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

using SixLabors.ImageSharp.Advanced;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;

namespace SixLabors.ImageSharp.Drawing.Processing {
  /// <summary>
  /// Extension methods for creating drawing canvas instances over ImageSharp image frames.
  /// </summary>
  public static class DrawingCanvasFactoryExtensions
  {
      /// <summary>
      /// Creates a drawing canvas over an existing typed image frame.
      /// </summary>
      /// <remarks>
      /// The caller owns the returned canvas and must dispose it to replay recorded work into the frame.
      /// </remarks>
      /// <typeparam name="TPixel">The pixel format.</typeparam>
      /// <param name="frame">The frame backing the canvas.</param>
      /// <param name="configuration">The configuration to use for this canvas instance.</param>
      /// <param name="options">Initial drawing options for this canvas instance.</param>
      /// <param name="clipPaths">Initial clip paths for this canvas instance.</param>
      /// <returns>A drawing canvas targeting <paramref name="frame"/>.</returns>
      public static DrawingCanvas CreateCanvas<TPixel>(
          this ImageFrame<TPixel> frame,
          Configuration configuration,
          DrawingOptions options,
          params IPath[] clipPaths)
          where TPixel : unmanaged, IPixel<TPixel>
      {
          Guard.NotNull(frame, nameof(frame));
          Guard.NotNull(options, nameof(options));
          Guard.NotNull(clipPaths, nameof(clipPaths));

          return new DrawingCanvas<TPixel>(
              configuration,
              options,
              frame.PixelBuffer.GetRegion(),
              clipPaths);
      }

      /// <summary>
      /// Creates a drawing canvas over an existing image frame.
      /// </summary>
      /// <remarks>
      /// The caller owns the returned canvas and must dispose it to replay recorded work into the frame.
      /// </remarks>
      /// <param name="frame">The frame backing the canvas.</param>
      /// <param name="configuration">The configuration to use for this canvas instance.</param>
      /// <param name="options">Initial drawing options for this canvas instance.</param>
      /// <param name="clipPaths">Initial clip paths for this canvas instance.</param>
      /// <returns>A drawing canvas targeting <paramref name="frame"/>.</returns>
      public static DrawingCanvas CreateCanvas(
          this ImageFrame frame,
          Configuration configuration,
          DrawingOptions options,
          params IPath[] clipPaths)
      {
          Guard.NotNull(frame, nameof(frame));
          Guard.NotNull(options, nameof(options));
          Guard.NotNull(clipPaths, nameof(clipPaths));

          CanvasFactoryVisitor visitor = new(configuration, options, clipPaths);
          frame.AcceptVisitor(visitor);
          return visitor.Value!;
      }

      private struct CanvasFactoryVisitor : IImageFrameVisitor
      {
          private readonly Configuration configuration;
          private readonly DrawingOptions options;
          private readonly IPath[] clipPaths;

          public CanvasFactoryVisitor(Configuration configuration, DrawingOptions options, IPath[] clipPaths)
          {
              this.configuration = configuration;
              this.options = options;
              this.clipPaths = clipPaths;
          }

          public DrawingCanvas? Value { get; private set; }

          void IImageFrameVisitor.Visit<TPixel>(ImageFrame<TPixel> frame)
              => this.Value = frame.CreateCanvas(this.configuration, this.options, this.clipPaths);
      }
  }
}