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

using System;
using System.Collections.Generic;

namespace SixLabors.PolygonClipper {
  /// <summary>
  /// Describes the lowest vertex of an edge bound for the sweep line.
  /// </summary>
  internal readonly struct LocalMinima : IEquatable<LocalMinima>
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="LocalMinima"/> struct.
      /// </summary>
      internal LocalMinima(SweepVertex vertex) => this.Vertex = vertex;

      /// <summary>
      /// Gets the vertex associated with this local minima.
      /// </summary>
      internal SweepVertex Vertex { get; }

      public static bool operator ==(LocalMinima lm1, LocalMinima lm2) => lm1.Equals(lm2);

      public static bool operator !=(LocalMinima lm1, LocalMinima lm2) => !(lm1 == lm2);

      public override bool Equals(object? obj) => obj is LocalMinima minima && this.Equals(minima);

      public override int GetHashCode() => this.Vertex.GetHashCode();

      public bool Equals(LocalMinima other) => ReferenceEquals(this.Vertex, other.Vertex);
  }

  /// <summary>
  /// Orders local minima so higher Y-values are processed first during the sweep.
  /// </summary>
  internal sealed class LocalMinimaComparer : IComparer<LocalMinima>
  {
      public int Compare(LocalMinima locMin1, LocalMinima locMin2)
          => locMin2.Vertex.Point.Y.CompareTo(locMin1.Vertex.Point.Y);
  }
}