using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using OpenNest.Collections;
using OpenNest.Geometry;
using OpenNest.Math;
using OpenNest.Shapes;

namespace OpenNest
{
    public class Plate
    {
        private int quadrant;

        public event EventHandler<ItemAddedEventArgs<Part>> PartAdded
        {
            add { Parts.ItemAdded += value; }
            remove { Parts.ItemAdded -= value; }
        }

        public event EventHandler<ItemRemovedEventArgs<Part>> PartRemoved
        {
            add { Parts.ItemRemoved += value; }
            remove { Parts.ItemRemoved -= value; }
        }

        public event EventHandler<ItemChangedEventArgs<Part>> PartChanged
        {
            add { Parts.ItemChanged += value; }
            remove { Parts.ItemChanged -= value; }
        }

        /// <summary>
        /// Raised once after the part order changes without adding or removing parts, including
        /// a committed cutting plan that also installed planned programs. Refresh order- and
        /// program-derived views; quantity accounting is unchanged.
        /// </summary>
        public event EventHandler PartsReordered
        {
            add { Parts.ItemsReordered += value; }
            remove { Parts.ItemsReordered -= value; }
        }

        public Plate()
            : this(60, 120) { }

        public Plate(double width, double length)
            : this(new Size(width, length)) { }

        public Plate(Size size)
        {
            EdgeSpacing = new Spacing();
            Size = size;
            Parts = new ObservableList<Part>();
            Parts.ItemAdded += Parts_PartAdded;
            Parts.ItemRemoved += Parts_PartRemoved;
            CutOffs = new ObservableList<CutOff>();
            ClampZones = new ObservableList<ClampZone>();
            ClampZones.ItemAdded += (_, _) => OnClampZonesChanged();
            ClampZones.ItemRemoved += (_, _) => OnClampZonesChanged();
            ClampZones.ItemChanged += (_, _) => OnClampZonesChanged();
            Quadrant = 1;
        }

        private void Parts_PartAdded(object sender, ItemAddedEventArgs<Part> e)
        {
            if (!e.Item.BaseDrawing.IsCutOff)
                e.Item.BaseDrawing.Quantity.Nested += Quantity;
        }

        private void Parts_PartRemoved(object sender, ItemRemovedEventArgs<Part> e)
        {
            if (!e.Item.BaseDrawing.IsCutOff)
                e.Item.BaseDrawing.Quantity.Nested -= Quantity;
        }

        /// <summary>
        /// The spacing between parts.
        /// </summary>
        public double PartSpacing { get; set; }

        /// <summary>
        /// The spacing along the edges of the plate.
        /// </summary>
        public Spacing EdgeSpacing;

        /// <summary>
        /// The size of the plate. A plate following a <see cref="ClampRail"/> re-resolves
        /// its clamp zones for the new size.
        /// </summary>
        public Size Size
        {
            get { return size; }
            set
            {
                size = value;
                ResolveClampRail();
            }
        }

        private Size size;

        public CNC.CuttingStrategy.CuttingParameters CuttingParameters { get; set; }

        /// <summary>
        /// Material grain direction in radians. 0 = horizontal.
        /// </summary>
        public double GrainAngle { get; set; }

        /// <summary>
        /// The parts that the plate contains.
        /// </summary>
        public ObservableList<Part> Parts { get; set; }

        /// <summary>
        /// The cut-off lines defined on this plate.
        /// </summary>
        public ObservableList<CutOff> CutOffs { get; set; }

        /// <summary>
        /// Fixed rectangular machine-clamp keep-outs in plate coordinates
        /// (<see cref="ClampZone"/>). Never parts: excluded from quantity, utilization,
        /// cut sequence and CNC output; placement rules and display consume them. Mutate
        /// through this list; <see cref="ClampZonesChanged"/> fires for every change.
        /// </summary>
        public ObservableList<ClampZone> ClampZones { get; }

        /// <summary>
        /// Raised after <see cref="ClampZones"/> content changes so views can refresh
        /// the zone overlay. Carries no geometry arguments.
        /// </summary>
        public event EventHandler? ClampZonesChanged;

        private void OnClampZonesChanged() => ClampZonesChanged?.Invoke(this, EventArgs.Empty);

        /// <summary>
        /// The machine clamp rail this plate follows, or null when its
        /// <see cref="ClampZones"/> are explicit (engine sheets, files without a rail). While
        /// set, the zones are derived: re-resolved whenever <see cref="Size"/> or
        /// <see cref="Quadrant"/> changes, because the clamps are fixed to the machine.
        /// </summary>
        public ClampRail ClampRail { get; private set; }

        private static readonly IReadOnlySet<string> NoRemovedClamps = ImmutableHashSet<string>.Empty;

        /// <summary>
        /// Rail clamp ids taken off this sheet as a last resort (D8) so a part that could not
        /// be nested anywhere with every clamp in place still fits. Empty unless
        /// <see cref="ClampRail"/> is set; <see cref="ClampZones"/> already excludes them, so
        /// nothing else needs to consult this list to avoid them. Ids stay listed across a
        /// resize/rotate even when the matching clamp is temporarily beyond the sheet, so it
        /// re-appears removed if a later resize brings it back onto the sheet (C13).
        /// </summary>
        public IReadOnlySet<string> RemovedClamps { get; private set; } = NoRemovedClamps;

        /// <summary>
        /// Minutes this sheet's cut-time estimate gains from <see cref="RemovedClamps"/> (D9):
        /// each listed clamp the rail places on this sheet adds
        /// <see cref="OpenNest.ClampRail.RemovalMinutes"/> once; a listed clamp that is beyond
        /// the sheet (or unknown to the rail) is not pulled and costs nothing. Zero when there
        /// is no rail (removal is meaningless without one to remove clamps from).
        /// </summary>
        public double ClampRemovalMinutes =>
            ClampRail == null || RemovedClamps.Count == 0
                ? 0
                : ClampRail.ResolveFor(Size, Quadrant).Count(zone => RemovedClamps.Contains(zone.Id))
                    * ClampRail.RemovalMinutes;

        /// <summary>
        /// Follows <paramref name="rail"/> and replaces the zones with its resolution for
        /// this sheet; null detaches and removes every zone. Unchanged zones raise no events.
        /// </summary>
        public void SetClampRail(ClampRail rail) => SetClampRail(rail, null);

        /// <summary>
        /// Follows <paramref name="rail"/> with the clamps named in <paramref name="removedClamps"/>
        /// taken off this sheet (D8): zones become the rail's resolution for this sheet minus
        /// those ids. Null <paramref name="rail"/> detaches, clears every zone and forgets the
        /// removed set (removal only means something while following a rail).
        /// </summary>
        public void SetClampRail(ClampRail rail, IEnumerable<string> removedClamps)
        {
            ClampRail = rail;
            RemovedClamps = rail == null || removedClamps == null
                ? NoRemovedClamps
                : removedClamps.ToImmutableHashSet(StringComparer.Ordinal);
            ReplaceClampZones(ResolveRailZones());
        }

        private void ResolveClampRail()
        {
            // Called from the constructor's Size assignment before the zone list exists.
            if (ClampRail != null)
                ReplaceClampZones(ResolveRailZones());
        }

        private IReadOnlyList<ClampZone> ResolveRailZones()
        {
            if (ClampRail == null)
                return Array.Empty<ClampZone>();
            var resolved = ClampRail.ResolveFor(Size, Quadrant);
            if (RemovedClamps.Count == 0)
                return resolved;
            var kept = new List<ClampZone>(resolved.Count);
            foreach (var zone in resolved)
                if (!RemovedClamps.Contains(zone.Id))
                    kept.Add(zone);
            return kept;
        }

        private void ReplaceClampZones(IReadOnlyList<ClampZone> zones)
        {
            if (ClampRail.SameZones(ClampZones, zones))
                return;
            ClampZones.Clear();
            foreach (var zone in zones)
                ClampZones.Add(zone);
        }

        /// <summary>
        /// Regenerates all cut-off drawings and materializes them as parts.
        /// Existing cut-off parts are removed first, then each cut-off is
        /// regenerated and put back at the same place in the cut sequence
        /// (<see cref="Parts"/> order). New cut-offs are added at the end.
        /// </summary>
        public void RegenerateCutOffs(CutOffSettings settings)
        {
            // Remember each cut-off's place in the cut sequence, so a part drag
            // or cut-off move doesn't send it to the end of the sequence.
            var sequence = new Dictionary<CutOff, int>();

            for (var i = Parts.Count - 1; i >= 0; i--)
            {
                if (!Parts[i].BaseDrawing.IsCutOff)
                    continue;

                var cutoff = CutOffs.FirstOrDefault(c => ReferenceEquals(c.Drawing, Parts[i].BaseDrawing));
                if (cutoff != null)
                    sequence[cutoff] = i;

                Parts.RemoveAt(i);
            }

            RegenerateCutOffs(settings, sequence);
        }

        /// <summary>
        /// Regenerates all cut-off drawings and materializes them as parts, placing
        /// each cut-off at its index in <paramref name="sequence"/> (its place in
        /// <see cref="Parts"/> order). Cut-offs missing from it are added at the end.
        /// Callers must remove existing cut-off parts first.
        /// </summary>
        public void RegenerateCutOffs(CutOffSettings settings, IReadOnlyDictionary<CutOff, int> sequence)
        {
            var cache = BuildPerimeterCache(this);
            var placed = new List<(int Index, Part Part)>();

            // Regenerate and materialize each cut-off
            foreach (var cutoff in CutOffs)
            {
                cutoff.Regenerate(this, settings, cache);

                if (cutoff.Drawing.Program.Codes.Count == 0)
                    continue;

                var part = new Part(cutoff.Drawing);

                if (sequence != null && sequence.TryGetValue(cutoff, out var index))
                    placed.Add((index, part));
                else
                    Parts.Add(part);
            }

            // Lowest index first: each insert then lands on its saved index, because
            // every part sequenced before it is already in place.
            foreach (var (index, part) in placed.OrderBy(p => p.Index))
                Parts.Insert(System.Math.Clamp(index, 0, Parts.Count), part);
        }

        /// <summary>
        /// Builds a dictionary mapping each non-cut-off part to its perimeter entity.
        /// Closed shapes use ShapeProfile; open contours fall back to ConvexHull.
        /// </summary>
        public static Dictionary<Part, Geometry.Entity> BuildPerimeterCache(Plate plate)
        {
            var cache = new Dictionary<Part, Geometry.Entity>();

            foreach (var part in plate.Parts)
            {
                if (part.BaseDrawing.IsCutOff)
                    continue;

                Geometry.Entity perimeter = null;
                try
                {
                    var entities = Converters
                        .ConvertProgram.ToGeometry(part.Program)
                        .Where(e => SpecialLayers.IsMaterial(e.Layer))
                        .ToList();

                    if (entities.Count > 0)
                    {
                        // Leads are cutting paths in scrap, not boundary edges. Chaining them
                        // into the outline can make a closed part appear open and replace its
                        // recesses with a convex hull. Keep the full geometry for the existing
                        // conservative fallback when the material contour really is open.
                        var outline = entities.Where(e => e.Layer != SpecialLayers.Leadin &&
                            e.Layer != SpecialLayers.Leadout).ToList();
                        var profile = new Geometry.ShapeProfile(outline);

                        if (profile.Perimeter.IsClosed())
                        {
                            perimeter = profile.Perimeter;
                            perimeter.Offset(part.Location);
                        }
                        else
                        {
                            var points = entities.CollectPoints();
                            if (points.Count >= 3)
                            {
                                var hull = Geometry.ConvexHull.Compute(points);
                                hull.Offset(part.Location);
                                perimeter = hull;
                            }
                        }
                    }
                }
                catch
                {
                    perimeter = null;
                }

                cache[part] = perimeter;
            }

            return cache;
        }

        /// <summary>
        /// The number of times to cut the plate.
        /// </summary>
        public int Quantity { get; set; }

        /// <summary>
        /// The quadrant the plate is located in.
        /// 1 = TopRight
        /// 2 = TopLeft
        /// 3 = BottomLeft
        /// 4 = BottomRight
        /// </summary>
        public int Quadrant
        {
            get { return quadrant; }
            set
            {
                quadrant = value <= 4 && value > 0 ? value : 1;
                ResolveClampRail();
            }
        }

        /// <summary>
        /// Rotates the plate clockwise or counter-clockwise along with all parts.
        /// </summary>
        /// <param name="rotationDirection"></param>
        /// <param name="keepSameQuadrant"></param>
        public void Rotate90(RotationType rotationDirection, bool keepSameQuadrant = true)
        {
            const double oneAndHalfPI = System.Math.PI * 1.5;

            Size = new Size(Size.Length, Size.Width);

            // After Size swap above, new Size.Width = old Length (old X extent),
            // new Size.Length = old Width (old Y extent).
            // Convention: Length = X axis, Width = Y axis.
            if (rotationDirection == RotationType.CW)
            {
                Rotate(oneAndHalfPI);

                if (keepSameQuadrant)
                {
                    switch (Quadrant)
                    {
                        case 1:
                            Offset(0, Size.Width);
                            break;

                        case 2:
                            Offset(-Size.Length, 0);
                            break;

                        case 3:
                            Offset(0, -Size.Width);
                            break;

                        case 4:
                            Offset(Size.Length, 0);
                            break;

                        default:
                            return;
                    }
                }
                else
                {
                    Quadrant = Quadrant < 2 ? 4 : Quadrant - 1;
                }
            }
            else
            {
                Rotate(Angle.HalfPI);

                if (keepSameQuadrant)
                {
                    switch (Quadrant)
                    {
                        case 1:
                            Offset(Size.Length, 0);
                            break;

                        case 2:
                            Offset(0, Size.Width);
                            break;

                        case 3:
                            Offset(-Size.Length, 0);
                            break;

                        case 4:
                            Offset(0, -Size.Width);
                            break;

                        default:
                            return;
                    }
                }
                else
                {
                    Quadrant = Quadrant > 3 ? 1 : Quadrant + 1;
                }
            }
        }

        /// <summary>
        /// Rotates the plate 180 degrees along with all parts.
        /// </summary>
        /// <param name="keepSameQuadrant"></param>
        public void Rotate180(bool keepSameQuadrant = true)
        {
            if (keepSameQuadrant)
            {
                Vector centerpt;

                switch (Quadrant)
                {
                    case 1:
                        centerpt = new Vector(Size.Length * 0.5, Size.Width * 0.5);
                        break;

                    case 2:
                        centerpt = new Vector(-Size.Length * 0.5, Size.Width * 0.5);
                        break;

                    case 3:
                        centerpt = new Vector(-Size.Length * 0.5, -Size.Width * 0.5);
                        break;

                    case 4:
                        centerpt = new Vector(Size.Length * 0.5, -Size.Width * 0.5);
                        break;

                    default:
                        return;
                }

                Rotate(System.Math.PI, centerpt);
            }
            else
            {
                Rotate(System.Math.PI);
                Quadrant = (Quadrant + 2) % 4;

                if (Quadrant == 0)
                    Quadrant = 4;
            }
        }

        /// <summary>
        /// Rotates the parts on the plate.
        /// </summary>
        /// <param name="angle"></param>
        public void Rotate(double angle)
        {
            for (var i = Parts.Count - 1; i >= 0; i--)
            {
                if (Parts[i].BaseDrawing.IsCutOff)
                    Parts.RemoveAt(i);
            }

            for (var i = 0; i < Parts.Count; ++i)
            {
                var part = Parts[i];
                part.Rotate(angle);
            }

            foreach (var cutoff in CutOffs)
                cutoff.Position = cutoff.Position.Rotate(angle);
        }

        /// <summary>
        /// Rotates the parts on the plate around the specified origin.
        /// </summary>
        /// <param name="angle"></param>
        /// <param name="origin"></param>
        public void Rotate(double angle, Vector origin)
        {
            for (var i = Parts.Count - 1; i >= 0; i--)
            {
                if (Parts[i].BaseDrawing.IsCutOff)
                    Parts.RemoveAt(i);
            }

            for (var i = 0; i < Parts.Count; ++i)
            {
                var part = Parts[i];
                part.Rotate(angle, origin);
            }

            foreach (var cutoff in CutOffs)
            {
                var pos = cutoff.Position - origin;
                pos = pos.Rotate(angle);
                cutoff.Position = pos + origin;
            }
        }

        /// <summary>
        /// Offsets the parts on the plate.
        /// </summary>
        /// <param name="x"></param>
        /// <param name="y"></param>
        public void Offset(double x, double y)
        {
            // Remove cut-off parts before transforming
            for (var i = Parts.Count - 1; i >= 0; i--)
            {
                if (Parts[i].BaseDrawing.IsCutOff)
                    Parts.RemoveAt(i);
            }

            for (var i = 0; i < Parts.Count; ++i)
            {
                var part = Parts[i];
                part.Offset(x, y);
            }

            // Transform cut-off positions
            foreach (var cutoff in CutOffs)
                cutoff.Position = new Vector(cutoff.Position.X + x, cutoff.Position.Y + y);
        }

        /// <summary>
        /// Offsets the parts on the plate.
        /// </summary>
        /// <param name="voffset"></param>
        public void Offset(Vector voffset)
        {
            for (var i = Parts.Count - 1; i >= 0; i--)
            {
                if (Parts[i].BaseDrawing.IsCutOff)
                    Parts.RemoveAt(i);
            }

            for (var i = 0; i < Parts.Count; ++i)
            {
                var part = Parts[i];
                part.Offset(voffset);
            }

            foreach (var cutoff in CutOffs)
                cutoff.Position = new Vector(
                    cutoff.Position.X + voffset.X,
                    cutoff.Position.Y + voffset.Y
                );
        }

        /// <summary>
        /// The smallest box that contains the plate.
        /// </summary>
        /// <param name="includeParts"></param>
        /// <returns></returns>
        public Box BoundingBox(bool includeParts = true)
        {
            var plateBox = new Box();

            // Width = Y axis (vertical), Length = X axis (horizontal)
            switch (Quadrant)
            {
                case 1:
                    plateBox.X = 0;
                    plateBox.Y = 0;
                    break;

                case 2:
                    plateBox.X = (float)-Size.Length;
                    plateBox.Y = 0;
                    break;

                case 3:
                    plateBox.X = (float)-Size.Length;
                    plateBox.Y = (float)-Size.Width;
                    break;

                case 4:
                    plateBox.X = 0;
                    plateBox.Y = (float)-Size.Width;
                    break;

                default:
                    return new Box();
            }

            plateBox.Width = Size.Width;
            plateBox.Length = Size.Length;

            if (!includeParts)
                return plateBox;

            var boundingBox = new Box();
            var partsBox = Parts.GetBoundingBox();

            boundingBox.X = partsBox.Left < plateBox.Left ? partsBox.Left : plateBox.Left;

            boundingBox.Y = partsBox.Bottom < plateBox.Bottom ? partsBox.Bottom : plateBox.Bottom;

            boundingBox.Length =
                partsBox.Right > plateBox.Right
                    ? partsBox.Right - boundingBox.X
                    : plateBox.Right - boundingBox.X;

            boundingBox.Width =
                partsBox.Top > plateBox.Top
                    ? partsBox.Top - boundingBox.Y
                    : plateBox.Top - boundingBox.Y;

            return boundingBox;
        }

        /// <summary>
        /// The area within the edge spacing.
        /// </summary>
        /// <returns></returns>
        public Box WorkArea()
        {
            var box = BoundingBox(false);

            box.X += EdgeSpacing.Left;
            box.Y += EdgeSpacing.Bottom;
            box.Length -= EdgeSpacing.Left + EdgeSpacing.Right;
            box.Width -= EdgeSpacing.Top + EdgeSpacing.Bottom;

            return box;
        }

        /// <summary>
        /// Automatically sizes the plate to fit the parts.
        /// </summary>
        /// <param name="roundingFactor">The factor to round the actual size up to.</param>
        /// <example>
        /// AutoSize 9.7 x 10.1
        /// * roundingFactor=1.0   new Size=10 x 11
        /// * roundingFactor=0.5   new Size=10 x 10.5
        /// * roundingFactor=0.25  new Size=9.75 x 10.25
        /// * roundingFactor=0.0   new Size=9.7 x 10.1
        /// </example>
        public void AutoSize(double roundingFactor = 1.0)
        {
            if (Parts.Count == 0)
                return;

            var bounds = Parts.GetBoundingBox();

            // Convention: Length = X axis, Width = Y axis
            double xExtent;
            double yExtent;

            switch (Quadrant)
            {
                case 1:
                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
                    break;

                case 2:
                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
                    break;

                case 3:
                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
                    break;

                case 4:
                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
                    break;

                default:
                    return;
            }

            Size = new Size(
                Rounding.RoundUpToNearest(yExtent, roundingFactor),
                Rounding.RoundUpToNearest(xExtent, roundingFactor)
            );
        }

        /// <summary>
        /// Sizes the plate using the <see cref="PlateSizes"/> catalog: small
        /// layouts snap to an increment, larger ones round up to the next
        /// standard mill sheet. The plate's long-axis orientation (X vs Y)
        /// is preserved. Does nothing if the plate has no parts.
        /// </summary>
        public PlateSizeResult SnapToStandardSize(PlateSizeOptions options = null)
        {
            if (Parts.Count == 0)
                return default;

            var bounds = Parts.GetBoundingBox();

            // Quadrant-aware extents relative to the plate origin, matching AutoSize.
            double xExtent;
            double yExtent;

            switch (Quadrant)
            {
                case 1:
                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
                    break;

                case 2:
                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
                    break;

                case 3:
                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
                    break;

                case 4:
                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
                    break;

                default:
                    return default;
            }

            // PlateSizes.Recommend takes (short, long); canonicalize then map
            // the result back so the plate's long axis stays aligned with the
            // parts' long axis.
            var shortDim = System.Math.Min(xExtent, yExtent);
            var longDim = System.Math.Max(xExtent, yExtent);
            var result = PlateSizes.Recommend(shortDim, longDim, options);

            // Plate convention: Length = X axis, Width = Y axis.
            if (xExtent >= yExtent)
                Size = new Size(result.Width, result.Length); // X is the long axis
            else
                Size = new Size(result.Length, result.Width); // Y is the long axis

            return result;
        }

        /// <summary>
        /// Gets the area of the top surface of the plate.
        /// </summary>
        /// <returns></returns>
        public double Area()
        {
            return Size.Width * Size.Length;
        }

        /// <summary>
        /// Gets the volume of the plate.
        /// </summary>
        public double Volume(double thickness)
        {
            return Area() * thickness;
        }

        /// <summary>
        /// Gets the weight of the plate.
        /// </summary>
        public double Weight(double thickness, double density)
        {
            return Volume(thickness) * density;
        }

        /// <summary>
        /// Percentage of the material used.
        /// </summary>
        /// <returns>Returns a number between 0.0 and 1.0</returns>
        public double Utilization()
        {
            return Parts.Where(p => !p.BaseDrawing.IsCutOff).Sum(part => part.BaseDrawing.Area)
                / Area();
        }

        public bool HasOverlappingParts(out List<Vector> pts)
        {
            pts = new List<Vector>();
            var realParts = Parts.Where(p => !p.BaseDrawing.IsCutOff).ToList();

            for (var i = 0; i < realParts.Count; i++)
            {
                var part1 = realParts[i];
                var b1 = part1.BoundingBox;

                for (var j = i + 1; j < realParts.Count; j++)
                {
                    var part2 = realParts[j];
                    var b2 = part2.BoundingBox;

                    // Skip pairs whose bounding boxes don't meaningfully overlap.
                    // Floating-point rounding can produce sub-epsilon overlaps for
                    // parts that are merely edge-touching, so require the overlap
                    // region to exceed Epsilon in both dimensions.
                    var overlapX =
                        System.Math.Min(b1.Right, b2.Right) - System.Math.Max(b1.Left, b2.Left);
                    var overlapY =
                        System.Math.Min(b1.Top, b2.Top) - System.Math.Max(b1.Bottom, b2.Bottom);

                    if (overlapX <= Math.Tolerance.Epsilon || overlapY <= Math.Tolerance.Epsilon)
                        continue;

                    if (part1.Intersects(part2, out var pts2))
                        pts.AddRange(pts2);
                }
            }

            return pts.Count > 0;
        }
    }
}