// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using System.Runtime.CompilerServices;

namespace SixLabors.PolygonClipper {
  /// <summary>
  /// Represents a stroke-processing vertex with a cached outgoing segment length.
  /// </summary>
  /// <remarks>
  /// This is an internal mutable value used by <see cref="PolygonStroker"/> while
  /// normalizing source contours and computing joins/caps.
  /// </remarks>
  internal struct StrokeVertexDistance
  {
      private const double VertexDistanceEpsilon = 1E-14D;
      private const double Dd = 1D / VertexDistanceEpsilon;

      /// <summary>
      /// The X-coordinate.
      /// </summary>
      public double X;

      /// <summary>
      /// The Y-coordinate.
      /// </summary>
      public double Y;

      /// <summary>
      /// Cached distance to another vertex measured by <see cref="Measure(in StrokeVertexDistance)"/>.
      /// </summary>
      public double Distance;

      /// <summary>
      /// Initializes a new instance of the <see cref="StrokeVertexDistance"/> struct.
      /// </summary>
      /// <param name="x">The X-coordinate.</param>
      /// <param name="y">The Y-coordinate.</param>
      /// <param name="distance">Initial cached distance value.</param>
      public StrokeVertexDistance(double x, double y, double distance)
      {
          this.X = x;
          this.Y = y;
          this.Distance = distance;
      }

      /// <summary>
      /// Measures the Euclidean distance from this vertex to <paramref name="vd"/> and stores it in <see cref="Distance"/>.
      /// </summary>
      /// <param name="vd">The vertex to measure to.</param>
      /// <returns>
      /// <see langword="true"/> when the measured distance is greater than the internal epsilon;
      /// otherwise <see langword="false"/>.
      /// </returns>
      /// <remarks>
      /// When points are closer than epsilon, <see cref="Distance"/> is set to a large sentinel value
      /// to avoid divide-by-near-zero behavior in downstream stroker math.
      /// </remarks>
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      public bool Measure(in StrokeVertexDistance vd)
      {
          bool ret = (this.Distance = Vertex.Distance(new Vertex(this.X, this.Y), new Vertex(vd.X, vd.Y))) > VertexDistanceEpsilon;
          if (!ret)
          {
              this.Distance = Dd;
          }

          return ret;
      }
  }
}