// Copyright (c) Six Labors.
// Licensed under the Apache License, Version 2.0.

using SixLabors.ImageSharp.Memory;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using Xunit;

namespace SixLabors.ImageSharp.Tests.Processing.Transforms
{
    public class IntegralImageTests : BaseImageOperationsExtensionTest
    {
        [Theory]
        [WithFile(TestImages.Png.Bradley01, PixelTypes.Rgba32)]
        [WithFile(TestImages.Png.Bradley02, PixelTypes.Rgba32)]
        [WithFile(TestImages.Png.Ducky, PixelTypes.Rgba32)]
        public void CalculateIntegralImage_Rgba32Works(TestImageProvider<Rgba32> provider)
        {
            using Image<Rgba32> image = provider.GetImage();

            // Act:
            Buffer2D<ulong> integralBuffer = image.CalculateIntegralImage();

            // Assert:
            VerifySumValues(provider, integralBuffer, (Rgba32 pixel) =>
            {
                L8 outputPixel = default;

                outputPixel.FromRgba32(pixel);

                return outputPixel.PackedValue;
            });
        }

        [Theory]
        [WithFile(TestImages.Png.Bradley01, PixelTypes.L8)]
        [WithFile(TestImages.Png.Bradley02, PixelTypes.L8)]
        public void CalculateIntegralImage_L8Works(TestImageProvider<L8> provider)
        {
            using Image<L8> image = provider.GetImage();

            // Act:
            Buffer2D<ulong> integralBuffer = image.CalculateIntegralImage();

            // Assert:
            VerifySumValues(provider, integralBuffer, (L8 pixel) => { return pixel.PackedValue; });
        }

        private static void VerifySumValues<TPixel>(
            TestImageProvider<TPixel> provider,
            Buffer2D<ulong> integralBuffer,
            System.Func<TPixel, ulong> getPixel)
            where TPixel : unmanaged, IPixel<TPixel>
        {
            Image<TPixel> image = provider.GetImage();

            // Check top-left corner
            Assert.Equal(getPixel(image[0, 0]), integralBuffer[0, 0]);

            ulong pixelValues = 0;

            pixelValues += getPixel(image[0, 0]);
            pixelValues += getPixel(image[1, 0]);
            pixelValues += getPixel(image[0, 1]);
            pixelValues += getPixel(image[1, 1]);

            // Check top-left 2x2 pixels
            Assert.Equal(pixelValues, integralBuffer[1, 1]);

            pixelValues = 0;

            pixelValues += getPixel(image[image.Width - 3, 0]);
            pixelValues += getPixel(image[image.Width - 2, 0]);
            pixelValues += getPixel(image[image.Width - 1, 0]);
            pixelValues += getPixel(image[image.Width - 3, 1]);
            pixelValues += getPixel(image[image.Width - 2, 1]);
            pixelValues += getPixel(image[image.Width - 1, 1]);

            // Check top-right 3x2 pixels
            Assert.Equal(pixelValues, integralBuffer[image.Width - 1, 1] + 0 - 0 - integralBuffer[image.Width - 4, 1]);

            pixelValues = 0;

            pixelValues += getPixel(image[0, image.Height - 3]);
            pixelValues += getPixel(image[0, image.Height - 2]);
            pixelValues += getPixel(image[0, image.Height - 1]);
            pixelValues += getPixel(image[1, image.Height - 3]);
            pixelValues += getPixel(image[1, image.Height - 2]);
            pixelValues += getPixel(image[1, image.Height - 1]);

            // Check bottom-left 2x3 pixels
            Assert.Equal(pixelValues, integralBuffer[1, image.Height - 1] + 0 - integralBuffer[1, image.Height - 4] - 0);

            pixelValues = 0;

            pixelValues += getPixel(image[image.Width - 3, image.Height - 3]);
            pixelValues += getPixel(image[image.Width - 2, image.Height - 3]);
            pixelValues += getPixel(image[image.Width - 1, image.Height - 3]);
            pixelValues += getPixel(image[image.Width - 3, image.Height - 2]);
            pixelValues += getPixel(image[image.Width - 2, image.Height - 2]);
            pixelValues += getPixel(image[image.Width - 1, image.Height - 2]);
            pixelValues += getPixel(image[image.Width - 3, image.Height - 1]);
            pixelValues += getPixel(image[image.Width - 2, image.Height - 1]);
            pixelValues += getPixel(image[image.Width - 1, image.Height - 1]);

            // Check bottom-right 3x3 pixels
            Assert.Equal(pixelValues, integralBuffer[image.Width - 1, image.Height - 1] + integralBuffer[image.Width - 4, image.Height - 4] - integralBuffer[image.Width - 1, image.Height - 4] - integralBuffer[image.Width - 4, image.Height - 1]);
        }
    }
}