets/routes.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Unity.UIWidgets.animation;
using Unity.UIWidgets.async;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.scheduler;
using Unity.UIWidgets.ui;

namespace Unity.UIWidgets.widgets {
    public abstract class OverlayRoute : Route {
       

        public OverlayRoute(
            RouteSettings settings = null
        ) : base(settings : settings) {
        }
        public override List<OverlayEntry> overlayEntries {
            get { return _overlayEntries; }
        }
        public readonly List<OverlayEntry> _overlayEntries = new List<OverlayEntry>();

        protected virtual bool finishedWhenPopped {
            get { return true; }
        }

        public abstract IEnumerable<OverlayEntry> createOverlayEntries();

        protected internal override void install(){
            D.assert(_overlayEntries.isEmpty());
            _overlayEntries.AddRange(createOverlayEntries());
            base.install();
        } 
        protected internal override bool didPop(object result) {
            var returnValue = base.didPop(result);
            D.assert(returnValue);
            if (finishedWhenPopped) {
                navigator.finalizeRoute(this);
            }
            return returnValue;
        }

        public override void dispose() {
            _overlayEntries.Clear();
            base.dispose();
        }
    }

    public abstract class OverlayRoute<T> : OverlayRoute {
        public readonly List<OverlayEntry> _overlayEntries = new List<OverlayEntry>();
        public OverlayRoute(
            RouteSettings settings = null
        ) : base(settings : settings) {
        }
        protected internal new bool didPop(T result) {
            var returnValue = base.didPop(result);
            D.assert(returnValue);
            if (finishedWhenPopped) {
                navigator.finalizeRoute(this);
            }
            return returnValue;
        }
      
    }

    public abstract class TransitionRoute : OverlayRoute {
        public TransitionRoute(
            RouteSettings settings = null
            ) : base(settings) {
        }

        public Future completed {
            get { return _transitionCompleter.future; }
        }
        internal readonly Completer _transitionCompleter = Completer.create();

        public virtual TimeSpan transitionDuration { get; }

        public virtual TimeSpan reverseTransitionDuration {
            get { return transitionDuration; }
        }
        public virtual bool opaque { get; }


        protected override bool finishedWhenPopped {
            get { return controller.status == AnimationStatus.dismissed; }
        }

        public virtual Animation<float> animation {
            get { return _animation; }
        }
        internal Animation<float> _animation;

        public AnimationController controller {
            get { return _controller; }
        }
        internal AnimationController _controller;

        public virtual Animation<float> secondaryAnimation {
            get { return _secondaryAnimation; }
        }
        readonly ProxyAnimation _secondaryAnimation = new ProxyAnimation(Animations.kAlwaysDismissedAnimation);

        public virtual AnimationController createAnimationController() {
            D.assert(!_transitionCompleter.isCompleted,
                () => $"Cannot reuse a {GetType()} after disposing it.");
            TimeSpan duration = transitionDuration;
            TimeSpan reverseDuration = reverseTransitionDuration;
            D.assert(duration >= TimeSpan.Zero && duration != null);
            return new AnimationController(
                duration: duration,
                reverseDuration: reverseDuration, 
                debugLabel: debugLabel,
                vsync: navigator
            );
        }

        public virtual Animation<float> createAnimation() {
            D.assert(!_transitionCompleter.isCompleted,
                () => $"Cannot reuse a {GetType()} after disposing it.");
            D.assert(_controller != null);
            return _controller.view;
        }

        object _result;

        internal void _handleStatusChanged(AnimationStatus status) {
            switch (status) {
                case AnimationStatus.completed:
                    if (overlayEntries.isNotEmpty()) {
                        overlayEntries.first().opaque = opaque;
                    }
                    break;
                
                case AnimationStatus.forward:
                case AnimationStatus.reverse:
                    if (overlayEntries.isNotEmpty()) {
                        overlayEntries.first().opaque = false;
                    }

                    break;
                case AnimationStatus.dismissed:
                    
                    if (!isActive) {
                        navigator.finalizeRoute(this);
                        D.assert(overlayEntries.isEmpty());
                    }

                    break;
            }

            changedInternalState();
        }

       
        protected internal override void install() {
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot install a {GetType()} after disposing it.");
            _controller = createAnimationController();
            D.assert(_controller != null, () => $"{GetType()}.createAnimationController() returned null.");
            _animation = createAnimation();
            D.assert(_animation != null, () => $"{GetType()}.createAnimation() returned null.");
            base.install();
        }

        protected internal override TickerFuture didPush() {
            D.assert(_controller != null,
                () => $"{GetType()}.didPush called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            _didPushOrReplace();
            base.didPush();
            return _controller.forward();
        }
        protected internal override void didAdd() {
            D.assert(_controller != null,
                () => $"{GetType()}.didPush called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            _didPushOrReplace();
            base.didAdd();
            _controller.setValue(_controller.upperBound); 
        }
        protected internal override void didReplace(Route oldRoute) {
            D.assert(_controller != null,
                () => $"{GetType()}.didReplace called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            if (oldRoute is TransitionRoute) {
                _controller.setValue(((TransitionRoute)oldRoute)._controller.value);
            }
            _didPushOrReplace();
            base.didReplace(oldRoute);
        }
        public void _didPushOrReplace() {
            _animation.addStatusListener(_handleStatusChanged);
           if (_animation.isCompleted && overlayEntries.isNotEmpty()) {
                overlayEntries[0].opaque = opaque;
            }
        }
        protected internal override bool didPop(object result) {
            D.assert(_controller != null,
                () => $"{GetType()}.didPop called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            _result = result;
            _controller.reverse();
            return base.didPop(result);
        }

        protected internal override void didPopNext(Route nextRoute) {
            D.assert(_controller != null,
                () => $"{GetType()}.didPopNext called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            _updateSecondaryAnimation(nextRoute);
            base.didPopNext(nextRoute);
        }

        protected internal override void didChangeNext(Route nextRoute) {
            D.assert(_controller != null,
                () => $"{GetType()}.didChangeNext called before calling install() or after calling dispose().");
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot reuse a {GetType()} after disposing it.");
            _updateSecondaryAnimation(nextRoute);
            base.didChangeNext(nextRoute);
        }
        VoidCallback _trainHoppingListenerRemover;
        void _updateSecondaryAnimation(Route nextRoute) {
            VoidCallback previousTrainHoppingListenerRemover = _trainHoppingListenerRemover;
            _trainHoppingListenerRemover = null;
            if (nextRoute is TransitionRoute && canTransitionTo((TransitionRoute)nextRoute) &&
                ((TransitionRoute) nextRoute).canTransitionFrom((TransitionRoute)this)) {
                Animation<float> current = _secondaryAnimation.parent;
                if (current != null) {
                    Animation<float> currentTrain = current is TrainHoppingAnimation ? ((TrainHoppingAnimation)current).currentTrain : current;
                    Animation<float> nextTrain = ((TransitionRoute)nextRoute)._animation;
                    if (
                        currentTrain.value == nextTrain.value ||
                        nextTrain.status == AnimationStatus.completed ||
                        nextTrain.status == AnimationStatus.dismissed
                    ) { 
                        _setSecondaryAnimation(nextTrain, ((TransitionRoute)nextRoute).completed);
                    } else {
                        
                        TrainHoppingAnimation newAnimation = null;
                        void _jumpOnAnimationEnd(AnimationStatus status) { 
                            switch (status) { 
                                case AnimationStatus.completed:
                                case AnimationStatus.dismissed:
                                    _setSecondaryAnimation(nextTrain, ((TransitionRoute)nextRoute).completed); 
                                    if (_trainHoppingListenerRemover != null) {
                                        _trainHoppingListenerRemover();
                                        _trainHoppingListenerRemover = null;
                                    } 
                                    break;
                                case AnimationStatus.forward:
                                case AnimationStatus.reverse: 
                                    break; 
                            } 
                        } 
                        _trainHoppingListenerRemover = ()=> {
                            nextTrain.removeStatusListener(_jumpOnAnimationEnd);
                            newAnimation?.dispose();
                        };
                        nextTrain.addStatusListener(_jumpOnAnimationEnd);
                        newAnimation = new TrainHoppingAnimation(
                            currentTrain,
                            nextTrain,
                            onSwitchedTrain: ()=> { 
                                D.assert(_secondaryAnimation.parent == newAnimation); 
                                D.assert(newAnimation.currentTrain == ((TransitionRoute)nextRoute)._animation); 
                                _setSecondaryAnimation(newAnimation.currentTrain, ((TransitionRoute)nextRoute).completed); 
                                if (_trainHoppingListenerRemover != null) { 
                                    _trainHoppingListenerRemover(); 
                                    _trainHoppingListenerRemover = null; 
                                } 
                            }
                      );
                      _setSecondaryAnimation(newAnimation, ((TransitionRoute)nextRoute).completed);
                    }
                } else {
                    _setSecondaryAnimation(((TransitionRoute)nextRoute)._animation, ((TransitionRoute)nextRoute).completed);
                }
            } else {
                _setSecondaryAnimation(Animations.kAlwaysDismissedAnimation);
            }
               
            if (previousTrainHoppingListenerRemover != null) {
                previousTrainHoppingListenerRemover();
            }
        }

        public void _setSecondaryAnimation(Animation<float> animation, Future disposed = null) {
            _secondaryAnimation.parent = animation;
            disposed?.then(( _) =>{
                if (_secondaryAnimation.parent == animation) {
                    _secondaryAnimation.parent = Animations.kAlwaysDismissedAnimation;
                    if (animation is TrainHoppingAnimation) {
                        ((TrainHoppingAnimation)animation).dispose();
                    }
                }
            });
        }



        public virtual bool canTransitionTo(TransitionRoute nextRoute) {
            return true;
        }

        public virtual bool canTransitionFrom(TransitionRoute previousRoute) {
            return true;
        }

        public override void dispose() {
            D.assert(!_transitionCompleter.isCompleted, () => $"Cannot dispose a {GetType()} twice.");
            _controller?.dispose();
            _transitionCompleter.complete(FutureOr.value(_result));
            base.dispose();
        }

        public string debugLabel {
            get { return $"{GetType()}"; }
        }

        public override string ToString() {
            return $"{GetType()}(animation: {_controller}";
        }
    }

    

    public class LocalHistoryEntry {
        public LocalHistoryEntry(VoidCallback onRemove = null) {
            this.onRemove = onRemove;
        }

        public readonly VoidCallback onRemove;

        internal LocalHistoryRoute _owner;

        public void remove() {
            _owner.removeLocalHistoryEntry(this);
            D.assert(_owner == null);
        }

        internal void _notifyRemoved() {
            onRemove?.Invoke();
        }
    }
    
    public interface LocalHistoryRoute {
        void addLocalHistoryEntry(LocalHistoryEntry entry);
        void removeLocalHistoryEntry(LocalHistoryEntry entry);

        Route route { get; }
    }

    // todo make it to mixin
    public abstract class LocalHistoryRouteTransitionRoute : TransitionRoute, LocalHistoryRoute {
        List<LocalHistoryEntry> _localHistory;

        protected LocalHistoryRouteTransitionRoute(RouteSettings settings = null) : base(settings: settings) {
        }

        public void addLocalHistoryEntry(LocalHistoryEntry entry) {
            D.assert(entry._owner == null);
            entry._owner = this;
            _localHistory = _localHistory ?? new List<LocalHistoryEntry>();
            var wasEmpty = _localHistory.isEmpty();
            _localHistory.Add(entry);
            if (wasEmpty) {
                changedInternalState();
            }
        }

        public void removeLocalHistoryEntry(LocalHistoryEntry entry) {
            D.assert(entry != null);
            D.assert(entry._owner == this);
            D.assert(_localHistory.Contains(entry));
            _localHistory.Remove(entry);
            entry._owner = null;
            entry._notifyRemoved();
            if (_localHistory.isEmpty()) {
                if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
                    SchedulerBinding.instance.addPostFrameCallback((TimeSpan timestamp) =>{
                        changedInternalState();
                    });
                } else {
                    changedInternalState();
                }
            }
        }

        public override Future<RoutePopDisposition> willPop() {
            //async
            if (willHandlePopInternally) {
                return Future.value(RoutePopDisposition.pop).to<RoutePopDisposition>();
            }
            return base.willPop();
        }

        protected internal override bool didPop(object result) {
            if (_localHistory != null && _localHistory.isNotEmpty()) {
                var entry = _localHistory.removeLast();
                D.assert(entry._owner == this);
                entry._owner = null;
                entry._notifyRemoved();
                if (_localHistory.isEmpty()) {
                    changedInternalState();
                }

                return false;
            }

            return base.didPop(result);
        }

        public override bool willHandlePopInternally {
            get { return _localHistory != null && _localHistory.isNotEmpty(); }
        }

        public Route route {
            get { return this; }
        }
    }


    public class _ModalScopeStatus : InheritedWidget {
        public _ModalScopeStatus(
            Key key = null, 
            bool isCurrent = false,
            bool canPop = false, 
            Route route = null, 
            Widget child = null) 
            : base(key: key, child: child) {
            D.assert(route != null);
            D.assert(child != null);

            this.isCurrent = isCurrent;
            this.canPop = canPop;
            this.route = route;
        }

        public readonly bool isCurrent;
        public readonly bool canPop;
        public readonly Route route;

        public override bool updateShouldNotify(InheritedWidget oldWidget) {
            return isCurrent != ((_ModalScopeStatus) oldWidget).isCurrent ||
                   canPop != ((_ModalScopeStatus) oldWidget).canPop ||
                   route != ((_ModalScopeStatus) oldWidget).route;
        }

        public override void debugFillProperties(DiagnosticPropertiesBuilder description) {
            base.debugFillProperties(description);
            description.add(new FlagProperty("isCurrent", value: isCurrent, ifTrue: "active",
                ifFalse: "inactive"));
            description.add(new FlagProperty("canPop", value: canPop, ifTrue: "can pop"));
        }
    }

    public class _ModalScope : StatefulWidget {
        public _ModalScope(
            Key key = null, 
            ModalRoute route = null) 
            : base(key) {
            this.route = route;
        }

        public readonly ModalRoute route;

        public override State createState() {
            return new _ModalScopeState();
        }
    }
    public class _ModalScope<T> : _ModalScope {
        public _ModalScope(
            Key key = null, 
            ModalRoute<T> route = null) 
            : base(key, route) {
            this.route = route;
        }

        public new readonly ModalRoute<T> route;

        public override State createState() {
            return new _ModalScopeState<T>();
        }
    }
    

    public class _ModalScopeState : State<_ModalScope> {
        Widget _page;

        Listenable _listenable;

        public readonly FocusScopeNode focusScopeNode = new FocusScopeNode(debugLabel: $"{typeof(_ModalScopeState)} Focus Scope");
        public override void initState() {
            base.initState();
            var animations = new List<Listenable>();
            if (widget.route.animation != null) {
                animations.Add(widget.route.animation);
            }

            if (widget.route.secondaryAnimation != null) {
                animations.Add(widget.route.secondaryAnimation);
            }
            _listenable = ListenableUtils.merge(animations);
            if (widget.route.isCurrent) {
                widget.route.navigator.focusScopeNode.setFirstFocus(focusScopeNode);
            }
        }

        public override void didUpdateWidget(StatefulWidget oldWidget) {
            base.didUpdateWidget(oldWidget);
            D.assert(widget.route == ((_ModalScope) oldWidget).route);
            if (widget.route.isCurrent) {
                widget.route.navigator.focusScopeNode.setFirstFocus(focusScopeNode);
            }
        }

        public override void didChangeDependencies() {
            base.didChangeDependencies();
            _page = null;
        }

        internal void _forceRebuildPage() {
            setState(() => { _page = null; });
        }
        public override void dispose() {
            focusScopeNode.dispose();
            base.dispose();
        }
        bool _shouldIgnoreFocusRequest {
            get {
                return widget.route.animation?.status == AnimationStatus.reverse ||
                       (widget.route.navigator?.userGestureInProgress ?? false);
            }
        }
        internal void _routeSetState(VoidCallback fn) {
            if (widget.route.isCurrent && !_shouldIgnoreFocusRequest) {
                widget.route.navigator.focusScopeNode.setFirstFocus(focusScopeNode);
            }
            setState(fn);
        }

        public override Widget build(BuildContext context) {
            _page = _page ?? new RepaintBoundary(
                key: widget.route._subtreeKey, // immutable
                child: new Builder(
                    builder: (BuildContext _context) => widget.route.buildPage(
                        _context,
                        widget.route.animation,
                        widget.route.secondaryAnimation
                    ))
            );

            return new _ModalScopeStatus(
                route: widget.route,
                isCurrent: widget.route.isCurrent,
                canPop: widget.route.canPop,
                child: new Offstage(
                    offstage: widget.route.offstage,
                    child: new PageStorage(
                        bucket: widget.route._storageBucket,
                        child: new FocusScope(
                            node: focusScopeNode,
                            child: new RepaintBoundary(
                                child: new AnimatedBuilder(
                                    animation: _listenable, // immutable
                                    builder: (BuildContext _context, Widget child) =>
                                        widget.route.buildTransitions(
                                            _context,
                                            widget.route.animation,
                                            widget.route.secondaryAnimation,
                                            new AnimatedBuilder(
                                                animation: widget.route.navigator?.userGestureInProgressNotifier ?? new ValueNotifier<bool>(false),
                                                builder: (BuildContext context1, Widget child1) =>{
                                                    bool ignoreEvents = _shouldIgnoreFocusRequest;
                                                    focusScopeNode.canRequestFocus = !ignoreEvents; 
                                                    return new IgnorePointer(
                                                        ignoring: ignoreEvents,
                                                        child: child1
                                                    );
                                                },
                                                child: child
                                             )
                                        ),
                                    child: _page  = _page ?? new RepaintBoundary(
                                        key: widget.route._subtreeKey, // immutable
                                        child: new Builder(
                                            builder: (BuildContext context2) =>{
                                                return widget.route.buildPage(
                                                    context2,
                                                    widget.route.animation,
                                                    widget.route.secondaryAnimation
                                                );
                                            }
                                        )
                                    )
                                )
                            )
                        )
                    )
                )
            );
        }
    }

    public class _ModalScopeState<T> : _ModalScopeState {
        public override void didUpdateWidget(StatefulWidget oldWidget) {
            base.didUpdateWidget(oldWidget);
            D.assert(widget.route == ((_ModalScope<T>) oldWidget).route);
            if (widget.route.isCurrent) {
                widget.route.navigator.focusScopeNode.setFirstFocus(focusScopeNode);
            }
        }
    }



    public abstract class ModalRoute : LocalHistoryRouteTransitionRoute {
        
        protected ModalRoute(
            RouteSettings settings = null,
            ImageFilter filter = null
            ) : base(settings) {
            _filter = filter;
        }

        public ImageFilter _filter;
        public static Color _kTransparent = new Color(0x00000000);

        public static ModalRoute of(BuildContext context) {
            _ModalScopeStatus widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
            return widget?.route as ModalRoute;
        }

        protected virtual void setState(VoidCallback fn) {
            if (_scopeKey.currentState != null) {
                _scopeKey.currentState._routeSetState(fn);
            }
            else {
                fn();
            }
        }

        public static RoutePredicate withName(string name) {
            return (Route route) => !route.willHandlePopInternally
                                    && route is ModalRoute
                                    && route.settings.name == name;
        }

        public abstract Widget buildPage(BuildContext context, Animation<float> animation,
            Animation<float> secondaryAnimation);

        public virtual Widget buildTransitions(
            BuildContext context,
            Animation<float> animation,
            Animation<float> secondaryAnimation,
            Widget child
        ) {
            return child;
        }

        public readonly FocusScopeNode focusScopeNode = new FocusScopeNode();

        protected internal override void install() {
            base.install();
            _animationProxy = new ProxyAnimation(base.animation);
            _secondaryAnimationProxy = new ProxyAnimation(base.secondaryAnimation);
        }

        protected internal override TickerFuture didPush() {
            if (_scopeKey.currentState != null) {
                navigator.focusScopeNode.setFirstFocus(_scopeKey.currentState.focusScopeNode);
            }
            return base.didPush();
        }
        protected internal override void didAdd() {
            if (_scopeKey.currentState != null) {
                navigator.focusScopeNode.setFirstFocus(_scopeKey.currentState.focusScopeNode);
            }
            base.didAdd();
        }
        

        public virtual bool barrierDismissible { get; }
        
        public virtual bool semanticsDismissible {
            get { return true; }
        }

        public virtual Color barrierColor { get; }
        public virtual string barrierLabel { get; }

        public virtual Curve barrierCurve {
            get { return  Curves.ease;}
        }
        public virtual bool maintainState { get; }

        public virtual bool offstage {
            get { return _offstage; }
            set {
                if (_offstage == value) {
                    return;
                }

                setState(() => { _offstage = value; });
                _animationProxy.parent = _offstage ? Animations.kAlwaysCompleteAnimation : base.animation;
                _secondaryAnimationProxy.parent =
                    _offstage ? Animations.kAlwaysDismissedAnimation : base.secondaryAnimation;
            }
        }

        bool _offstage = false;

        public BuildContext subtreeContext {
            get { return _subtreeKey.currentContext; }
        }

        public override Animation<float> animation {
            get { return _animationProxy; }
        }
        ProxyAnimation _animationProxy;

        public override Animation<float> secondaryAnimation {
            get { return _secondaryAnimationProxy; }
        }
        ProxyAnimation _secondaryAnimationProxy;

        public readonly List<WillPopCallback> _willPopCallbacks = new List<WillPopCallback>();

        public override Future<RoutePopDisposition> willPop() {
            //async
            _ModalScopeState scope = _scopeKey.currentState as _ModalScopeState ;
            D.assert(scope != null);

            Future InvokePopCallbacks(int index) {
                if (index == _willPopCallbacks.Count) {
                    return base.willPop();
                }
                var callback = _willPopCallbacks[index];
                return callback.Invoke().then(v => {
                    if (!(bool) v) {
                        return Future.value(RoutePopDisposition.doNotPop);
                    }

                    return InvokePopCallbacks(index + 1);
                });
            }

            return InvokePopCallbacks(0).to<RoutePopDisposition>();
        }

        public void addScopedWillPopCallback(WillPopCallback callback) {
            D.assert(_scopeKey.currentState != null,
                () => "Tried to add a willPop callback to a route that is not currently in the tree.");
            _willPopCallbacks.Add(callback);
        }

        public void removeScopedWillPopCallback(WillPopCallback callback) {
            D.assert(_scopeKey.currentState != null,
                () => "Tried to remove a willPop callback from a route that is not currently in the tree.");
            _willPopCallbacks.Remove(callback);
        }

        public bool hasScopedWillPopCallback {
            get { return _willPopCallbacks.isNotEmpty(); }
        }

        protected internal override void didChangePrevious(Route previousRoute) {
            base.didChangePrevious(previousRoute);
            changedInternalState();
        }

        protected internal override void changedInternalState() {
            base.changedInternalState();
            setState(() => { });
            _modalBarrier.markNeedsBuild();
        }

        protected internal override void changedExternalState() {
            base.changedExternalState();
            if (_scopeKey.currentState != null)
                _scopeKey.currentState._forceRebuildPage();
        }

        public bool canPop {
            get { return !isFirst || willHandlePopInternally; }
        }


        public readonly GlobalKey<_ModalScopeState> _scopeKey = new LabeledGlobalKey<_ModalScopeState>();
        internal readonly GlobalKey _subtreeKey = GlobalKey.key();
        internal readonly PageStorageBucket _storageBucket = new PageStorageBucket();
        
        OverlayEntry _modalBarrier;

        Widget _buildModalBarrier(BuildContext context) {
            Widget barrier;
            if (barrierColor != null && !offstage) {
                // changedInternalState is called if these update
                D.assert(barrierColor != _kTransparent);
                Animation<Color> color =
                    animation.drive(new ColorTween(
                        begin: _kTransparent,
                        end: barrierColor // changedInternalState is called if this updates
                    ).chain(new CurveTween(curve: barrierCurve)));
                barrier = new AnimatedModalBarrier(
                    color: color,
                    dismissible: barrierDismissible
                   
                );
            }
            else {
                barrier = new ModalBarrier(
                    dismissible: barrierDismissible
               
                );
            }
            if (_filter != null) {
                barrier = new BackdropFilter(
                    filter: _filter,
                    child: barrier
                );
            }
            return new IgnorePointer(
                ignoring: animation.status == AnimationStatus.reverse ||
                          animation.status == AnimationStatus.dismissed,
                child: barrier
            );
        }

        public Widget _modalScopeCache;

        public virtual Widget _buildModalScope(BuildContext context) {
            return _modalScopeCache = _modalScopeCache ?? new _ModalScope(key: _scopeKey, route: this);
        }

        public override IEnumerable<OverlayEntry> createOverlayEntries() {
            _modalBarrier = new OverlayEntry(builder: _buildModalBarrier);
            var content = new OverlayEntry(
                builder: _buildModalScope, maintainState: maintainState
            );
            return new List<OverlayEntry> {_modalBarrier, content};
        }

        public override string ToString() {
            return $"{GetType()}({settings}, animation: {_animation})";
        }
    }
    
    public abstract class ModalRoute<T> : ModalRoute {

        public ModalRoute(
            RouteSettings settings = null,
            ImageFilter filter = null
        ) : base(settings) {
            _filter = filter;
        }
        
        public static ModalRoute<T> of<T>(BuildContext context) {
            _ModalScopeStatus widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
            return widget?.route as ModalRoute<T>;
        }
        public new GlobalKey<_ModalScopeState<T>> _scopeKey = new LabeledGlobalKey<_ModalScopeState<T>>();

        public override Future<RoutePopDisposition> willPop() {
            //async
            _ModalScopeState<T> scope = _scopeKey.currentState as _ModalScopeState<T> ;
            D.assert(scope != null);

            bool result = false;
            foreach (WillPopCallback callback in _willPopCallbacks) {
                callback.Invoke().then(v => result = !(bool)v);
                if (result) {
                    return Future.value(RoutePopDisposition.doNotPop).to<RoutePopDisposition>();
                }
            }
            return base.willPop();
            
        }
        public override Widget _buildModalScope(BuildContext context) {
            return _modalScopeCache = _modalScopeCache ?? new _ModalScope<T>(key: _scopeKey, route: this);
        }

        
    }

    public abstract class PopupRoute : ModalRoute {
        public PopupRoute(
            RouteSettings settings = null,
            ImageFilter filter = null
        ) : base(settings: settings,filter:filter) {
        }

        public override bool opaque {
            get { return false; }
        }

        public override bool maintainState {
            get { return true; }
        }
    }

    public abstract class PopupRoute<T> : ModalRoute<T> {
        public PopupRoute(
            RouteSettings settings = null,
            ImageFilter filter = null
        ) : base(settings: settings,filter:filter) {
        }

        public override bool opaque {
            get { return false; }
        }

        public override bool maintainState {
            get { return true; }
        }
    }


    public class RouteObserve<R> : NavigatorObserver where R : Route {
        readonly Dictionary<R, HashSet<RouteAware>> _listeners = new Dictionary<R, HashSet<RouteAware>>();

        public void subscribe(RouteAware routeAware, R route) {
            D.assert(routeAware != null);
            D.assert(route != null);
            HashSet<RouteAware> subscribers = _listeners.putIfAbsent(route, () => new HashSet<RouteAware>());
            if (subscribers.Add(routeAware)) {
                routeAware.didPush();
            }
        }

        public void unsubscribe(RouteAware routeAware) {
            D.assert(routeAware != null);
            foreach (R route in _listeners.Keys) {
                HashSet<RouteAware> subscribers = _listeners[route];
                subscribers?.Remove(routeAware);
            }
        }

        public override void didPop(Route route, Route previousRoute) {
            if (route is R && previousRoute is R) {
                var previousSubscribers = _listeners.getOrDefault((R) previousRoute);

                if (previousSubscribers != null) {
                    foreach (RouteAware routeAware in previousSubscribers) {
                        routeAware.didPopNext();
                    }
                }

                var subscribers =_listeners.getOrDefault((R) route);
               
                if (subscribers != null) {
                    foreach (RouteAware routeAware in subscribers) {
                        routeAware.didPop();
                    }
                }
            }
        }

        public override void didPush(Route route, Route previousRoute) {
            if (route is R && previousRoute is R) {
                var previousSubscribers = _listeners.getOrDefault((R) previousRoute);

                if (previousSubscribers != null) {
                    foreach (RouteAware routeAware in previousSubscribers) {
                        routeAware.didPushNext();
                    }
                }
            }
        }
    }

    public interface RouteAware {
        void didPopNext();

        void didPush();

        void didPop();

        void didPushNext();
    }

    class _DialogRoute : PopupRoute {
        internal _DialogRoute(
            RoutePageBuilder pageBuilder = null, 
            bool barrierDismissible = true,
            string barrierLabel = null,
            Color barrierColor = null,
            TimeSpan? transitionDuration = null,
            RouteTransitionsBuilder transitionBuilder = null,
            RouteSettings settings = null
            ) : base(settings: settings) {
            D.assert(barrierDismissible != null);
            _pageBuilder = pageBuilder;
            _barrierLabel = barrierLabel;
            _barrierDismissible = barrierDismissible;
            _barrierColor = barrierColor ?? new Color(0x80000000);
            _transitionDuration = transitionDuration ?? TimeSpan.FromMilliseconds(200);
            _transitionBuilder = transitionBuilder;
        }

        readonly RoutePageBuilder _pageBuilder;

          
        public override bool barrierDismissible {
            get { return _barrierDismissible; }
        }
        public readonly bool _barrierDismissible;

        public override string barrierLabel {
            get { return _barrierLabel;}
        }
        public readonly string _barrierLabel;

        public override Color barrierColor {
            get { return _barrierColor; }
        }
        public readonly Color _barrierColor;

        public override TimeSpan transitionDuration {
            get { return _transitionDuration; }
        }
        public readonly TimeSpan _transitionDuration;

        readonly RouteTransitionsBuilder _transitionBuilder;

        public override Widget buildPage(
            BuildContext context,
            Animation<float> animation,
            Animation<float> secondaryAnimation) {
            
            return _pageBuilder(context, animation, secondaryAnimation);
        }

        public override Widget buildTransitions(
            BuildContext context,
            Animation<float> animation,
            Animation<float> secondaryAnimation,
            Widget child) {
            if (_transitionBuilder == null) {
                return new FadeTransition(
                    opacity: new CurvedAnimation(
                        parent: animation,
                        curve: Curves.linear
                    ),
                    child: child);
            }

            return _transitionBuilder(context, animation, secondaryAnimation, child);
        }
    }

    public static class DialogUtils {
        public static Future<T> showGeneralDialog<T>(
            BuildContext context = null,
            RoutePageBuilder pageBuilder = null,
            bool? barrierDismissible = null,
            string barrierLabel = null,
            Color barrierColor = null,
            TimeSpan? transitionDuration = null,
            RouteTransitionsBuilder transitionBuilder = null,
            bool useRootNavigator = true,
            RouteSettings routeSettings = null
        ) {
            //D.assert(!barrierDismissible || barrierLabel != null);
            D.assert(pageBuilder != null);
            return Navigator.of(context, rootNavigator: true).push(
                new _DialogRoute(
                    pageBuilder: pageBuilder,
                    barrierDismissible: barrierDismissible ?? false,
                    barrierLabel: barrierLabel,
                    barrierColor: barrierColor,
                    transitionDuration: transitionDuration,
                    transitionBuilder: transitionBuilder,
                    settings: routeSettings)  as Route
            ).to<T>();
        }
    }

    public delegate Widget RoutePageBuilder(BuildContext context, Animation<float> animation,
        Animation<float> secondaryAnimation);

    public delegate Widget RouteTransitionsBuilder(BuildContext context, Animation<float> animation,
        Animation<float> secondaryAnimation, Widget child);
}