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

using System.Diagnostics.CodeAnalysis;
using System.Numerics;
using System.Threading;

namespace SixLabors.ImageSharp.Drawing {
  /// <summary>
  /// Single-entry memoization slot for a scale-baked <see cref="LinearGeometry"/> derived from an <see cref="IPath"/>.
  /// Entries are keyed on the X/Y scale so text and panning workloads — which re-render the same shapes at a fixed
  /// zoom level while their rotation/translation/perspective drift — hit a stable cached bake.
  /// </summary>
  /// <remarks>
  /// Safe for concurrent readers and writers. Publication uses <see cref="Volatile.Write{T}(ref T, T)"/> so a reader
  /// either observes <see langword="null"/> or a fully-constructed entry.
  /// </remarks>
  internal struct LinearGeometryCache
  {
      private Entry? entry;

      public bool TryGet(Vector2 scale, [NotNullWhen(true)] out LinearGeometry? value)
      {
          Entry? hit = Volatile.Read(ref this.entry);
          if (hit is not null && hit.Scale == scale)
          {
              value = hit.Value;
              return true;
          }

          value = null;
          return false;
      }

      public LinearGeometry Store(Vector2 scale, LinearGeometry value)
      {
          Volatile.Write(ref this.entry, new Entry(scale, value));
          return value;
      }

      private sealed class Entry(Vector2 scale, LinearGeometry value)
      {
          public Vector2 Scale { get; } = scale;

          public LinearGeometry Value { get; } = value;
      }
  }
}