#nullable enable
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.ExceptionServices;
using System.Threading;
using OpenNest.Engine.Jobs;
using OpenNest.Engine.NestingEngines.Circles;
using OpenNest.Engine.NestingEngines.Irregular;
using OpenNest.Engine.NestingEngines.Rectangles;

namespace OpenNest.Engine.NestingEngines.Default;

/// <summary>
/// The engine used when the caller names none. It runs each candidate engine on the whole job,
/// checks every result with <see cref="NestLayoutCheck"/> and returns the best one: a valid
/// layout before an invalid one, then the fewest unplaced parts, then the lowest
/// <see cref="NestJobCost"/>; remaining ties keep candidate order.
///
/// Candidates are Irregular, then Rectangles, then Circles. Neither of the first two wins every
/// job: Rectangles packs each part as its box, which is often best for plain plates and is a
/// cheap, valid fallback for the rest. Circles bids only when every part is round, and otherwise
/// returns everything unplaced at once.
/// A candidate that throws or returns no result is skipped; when every candidate throws, the
/// first exception is rethrown. Cancellation stops the search. Candidates' plate commits are not forwarded; the chosen
/// result's commits are reported once it is selected.
///
/// Deterministic: candidates run one after another and the choice uses no clock.
/// </summary>
public sealed class DefaultNestingEngine : INestingEngine
{
    private readonly IReadOnlyList<Func<INestingEngine>> candidates;

    public DefaultNestingEngine()
        : this(new Func<INestingEngine>[]
        {
            () => new IrregularNestingEngine(), () => new RectanglesNestingEngine(), () => new CirclesNestingEngine(),
        })
    {
    }

    /// <summary>Test seam: candidate engines in tie-break order.</summary>
    internal DefaultNestingEngine(IReadOnlyList<Func<INestingEngine>> candidates)
    {
        ArgumentNullException.ThrowIfNull(candidates);
        if (candidates.Count == 0)
            throw new ArgumentException("At least one candidate engine is required.", nameof(candidates));
        this.candidates = candidates;
    }

    public NestJobResult Solve(
        NestJob job,
        IProgress<NestJobProgress>? progress = null,
        CancellationToken token = default
    )
    {
        ArgumentNullException.ThrowIfNull(job);
        token.ThrowIfCancellationRequested();
        var forward = progress == null ? null : new CandidateProgress(progress);
        CandidateScore? best = null;
        ExceptionDispatchInfo? firstFailure = null;

        for (var order = 0; order < candidates.Count; order++)
        {
            token.ThrowIfCancellationRequested();
            NestJobResult? result;
            try
            {
                result = candidates[order]().Solve(job, forward, token);
            }
            catch (Exception ex)
            {
                // A cancelled solve is rethrown by the token checks around each candidate.
                firstFailure ??= ExceptionDispatchInfo.Capture(ex);
                continue;
            }
            if (result == null)
                continue;

            var scored = CandidateScore.Of(job, result, order);
            if (best == null || scored.IsBetterThan(best))
                best = scored;
        }

        token.ThrowIfCancellationRequested();
        if (best == null)
        {
            firstFailure?.Throw();
            throw new InvalidOperationException("No candidate engine returned a result.");
        }

        CandidateProgress.ReportCommits(best.Result, progress);
        return best.Result;
    }
}