using OpenNest.Engine;
using OpenNest.Engine.BestFit;
using OpenNest.Engine.Fill;
using OpenNest.Engine.Strategies;
using OpenNest.Geometry;
using OpenNest.Math;
using OpenNest.RectanglePacking;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;

namespace OpenNest
{
    public class DefaultNestEngine : NestEngineBase
    {
        public DefaultNestEngine(Plate plate) : base(plate) { }

        public override string Name => "Default";

        public override string Description => "Multi-phase nesting (Linear, Pairs, RectBestFit, Extents)";

        private readonly AngleCandidateBuilder angleBuilder = new();

        public bool ForceFullAngleSweep
        {
            get => angleBuilder.ForceFullSweep;
            set => angleBuilder.ForceFullSweep = value;
        }

        public override List<double> BuildAngles(NestItem item, ClassificationResult classification, Box workArea)
        {
            return angleBuilder.Build(item, classification, workArea);
        }

        protected override void RecordProductiveAngles(List<AngleResult> angleResults)
        {
            angleBuilder.RecordProductive(angleResults);
        }

        // --- Public Fill API ---

        public override List<Part> Fill(NestItem item, Box workArea,
            IProgress<NestProgress> progress, CancellationToken token)
        {
            PhaseResults.Clear();
            AngleResults.Clear();

            // Fast path: for very small quantities, skip the full strategy pipeline.
            if (item.Quantity > 0 && item.Quantity <= 2)
            {
                var fast = TryFillSmallQuantity(item, workArea);
                if (fast != null && fast.Count >= item.Quantity)
                {
                    Debug.WriteLine($"[Fill] Fast path: placed {fast.Count} parts for qty={item.Quantity}");
                    WinnerPhase = NestPhase.Pairs;
                    ReportProgress(progress, new ProgressReport
                    {
                        Phase = WinnerPhase,
                        PlateNumber = PlateNumber,
                        Parts = fast,
                        WorkArea = workArea,
                        Description = $"Fast path: {fast.Count} parts",
                        IsOverallBest = true,
                    });
                    return fast;
                }
            }

            // For low quantities, shrink the work area in both dimensions to avoid
            // running expensive strategies against the full plate.
            var effectiveWorkArea = workArea;
            if (item.Quantity > 0)
            {
                effectiveWorkArea = ShrinkWorkArea(item, workArea, Plate.PartSpacing);

                if (effectiveWorkArea != workArea)
                    Debug.WriteLine($"[Fill] Low-qty shrink: {item.Quantity} requested, " +
                        $"from {workArea.Width:F1}x{workArea.Length:F1} " +
                        $"to {effectiveWorkArea.Width:F1}x{effectiveWorkArea.Length:F1}");
            }

            var best = RunFillPipeline(item, effectiveWorkArea, progress, token);

            // Fallback: if the reduced area didn't yield enough, retry with full area.
            if (item.Quantity > 0 && best.Count < item.Quantity && effectiveWorkArea != workArea)
            {
                Debug.WriteLine($"[Fill] Low-qty fallback: got {best.Count}, need {item.Quantity}, retrying full area");
                PhaseResults.Clear();
                AngleResults.Clear();
                best = RunFillPipeline(item, workArea, progress, token);
            }

            if (item.Quantity > 0 && best.Count > item.Quantity)
                best = ShrinkFiller.TrimToCount(best, item.Quantity, TrimAxis);

            ReportProgress(progress, new ProgressReport
            {
                Phase = WinnerPhase,
                PlateNumber = PlateNumber,
                Parts = best,
                WorkArea = workArea,
                Description = BuildProgressSummary(),
                IsOverallBest = true,
            });

            return best;
        }

        /// <summary>
        /// Fast path for qty 1-2: place a single part or a best-fit pair
        /// without running the full strategy pipeline.
        /// </summary>
        private List<Part> TryFillSmallQuantity(NestItem item, Box workArea)
        {
            if (item.Quantity == 1)
                return TryPlaceSingle(item.Drawing, workArea);

            if (item.Quantity == 2)
                return TryPlaceBestFitPair(item.Drawing, workArea);

            return null;
        }

        private static List<Part> TryPlaceSingle(Drawing drawing, Box workArea)
        {
            var part = Part.CreateAtOrigin(drawing);
            if (part.BoundingBox.Width > workArea.Width + Tolerance.Epsilon ||
                part.BoundingBox.Length > workArea.Length + Tolerance.Epsilon)
                return null;

            part.Offset(workArea.Location - part.BoundingBox.Location);
            return new List<Part> { part };
        }

        private List<Part> TryPlaceBestFitPair(Drawing drawing, Box workArea)
        {
            var bestFits = BestFitCache.GetOrCompute(
                drawing, Plate.Size.Length, Plate.Size.Width, Plate.PartSpacing);

            var best = bestFits.FirstOrDefault(r => r.Keep);
            if (best == null)
                return null;

            var parts = best.BuildParts(drawing);

            // BuildParts positions at origin — offset to work area.
            var bbox = ((IEnumerable<IBoundable>)parts).GetBoundingBox();
            var offset = workArea.Location - bbox.Location;
            foreach (var p in parts)
            {
                p.Offset(offset);
                p.UpdateBounds();
            }

            // Verify pair fits in work area.
            bbox = ((IEnumerable<IBoundable>)parts).GetBoundingBox();
            if (bbox.Width > workArea.Width + Tolerance.Epsilon ||
                bbox.Length > workArea.Length + Tolerance.Epsilon)
                return null;

            return parts;
        }

        /// <summary>
        /// Shrinks the work area in both dimensions proportionally when the
        /// requested quantity is much less than the plate capacity.
        /// </summary>
        private static Box ShrinkWorkArea(NestItem item, Box workArea, double spacing)
        {
            var bbox = item.Drawing.Program.BoundingBox();
            if (bbox.Width <= 0 || bbox.Length <= 0)
                return workArea;

            var bin = new Bin { Size = new Size(workArea.Width, workArea.Length) };
            var packItem = new Item { Size = new Size(bbox.Width + spacing, bbox.Length + spacing) };
            var packer = new FillBestFit(bin);
            packer.Fill(packItem);
            var fullCount = bin.Items.Count;

            if (fullCount <= 0 || fullCount <= item.Quantity)
                return workArea;

            // Scale both dimensions by sqrt(ratio) so the area shrinks
            // proportionally. 2x margin gives strategies room to optimize.
            var ratio = (double)item.Quantity / fullCount;
            var scale = System.Math.Sqrt(ratio) * 2.0;

            var newWidth = workArea.Width * scale;
            var newLength = workArea.Length * scale;

            // Ensure at least one part fits.
            var minWidth = bbox.Width + spacing * 2;
            var minLength = bbox.Length + spacing * 2;
            newWidth = System.Math.Max(newWidth, minWidth);
            newLength = System.Math.Max(newLength, minLength);

            // Clamp to original dimensions.
            newWidth = System.Math.Min(newWidth, workArea.Width);
            newLength = System.Math.Min(newLength, workArea.Length);

            if (newWidth >= workArea.Width && newLength >= workArea.Length)
                return workArea;

            return new Box(workArea.X, workArea.Y, newWidth, newLength);
        }

        private List<Part> RunFillPipeline(NestItem item, Box workArea,
            IProgress<NestProgress> progress, CancellationToken token)
        {
            var context = new FillContext
            {
                Item = item,
                WorkArea = workArea,
                Plate = Plate,
                PlateNumber = PlateNumber,
                Token = token,
                Progress = progress,
                Policy = BuildPolicy(),
                MaxQuantity = item.Quantity,
            };

            RunPipeline(context);

            AngleResults.AddRange(context.AngleResults);
            WinnerPhase = context.WinnerPhase;

            return context.CurrentBest ?? new List<Part>();
        }

        public override List<Part> Fill(List<Part> groupParts, Box workArea,
            IProgress<NestProgress> progress, CancellationToken token)
        {
            if (groupParts == null || groupParts.Count == 0)
                return new List<Part>();

            // Single part: delegate to the strategy pipeline.
            if (groupParts.Count == 1)
            {
                var nestItem = new NestItem { Drawing = groupParts[0].BaseDrawing };
                return Fill(nestItem, workArea, progress, token);
            }

            // Multi-part group: linear pattern fill only.
            PhaseResults.Clear();
            var engine = new FillLinear(workArea, Plate.PartSpacing) { Label = "GroupPattern" };
            var angles = RotationAnalysis.FindHullEdgeAngles(groupParts);
            var best = FillHelpers.FillPattern(engine, groupParts, angles, workArea, Comparer);
            PhaseResults.Add(new PhaseResult(NestPhase.Linear, best?.Count ?? 0, 0));

            Debug.WriteLine($"[Fill(groupParts,Box)] Linear pattern: {best?.Count ?? 0} parts | WorkArea: {workArea.Width:F1}x{workArea.Length:F1}");

            ReportProgress(progress, new ProgressReport
            {
                Phase = NestPhase.Linear,
                PlateNumber = PlateNumber,
                Parts = best,
                WorkArea = workArea,
                Description = BuildProgressSummary(),
                IsOverallBest = true,
            });

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

        // --- Pack API ---

        public override List<Part> PackArea(Box box, List<NestItem> items,
            IProgress<NestProgress> progress, CancellationToken token)
        {
            var binItems = BinConverter.ToItems(items, Plate.PartSpacing, Plate.Area());
            var bin = BinConverter.CreateBin(box, Plate.PartSpacing);

            var engine = new PackBottomLeft(bin);
            engine.Pack(binItems);

            return BinConverter.ToParts(bin, items);
        }

        // --- RunPipeline: strategy-based orchestration ---

        protected virtual void RunPipeline(FillContext context)
        {
            var classification = PartClassifier.Classify(context.Item.Drawing);
            context.PartType = classification.Type;
            context.SharedState["BestRotation"] = classification.PrimaryAngle;
            context.SharedState["Classification"] = classification;

            var angles = BuildAngles(context.Item, classification, context.WorkArea);
            context.SharedState["AngleCandidates"] = angles;

            try
            {
                foreach (var strategy in FillStrategyRegistry.Strategies)
                {
                    context.Token.ThrowIfCancellationRequested();

                    var sw = Stopwatch.StartNew();
                    var result = strategy.Fill(context);
                    sw.Stop();

                    var phaseResult = new PhaseResult(
                        strategy.Phase, result?.Count ?? 0, sw.ElapsedMilliseconds);
                    context.PhaseResults.Add(phaseResult);

                    // Keep engine's PhaseResults in sync so BuildProgressSummary() works
                    // during progress reporting.
                    PhaseResults.Add(phaseResult);

                    if (context.Policy.Comparer.IsBetter(result, context.CurrentBest, context.WorkArea))
                    {
                        context.CurrentBest = result;
                        context.CurrentBestScore = FillScore.Compute(result, context.WorkArea);
                        context.WinnerPhase = strategy.Phase;
                    }

                    if (context.CurrentBest != null && context.CurrentBest.Count > 0)
                    {
                        ReportProgress(context.Progress, new ProgressReport
                        {
                            Phase = context.WinnerPhase,
                            PlateNumber = PlateNumber,
                            Parts = context.CurrentBest,
                            WorkArea = context.WorkArea,
                            Description = BuildProgressSummary(),
                            IsOverallBest = true,
                        });
                    }
                }
            }
            catch (OperationCanceledException)
            {
                Debug.WriteLine("[RunPipeline] Cancelled, returning current best");
            }

            RecordProductiveAngles(context.AngleResults);
        }

    }
}