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

using System;
using System.Collections.Generic;
using System.Linq;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.rendering;
using Unity.UIWidgets.scheduler;
using Unity.UIWidgets.ui;
using UnityEngine;
using Rect = Unity.UIWidgets.ui.Rect;

namespace Unity.UIWidgets.widgets {
    public class OverlayEntry {
        public OverlayEntry(
            WidgetBuilder builder = null, 
            bool opaque = false, 
            bool maintainState = false) {
            D.assert(builder != null);
            _opaque = opaque;
            _maintainState = maintainState;
            this.builder = builder;
        }

        public readonly WidgetBuilder builder;

        bool _opaque;

        public bool opaque {
            get { return _opaque; }
            set {
                if (_opaque == value) {
                    return;
                }

                _opaque = value;
                _overlay?._didChangeEntryOpacity();
            }
        }

        bool _maintainState;

        public bool maintainState {
            get { return _maintainState; }
            set {
                if (_maintainState == value) {
                    return;
                }

                _maintainState = value;
                D.assert(_overlay != null);
                _overlay?._didChangeEntryOpacity();
            }
        }

        internal OverlayState _overlay;

        internal readonly GlobalKey<_OverlayEntryWidgetState> _key = GlobalKey<_OverlayEntryWidgetState>.key();//new LabeledGlobalKey<_OverlayEntryWidgetState>();

        public void remove() {
            D.assert(_overlay != null);
            OverlayState overlay = _overlay;
            _overlay = null;
            if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
                SchedulerBinding.instance.addPostFrameCallback((duration) => { overlay._remove(this); });
            }
            else {
                overlay._remove(this);
            }
        }

        public void markNeedsBuild() {
            _key.currentState?._markNeedsBuild();
        }

        public override string ToString() {
            return $"{foundation_.describeIdentity(this)}(opaque: {opaque}; maintainState: {maintainState})";
        }
    }


    class _OverlayEntryWidget : StatefulWidget {
        internal _OverlayEntryWidget(
            Key key, 
            OverlayEntry entry, 
            bool tickerEnabled = true) : base(key: key) {
            D.assert(key != null);
            D.assert(entry != null);
            this.entry = entry;
            this.tickerEnabled = tickerEnabled;
        }

        public readonly OverlayEntry entry;
        public readonly bool tickerEnabled;

        public override State createState() {
            return new _OverlayEntryWidgetState();
        }
    }

    class _OverlayEntryWidgetState : State<_OverlayEntryWidget> {
        public override Widget build(
            BuildContext context) {
            return new TickerMode(
                enabled: widget.tickerEnabled,
                child: widget.entry.builder(context)
            );
        }

        internal void _markNeedsBuild() {
            setState(() => {
            });
        }
    }

    public class Overlay : StatefulWidget {
        public Overlay(
            Key key = null, 
            List<OverlayEntry> initialEntries = null) : base(key) {
            D.assert(initialEntries != null);
            this.initialEntries = initialEntries;
        }

        public readonly List<OverlayEntry> initialEntries;

        public static OverlayState of(
            BuildContext context, 
            bool rootOverlay = false,
            Widget debugRequiredFor = null) {
           
            OverlayState result = rootOverlay
                ? context.findRootAncestorStateOfType<OverlayState>()
                : context.findAncestorStateOfType<OverlayState>();
            D.assert(() => {
                if (debugRequiredFor != null && result == null) {
                    
                    var additional = context.widget != debugRequiredFor
                        ? context.describeElement($"\nThe context from which that widget was searching for an overlay was:\n  {context}")
                        : context.describeElement("");
                    throw new UIWidgetsError(
                        new List<DiagnosticsNode>()
                        {
                            new ErrorSummary("No Overlay widget found."),
                            new ErrorDescription($"{debugRequiredFor.GetType()} widgets require an Overlay widget ancestor for correct operation."),
                            new ErrorHint("The most common way to add an Overlay to an application is to include a MaterialApp or Navigator widget in the runApp() call."),
                            new DiagnosticsProperty<Widget>("The specific widget that failed to find an overlay was", debugRequiredFor, style: DiagnosticsTreeStyle.errorProperty),
                            additional
                        });
                          
                }

                return true;
            });
            return result;
        }

        public override State createState() {
            return new OverlayState();
        }
    }

    public class OverlayState : TickerProviderStateMixin<Overlay> {
        readonly List<OverlayEntry> _entries = new List<OverlayEntry>();

        public override void initState() {
            base.initState();
            insertAll(widget.initialEntries);
        }

        internal int _insertionIndex(OverlayEntry below, OverlayEntry above) {
            D.assert(below == null || above == null);
            if (below != null) {
                return _entries.IndexOf(below);
            }

            if (above != null) {
                return _entries.IndexOf(above) + 1;
            }

            return _entries.Count;
        }

        public void insert(OverlayEntry entry, OverlayEntry below = null, OverlayEntry above = null) {
            D.assert(above == null || below == null, () => "Only one of `above` and `below` may be specified.");
            D.assert(above == null || (above._overlay == this && _entries.Contains(above)),
                () => "The provided entry for `above` is not present in the Overlay.");
            D.assert(below == null || (below._overlay == this && _entries.Contains(below)),
                () => "The provided entry for `below` is not present in the Overlay.");
            D.assert(!_entries.Contains(entry), () => "The specified entry is already present in the Overlay.");
            D.assert(entry._overlay == null, () => "The specified entry is already present in another Overlay.");
            entry._overlay = this;
            setState(() => { _entries.Insert(_insertionIndex(below, above), entry); });
        }

        public void insertAll(ICollection<OverlayEntry> entries, OverlayEntry below = null, OverlayEntry above = null) {
            D.assert(above == null || below == null, () => "Only one of `above` and `below` may be specified.");
            D.assert(above == null || (above._overlay == this && _entries.Contains(above)),
                () => "The provided entry for `above` is not present in the Overlay.");
            D.assert(below == null || (below._overlay == this && _entries.Contains(below)),
                () => "The provided entry for `below` is not present in the Overlay.");
            D.assert(entries.All(entry => !_entries.Contains(entry)),
                () => "One or more of the specified entries are already present in the Overlay.");
            D.assert(entries.All(entry => entry._overlay == null),
                () => "One or more of the specified entries are already present in another Overlay.");
            if (entries.isEmpty()) {
                return;
            }

            foreach (OverlayEntry entry in entries) {
                D.assert(entry._overlay == null);
                entry._overlay = this;
            }

            setState(() => { _entries.InsertRange(_insertionIndex(below, above), entries); });
        }

        public void rearrange(IEnumerable<OverlayEntry> newEntries, 
            OverlayEntry below = null,
            OverlayEntry above = null) 
        {
            List<OverlayEntry> newEntriesList =
                newEntries is List<OverlayEntry> ? (newEntries as List<OverlayEntry>) : newEntries.ToList();
            
            D.assert(
                above == null || below == null, 
                () => "Only one of `above` and `below` may be specified."
                );
            D.assert(
                above == null || (above._overlay == this && _entries.Contains(above)),
                () => "The provided entry for `above` is not present in the Overlay."
                );
            D.assert(
                below == null || (below._overlay == this && _entries.Contains(below)),
                () => "The provided entry for `below` is not present in the Overlay."
                );
            D.assert(
                newEntriesList.All(entry => entry._overlay == null || entry._overlay == this),
                () => "One or more of the specified entries are already present in another Overlay."
                );
            D.assert(
                newEntriesList.All(entry => _entries.IndexOf(entry) == _entries.LastIndexOf(entry)),
                () => "One or more of the specified entries are specified multiple times."
                );
            
            if (newEntriesList.isEmpty()) {
                return;
            }

            if (_entries.SequenceEqual(newEntriesList)) {
                return;
            }

            HashSet<OverlayEntry> old = new HashSet<OverlayEntry>(_entries);
            foreach (OverlayEntry entry in newEntriesList) {
                entry._overlay = entry._overlay ?? this;
            }

            setState(() => {
                _entries.Clear();
                _entries.AddRange(newEntriesList);
                foreach (OverlayEntry entry in newEntriesList) {
                    old.Remove(entry);
                }
                _entries.InsertRange(_insertionIndex(below, above), old);
            });
        }

        internal void _remove(OverlayEntry entry) {
            if (mounted) {
                setState(() => { _entries.Remove(entry); });
            }
        }

        public bool debugIsVisible(OverlayEntry entry) {
            bool result = false;
            D.assert(_entries.Contains(entry));
            D.assert(() => {
                for (int i = _entries.Count - 1; i > 0; i -= 1) {
                    // todo why not including 0?
                    OverlayEntry candidate = _entries[i];
                    if (candidate == entry) {
                        result = true;
                        break;
                    }

                    if (candidate.opaque) {
                        break;
                    }
                }

                return true;
            });
            return result;
        }

        internal void _didChangeEntryOpacity() {
            setState(() => { });
        }

        public override Widget build(BuildContext context) {
            var children = new List<Widget>();
            var onstage = true;
            int onstageCount = 0;
            for (var i = _entries.Count - 1; i >= 0; i -= 1) {
                var entry = _entries[i];
                if (onstage) {
                    onstageCount += 1;
                    children.Add(new _OverlayEntryWidget(entry._key, entry));
                    if (entry.opaque) {
                        onstage = false;
                    }
                }
                else if (entry.maintainState) {
                    children.Add(new _OverlayEntryWidget(
                        key: entry._key,
                        entry: entry,
                        tickerEnabled: false
                    ));
                }
            }

            children.Reverse();
            return new _Theatre(
                skipCount: children.Count - onstageCount,
                children: children.ToList()
            );
        }
        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new DiagnosticsProperty<List<OverlayEntry>>("entries", _entries));
        }
    }

    class _Theatre : MultiChildRenderObjectWidget {
        internal _Theatre(
            Key key = null,
            int skipCount = 0,
            List<Widget> children = null) : base(key: key, children: children) {
            D.assert(skipCount >= 0);
            D.assert(children != null);
            D.assert(children.Count() >= skipCount);
            this.skipCount = skipCount;
        }

        public readonly int skipCount;

        public override Element createElement() {
            return new _TheatreElement(this);
        }

        public override RenderObject createRenderObject(BuildContext context) {
            return new _RenderTheatre(
                skipCount: skipCount,
                textDirection: Directionality.of(context));
        }

        public void updateRenderObject(BuildContext context, _RenderTheatre renderObject) {
            renderObject.skipCount = skipCount;
            renderObject.textDirection = Directionality.of(context);
        }
        
        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new IntProperty("skipCount", skipCount));
        }
    }

    class _TheatreElement : MultiChildRenderObjectElement {
        public _TheatreElement(_Theatre widget) : base(widget) {
        }

        public new _Theatre widget {
            get { return (_Theatre) base.widget; }
        }

        public new _RenderTheatre renderObject {
            get { return (_RenderTheatre) base.renderObject; }
        }

        public override void debugVisitOnstageChildren(ElementVisitor visitor) {
            D.assert(children.Count() >= widget.skipCount);
            foreach (var item in children.Skip(widget.skipCount)) {
                visitor(item);
            }
        }
    }

    class _RenderTheatre : ContainerRenderObjectMixinRenderBox<RenderBox, StackParentData> {
        internal _RenderTheatre(
            TextDirection textDirection ,
            List<RenderBox> children = null,
            int skipCount = 0
        ) {
            D.assert(skipCount >= 0);
            _textDirection = textDirection;
            _skipCount = skipCount;
            addAll(children);
        }

        bool _hasVisualOverflow = false;
        
        public override void setupParentData(RenderObject child) {
            if (!(child.parentData is StackParentData)) {
                child.parentData = new StackParentData();
            }
        }

        Alignment _resolvedAlignment;

        void _resolve() {
            if (_resolvedAlignment != null) {
                return;
            }
            _resolvedAlignment = AlignmentDirectional.topStart.resolve(textDirection);
        }

        void _markNeedResolution() {
            _resolvedAlignment = null;
            markNeedsLayout();
        }

        public TextDirection textDirection {
            get { return _textDirection; }
            set {
                if (_textDirection == value)
                    return;
                _textDirection = value;
                _markNeedResolution();
            }
        }

        TextDirection _textDirection;

        public int skipCount {
            get { return _skipCount; }
            set {
                if (_skipCount != value) {
                    _skipCount = value;
                    markNeedsLayout();
                }
            }
        }

        int _skipCount;

        RenderBox _firstOnstageChild {
            get {
                if (skipCount == base.childCount) {
                    return null;
                }

                RenderBox child = firstChild;
                for (int toSkip = skipCount; toSkip > 0; toSkip--) {
                    StackParentData childParentData = child.parentData as StackParentData;
                    child = childParentData.nextSibling;
                    D.assert(child != null);
                }

                return child;
            }
        }

        RenderBox _lastOnstageChild {
            get { return skipCount == childCount ? null : lastChild; }
        }

        int _onstageChildCount {
            get { return childCount - skipCount; }
        }

        protected internal override float computeMinIntrinsicWidth(float height) {
            return RenderStack.getIntrinsicDimension(_firstOnstageChild,
                (RenderBox child) => child.getMinIntrinsicWidth(height));
        }

        protected internal override float computeMaxIntrinsicWidth(float height) {
            return RenderStack.getIntrinsicDimension(_firstOnstageChild,
                (RenderBox child) => child.getMaxIntrinsicWidth(height));
        }

        protected internal override float computeMinIntrinsicHeight(float width) {
            return RenderStack.getIntrinsicDimension(_firstOnstageChild,
                (RenderBox child) => child.getMinIntrinsicHeight(width));
        }

        protected internal override float computeMaxIntrinsicHeight(float width) {
            return RenderStack.getIntrinsicDimension(_firstOnstageChild,
                (RenderBox child) => child.getMaxIntrinsicHeight(width));
        }

        public override float? computeDistanceToActualBaseline(TextBaseline baseline) {
            D.assert(!debugNeedsLayout);
            float? result = null;
            RenderBox child = _firstOnstageChild;
            while (child != null) {
                D.assert(!child.debugNeedsLayout);
                StackParentData childParentData = child.parentData as StackParentData;
                float? candidate = child.getDistanceToActualBaseline(baseline);
                if (candidate != null) {
                    candidate += childParentData.offset.dy;
                    if (result != null) {
                        result = Mathf.Min(result.Value, candidate.Value);
                    }
                    else {
                        result = candidate;
                    }
                }

                child = childParentData.nextSibling;
            }

            return result;
        }

        protected override bool sizedByParent {
            get { return true; }
        }

        protected override void performResize() {
            size = constraints.biggest;
            D.assert(size.isFinite);
        }

        protected override void performLayout() {
            _hasVisualOverflow = false;

            if (_onstageChildCount == 0) {
                return;
            }

            _resolve();
            D.assert(_resolvedAlignment != null);
            
            BoxConstraints nonPositionedConstraints = BoxConstraints.tight(constraints.biggest);

            RenderBox child = _firstOnstageChild;
            while (child != null) {
                StackParentData childParentData = child.parentData as StackParentData;

                if (!childParentData.isPositioned) {
                    child.layout(nonPositionedConstraints, parentUsesSize: true);
                    childParentData.offset = _resolvedAlignment.alongOffset(size - child.size as Offset);
                }
                else {
                    _hasVisualOverflow =
                        RenderStack.layoutPositionedChild(child, childParentData, size, _resolvedAlignment) ||
                        _hasVisualOverflow;
                }

                D.assert(child.parentData == childParentData);
                child = childParentData.nextSibling;
            }
        }

        protected override bool hitTestChildren(BoxHitTestResult result, Offset position = null) {
            RenderBox child = _lastOnstageChild;
            for (int i = 0; i < _onstageChildCount; i++) {
                D.assert(child != null);
                StackParentData childParentData = child.parentData as StackParentData;
                
                bool isHit = result.addWithPaintOffset(
                    offset: childParentData.offset,
                    position: position,
                    hitTest: (BoxHitTestResult resultIn, Offset transformed) => {
                        D.assert(transformed == position - childParentData.offset);
                        return child.hitTest(resultIn, position: transformed);
                    }
                );
                if (isHit)
                    return true;
                child = childParentData.previousSibling;
            }

            return false;
        }

        void paintStack(PaintingContext context, Offset offset) {
            RenderBox child = _firstOnstageChild;
            while (child != null) {
                StackParentData childParentData = child.parentData as StackParentData;
                context.paintChild(child, childParentData.offset + offset);
                child = childParentData.nextSibling;
            }
        }

        public override void paint(PaintingContext context, Offset offset) {
            if (_hasVisualOverflow) {
                context.pushClipRect(needsCompositing, offset, Offset.zero & size, paintStack);
            }
            else {
                paintStack(context, offset);
            }
        }

        public override Rect describeApproximatePaintClip(RenderObject child) =>
            _hasVisualOverflow ? Offset.zero & size : null;

        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new IntProperty("skipCount", skipCount));
            properties.add(new EnumProperty<TextDirection>("textDirection", textDirection));
        }

        public override List<DiagnosticsNode> debugDescribeChildren() {
            List<DiagnosticsNode> offstageChildren = new List<DiagnosticsNode>();
            List<DiagnosticsNode> onstageChildren = new List<DiagnosticsNode>();
            
            int count = 1;
            bool onstage = false;
            RenderBox child = firstChild;
            RenderBox firstOnstageChild = _firstOnstageChild;
            while (child != null) {
                if (child == firstOnstageChild) {
                    onstage = true;
                    count = 1;
                }

                if (onstage) {
                    onstageChildren.Add(
                        child.toDiagnosticsNode(
                            name: $"onstage {count}"
                        )
                    );
                } else {
                    offstageChildren.Add(
                        child.toDiagnosticsNode(
                            name: $"offstage {count}",
                            style: DiagnosticsTreeStyle.offstage
                        )
                    );
                }

                StackParentData childParentData = child.parentData as StackParentData;
                child = childParentData.nextSibling;
                count += 1;
            }

            List<DiagnosticsNode> result = new List<DiagnosticsNode>();
            result.AddRange(onstageChildren);
            if (offstageChildren.isNotEmpty()) {
                result.AddRange(offstageChildren);
            }
            else {
                result.Add(DiagnosticsNode.message("no offstage children", style: DiagnosticsTreeStyle.offstage));
            }

            return result;
        }
    }
}