using System;
using System.Collections.Generic;
using OpenNest.Converters;
using OpenNest.Geometry;
using OpenNest.Math;

namespace OpenNest;

/// <summary>Validates a trial against immutable job geometry before the runner commits accounting.</summary>
internal static class NestJobPlacementValidator
{
    private const double Epsilon = 0.0000001;

    internal static void ValidateCandidate(
        PlateCandidate candidate,
        NestPlateStock stock,
        IReadOnlyDictionary<string, int> remaining,
        IReadOnlyDictionary<string, NestJobPart> parts
    )
    {
        if (candidate == null)
            throw new InvalidOperationException("The plate nester returned a null candidate.");
        var counts = new Dictionary<string, int>(StringComparer.Ordinal);
        var placed = new List<ShapeTopology>();
        foreach (var placement in candidate.Placements)
        {
            if (
                placement.PartId == null
                || !remaining.TryGetValue(placement.PartId, out var available)
                || !parts.TryGetValue(placement.PartId, out var part)
            )
                throw new InvalidOperationException(
                    "Candidate references an unknown requirement ID."
                );
            if (
                !double.IsFinite(placement.X)
                || !double.IsFinite(placement.Y)
                || !double.IsFinite(placement.Rotation)
            )
                throw new InvalidOperationException("Candidate poses must be finite.");
            counts.TryGetValue(placement.PartId, out var count);
            if (count >= available)
                throw new InvalidOperationException("Candidate overproduces a requirement.");
            if (!RotationIsAllowed(part.Rotation, placement.Rotation))
                throw new InvalidOperationException(
                    "Candidate rotation is not allowed for the requirement."
                );

            var shape = Transform(CreateShape(part.Geometry), placement);
            if (!FitsWorkArea(shape, stock))
                throw new InvalidOperationException(
                    "Candidate placement falls outside the usable stock area."
                );
            foreach (var other in placed)
            {
                if (Overlaps(shape, other))
                    throw new InvalidOperationException("Candidate placements overlap.");
                if (stock.PartSpacing > 0 && Distance(shape, other) < stock.PartSpacing - Epsilon)
                    throw new InvalidOperationException(
                        "Candidate placements violate required part spacing."
                    );
            }

            placed.Add(shape);
            counts[placement.PartId] = count + 1;
        }
    }

    internal static void ValidateGeometry(PartGeometrySnapshot geometry)
    {
        _ = CreateShape(geometry);
    }

    private static bool RotationIsAllowed(RotationPolicy policy, double rotation)
    {
        if (policy.Kind == RotationPolicyKind.Automatic)
            return true;
        if (policy.Kind == RotationPolicyKind.Fixed)
            return AnglesEqual(rotation, policy.Start);
        if (rotation < policy.Start - Epsilon || rotation > policy.End + Epsilon)
            return false;
        var steps = (rotation - policy.Start) / policy.Step;
        return System.Math.Abs(steps - System.Math.Round(steps)) <= Epsilon;
    }

    private static bool AnglesEqual(double left, double right)
    {
        var delta = (left - right) % (System.Math.PI * 2);
        return System.Math.Abs(delta) <= Epsilon
            || System.Math.Abs(System.Math.Abs(delta) - System.Math.PI * 2) <= Epsilon;
    }

    private static ShapeTopology CreateShape(PartGeometrySnapshot geometry)
    {
        var entities = ConvertProgram.ToGeometry(DrawingJobMapper.ToProgram(geometry));
        var cutEntities = new List<Entity>();
        foreach (var entity in entities)
            if (!ReferenceEquals(entity.Layer, SpecialLayers.Rapid))
                cutEntities.Add(entity);

        var contours = ShapeBuilder.GetShapes(cutEntities);
        if (contours.Count == 0)
            throw new ArgumentException("Geometry must contain a closed contour.");
        var closedEntities = new List<Entity>();
        var marks = new List<Shape>();
        foreach (var contour in contours)
        {
            if (contour.IsClosed())
            {
                ValidateContour(contour);
                closedEntities.AddRange(contour.Entities);
            }
            else
                marks.Add(contour);
        }
        if (closedEntities.Count == 0)
            throw new ArgumentException("Geometry must contain a closed outer contour.");

        // ShapeProfile selects the outer profile, but does not validate containment and
        // treats open chains as cutouts. Only validated closed contours may define material.
        var profile = new ShapeProfile(closedEntities);
        foreach (var cutout in profile.Cutouts)
            ValidateInternalChain(cutout, profile.Perimeter, new List<Shape>());
        foreach (var mark in marks)
            ValidateMark(mark, profile.Perimeter, profile.Cutouts);
        profile.NormalizeWinding();
        return new ShapeTopology(profile.Perimeter, profile.Cutouts);
    }

    private static void ValidateMark(Shape mark, Shape perimeter, List<Shape> holes)
    {
        const double chordTolerance = 0.00001;
        var boundaries = new List<Shape> { perimeter };
        boundaries.AddRange(holes);
        var polygons = boundaries.ConvertAll(s => s.ToPolygonWithTolerance(chordTolerance));
        foreach (var entity in mark.Entities)
        {
            if (entity.Length <= Epsilon || entity is not (Line or Arc))
                throw new ArgumentException("Unsupported or degenerate internal mark.");
            var parameters = new List<double> { 0, 1 };
            foreach (var boundary in boundaries)
            {
                entity.Intersects(boundary, out var intersections);
                foreach (var point in intersections)
                    AddParameter(point);
                // Include endpoints of coincident edges (parallel intersections may be empty).
                foreach (var point in boundary.Entities.CollectPoints())
                    if (entity.ClosestPointTo(point).DistanceTo(point) <= Epsilon)
                        AddParameter(point);
            }
            parameters.Sort();
            for (var index = 0; index < parameters.Count; index++)
            {
                Check(PointAt(parameters[index]));
                if (index > 0)
                    Check(PointAt((parameters[index - 1] + parameters[index]) / 2));
            }

            void AddParameter(Vector point)
            {
                if (!point.IsValid())
                    throw new ArgumentException("Indeterminate mark intersection.");
                var value = entity is Line line
                    ? line.StartPoint.DistanceTo(point) / line.Length
                    : Angle.NormalizeRad(
                        ((Arc)entity).IsReversed
                            ? ((Arc)entity).StartAngle - ((Arc)entity).Center.AngleTo(point)
                            : ((Arc)entity).Center.AngleTo(point) - ((Arc)entity).StartAngle
                    ) / ((Arc)entity).SweepAngle();
                if (value >= 0 && value <= 1)
                    parameters.Add(value);
            }
            Vector PointAt(double value)
            {
                if (entity is Line line)
                    return line.StartPoint + (line.EndPoint - line.StartPoint) * value;
                var arc = (Arc)entity;
                var angle = arc.StartAngle + (arc.IsReversed ? -1 : 1) * arc.SweepAngle() * value;
                return arc.Center
                    + new Vector(System.Math.Cos(angle), System.Math.Sin(angle)) * arc.Radius;
            }
            void Check(Vector point)
            {
                for (var index = 0; index < boundaries.Count; index++)
                {
                    // Exact analytic boundary contact is allowed; near-boundary uncertainty is not.
                    var onBoundary = false;
                    foreach (var edge in boundaries[index].Entities)
                        if (edge.ClosestPointTo(point).DistanceTo(point) <= Epsilon)
                            onBoundary = true;
                    if (onBoundary)
                        continue;
                    foreach (var edge in polygons[index].ToLines())
                        if (edge.ClosestPointTo(point).DistanceTo(point) <= 2 * chordTolerance)
                            throw new ArgumentException(
                                "Internal mark is too close to a material boundary."
                            );
                    var inside = StrictlyInside(polygons[index], point);
                    if (index == 0 ? !inside : inside)
                        throw new ArgumentException(
                            "Open geometry leaves the closed material region."
                        );
                }
            }
        }
    }

    private static void ValidateInternalChain(Shape chain, Shape perimeter, List<Shape> holes)
    {
        // A connected analytic entity cannot leave material without crossing its boundary.
        // Reject contact too: conservative, rather than guessing at tangent/collinear cuts.
        // The witness point is farther than the polygonization error from every boundary.
        const double chordTolerance = 0.00001;
        var boundaries = new List<Shape> { perimeter };
        boundaries.AddRange(holes);
        var polygons = boundaries.ConvertAll(s => s.ToPolygonWithTolerance(chordTolerance));
        foreach (var entity in chain.Entities)
        {
            if (entity.Length <= Epsilon)
                throw new ArgumentException("Geometry contains a zero-length internal edge.");
            var point = entity switch
            {
                Line line => line.StartPoint,
                Arc arc => arc.StartPoint(),
                Circle circle => circle.Center.Offset(circle.Radius, 0),
                _ => throw new ArgumentException("Unsupported internal geometry."),
            };
            if (!StrictlyInside(polygons[0], point))
                throw new ArgumentException(
                    "Open or disconnected geometry lies outside the closed perimeter."
                );
            for (var index = 0; index < boundaries.Count; index++)
            {
                if (index > 0 && polygons[index].ContainsPoint(point))
                    throw new ArgumentException("Internal geometry lies in a cutout.");
                foreach (var edge in polygons[index].ToLines())
                    if (edge.ClosestPointTo(point).DistanceTo(point) <= 2 * chordTolerance)
                        throw new ArgumentException(
                            "Internal geometry is too close to a material boundary."
                        );
                if (entity.Intersects(boundaries[index]))
                    throw new ArgumentException(
                        "Internal geometry crosses or touches a material boundary."
                    );
            }
        }
    }

    private static void ValidateContour(Shape contour)
    {
        if (!contour.IsClosed())
            throw new ArgumentException("Geometry must contain closed contours with usable edges.");
        foreach (var entity in contour.Entities)
            if (entity.Length <= Epsilon)
                throw new ArgumentException("Geometry contains a zero-length edge.");
        if (contour.Area() <= Epsilon)
            throw new ArgumentException("Geometry must contain non-degenerate contours.");
    }

    private static ShapeTopology Transform(ShapeTopology source, NestJobPlacement placement)
    {
        var perimeter = TransformContour(source.Perimeter, placement);
        var cutouts = new List<Shape>(source.Cutouts.Count);
        foreach (var cutout in source.Cutouts)
            cutouts.Add(TransformContour(cutout, placement));
        return new ShapeTopology(perimeter, cutouts);
    }

    private static Shape TransformContour(Shape source, NestJobPlacement placement)
    {
        var contour = (Shape)source.Clone();
        contour.Rotate(placement.Rotation);
        contour.Offset(placement.X, placement.Y);
        return contour;
    }

    private static bool FitsWorkArea(ShapeTopology shape, NestPlateStock stock)
    {
        var workArea = WorkArea(stock);
        if (!FitsWorkArea(shape.Perimeter, workArea))
            return false;
        foreach (var cutout in shape.Cutouts)
            if (!FitsWorkArea(cutout, workArea))
                return false;
        return true;
    }

    private static Box WorkArea(NestPlateStock stock)
    {
        var left = stock.Quadrant is 1 or 4 ? 0 : -stock.Size.Length;
        var bottom = stock.Quadrant is 1 or 2 ? 0 : -stock.Size.Width;
        return new Box(
            left + stock.EdgeSpacing.Left,
            bottom + stock.EdgeSpacing.Bottom,
            stock.Size.Length - stock.EdgeSpacing.Left - stock.EdgeSpacing.Right,
            stock.Size.Width - stock.EdgeSpacing.Bottom - stock.EdgeSpacing.Top
        );
    }

    private static bool FitsWorkArea(Shape contour, Box workArea)
    {
        var bounds = contour.BoundingBox;
        return bounds.Left >= workArea.Left - Epsilon
            && bounds.Right <= workArea.Right + Epsilon
            && bounds.Bottom >= workArea.Bottom - Epsilon
            && bounds.Top <= workArea.Top + Epsilon;
    }

    private static bool Overlaps(ShapeTopology left, ShapeTopology right)
    {
        var leftPoly = ToPolygon(left.Perimeter);
        var rightPoly = ToPolygon(right.Perimeter);
        if (!leftPoly.BoundingBox.Intersects(rightPoly.BoundingBox))
            return false;
        // True material overlap requires shared interior area, not boundary touching.
        // Edge/corner contact (zero clearance) is a valid placement when part spacing is zero.
        // Collision checks this by clipping triangulated polygons and rejecting zero-area
        // slivers, so it catches containment and small corner intersections that a witness
        // probe can miss, while contact stays legal; cutouts are subtracted from both sides.
        return Collision.HasOverlap(
            leftPoly,
            rightPoly,
            ToPolygons(left.Cutouts),
            ToPolygons(right.Cutouts)
        );
    }

    /// <summary>
    /// Winding-number point-in-polygon. Returns false for points on an edge or vertex.
    /// </summary>
    private static bool StrictlyInside(Polygon polygon, Vector point)
    {
        var n = polygon.IsClosed() ? polygon.Vertices.Count - 1 : polygon.Vertices.Count;
        if (n < 3)
            return false;
        var winding = 0;
        for (var i = 0; i < n; i++)
        {
            var p1 = polygon.Vertices[i];
            var p2 = polygon.Vertices[(i + 1) % n];
            if (OnSegment(p1, p2, point))
                return false;
            if (p1.Y <= point.Y)
            {
                if (p2.Y > point.Y && IsLeft(p1, p2, point) > 0)
                    winding++;
            }
            else if (p2.Y <= point.Y && IsLeft(p1, p2, point) < 0)
            {
                winding--;
            }
        }
        return winding != 0;
    }

    private static bool OnSegment(Vector a, Vector b, Vector p)
    {
        var cross = (b.X - a.X) * (p.Y - a.Y) - (b.Y - a.Y) * (p.X - a.X);
        if (!cross.IsEqualTo(0.0))
            return false;
        return System.Math.Min(a.X, b.X) - Epsilon <= p.X
            && p.X <= System.Math.Max(a.X, b.X) + Epsilon
            && System.Math.Min(a.Y, b.Y) - Epsilon <= p.Y
            && p.Y <= System.Math.Max(a.Y, b.Y) + Epsilon;
    }

    private static double IsLeft(Vector p1, Vector p2, Vector p) =>
        (p2.X - p1.X) * (p.Y - p1.Y) - (p2.Y - p1.Y) * (p.X - p1.X);

    private static double Distance(ShapeTopology left, ShapeTopology right)
    {
        var result = double.PositiveInfinity;
        foreach (var leftContour in AllContours(left))
        foreach (var rightContour in AllContours(right))
            result = System.Math.Min(
                result,
                BoundaryDistance(ToPolygon(leftContour), ToPolygon(rightContour))
            );
        return result;
    }

    private static IEnumerable<Shape> AllContours(ShapeTopology shape)
    {
        yield return shape.Perimeter;
        foreach (var cutout in shape.Cutouts)
            yield return cutout;
    }

    private static List<Polygon> ToPolygons(List<Shape> contours)
    {
        var polygons = new List<Polygon>(contours.Count);
        foreach (var contour in contours)
            polygons.Add(ToPolygon(contour));
        return polygons;
    }

    private static Polygon ToPolygon(Shape contour)
    {
        var polygon = contour.ToPolygon();
        polygon.UpdateBounds();
        return polygon;
    }

    private static double BoundaryDistance(Polygon left, Polygon right)
    {
        var result = double.PositiveInfinity;
        foreach (var leftLine in left.ToLines())
        {
            foreach (var rightLine in right.ToLines())
            {
                if (leftLine.Intersects(rightLine))
                    return 0;
                result = System.Math.Min(
                    result,
                    leftLine.ClosestPointTo(rightLine.StartPoint).DistanceTo(rightLine.StartPoint)
                );
                result = System.Math.Min(
                    result,
                    leftLine.ClosestPointTo(rightLine.EndPoint).DistanceTo(rightLine.EndPoint)
                );
                result = System.Math.Min(
                    result,
                    rightLine.ClosestPointTo(leftLine.StartPoint).DistanceTo(leftLine.StartPoint)
                );
                result = System.Math.Min(
                    result,
                    rightLine.ClosestPointTo(leftLine.EndPoint).DistanceTo(leftLine.EndPoint)
                );
            }
        }
        return result;
    }

    private sealed class ShapeTopology(Shape perimeter, List<Shape> cutouts)
    {
        internal Shape Perimeter { get; } = perimeter;
        internal List<Shape> Cutouts { get; } = cutouts;
    }
}