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

using System;
using System.Numerics;

namespace SixLabors.ImageSharp.Drawing {
  /// <summary>
  /// A pie sector polygon defined by a center point, radii, rotation, and arc sweep.
  /// </summary>
  public sealed class PiePolygon : Polygon
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="PiePolygon"/> class.
      /// </summary>
      /// <param name="center">The center point of the pie sector.</param>
      /// <param name="radius">The x and y radii of the pie ellipse.</param>
      /// <param name="rotation">The ellipse rotation in degrees.</param>
      /// <param name="startAngle">The pie start angle in degrees.</param>
      /// <param name="sweepAngle">The pie sweep angle in degrees.</param>
      public PiePolygon(PointF center, SizeF radius, float rotation, float startAngle, float sweepAngle)
          : base(CreateSegments(center, radius, rotation, startAngle, sweepAngle))
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="PiePolygon"/> class.
      /// </summary>
      /// <param name="center">The center point of the pie sector.</param>
      /// <param name="radius">The x and y radii of the pie ellipse.</param>
      /// <param name="startAngle">The pie start angle in degrees.</param>
      /// <param name="sweepAngle">The pie sweep angle in degrees.</param>
      public PiePolygon(PointF center, SizeF radius, float startAngle, float sweepAngle)
          : this(center, radius, 0F, startAngle, sweepAngle)
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="PiePolygon"/> class.
      /// </summary>
      /// <param name="x">The x-coordinate of the pie center.</param>
      /// <param name="y">The y-coordinate of the pie center.</param>
      /// <param name="radiusX">The x-radius of the pie ellipse.</param>
      /// <param name="radiusY">The y-radius of the pie ellipse.</param>
      /// <param name="rotation">The ellipse rotation in degrees.</param>
      /// <param name="startAngle">The pie start angle in degrees.</param>
      /// <param name="sweepAngle">The pie sweep angle in degrees.</param>
      public PiePolygon(float x, float y, float radiusX, float radiusY, float rotation, float startAngle, float sweepAngle)
          : this(new PointF(x, y), new SizeF(radiusX, radiusY), rotation, startAngle, sweepAngle)
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="PiePolygon"/> class.
      /// </summary>
      /// <param name="x">The x-coordinate of the pie center.</param>
      /// <param name="y">The y-coordinate of the pie center.</param>
      /// <param name="radiusX">The x-radius of the pie ellipse.</param>
      /// <param name="radiusY">The y-radius of the pie ellipse.</param>
      /// <param name="startAngle">The pie start angle in degrees.</param>
      /// <param name="sweepAngle">The pie sweep angle in degrees.</param>
      public PiePolygon(float x, float y, float radiusX, float radiusY, float startAngle, float sweepAngle)
          : this(x, y, radiusX, radiusY, 0F, startAngle, sweepAngle)
      {
      }

      private PiePolygon(ILineSegment[] segments)
          : base(segments, true)
      {
      }

      /// <inheritdoc />
      public override IPath Transform(Matrix4x4 matrix)
      {
          if (matrix.IsIdentity)
          {
              return this;
          }

          ILineSegment[] segments = new ILineSegment[this.LineSegments.Count];

          for (int i = 0; i < segments.Length; i++)
          {
              segments[i] = this.LineSegments[i].Transform(matrix);
          }

          return new PiePolygon(segments);
      }

      private static ILineSegment[] CreateSegments(PointF center, SizeF radius, float rotation, float startAngle, float sweepAngle)
      {
          Guard.MustBeGreaterThan(radius.Width, 0, "radiusX");
          Guard.MustBeGreaterThan(radius.Height, 0, "radiusY");

          PointF arcStart = GetArcPoint(center, radius, rotation, startAngle);
          ArcLineSegment arc = new(center, radius, rotation, startAngle, sweepAngle);

          return
          [
              new LinearLineSegment(center, arcStart),
              arc,
              new LinearLineSegment(arc.EndPoint, center)
          ];
      }

      private static PointF GetArcPoint(PointF center, SizeF radius, float rotation, float angle)
      {
          float rotationRadians = rotation * (MathF.PI / 180F);
          float angleRadians = angle * (MathF.PI / 180F);
          float cosRotation = MathF.Cos(rotationRadians);
          float sinRotation = MathF.Sin(rotationRadians);
          float cosAngle = MathF.Cos(angleRadians);
          float sinAngle = MathF.Sin(angleRadians);

          return new PointF(
              center.X + (radius.Width * cosRotation * cosAngle) - (radius.Height * sinRotation * sinAngle),
              center.Y + (radius.Width * sinRotation * cosAngle) + (radius.Height * cosRotation * sinAngle));
      }
  }
}