using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.ExceptionServices;
using System.Threading;
using System.Threading.Tasks;
using OpenNest.Engine;
using OpenNest.Engine.BestFit;
using OpenNest.Engine.Strategies;
using OpenNest.Geometry;
using OpenNest.Math;

namespace OpenNest.Engine.Fill;

public class StripeFiller
{
    private const int MaxPairCandidates = 5;
    private const int MaxConvergenceIterations = 20;
    private const int AngleSamples = 36;

    private readonly FillContext _context;
    private readonly NestDirection _primaryAxis;
    private readonly IFillComparer _comparer;
    private readonly GridDedup _dedup;

    /// <summary>
    /// When true, only complete stripes are placed — no partial rows/columns.
    /// </summary>
    public bool CompleteStripesOnly { get; set; }

    public StripeFiller(FillContext context, NestDirection primaryAxis)
    {
        _context = context;
        _primaryAxis = primaryAxis;
        _comparer = context.Policy?.Comparer ?? new DefaultFillComparer();
        _dedup = GridDedup.GetOrCreate(context.SharedState);
    }

    public List<Part> Fill()
    {
        var bestFits = GetPairCandidates();
        if (bestFits.Count == 0)
            return new List<Part>();

        var workArea = _context.WorkArea;
        var drawing = _context.Item.Drawing;
        var strategyName = _primaryAxis == NestDirection.Horizontal ? "Row" : "Column";

        var layouts = ComputeLayouts(bestFits, drawing);

        List<Part> bestParts = null;

        for (var i = 0; i < bestFits.Count; i++)
        {
            _context.Token.ThrowIfCancellationRequested();

            for (var a = 0; a < Axes.Length; a++)
            {
                var axis = Axes[a];
                var dirLabel = axis == NestDirection.Horizontal ? "Row" : "Col";

                for (var v = 0; v < VariantsPerAxis; v++)
                {
                    var layout = layouts[LayoutIndex(i, a, v)];
                    if (layout.Count <= 0)
                        continue;

                    var result = ClaimGrid(layout, axis);

                    if (result == null || result.Count == 0)
                        continue;

                    Debug.WriteLine(
                        $"[StripeFiller] {strategyName} candidate {i} {dirLabel}: "
                            + $"angle={Angle.ToDegrees(layout.Angle):F1}°, N={layout.Count}, waste={layout.Waste:F2}, "
                            + $"grid={result.Count} parts"
                    );

                    if (_comparer.IsBetter(result, bestParts, workArea))
                    {
                        bestParts = result;
                    }
                }
            }

            _context.ReportProgress(
                bestParts,
                $"{strategyName}: {i + 1}/{bestFits.Count} pairs, best = {bestParts?.Count ?? 0} parts"
            );
        }

        return bestParts ?? new List<Part>();
    }

    private static readonly NestDirection[] Axes = { NestDirection.Horizontal, NestDirection.Vertical };

    /// <summary>Expanding (<see cref="ConvergeStripeAngle"/>) then shrinking convergence.</summary>
    private const int VariantsPerAxis = 2;

    private static int LayoutIndex(int candidate, int axis, int variant) =>
        (candidate * Axes.Length + axis) * VariantsPerAxis + variant;

    /// <summary>
    /// A converged stripe angle and, when it holds a pattern, the rotated pattern and the grid
    /// it tiles before the order-dependent steps (<see cref="GridDedup"/> claim, cached remnant
    /// fill).
    /// </summary>
    private sealed class StripeLayout
    {
        public double Angle;
        public double Waste;
        public int Count;
        public Pattern Pattern;
        public bool GridReady;
        public List<Part> Grid;
    }

    /// <summary>
    /// Converges every candidate's stripe angle per axis and variant, then tiles the grids that
    /// <see cref="Fill"/> will claim, each step in parallel. Every layout is a pure function of
    /// its candidate, axis and variant (fresh part clones, per-call <see cref="FillLinear"/>
    /// state), so the results do not depend on the thread count. A grid is tiled only when its
    /// configuration is not yet claimed and no earlier layout shares it: claims are only ever
    /// added, so exactly those are the grids the sequential loop would have tiled.
    /// <see cref="Fill"/> then claims, fills remnants and ranks in the original order.
    /// </summary>
    private StripeLayout[] ComputeLayouts(List<BestFitResult> bestFits, Drawing drawing)
    {
        var layouts = new StripeLayout[bestFits.Count * Axes.Length * VariantsPerAxis];

        RunParallel(layouts.Length, index =>
        {
            var variant = index % VariantsPerAxis;
            var axis = Axes[index / VariantsPerAxis % Axes.Length];
            var candidate = bestFits[index / VariantsPerAxis / Axes.Length];
            layouts[index] = Converge(candidate.BuildParts(drawing), axis, variant);
        });

        var batch = new GridDedup();
        var toTile = new List<int>();
        for (var index = 0; index < layouts.Length; index++)
        {
            var layout = layouts[index];
            if (layout.Count <= 0)
                continue;

            var axis = Axes[index / VariantsPerAxis % Axes.Length];
            var box = layout.Pattern.BoundingBox;
            if (!_dedup.Contains(box, _context.WorkArea, axis) && batch.TryAdd(box, _context.WorkArea, axis))
                toTile.Add(index);
        }

        RunParallel(toTile.Count, k =>
        {
            var index = toTile[k];
            var layout = layouts[index];
            layout.Grid = BuildGrid(layout.Pattern, Axes[index / VariantsPerAxis % Axes.Length]);
            layout.GridReady = true;
        });

        return layouts;
    }

    private void RunParallel(int count, Action<int> body)
    {
        try
        {
            Parallel.For(0, count, new ParallelOptions { CancellationToken = _context.Token }, body);
        }
        catch (AggregateException ex)
        {
            // Surface the failure itself, cancellation included, as the sequential loop did.
            ExceptionDispatchInfo.Capture(ex.InnerExceptions[0]).Throw();
            throw;
        }
    }

    private StripeLayout Converge(List<Part> pairParts, NestDirection axis, int variant)
    {
        var spacing = _context.Plate.PartSpacing;
        var sheetSpan = GetDimension(_context.WorkArea, axis);

        var (angle, waste, count) = variant == 0
            ? ConvergeStripeAngle(pairParts, sheetSpan, spacing, axis, _context.Token, _context.MaxQuantity)
            : ConvergeStripeAngleShrink(pairParts, sheetSpan, spacing, axis, _context.Token, _context.MaxQuantity);

        var layout = new StripeLayout { Angle = angle, Waste = waste, Count = count };
        if (count > 0)
            layout.Pattern = FillHelpers.BuildRotatedPattern(pairParts, angle);

        return layout;
    }

    /// <summary>
    /// The order-dependent half of a stripe grid: claims its configuration and adds the cached
    /// remnant fill. Null when the configuration was already evaluated or no grid fits.
    /// </summary>
    private List<Part> ClaimGrid(StripeLayout layout, NestDirection primaryAxis)
    {
        if (!_dedup.TryAdd(layout.Pattern.BoundingBox, _context.WorkArea, primaryAxis))
            return null;

        // ComputeLayouts tiled every grid a claim can succeed for; tile here should it not have.
        var gridParts = layout.GridReady ? layout.Grid : BuildGrid(layout.Pattern, primaryAxis);
        if (gridParts == null)
            return null;

        var allParts = new List<Part>(gridParts);

        // A capped fill that already holds the quantity needs no remnant parts.
        if (_context.MaxQuantity > 0 && gridParts.Count >= _context.MaxQuantity)
            return allParts;

        var remnantParts = FillRemnant(gridParts, primaryAxis);
        if (remnantParts != null)
        {
            Debug.WriteLine($"[StripeFiller] Remnant: {remnantParts.Count} parts");
            allParts.AddRange(remnantParts);
        }

        return allParts;
    }

    /// <summary>
    /// Tiles the rotated pattern into a stripe and the stripe into a grid. Pure: reads only the
    /// pattern and the context's fixed inputs.
    /// </summary>
    private List<Part> BuildGrid(Pattern rotatedPattern, NestDirection primaryAxis)
    {
        var perpAxis =
            primaryAxis == NestDirection.Horizontal ? NestDirection.Vertical : NestDirection.Horizontal;
        var workArea = _context.WorkArea;
        var spacing = _context.Plate.PartSpacing;

        var perpDim = GetDimension(rotatedPattern.BoundingBox, perpAxis);
        var stripeBox = MakeStripeBox(workArea, perpDim, primaryAxis);

        var stripeEngine = new FillLinear(stripeBox, spacing)
        {
            Label = "Stripe",
            MaxParts = _context.MaxQuantity,
        };
        var stripeParts = stripeEngine.Fill(rotatedPattern, primaryAxis);

        if (stripeParts == null || stripeParts.Count == 0)
            return null;

        var partsPerStripe = stripeParts.Count;

        Debug.WriteLine(
            $"[StripeFiller] Stripe: {partsPerStripe} parts, "
                + $"box={stripeBox.Width:F2}x{stripeBox.Length:F2}"
        );

        var stripePattern = new Pattern();
        stripePattern.Parts.AddRange(stripeParts);
        stripePattern.UpdateBounds();

        var gridEngine = new FillLinear(workArea, spacing)
        {
            Label = "Stripe-Grid",
            MaxParts = _context.MaxQuantity,
        };
        var gridParts = gridEngine.Fill(stripePattern, perpAxis);

        if (gridParts == null || gridParts.Count == 0)
            return null;

        if (CompleteStripesOnly)
        {
            var completeCount = gridParts.Count / partsPerStripe * partsPerStripe;
            if (completeCount < gridParts.Count)
            {
                Debug.WriteLine(
                    $"[StripeFiller] CompleteOnly: {gridParts.Count} → {completeCount} "
                        + $"(dropped {gridParts.Count - completeCount} partial)"
                );
                gridParts = gridParts.GetRange(0, completeCount);
            }
        }

        Debug.WriteLine($"[StripeFiller] Grid: {gridParts.Count} parts");

        if (gridParts.Count == 0)
            return null;

        // Reject results where bounding boxes overlap — the angle convergence
        // can produce slightly off-axis rotations where FillLinear's copy
        // distance calculation doesn't fully account for the rotated geometry.
        if (HasOverlappingParts(gridParts))
        {
            Debug.WriteLine($"[StripeFiller] Rejected grid: overlapping bounding boxes detected");
            return null;
        }

        return gridParts;
    }

    private List<BestFitResult> GetPairCandidates()
    {
        List<BestFitResult> bestFits;

        if (_context.SharedState.TryGetValue("BestFits", out var cached))
            bestFits = (List<BestFitResult>)cached;
        else
            bestFits = BestFitCache.GetOrCompute(
                _context.Item.Drawing,
                _context.Plate.Size.Length,
                _context.Plate.Size.Width,
                _context.Plate.PartSpacing,
                _context.Token
            );

        return bestFits.Where(r => r.Keep).Take(MaxPairCandidates).ToList();
    }

    private static Box MakeStripeBox(Box workArea, double perpDim, NestDirection primaryAxis)
    {
        return primaryAxis == NestDirection.Horizontal
            ? new Box(workArea.X, workArea.Y, workArea.Length, perpDim)
            : new Box(workArea.X, workArea.Y, perpDim, workArea.Width);
    }

    private List<Part> FillRemnant(List<Part> gridParts, NestDirection primaryAxis)
    {
        var workArea = _context.WorkArea;
        var spacing = _context.Plate.PartSpacing;
        var drawing = _context.Item.Drawing;

        var gridBox = gridParts.GetBoundingBox();
        var minDim = System.Math.Min(
            drawing.Program.BoundingBox().Width,
            drawing.Program.BoundingBox().Length
        );

        Box remnantBox;

        if (primaryAxis == NestDirection.Horizontal)
        {
            var remnantY = gridBox.Top + spacing;
            var remnantLength = workArea.Top - remnantY;
            if (remnantLength < minDim)
                return null;
            remnantBox = new Box(workArea.X, remnantY, workArea.Length, remnantLength);
        }
        else
        {
            var remnantX = gridBox.Right + spacing;
            var remnantWidth = workArea.Right - remnantX;
            if (remnantWidth < minDim)
                return null;
            remnantBox = new Box(remnantX, workArea.Y, remnantWidth, workArea.Width);
        }

        Debug.WriteLine(
            $"[StripeFiller] Remnant box: {remnantBox.Width:F2}x{remnantBox.Length:F2}"
        );

        var cachedResult = FillResultCache.Get(drawing, remnantBox, spacing);
        if (cachedResult != null)
        {
            Debug.WriteLine($"[StripeFiller] Remnant CACHE HIT: {cachedResult.Count} parts");
            return cachedResult;
        }

        var filler = new FillLinear(remnantBox, spacing) { Label = "Stripe-Remnant" };
        List<Part> best = null;

        foreach (var angle in new[] { 0.0, Angle.HalfPI })
        {
            _context.Token.ThrowIfCancellationRequested();
            var result = FillHelpers.FillWithDirectionPreference(
                dir => filler.Fill(drawing, angle, dir),
                null,
                _comparer,
                remnantBox
            );

            if (result != null && result.Count > (best?.Count ?? 0))
                best = result;
        }

        Debug.WriteLine($"[StripeFiller] Remnant linear: {best?.Count ?? 0} parts");

        if (best != null && best.Count > 0)
        {
            FillResultCache.Store(drawing, remnantBox, spacing, best);
            return best;
        }

        return null;
    }

    public static double FindAngleForTargetSpan(
        List<Part> patternParts,
        double targetSpan,
        NestDirection axis
    )
    {
        var bestAngle = 0.0;
        var bestDiff = double.MaxValue;
        var samples = new (double angle, double span)[AngleSamples + 1];

        for (var i = 0; i <= AngleSamples; i++)
        {
            var angle = i * Angle.HalfPI / AngleSamples;
            var span = GetRotatedSpan(patternParts, angle, axis);
            samples[i] = (angle, span);

            var diff = System.Math.Abs(span - targetSpan);
            if (diff < bestDiff)
            {
                bestDiff = diff;
                bestAngle = angle;
            }
        }

        if (bestDiff < Tolerance.Epsilon)
            return bestAngle;

        for (var i = 0; i < samples.Length - 1; i++)
        {
            var (a1, s1) = samples[i];
            var (a2, s2) = samples[i + 1];

            if ((s1 <= targetSpan && targetSpan <= s2) || (s2 <= targetSpan && targetSpan <= s1))
            {
                var result = BisectForTarget(patternParts, a1, a2, targetSpan, axis);
                var resultSpan = GetRotatedSpan(patternParts, result, axis);
                var resultDiff = System.Math.Abs(resultSpan - targetSpan);

                if (resultDiff < bestDiff)
                {
                    bestDiff = resultDiff;
                    bestAngle = result;
                }
            }
        }

        return bestAngle;
    }

    /// <summary>
    /// Returns the rotation angle that orients the pair with its short side
    /// along the given axis. Returns 0 if already oriented, PI/2 if rotated.
    /// </summary>
    private static double OrientShortSideAlong(List<Part> patternParts, NestDirection axis)
    {
        var box = FillHelpers.BuildRotatedPattern(patternParts, 0).BoundingBox;
        var span0 = GetDimension(box, axis);
        var perpSpan0 = axis == NestDirection.Horizontal ? box.Width : box.Length;

        if (span0 <= perpSpan0)
            return 0;

        return Angle.HalfPI;
    }

    /// <summary>
    /// Iteratively finds the rotation angle where N copies of the pattern
    /// span the given dimension with minimal waste by expanding pair width.
    /// Returns (angle, waste, pairCount). A positive <paramref name="maxParts"/> caps
    /// the estimate rows like <see cref="FillLinear.MaxParts"/>.
    /// </summary>
    public static (double Angle, double Waste, int Count) ConvergeStripeAngle(
        List<Part> patternParts,
        double sheetSpan,
        double spacing,
        NestDirection axis,
        CancellationToken token = default,
        int maxParts = 0
    )
    {
        var startAngle = OrientShortSideAlong(patternParts, axis);
        return ConvergeFromAngle(patternParts, startAngle, sheetSpan, spacing, axis, token, maxParts);
    }

    /// <summary>
    /// Tries fitting N+1 narrower pairs by shrinking the pair width.
    /// Complements ConvergeStripeAngle which only expands.
    /// </summary>
    public static (double Angle, double Waste, int Count) ConvergeStripeAngleShrink(
        List<Part> patternParts,
        double sheetSpan,
        double spacing,
        NestDirection axis,
        CancellationToken token = default,
        int maxParts = 0
    )
    {
        var baseAngle = OrientShortSideAlong(patternParts, axis);
        var naturalPattern = FillHelpers.BuildRotatedPattern(patternParts, baseAngle);
        var naturalSpan = GetDimension(naturalPattern.BoundingBox, axis);

        if (naturalSpan + spacing <= 0)
            return (0, double.MaxValue, 0);

        var naturalN = (int)System.Math.Floor((sheetSpan + spacing) / (naturalSpan + spacing));
        var targetN = naturalN + 1;
        var targetSpan = (sheetSpan + spacing) / targetN - spacing;

        if (targetSpan <= 0)
            return (0, double.MaxValue, 0);

        var startAngle = FindAngleForTargetSpan(patternParts, targetSpan, axis);
        return ConvergeFromAngle(patternParts, startAngle, sheetSpan, spacing, axis, token, maxParts);
    }

    private static (double Angle, double Waste, int Count) ConvergeFromAngle(
        List<Part> patternParts,
        double startAngle,
        double sheetSpan,
        double spacing,
        NestDirection axis,
        CancellationToken token,
        int maxParts
    )
    {
        var bestWaste = double.MaxValue;
        var bestAngle = startAngle;
        var bestCount = 0;
        var tolerance = sheetSpan * 0.001;
        var currentAngle = startAngle;

        for (var iteration = 0; iteration < MaxConvergenceIterations; iteration++)
        {
            token.ThrowIfCancellationRequested();

            var rotated = FillHelpers.BuildRotatedPattern(patternParts, currentAngle);
            var pairSpan = GetDimension(rotated.BoundingBox, axis);
            var perpDim =
                axis == NestDirection.Horizontal
                    ? rotated.BoundingBox.Width
                    : rotated.BoundingBox.Length;

            if (pairSpan + spacing <= 0)
                break;

            var stripeBox =
                axis == NestDirection.Horizontal
                    ? new Box(0, 0, sheetSpan, perpDim)
                    : new Box(0, 0, perpDim, sheetSpan);
            var engine = new FillLinear(stripeBox, spacing)
            {
                Label = "Stripe-EstimateRow",
                MaxParts = maxParts,
            };
            var filled = engine.Fill(rotated, axis);
            var n = filled?.Count ?? 0;

            if (n <= 0)
                break;

            var filledBox = ((IEnumerable<IBoundable>)filled).GetBoundingBox();
            var remaining = sheetSpan - GetDimension(filledBox, axis);

            Debug.WriteLine(
                $"[Converge] iter={iteration}: angle={Angle.ToDegrees(currentAngle):F2}°, "
                    + $"pairSpan={pairSpan:F4}, perpDim={perpDim:F4}, N={n}, waste={remaining:F3}"
            );

            if (remaining < bestWaste)
            {
                bestWaste = remaining;
                bestAngle = currentAngle;
                bestCount = n;
            }

            if (remaining <= tolerance)
                break;

            var bboxN = (int)System.Math.Floor((sheetSpan + spacing) / (pairSpan + spacing));
            if (bboxN <= 0)
                bboxN = 1;
            var delta = remaining / bboxN;
            var targetSpan = pairSpan + delta;

            var prevAngle = currentAngle;
            currentAngle = FindAngleForTargetSpan(patternParts, targetSpan, axis);

            if (System.Math.Abs(currentAngle - prevAngle) < Tolerance.Epsilon)
                break;
        }

        return (bestAngle, bestWaste, bestCount);
    }

    private static double BisectForTarget(
        List<Part> patternParts,
        double lo,
        double hi,
        double targetSpan,
        NestDirection axis
    )
    {
        var bestAngle = lo;
        var bestDiff = double.MaxValue;

        for (var i = 0; i < 30; i++)
        {
            var mid = (lo + hi) / 2;
            var span = GetRotatedSpan(patternParts, mid, axis);
            var diff = System.Math.Abs(span - targetSpan);

            if (diff < bestDiff)
            {
                bestDiff = diff;
                bestAngle = mid;
            }

            if (diff < Tolerance.Epsilon)
                break;

            var loSpan = GetRotatedSpan(patternParts, lo, axis);
            if (
                (loSpan < targetSpan && span < targetSpan)
                || (loSpan > targetSpan && span > targetSpan)
            )
                lo = mid;
            else
                hi = mid;
        }

        return bestAngle;
    }

    private static double GetRotatedSpan(List<Part> patternParts, double angle, NestDirection axis)
    {
        var rotated = FillHelpers.BuildRotatedPattern(patternParts, angle);
        return axis == NestDirection.Horizontal
            ? rotated.BoundingBox.Length
            : rotated.BoundingBox.Width;
    }

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

    private static bool HasOverlappingParts(List<Part> parts) =>
        FillHelpers.HasOverlappingParts(parts);
}