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

using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using System;
using System.Collections.Generic;

namespace SixLabors.ImageSharp.Drawing.Processing.Backends {
  /// <summary>
  /// Processor barrier recorded in a drawing backend timeline.
  /// </summary>
  internal sealed class ApplyBarrier
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="ApplyBarrier"/> class.
      /// </summary>
      /// <param name="path">The closed path defining the processed region.</param>
      /// <param name="options">The drawing options captured when the barrier was recorded.</param>
      /// <param name="clipPaths">The active clip paths captured when the barrier was recorded.</param>
      /// <param name="canvasBounds">The canvas-local bounds captured when the barrier was recorded.</param>
      /// <param name="targetBounds">The absolute target bounds captured when the barrier was recorded.</param>
      /// <param name="destinationOffset">The absolute destination offset captured when the barrier was recorded.</param>
      /// <param name="isInsideLayer">Indicates whether the barrier was recorded inside a layer.</param>
      /// <param name="operation">The processor operation to run against the replay-time snapshot.</param>
      internal ApplyBarrier(
          IPath path,
          DrawingOptions options,
          IReadOnlyList<IPath> clipPaths,
          Rectangle canvasBounds,
          Rectangle targetBounds,
          Point destinationOffset,
          bool isInsideLayer,
          Action<IImageProcessingContext> operation)
      {
          this.Path = path;
          this.Options = options;
          this.ClipPaths = clipPaths;
          this.CanvasBounds = canvasBounds;
          this.TargetBounds = targetBounds;
          this.DestinationOffset = destinationOffset;
          this.IsInsideLayer = isInsideLayer;
          this.Operation = operation;
      }

      /// <summary>
      /// Gets the closed path defining the processed region.
      /// </summary>
      public IPath Path { get; }

      /// <summary>
      /// Gets the drawing options captured when the barrier was recorded.
      /// </summary>
      public DrawingOptions Options { get; }

      /// <summary>
      /// Gets the active clip paths captured when the barrier was recorded.
      /// </summary>
      public IReadOnlyList<IPath> ClipPaths { get; }

      /// <summary>
      /// Gets the canvas-local bounds captured when the barrier was recorded.
      /// </summary>
      public Rectangle CanvasBounds { get; }

      /// <summary>
      /// Gets the absolute target bounds captured when the barrier was recorded.
      /// </summary>
      public Rectangle TargetBounds { get; }

      /// <summary>
      /// Gets the absolute destination offset captured when the barrier was recorded.
      /// </summary>
      public Point DestinationOffset { get; }

      /// <summary>
      /// Gets a value indicating whether the barrier was recorded inside a layer.
      /// </summary>
      public bool IsInsideLayer { get; }

      /// <summary>
      /// Gets the processor operation to run against the replay-time snapshot.
      /// </summary>
      public Action<IImageProcessingContext> Operation { get; }

      /// <summary>
      /// Creates the transient image-brush draw command that writes this barrier's processed snapshot back to the target.
      /// </summary>
      /// <typeparam name="TPixel">The pixel format.</typeparam>
      /// <param name="configuration">The active processing configuration.</param>
      /// <param name="backend">The backend used to read the replay-time target pixels.</param>
      /// <param name="target">The target frame.</param>
      /// <param name="ownedResource">The image resource that must stay alive while the returned command batch is rendered.</param>
      /// <returns>The transient write-back command batch, or <see langword="null"/> when the barrier has no target coverage.</returns>
      public DrawingCommandBatch? CreateWriteBackBatch<TPixel>(
          Configuration configuration,
          IDrawingBackend backend,
          ICanvasFrame<TPixel> target,
          out IDisposable? ownedResource)
          where TPixel : unmanaged, IPixel<TPixel>
      {
          RectangleF rawBounds = RectangleF.Transform(this.Path.Bounds, this.Options.Transform);
          Rectangle sourceRect = ToConservativeBounds(rawBounds);
          sourceRect = Rectangle.Intersect(this.CanvasBounds, sourceRect);

          if (sourceRect.Width <= 0 || sourceRect.Height <= 0)
          {
              ownedResource = null;
              return null;
          }

          Image<TPixel> sourceImage = new(configuration, sourceRect.Width, sourceRect.Height);
          try
          {
              backend.ReadRegion(
                  configuration,
                  target,
                  sourceRect,
                  sourceImage.Frames.RootFrame.PixelBuffer.GetRegion());

              sourceImage.Mutate(this.Operation);

              Point brushOffset = new(
                  sourceRect.X - (int)MathF.Floor(rawBounds.Left),
                  sourceRect.Y - (int)MathF.Floor(rawBounds.Top));

              ImageBrush<TPixel> brush = new(sourceImage, sourceImage.Bounds, brushOffset);
              GraphicsOptions graphicsOptions = this.Options.GraphicsOptions;
              RasterizationMode rasterizationMode = graphicsOptions.Antialias
                  ? RasterizationMode.Antialiased
                  : RasterizationMode.Aliased;

              RectangleF pathBounds = this.Path.Bounds;
              Rectangle interest = Rectangle.FromLTRB(
                  (int)MathF.Floor(pathBounds.Left),
                  (int)MathF.Floor(pathBounds.Top),
                  (int)MathF.Ceiling(pathBounds.Right),
                  (int)MathF.Ceiling(pathBounds.Bottom));

              RasterizerOptions rasterizerOptions = new(
                  interest,
                  this.Options.ShapeOptions.IntersectionRule,
                  rasterizationMode,
                  RasterizerSamplingOrigin.PixelBoundary,
                  graphicsOptions.AntialiasThreshold);

              CompositionCommand command = CompositionCommand.Create(
                  this.Path,
                  brush,
                  this.Options,
                  in rasterizerOptions,
                  this.TargetBounds,
                  this.DestinationOffset,
                  this.ClipPaths,
                  this.IsInsideLayer);

              ownedResource = sourceImage;
              CompositionSceneCommand[] commands = [new PathCompositionSceneCommand(command)];
              return new DrawingCommandBatch(commands, hasLayers: false);
          }
          catch
          {
              sourceImage.Dispose();
              throw;
          }
      }

      private static Rectangle ToConservativeBounds(RectangleF bounds)
          => Rectangle.FromLTRB(
              (int)MathF.Floor(bounds.Left),
              (int)MathF.Floor(bounds.Top),
              (int)MathF.Ceiling(bounds.Right),
              (int)MathF.Ceiling(bounds.Bottom));
  }
}