// <copyright file="Crop.cs" company="James Jackson-South">
// Copyright (c) James Jackson-South and contributors.
// Licensed under the Apache License, Version 2.0.
// </copyright>

namespace SixLabors.ImageSharp.Benchmarks
{

    using BenchmarkDotNet.Attributes;
    using SixLabors.ImageSharp.PixelFormats;

    using CoreSize = SixLabors.Primitives.Size;
    using System.Numerics;
    using System;
    using System.Threading.Tasks;

    using SixLabors.ImageSharp.Memory;
    using SixLabors.Primitives;
    using SixLabors.ImageSharp.Processing.Overlays.Processors;
    using SixLabors.ImageSharp.Processing.Processors;

    public class Glow : BenchmarkBase
    {
        private GlowProcessor<Rgba32> bulk;
        private GlowProcessorParallel<Rgba32> parallel;

        [GlobalSetup]
        public void Setup()
        {
            this.bulk = new GlowProcessor<Rgba32>(NamedColors<Rgba32>.Beige, 800 * .5f, GraphicsOptions.Default);
            this.parallel = new GlowProcessorParallel<Rgba32>(NamedColors<Rgba32>.Beige) { Radius = 800 * .5f, };

        }
        [Benchmark(Description = "ImageSharp Glow - Bulk")]
        public CoreSize GlowBulk()
        {
            using (Image<Rgba32> image = new Image<Rgba32>(800, 800))
            {
                this.bulk.Apply(image, image.Bounds());
                return new CoreSize(image.Width, image.Height);
            }
        }

        [Benchmark(Description = "ImageSharp Glow - Parallel")]
        public CoreSize GLowSimple()
        {
            using (Image<Rgba32> image = new Image<Rgba32>(800, 800))
            {
                this.parallel.Apply(image, image.Bounds());
                return new CoreSize(image.Width, image.Height);
            }
        }

        internal class GlowProcessorParallel<TPixel> : ImageProcessor<TPixel>
        where TPixel : struct, IPixel<TPixel>
        {
            /// <summary>
            /// Initializes a new instance of the <see cref="GlowProcessorParallel{TPixel}" /> class.
            /// </summary>
            /// <param name="color">The color or the glow.</param>
            public GlowProcessorParallel(TPixel color)
            {
                this.GlowColor = color;
            }

            /// <summary>
            /// Gets or sets the glow color to apply.
            /// </summary>
            public TPixel GlowColor { get; set; }

            /// <summary>
            /// Gets or sets the the radius.
            /// </summary>
            public float Radius { get; set; }

            /// <inheritdoc/>
            protected override void OnFrameApply(ImageFrame<TPixel> source, Rectangle sourceRectangle, Configuration configuration)
            {
                int startY = sourceRectangle.Y;
                int endY = sourceRectangle.Bottom;
                int startX = sourceRectangle.X;
                int endX = sourceRectangle.Right;
                TPixel glowColor = this.GlowColor;
                Vector2 centre = Rectangle.Center(sourceRectangle);
                float maxDistance = this.Radius > 0 ? Math.Min(this.Radius, sourceRectangle.Width * .5F) : sourceRectangle.Width * .5F;

                // Align start/end positions.
                int minX = Math.Max(0, startX);
                int maxX = Math.Min(source.Width, endX);
                int minY = Math.Max(0, startY);
                int maxY = Math.Min(source.Height, endY);

                // Reset offset if necessary.
                if (minX > 0)
                {
                    startX = 0;
                }

                if (minY > 0)
                {
                    startY = 0;
                }

                int width = maxX - minX;
                using (IBuffer<TPixel> rowColors = Configuration.Default.MemoryManager.Allocate<TPixel>(width))
                using (PixelAccessor<TPixel> sourcePixels = source.Lock())
                {
                    rowColors.Span.Fill(glowColor);

                    Parallel.For(
                        minY,
                        maxY,
                        configuration.ParallelOptions,
                        y =>
                        {
                            int offsetY = y - startY;

                            for (int x = minX; x < maxX; x++)
                            {
                                int offsetX = x - startX;
                                float distance = Vector2.Distance(centre, new Vector2(offsetX, offsetY));
                                Vector4 sourceColor = sourcePixels[offsetX, offsetY].ToVector4();
                                TPixel packed = default(TPixel);
                                packed.PackFromVector4(PremultipliedLerp(sourceColor, glowColor.ToVector4(), 1 - (.95F * (distance / maxDistance))));
                                sourcePixels[offsetX, offsetY] = packed;
                            }
                        });
                }
            }
            public static Vector4 PremultipliedLerp(Vector4 backdrop, Vector4 source, float amount)
            {
                amount = amount.Clamp(0, 1);

                // Santize on zero alpha
                if (Math.Abs(backdrop.W) < Constants.Epsilon)
                {
                    source.W *= amount;
                    return source;
                }

                if (Math.Abs(source.W) < Constants.Epsilon)
                {
                    return backdrop;
                }

                // Premultiply the source vector.
                // Oddly premultiplying the background vector creates dark outlines when pixels
                // Have low alpha values.
                source = new Vector4(source.X, source.Y, source.Z, 1) * (source.W * amount);

                // This should be implementing the following formula
                // https://en.wikipedia.org/wiki/Alpha_compositing
                // Vout =  Vs + Vb (1 - Vsa)
                // Aout = Vsa + Vsb (1 - Vsa)
                Vector3 inverseW = new Vector3(1 - source.W);
                Vector3 xyzB = new Vector3(backdrop.X, backdrop.Y, backdrop.Z);
                Vector3 xyzS = new Vector3(source.X, source.Y, source.Z);

                return new Vector4(xyzS + (xyzB * inverseW), source.W + (backdrop.W * (1 - source.W)));
            }
        }
    }
}