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

using System;

namespace SixLabors.ImageSharp.Drawing.Processing {
  /// <summary>
  /// The base class for pens that can apply a pattern to a line with a set brush and thickness
  /// </summary>
  /// <remarks>
  /// The pattern will be in to the form of
  /// <code>
  /// new float[]{ 1f, 2f, 0.5f}
  /// </code>
  /// this will be converted into a pattern that is 3.5 times longer that the width with 3 sections.
  /// <list type="bullet">
  /// <item>Section 1 will be width long (making a square) and will be filled by the brush.</item>
  /// <item>Section 2 will be width * 2 long and will be empty.</item>
  /// <item>Section 3 will be width/2 long and will be filled.</item>
  /// </list>
  /// The pattern will immediately repeat without gap.
  /// </remarks>
  public abstract class Pen : IEquatable<Pen>
  {
      private readonly float[] pattern;

      /// <summary>
      /// Initializes a new instance of the <see cref="Pen"/> class.
      /// </summary>
      /// <param name="strokeFill">The brush used to fill the stroke outline.</param>
      protected Pen(Brush strokeFill)
          : this(strokeFill, 1)
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="Pen"/> class.
      /// </summary>
      /// <param name="strokeFill">The brush used to fill the stroke outline.</param>
      /// <param name="strokeWidth">The stroke width in the path's local coordinate space before any drawing transform is applied.</param>
      protected Pen(Brush strokeFill, float strokeWidth)
          : this(strokeFill, strokeWidth, Pens.EmptyPattern)
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="Pen"/> class.
      /// </summary>
      /// <param name="strokeFill">The brush used to fill the stroke outline.</param>
      /// <param name="strokeWidth">The stroke width in the path's local coordinate space before any drawing transform is applied.</param>
      /// <param name="strokePattern">The stroke pattern.</param>
      protected Pen(Brush strokeFill, float strokeWidth, float[] strokePattern)
      {
          Guard.NotNull(strokeFill, nameof(strokeFill));

          Guard.MustBeGreaterThan(strokeWidth, 0, nameof(strokeWidth));
          Guard.NotNull(strokePattern, nameof(strokePattern));

          this.StrokeFill = strokeFill;
          this.StrokeWidth = strokeWidth;
          this.pattern = strokePattern;
          this.StrokeOptions = new StrokeOptions();
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="Pen"/> class.
      /// </summary>
      /// <param name="options">The pen options.</param>
      protected Pen(PenOptions options)
      {
          this.StrokeFill = options.StrokeFill;
          this.StrokeWidth = options.StrokeWidth;
          this.pattern = options.StrokePattern;
          this.StrokeOptions = options.StrokeOptions ?? new StrokeOptions();
      }

      /// <inheritdoc cref="PenOptions.StrokeFill"/>
      public Brush StrokeFill { get; }

      /// <inheritdoc cref="PenOptions.StrokeWidth"/>
      public float StrokeWidth { get; }

      /// <inheritdoc cref="PenOptions.StrokePattern"/>
      public ReadOnlyMemory<float> StrokePattern => this.pattern;

      /// <inheritdoc cref="PenOptions.StrokeOptions"/>
      public StrokeOptions StrokeOptions { get; }

      /// <summary>
      /// Applies the styling from the pen to a path and generate a new path with the final vector.
      /// </summary>
      /// <param name="path">The source path</param>
      /// <returns>The <see cref="IPath"/> with the pen styling applied.</returns>
      public IPath GeneratePath(IPath path)
          => this.GeneratePath(path, this.StrokeWidth);

      /// <summary>
      /// Applies the styling from the pen to a path and generate a new path with the final vector.
      /// </summary>
      /// <param name="path">The source path</param>
      /// <param name="strokeWidth">The stroke width in the path's local coordinate space before any drawing transform is applied.</param>
      /// <returns>The <see cref="IPath"/> with the pen styling applied.</returns>
      public abstract IPath GeneratePath(IPath path, float strokeWidth);

      /// <inheritdoc/>
      public virtual bool Equals(Pen? other)
          => other != null
          && this.StrokeWidth == other.StrokeWidth
          && this.StrokeFill.Equals(other.StrokeFill)
          && this.StrokeOptions.Equals(other.StrokeOptions)
          && this.StrokePattern.Span.SequenceEqual(other.StrokePattern.Span);

      /// <inheritdoc/>
      public override bool Equals(object? obj) => this.Equals(obj as Pen);

      /// <inheritdoc/>
      public override int GetHashCode()
          => HashCode.Combine(this.StrokeWidth, this.StrokeFill, this.StrokeOptions, this.pattern);
  }
}