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

using System.Diagnostics.CodeAnalysis;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;

namespace SixLabors.ImageSharp.Drawing.Processing.Backends {
  /// <summary>
  /// Frame adapter that exposes a clipped subregion of another frame.
  /// </summary>
  /// <typeparam name="TPixel">The pixel format.</typeparam>
  internal sealed class CanvasRegionFrame<TPixel> : ICanvasFrame<TPixel>
      where TPixel : unmanaged, IPixel<TPixel>
  {
      private readonly ICanvasFrame<TPixel> parent;
      private readonly Rectangle region;

      /// <summary>
      /// Initializes a new instance of the <see cref="CanvasRegionFrame{TPixel}"/> class.
      /// </summary>
      /// <param name="parent">The parent frame that owns the target pixels.</param>
      /// <param name="region">The child region in parent-local coordinates.</param>
      public CanvasRegionFrame(ICanvasFrame<TPixel> parent, Rectangle region)
      {
          Guard.NotNull(parent, nameof(parent));
          Guard.MustBeGreaterThanOrEqualTo(region.Width, 0, nameof(region));
          Guard.MustBeGreaterThanOrEqualTo(region.Height, 0, nameof(region));

          this.parent = parent;
          this.region = region;
      }

      /// <inheritdoc />
      public Rectangle Bounds => new(
          this.parent.Bounds.X + this.region.X,
          this.parent.Bounds.Y + this.region.Y,
          this.region.Width,
          this.region.Height);

      /// <inheritdoc />
      public bool TryGetCpuRegion(out Buffer2DRegion<TPixel> region)
      {
          if (!this.parent.TryGetCpuRegion(out Buffer2DRegion<TPixel> parentRegion))
          {
              region = default;
              return false;
          }

          region = parentRegion.GetSubRegion(this.region);
          return true;
      }

      /// <inheritdoc />
      public bool TryGetNativeSurface([NotNullWhen(true)] out NativeSurface? surface)
          => this.parent.TryGetNativeSurface(out surface);
  }
}