using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace OpenNest.Engine.Jobs;

/// <summary>
/// Physical-sheet allocation. Every available stock entry is tried independently and only the selected
/// candidate changes demand or inventory accounting.
/// </summary>
public sealed class NestJobRunner : INestingEngine
{
    private readonly Func<string, IPlateNester> plateNesterFactory;

    /// <summary>Runner-local strategy resolution. A factory must reject unknown keys or return null.</summary>
    public NestJobRunner(Func<string, IPlateNester> plateNesterFactory)
    {
        ArgumentNullException.ThrowIfNull(plateNesterFactory);
        this.plateNesterFactory = plateNesterFactory;
    }

    public NestJobResult Solve(
        NestJob job,
        IProgress<NestJobProgress> progress = null,
        CancellationToken token = default
    )
    {
        ArgumentNullException.ThrowIfNull(job);
        token.ThrowIfCancellationRequested();
        NestJobValidator.Validate(job);
        var plates = new List<NestJobPlateResult>();
        var remaining = job.Parts.ToDictionary(
            part => part.Id,
            part => part.Quantity,
            StringComparer.Ordinal
        );
        var placed = job.Parts.ToDictionary(part => part.Id, _ => 0, StringComparer.Ordinal);
        var parts = job.Parts.ToDictionary(part => part.Id, StringComparer.Ordinal);
        var used = job.Plates.ToDictionary(stock => stock.Id, _ => 0, StringComparer.Ordinal);
        var comparer = new NestJobCandidateComparer(job.Parts);
        var nester =
            job.Parts.Count == 0
                ? null
                : plateNesterFactory(job.Options.PlacementStrategy)
                    ?? throw new NotSupportedException(
                        $"Unknown placement strategy: {job.Options.PlacementStrategy}."
                    );
        var reason = NestJobStopReason.Completed;
        while (remaining.Values.Any(count => count > 0))
        {
            token.ThrowIfCancellationRequested();
            if (job.Options.MaxPlates <= plates.Count)
            {
                reason = NestJobStopReason.PlateLimitReached;
                break;
            }

            CandidateTrial winner = null;
            var hasAvailableStock = false;
            for (var index = 0; index < job.Plates.Count; index++)
            {
                var stock = job.Plates[index];
                if (stock.Quantity is int quantity && used[stock.Id] >= quantity)
                    continue;
                hasAvailableStock = true;
                var request = new PlatePlacementRequest(
                    stock,
                    job.Parts.Where(part => remaining[part.Id] > 0)
                        .Select(part => new NestJobPart(
                            part.Id,
                            part.Geometry,
                            remaining[part.Id],
                            part.Priority,
                            part.Rotation
                        ))
                );
                progress?.Report(
                    new NestJobProgress(
                        NestJobStage.EvaluatingCandidate,
                        stock.Id,
                        plates.Count,
                        plates.Count,
                        placed.Values.Sum()
                    )
                );
                token.ThrowIfCancellationRequested();
                var candidateProgress =
                    progress == null
                        ? null
                        : new CandidateProgress(
                            progress,
                            stock.Id,
                            plates.Count,
                            plates.Count,
                            placed.Values.Sum()
                        );
                var candidate = nester.Place(request, candidateProgress, token);
                token.ThrowIfCancellationRequested();
                NestJobValidator.ValidateCandidate(candidate, stock, remaining, parts);
                var trial = new CandidateTrial(candidate, stock, index);
                if (
                    winner == null
                    || comparer.Compare(
                        trial.Candidate,
                        trial.Stock,
                        trial.StockIndex,
                        winner.Candidate,
                        winner.Stock,
                        winner.StockIndex
                    ) > 0
                )
                    winner = trial;
            }

            if (!hasAvailableStock)
            {
                reason = NestJobStopReason.StockExhausted;
                break;
            }
            if (winner.Candidate.Placements.Count == 0)
            {
                reason = NestJobStopReason.NoPlacementFound;
                break;
            }

            var committed = new List<NestJobPlacement>();
            foreach (var pose in winner.Candidate.Placements)
            {
                committed.Add(pose with { InstanceIndex = placed[pose.PartId]++ });
                remaining[pose.PartId]--;
            }
            used[winner.Stock.Id]++;
            plates.Add(new NestJobPlateResult(plates.Count, winner.Stock, committed));
            progress?.Report(
                new NestJobProgress(
                    NestJobStage.PlateCommitted,
                    winner.Stock.Id,
                    plates.Count - 1,
                    plates.Count,
                    placed.Values.Sum()
                )
            );
        }

        token.ThrowIfCancellationRequested();
        return new NestJobResult(
            reason == NestJobStopReason.Completed
                ? NestJobStatus.Complete
                : NestJobStatus.Incomplete,
            reason,
            plates,
            job.Parts.Select(part => new PartFulfillment(
                part.Id,
                part.Quantity,
                placed[part.Id],
                remaining[part.Id]
            )),
            job.Plates.Select(stock => new StockUsage(
                stock.Id,
                used[stock.Id],
                stock.Quantity is int quantity ? quantity - used[stock.Id] : null
            ))
        );
    }

    private sealed record CandidateTrial(
        PlateCandidate Candidate,
        NestPlateStock Stock,
        int StockIndex
    );

    private sealed class CandidateProgress(
        IProgress<NestJobProgress> progress,
        string stockId,
        int plateIndex,
        int committedPlates,
        int committedParts
    ) : IProgress<NestJobProgress>
    {
        public void Report(NestJobProgress value)
        {
            ArgumentNullException.ThrowIfNull(value);
            progress.Report(
                new NestJobProgress(
                    NestJobStage.EvaluatingCandidate,
                    stockId,
                    plateIndex,
                    committedPlates,
                    committedParts,
                    value.LegacyProgress
                )
            );
        }
    }
}