using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace MultiWheelC.TrajectoryPlanning.PathSmoothing;

/// <summary>路径平滑的最终不可变结果。</summary>
public sealed class PathSmoothingResult
{
    private static readonly IReadOnlyList<SmoothedPathPoint> EmptyPath =
        new ReadOnlyCollection<SmoothedPathPoint>(new List<SmoothedPathPoint>());
    private static readonly IReadOnlyList<SmoothedPathSegment> EmptySegments =
        new ReadOnlyCollection<SmoothedPathSegment>(new List<SmoothedPathSegment>());

    private PathSmoothingResult(
        PathSmoothingStatus status,
        SmoothingMethod? method,
        IReadOnlyList<SmoothedPathPoint> path,
        IReadOnlyList<SmoothedPathSegment> segments,
        PathSmoothingDiagnostics diagnostics)
    {
        Status = status;
        Method = method;
        Path = path;
        Segments = segments;
        Diagnostics = diagnostics ?? new PathSmoothingDiagnostics(
            new PathQualityMetrics(),
            TimeSpan.Zero,
            0,
            0d,
            "No smoothing diagnostics were supplied.");
    }

    /// <summary>最终发布状态。</summary>
    public PathSmoothingStatus Status { get; }

    /// <summary>成功或回退时的实际（或尝试）平滑方法；失败时为空。</summary>
    public SmoothingMethod? Method { get; }

    /// <summary>成功或经过复核的回退路径；其他状态始终为空且不可变。</summary>
    public IReadOnlyList<SmoothedPathPoint> Path { get; }

    /// <summary>覆盖 <see cref="Path"/> 的方向分段；其他状态始终为空且不可变。</summary>
    public IReadOnlyList<SmoothedPathSegment> Segments { get; }

    /// <summary>本次平滑的质量和终止诊断；始终非空。</summary>
    public PathSmoothingDiagnostics Diagnostics { get; }

    /// <summary>创建已通过所有复核的平滑结果。</summary>
    public static PathSmoothingResult Success(
        SmoothingMethod method,
        IReadOnlyList<SmoothedPathPoint> path,
        IReadOnlyList<SmoothedPathSegment> segments,
        PathSmoothingDiagnostics diagnostics)
    {
        ValidatePublishedResult(method, path, segments, diagnostics);
        return new PathSmoothingResult(
            PathSmoothingStatus.Success,
            method,
            CopyReadOnly(path),
            CopyReadOnly(segments),
            diagnostics);
    }

    /// <summary>创建经过完整复核的原始粗路径回退结果。</summary>
    public static PathSmoothingResult Fallback(
        SmoothingMethod attemptedMethod,
        IReadOnlyList<SmoothedPathPoint> path,
        IReadOnlyList<SmoothedPathSegment> segments,
        PathSmoothingDiagnostics diagnostics)
    {
        ValidatePublishedResult(attemptedMethod, path, segments, diagnostics);
        return new PathSmoothingResult(
            PathSmoothingStatus.FallbackToCoarsePath,
            attemptedMethod,
            CopyReadOnly(path),
            CopyReadOnly(segments),
            diagnostics);
    }

    /// <summary>创建不发布路径的失败、不可行、取消或输入无效结果。</summary>
    public static PathSmoothingResult Failure(PathSmoothingStatus status, PathSmoothingDiagnostics diagnostics)
    {
        if (status == PathSmoothingStatus.Success || status == PathSmoothingStatus.FallbackToCoarsePath)
            throw new ArgumentException("Use Success or Fallback to publish a path.", nameof(status));
        if (!Enum.IsDefined(typeof(PathSmoothingStatus), status))
            throw new ArgumentOutOfRangeException(nameof(status));
        return new PathSmoothingResult(status, null, EmptyPath, EmptySegments, diagnostics);
    }

    private static void ValidatePublishedResult(
        SmoothingMethod method,
        IReadOnlyList<SmoothedPathPoint> path,
        IReadOnlyList<SmoothedPathSegment> segments,
        PathSmoothingDiagnostics diagnostics)
    {
        if (!Enum.IsDefined(typeof(SmoothingMethod), method))
            throw new ArgumentOutOfRangeException(nameof(method));
        if (path == null || path.Count == 0)
            throw new ArgumentException("Published smoothing results require a non-empty path.", nameof(path));
        if (segments == null || segments.Count == 0)
            throw new ArgumentException("Published smoothing results require non-empty segments.", nameof(segments));
        if (diagnostics == null || diagnostics.Metrics == null || !diagnostics.Metrics.IsFeasible)
            throw new ArgumentException("Published smoothing results require feasible diagnostics.", nameof(diagnostics));
    }

    private static IReadOnlyList<T> CopyReadOnly<T>(IReadOnlyList<T> source)
    {
        var copy = new List<T>(source.Count);
        for (int index = 0; index < source.Count; index++)
            copy.Add(source[index]);
        return new ReadOnlyCollection<T>(copy);
    }
}