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

namespace ImageSharp.Processing.Processors
{
    using System;
    using System.Numerics;
    using System.Threading.Tasks;

    /// <summary>
    /// An <see cref="IImageProcessor{TColor}"/> to apply an oil painting effect to an <see cref="Image{TColor}"/>.
    /// </summary>
    /// <remarks>Adapted from <see href="https://softwarebydefault.com/2013/06/29/oil-painting-cartoon-filter/"/> by Dewald Esterhuizen.</remarks>
    /// <typeparam name="TColor">The pixel format.</typeparam>
    public class OilPaintingProcessor<TColor> : ImageProcessor<TColor>
        where TColor : struct, IPackedPixel, IEquatable<TColor>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="OilPaintingProcessor{TColor}"/> class.
        /// </summary>
        /// <param name="levels">
        /// The number of intensity levels. Higher values result in a broader range of color intensities forming part of the result image.
        /// </param>
        /// <param name="brushSize">
        /// The number of neighboring pixels used in calculating each individual pixel value.
        /// </param>
        public OilPaintingProcessor(int levels, int brushSize)
        {
            Guard.MustBeGreaterThan(levels, 0, nameof(levels));
            Guard.MustBeGreaterThan(brushSize, 0, nameof(brushSize));

            this.Levels = levels;
            this.BrushSize = brushSize;
        }

        /// <summary>
        /// Gets the intensity levels
        /// </summary>
        public int Levels { get; }

        /// <summary>
        /// Gets the brush size
        /// </summary>
        public int BrushSize { get; }

        /// <inheritdoc/>
        protected override void OnApply(ImageBase<TColor> source, Rectangle sourceRectangle)
        {
            int startY = sourceRectangle.Y;
            int endY = sourceRectangle.Bottom;
            int startX = sourceRectangle.X;
            int endX = sourceRectangle.Right;
            int radius = this.BrushSize >> 1;
            int levels = this.Levels;

            // 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;
            }

            using (PixelAccessor<TColor> targetPixels = new PixelAccessor<TColor>(source.Width, source.Height))
            {
                using (PixelAccessor<TColor> sourcePixels = source.Lock())
                {
                    Parallel.For(
                        minY,
                        maxY,
                        this.ParallelOptions,
                        y =>
                        {
                            for (int x = startX; x < endX; x++)
                            {
                                int maxIntensity = 0;
                                int maxIndex = 0;

                                int[] intensityBin = new int[levels];
                                float[] redBin = new float[levels];
                                float[] blueBin = new float[levels];
                                float[] greenBin = new float[levels];

                                for (int fy = 0; fy <= radius; fy++)
                                {
                                    int fyr = fy - radius;
                                    int offsetY = y + fyr;

                                    // Skip the current row
                                    if (offsetY < minY)
                                    {
                                        continue;
                                    }

                                    // Outwith the current bounds so break.
                                    if (offsetY >= maxY)
                                    {
                                        break;
                                    }

                                    for (int fx = 0; fx <= radius; fx++)
                                    {
                                        int fxr = fx - radius;
                                        int offsetX = x + fxr;

                                        // Skip the column
                                        if (offsetX < 0)
                                        {
                                            continue;
                                        }

                                        if (offsetX < maxX)
                                        {
                                            // ReSharper disable once AccessToDisposedClosure
                                            Vector4 color = sourcePixels[offsetX, offsetY].ToVector4();

                                            float sourceRed = color.X;
                                            float sourceBlue = color.Z;
                                            float sourceGreen = color.Y;

                                            int currentIntensity = (int)Math.Round((sourceBlue + sourceGreen + sourceRed) / 3.0 * (levels - 1));

                                            intensityBin[currentIntensity] += 1;
                                            blueBin[currentIntensity] += sourceBlue;
                                            greenBin[currentIntensity] += sourceGreen;
                                            redBin[currentIntensity] += sourceRed;

                                            if (intensityBin[currentIntensity] > maxIntensity)
                                            {
                                                maxIntensity = intensityBin[currentIntensity];
                                                maxIndex = currentIntensity;
                                            }
                                        }
                                    }

                                    float red = Math.Abs(redBin[maxIndex] / maxIntensity);
                                    float green = Math.Abs(greenBin[maxIndex] / maxIntensity);
                                    float blue = Math.Abs(blueBin[maxIndex] / maxIntensity);

                                    TColor packed = default(TColor);
                                    packed.PackFromVector4(new Vector4(red, green, blue, sourcePixels[x, y].ToVector4().W));
                                    targetPixels[x, y] = packed;
                                }
                            }
                        });
                }

                source.SwapPixelsBuffers(targetPixels);
            }
        }
    }
}