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

using System;
using System.Buffers;
using System.Numerics;
using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;

namespace SixLabors.ImageSharp.Drawing.Processing {
  /// <summary>
  /// Worker-local scratch workspace used by prepared brushes during row composition.
  /// </summary>
  /// <typeparam name="TPixel">The target pixel format.</typeparam>
  public sealed class BrushWorkspace<TPixel> : IDisposable
      where TPixel : unmanaged, IPixel<TPixel>
  {
      private readonly IMemoryOwner<float> amountsOwner;
      private readonly IMemoryOwner<TPixel> overlaysOwner;
      private readonly IMemoryOwner<Vector4> blendScratchOwner;

      internal BrushWorkspace(MemoryAllocator allocator, int rowWidth)
      {
          int capacity = Math.Max(1, rowWidth);
          this.amountsOwner = allocator.Allocate<float>(capacity);
          this.overlaysOwner = allocator.Allocate<TPixel>(capacity);
          this.blendScratchOwner = allocator.Allocate<Vector4>(capacity * 3);
      }

      /// <summary>
      /// Gets the shared amount buffer for the requested length.
      /// </summary>
      /// <param name="length">The number of elements required.</param>
      /// <returns>A slice of the worker-local pooled amount buffer.</returns>
      public Span<float> GetAmounts(int length)
      {
          ArgumentOutOfRangeException.ThrowIfNegative(length);
          return this.amountsOwner.Memory.Span[..length];
      }

      /// <summary>
      /// Gets the shared overlay buffer for the requested length.
      /// </summary>
      /// <param name="length">The number of elements required.</param>
      /// <returns>A slice of the worker-local pooled overlay buffer.</returns>
      public Span<TPixel> GetOverlays(int length)
      {
          ArgumentOutOfRangeException.ThrowIfNegative(length);
          return this.overlaysOwner.Memory.Span[..length];
      }

      /// <summary>
      /// Gets the shared vector scratch for the requested row length and vector row count.
      /// </summary>
      /// <param name="length">The number of pixels in the row.</param>
      /// <param name="vectorRows">The number of temporary vector rows required.</param>
      /// <returns>A slice of the worker-local pooled vector scratch buffer.</returns>
      public Span<Vector4> GetBlendScratch(int length, int vectorRows)
      {
          ArgumentOutOfRangeException.ThrowIfNegative(length);
          ArgumentOutOfRangeException.ThrowIfLessThan(vectorRows, 1);
          return this.blendScratchOwner.Memory.Span[..(length * vectorRows)];
      }

      /// <inheritdoc />
      public void Dispose()
      {
          this.amountsOwner.Dispose();
          this.overlaysOwner.Dispose();
          this.blendScratchOwner.Dispose();
      }
  }
}