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

using System;
using System.Numerics;
using SixLabors.ImageSharp.Drawing.Helpers;

namespace SixLabors.ImageSharp.Drawing {
  /// <summary>
  /// Represents a series of control points that will be joined by straight lines
  /// </summary>
  /// <seealso cref="ILineSegment" />
  public sealed class LinearLineSegment : ILineSegment
  {
      /// <summary>
      /// The collection of points.
      /// </summary>
      private readonly PointF[] points;

      /// <summary>
      /// Initializes a new instance of the <see cref="LinearLineSegment"/> class.
      /// </summary>
      /// <param name="start">The start.</param>
      /// <param name="end">The end.</param>
      public LinearLineSegment(PointF start, PointF end)
          : this([start, end])
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="LinearLineSegment" /> class.
      /// </summary>
      /// <param name="point1">The point1.</param>
      /// <param name="point2">The point2.</param>
      /// <param name="additionalPoints">Additional points</param>
      public LinearLineSegment(PointF point1, PointF point2, params PointF[] additionalPoints)
          : this(new[] { point1, point2 }.Concat(additionalPoints))
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="LinearLineSegment"/> class.
      /// </summary>
      /// <param name="points">The points.</param>
      public LinearLineSegment(PointF[] points)
      {
          Guard.NotNull(points, nameof(points));
          Guard.MustBeGreaterThanOrEqualTo(points.Length, 2, nameof(points));
          this.points = points;
          this.Bounds = CalculateBounds(points);
      }

      /// <summary>
      /// Gets the start point.
      /// </summary>
      public PointF StartPoint => this.points[0];

      /// <summary>
      /// Gets the end point.
      /// </summary>
      /// <value>
      /// The end point.
      /// </value>
      public PointF EndPoint => this.points[^1];

      /// <inheritdoc />
      public RectangleF Bounds { get; }

      /// <inheritdoc />
      public int LinearVertexCount(Vector2 scale) => this.points.Length;

      /// <inheritdoc />
      public void CopyTo(Span<PointF> destination, bool skipFirstPoint, Vector2 scale)
      {
          int startIndex = skipFirstPoint ? 1 : 0;
          ReadOnlySpan<PointF> source = this.points.AsSpan(startIndex);

          if (scale == Vector2.One)
          {
              source.CopyTo(destination);
              return;
          }

          for (int i = 0; i < source.Length; i++)
          {
              destination[i] = new PointF(source[i].X * scale.X, source[i].Y * scale.Y);
          }
      }

      /// <summary>
      /// Transforms the current LineSegment using specified matrix.
      /// </summary>
      /// <param name="matrix">The matrix.</param>
      /// <returns>
      /// A line segment with the matrix applied to it.
      /// </returns>
      public LinearLineSegment Transform(Matrix4x4 matrix)
      {
          if (matrix.IsIdentity)
          {
              // no transform to apply skip it
              return this;
          }

          PointF[] transformedPoints = new PointF[this.points.Length];

          for (int i = 0; i < this.points.Length; i++)
          {
              transformedPoints[i] = PointF.Transform(this.points[i], matrix);
          }

          return new LinearLineSegment(transformedPoints);
      }

      /// <summary>
      /// Transforms the current LineSegment using specified matrix.
      /// </summary>
      /// <param name="matrix">The matrix.</param>
      /// <returns>A line segment with the matrix applied to it.</returns>
      ILineSegment ILineSegment.Transform(Matrix4x4 matrix) => this.Transform(matrix);

      /// <summary>
      /// Computes the bounds for the retained linear point run.
      /// </summary>
      private static RectangleF CalculateBounds(ReadOnlySpan<PointF> points)
      {
          float minX = float.MaxValue;
          float minY = float.MaxValue;
          float maxX = float.MinValue;
          float maxY = float.MinValue;

          for (int i = 0; i < points.Length; i++)
          {
              PointF point = points[i];
              minX = MathF.Min(minX, point.X);
              minY = MathF.Min(minY, point.Y);
              maxX = MathF.Max(maxX, point.X);
              maxY = MathF.Max(maxY, point.Y);
          }

          return RectangleF.FromLTRB(minX, minY, maxX, maxY);
      }
  }
}