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

namespace OpenNest;

/// <summary>
/// Migrated built-in placement strategy for the whole-job runner. Reuses <see cref="DefaultNestEngine"/>
/// fill/pack geometry but owns its own run-scoped bookkeeping: remaining demand is read from the
/// request and placement counts are derived from returned placements, so the engine's private
/// <see cref="NestItem.Quantity"/> mutations never feed back into job accounting.
/// </summary>
/// <remarks>
/// A private <see cref="Drawing"/> per requirement is created once per solve and reused across every
/// candidate trial (the runner reuses one <see cref="IPlateNester"/> instance per job). This is safe
/// because the engines mutate <see cref="NestItem.Quantity"/> (per-trial) and canonical-frame copies,
/// never the shared <see cref="Drawing"/> or its <c>Quantity</c>. Identity is by Drawing reference,
/// never by name. Each trial still gets a fresh private <see cref="Plate"/>.
/// </remarks>
public sealed class DefaultPlateNester : IPlateNester
{
    private readonly Func<Plate, DefaultNestEngine> engineFactory;
    private readonly Dictionary<string, Drawing> drawingsById = new(StringComparer.Ordinal);
    private readonly Dictionary<Drawing, string> idByDrawing = new(ReferenceEqualityComparer.Instance);

    public DefaultPlateNester() : this(static plate => new DefaultNestEngine(plate))
    {
    }

    /// <param name="engineFactory">Injectable for tests; defaults to <see cref="DefaultNestEngine"/>.</param>
    public DefaultPlateNester(Func<Plate, DefaultNestEngine> engineFactory)
    {
        this.engineFactory = engineFactory ?? throw new ArgumentNullException(nameof(engineFactory));
    }

    public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress> progress = null,
        CancellationToken token = default)
    {
        ArgumentNullException.ThrowIfNull(request);
        token.ThrowIfCancellationRequested();

        var plate = DrawingJobMapper.CreatePlate(request.Stock);
        var items = new List<NestItem>(request.Parts.Count);
        foreach (var requirement in request.Parts)
        {
            if (!drawingsById.TryGetValue(requirement.Id, out var drawing))
            {
                drawing = DrawingJobMapper.CreateDrawing(requirement);
                drawingsById.Add(requirement.Id, drawing);
                idByDrawing.Add(drawing, requirement.Id);
            }

            // Quantity is the request's remaining demand; the engine may mutate this per-trial item,
            // and that mutation is deliberately discarded — placement counts come from the result.
            items.Add(new NestItem
            {
                Drawing = drawing,
                Quantity = requirement.Quantity,
                Priority = requirement.Priority,
                StepAngle = DrawingJobMapper.LegacyStep(requirement.Rotation),
                RotationStart = requirement.Rotation.Start,
                RotationEnd = requirement.Rotation.End
            });
        }

        var engine = engineFactory(plate) ?? throw new InvalidOperationException("Engine factory returned null.");
        var legacyProgress = CandidateProgressBridge.Create(progress, request.Stock.Id);
        var parts = engine.Nest(items, legacyProgress, token);
        token.ThrowIfCancellationRequested();
        if (parts == null) throw new InvalidOperationException("Engine returned null placements.");

        var placements = new List<NestJobPlacement>(parts.Count);
        foreach (var part in parts)
        {
            if (part?.BaseDrawing == null || !idByDrawing.TryGetValue(part.BaseDrawing, out var id))
                throw new InvalidOperationException("Placement does not reference a known requirement drawing.");
            placements.Add(new NestJobPlacement(id, 0, part.Location.X, part.Location.Y, part.Rotation));
        }

        return new PlateCandidate(placements);
    }
}