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

namespace OpenNest
{
    public class FillLinear
    {
        public FillLinear(Box workArea, double partSpacing)
        {
            PartSpacing = partSpacing;
            WorkArea = new Box(workArea.X, workArea.Y, workArea.Width, workArea.Height);
        }

        public Box WorkArea { get; }

        public double PartSpacing { get; }
        
        public double HalfSpacing => PartSpacing / 2;

        private static Vector MakeOffset(NestDirection direction, double distance)
        {
            return direction == NestDirection.Horizontal
                ? new Vector(distance, 0)
                : new Vector(0, distance);
        }

        private static PushDirection GetPushDirection(NestDirection direction)
        {
            return direction == NestDirection.Horizontal
                ? PushDirection.Left
                : PushDirection.Down;
        }

        private static double GetDimension(Box box, NestDirection direction)
        {
            return direction == NestDirection.Horizontal ? box.Width : box.Height;
        }

        private static double GetStart(Box box, NestDirection direction)
        {
            return direction == NestDirection.Horizontal ? box.Left : box.Bottom;
        }

        private double GetLimit(NestDirection direction)
        {
            return direction == NestDirection.Horizontal ? WorkArea.Right : WorkArea.Top;
        }

        private static NestDirection PerpendicularAxis(NestDirection direction)
        {
            return direction == NestDirection.Horizontal
                ? NestDirection.Vertical
                : NestDirection.Horizontal;
        }

        /// <summary>
        /// Computes the slide distance for the push algorithm, returning the
        /// geometry-aware copy distance along the given axis.
        /// </summary>
        private double ComputeCopyDistance(double bboxDim, double slideDistance)
        {
            if (slideDistance >= double.MaxValue || slideDistance < 0)
                return bboxDim + PartSpacing;

            return bboxDim - slideDistance;
        }

        /// <summary>
        /// Finds the geometry-aware copy distance between two identical parts along an axis.
        /// Both parts are inflated by half-spacing for symmetric spacing.
        /// </summary>
        private double FindCopyDistance(Part partA, NestDirection direction, PartBoundary boundary)
        {
            var bboxDim = GetDimension(partA.BoundingBox, direction);
            var pushDir = GetPushDirection(direction);
            var opposite = Helper.OppositeDirection(pushDir);

            var partB = partA.CloneAtOffset(MakeOffset(direction, bboxDim));

            var movingLines = boundary.GetLines(partB.Location, pushDir);
            var stationaryLines = boundary.GetLines(partA.Location, opposite);
            var slideDistance = Helper.DirectionalDistance(movingLines, stationaryLines, pushDir);

            return ComputeCopyDistance(bboxDim, slideDistance);
        }

        /// <summary>
        /// Finds the geometry-aware copy distance between two identical patterns along an axis.
        /// Checks every pair of parts across adjacent patterns so that multi-part
        /// patterns (e.g. interlocking pairs) maintain spacing between ALL parts.
        /// Both sides are inflated by half-spacing for symmetric spacing.
        /// </summary>
        private double FindPatternCopyDistance(Pattern patternA, NestDirection direction, PartBoundary[] boundaries)
        {
            if (patternA.Parts.Count <= 1)
                return FindSinglePartPatternCopyDistance(patternA, direction, boundaries[0]);

            var bboxDim = GetDimension(patternA.BoundingBox, direction);
            var pushDir = GetPushDirection(direction);
            var opposite = Helper.OppositeDirection(pushDir);

            // Compute a starting offset large enough that every part-pair in
            // patternB has its offset geometry beyond patternA's offset geometry.
            var startOffset = bboxDim;

            for (var i = 0; i < patternA.Parts.Count; i++)
            {
                var aUpper = direction == NestDirection.Horizontal
                    ? patternA.Parts[i].BoundingBox.Right : patternA.Parts[i].BoundingBox.Top;

                for (var j = 0; j < patternA.Parts.Count; j++)
                {
                    var bLower = direction == NestDirection.Horizontal
                        ? patternA.Parts[j].BoundingBox.Left : patternA.Parts[j].BoundingBox.Bottom;

                    var required = aUpper - bLower + PartSpacing + Tolerance.Epsilon;

                    if (required > startOffset)
                        startOffset = required;
                }
            }

            var patternB = patternA.Clone(MakeOffset(direction, startOffset));

            // Pre-compute stationary lines for patternA parts.
            var stationaryCache = new List<Line>[patternA.Parts.Count];

            for (var i = 0; i < patternA.Parts.Count; i++)
                stationaryCache[i] = boundaries[i].GetLines(patternA.Parts[i].Location, opposite);

            var maxCopyDistance = 0.0;

            for (var j = 0; j < patternB.Parts.Count; j++)
            {
                var partB = patternB.Parts[j];
                var movingLines = boundaries[j].GetLines(partB.Location, pushDir);

                for (var i = 0; i < patternA.Parts.Count; i++)
                {
                    var slideDistance = Helper.DirectionalDistance(movingLines, stationaryCache[i], pushDir);

                    if (slideDistance >= double.MaxValue || slideDistance < 0)
                        continue;

                    var copyDist = startOffset - slideDistance;

                    if (copyDist > maxCopyDistance)
                        maxCopyDistance = copyDist;
                }
            }

            // Fallback: if no pair interacted (shouldn't happen for real parts),
            // use the simple bounding-box + spacing distance.
            if (maxCopyDistance <= 0)
                return bboxDim + PartSpacing;

            return maxCopyDistance;
        }

        /// <summary>
        /// Fast path for single-part patterns — no cross-part conflicts possible.
        /// </summary>
        private double FindSinglePartPatternCopyDistance(Pattern patternA, NestDirection direction, PartBoundary boundary)
        {
            var bboxDim = GetDimension(patternA.BoundingBox, direction);
            var pushDir = GetPushDirection(direction);
            var opposite = Helper.OppositeDirection(pushDir);

            var patternB = patternA.Clone(MakeOffset(direction, bboxDim));

            var movingLines = GetPatternLines(patternB, boundary, pushDir);
            var stationaryLines = GetPatternLines(patternA, boundary, opposite);
            var slideDistance = Helper.DirectionalDistance(movingLines, stationaryLines, pushDir);

            return ComputeCopyDistance(bboxDim, slideDistance);
        }

        /// <summary>
        /// Gets offset boundary lines for all parts in a pattern using a shared boundary.
        /// </summary>
        private static List<Line> GetPatternLines(Pattern pattern, PartBoundary boundary, PushDirection direction)
        {
            var lines = new List<Line>();

            foreach (var part in pattern.Parts)
                lines.AddRange(boundary.GetLines(part.Location, direction));

            return lines;
        }

        /// <summary>
        /// Creates boundaries for all parts in a pattern. Parts that share the same
        /// program geometry (same drawing and rotation) reuse the same boundary instance.
        /// </summary>
        private PartBoundary[] CreateBoundaries(Pattern pattern)
        {
            var boundaries = new PartBoundary[pattern.Parts.Count];
            var cache = new List<(Drawing drawing, double rotation, PartBoundary boundary)>();

            for (var i = 0; i < pattern.Parts.Count; i++)
            {
                var part = pattern.Parts[i];
                PartBoundary found = null;

                foreach (var entry in cache)
                {
                    if (entry.drawing == part.BaseDrawing && entry.rotation.IsEqualTo(part.Rotation))
                    {
                        found = entry.boundary;
                        break;
                    }
                }

                if (found == null)
                {
                    found = new PartBoundary(part, HalfSpacing);
                    cache.Add((part.BaseDrawing, part.Rotation, found));
                }

                boundaries[i] = found;
            }

            return boundaries;
        }

        /// <summary>
        /// Tiles a pattern along the given axis, returning the cloned parts
        /// (does not include the original pattern's parts). For multi-part
        /// patterns, also adds individual parts from the next incomplete copy
        /// that still fit within the work area.
        /// </summary>
        private List<Part> TilePattern(Pattern basePattern, NestDirection direction, PartBoundary[] boundaries)
        {
            var result = new List<Part>();
            var copyDistance = FindPatternCopyDistance(basePattern, direction, boundaries);

            if (copyDistance <= 0)
                return result;

            var dim = GetDimension(basePattern.BoundingBox, direction);
            var start = GetStart(basePattern.BoundingBox, direction);
            var limit = GetLimit(direction);

            var count = 1;

            while (true)
            {
                var nextPos = start + copyDistance * count;

                if (nextPos + dim > limit + Tolerance.Epsilon)
                    break;

                var clone = basePattern.Clone(MakeOffset(direction, copyDistance * count));
                result.AddRange(clone.Parts);
                count++;
            }

            // For multi-part patterns, try to place individual parts from the
            // next copy that didn't fit as a whole. This handles cases where
            // e.g. a 2-part pair only partially fits — one part may still be
            // within the work area even though the full pattern exceeds it.
            if (basePattern.Parts.Count > 1)
            {
                var partialClone = basePattern.Clone(MakeOffset(direction, copyDistance * count));

                foreach (var part in partialClone.Parts)
                {
                    if (part.BoundingBox.Right <= WorkArea.Right + Tolerance.Epsilon &&
                        part.BoundingBox.Top <= WorkArea.Top + Tolerance.Epsilon &&
                        part.BoundingBox.Left >= WorkArea.Left - Tolerance.Epsilon &&
                        part.BoundingBox.Bottom >= WorkArea.Bottom - Tolerance.Epsilon)
                    {
                        result.Add(part);
                    }
                }
            }

            return result;
        }

        /// <summary>
        /// Creates a seed pattern containing a single part positioned at the work area origin.
        /// Returns an empty pattern if the part does not fit.
        /// </summary>
        private Pattern MakeSeedPattern(Drawing drawing, double rotationAngle)
        {
            var pattern = new Pattern();

            var template = new Part(drawing);

            if (!rotationAngle.IsEqualTo(0))
                template.Rotate(rotationAngle);

            var bbox = template.Program.BoundingBox();
            template.Offset(WorkArea.Location - bbox.Location);
            template.UpdateBounds();

            if (template.BoundingBox.Width > WorkArea.Width + Tolerance.Epsilon ||
                template.BoundingBox.Height > WorkArea.Height + Tolerance.Epsilon)
                return pattern;

            pattern.Parts.Add(template);
            pattern.UpdateBounds();
            return pattern;
        }

        /// <summary>
        /// Recursively fills the work area. At depth 0, tiles the pattern along the
        /// primary axis, then recurses perpendicular. At depth 1, tiles and returns.
        /// </summary>
        private List<Part> FillRecursive(Pattern pattern, NestDirection direction, int depth)
        {
            var boundaries = CreateBoundaries(pattern);
            var result = new List<Part>(pattern.Parts);
            result.AddRange(TilePattern(pattern, direction, boundaries));

            if (depth == 0 && result.Count > pattern.Parts.Count)
            {
                var rowPattern = new Pattern();
                rowPattern.Parts.AddRange(result);
                rowPattern.UpdateBounds();
                return FillRecursive(rowPattern, PerpendicularAxis(direction), depth + 1);
            }

            if (depth == 0)
            {
                // Single part didn't tile along primary — still try perpendicular.
                return FillRecursive(pattern, PerpendicularAxis(direction), depth + 1);
            }

            return result;
        }

        /// <summary>
        /// Fills a single row of identical parts along one axis using geometry-aware spacing.
        /// </summary>
        public Pattern FillRow(Drawing drawing, double rotationAngle, NestDirection direction)
        {
            var seed = MakeSeedPattern(drawing, rotationAngle);

            if (seed.Parts.Count == 0)
                return seed;

            var template = seed.Parts[0];
            var boundary = new PartBoundary(template, HalfSpacing);

            var copyDistance = FindCopyDistance(template, direction, boundary);

            if (copyDistance <= 0)
                return seed;

            var dim = GetDimension(template.BoundingBox, direction);
            var start = GetStart(template.BoundingBox, direction);
            var limit = GetLimit(direction);

            var count = 1;

            while (true)
            {
                var nextPos = start + copyDistance * count;

                if (nextPos + dim > limit + Tolerance.Epsilon)
                    break;

                var clone = template.CloneAtOffset(MakeOffset(direction, copyDistance * count));
                seed.Parts.Add(clone);
                count++;
            }

            seed.UpdateBounds();
            return seed;
        }

        /// <summary>
        /// Fills the work area by tiling a pre-built pattern along both axes.
        /// </summary>
        public List<Part> Fill(Pattern pattern, NestDirection primaryAxis)
        {
            if (pattern.Parts.Count == 0)
                return new List<Part>();

            var offset = WorkArea.Location - pattern.BoundingBox.Location;
            var basePattern = pattern.Clone(offset);

            if (basePattern.BoundingBox.Width > WorkArea.Width + Tolerance.Epsilon ||
                basePattern.BoundingBox.Height > WorkArea.Height + Tolerance.Epsilon)
                return new List<Part>();

            return FillRecursive(basePattern, primaryAxis, depth: 0);
        }

        /// <summary>
        /// Fills the work area by creating a seed part, then recursively tiling
        /// along the primary axis and then the perpendicular axis.
        /// </summary>
        public List<Part> Fill(Drawing drawing, double rotationAngle, NestDirection primaryAxis)
        {
            var seed = MakeSeedPattern(drawing, rotationAngle);

            if (seed.Parts.Count == 0)
                return new List<Part>();

            return FillRecursive(seed, primaryAxis, depth: 0);
        }
    }
}