using System;

using BCnEncoder.Shared;

using BCnEncTests.Support;

using CommunityToolkit.HighPerformance;

using SixLabors.ImageSharp;

using SixLabors.ImageSharp.Processing;

using Xunit;

using Xunit.Abstractions;

namespace BCnEncTests

{

public class MipMapperTests

{

private readonly ITestOutputHelper output;

public MipMapperTests(ITestOutputHelper output) => this.output = output;

[Fact]

public void MipChainHasCorrectDimensions()

{

var image = ImageLoader.TestGradient1; // 512x416

var numMips = 0;

var chain = MipMapper.GenerateMipChain(image, ref numMips);

Assert.Equal(chain.Length, numMips);

Assert.True(numMips > 1);

for (var i = 0; i < numMips; i++)

{

Assert.Equal(Math.Max(1, image.Width >> i), chain[i].Width);

Assert.Equal(Math.Max(1, image.Height >> i), chain[i].Height);

}

// Last level must be 1x1

Assert.Equal(1, chain[numMips - 1].Width);

Assert.Equal(1, chain[numMips - 1].Height);

}

/// <summary>

/// Compares each mip level produced by MipMapper against the equivalent

/// ImageSharp Box-filter resize (Compand=false so both operate in sRGB

/// byte space without gamma correction). The PSNR should be very high

/// because both algorithms perform the same 2x2 box average.

/// </summary>

[Theory]

[InlineData(1)]

[InlineData(2)]

[InlineData(3)]

[InlineData(4)]

public void MipLevelMatchesImageSharpBoxFilter(int mipLevel)

{

var image = ImageLoader.TestGradient1;

var numMips = mipLevel + 1;

var chain = MipMapper.GenerateMipChain(image, ref numMips);

var mipW = chain[mipLevel].Width;

var mipH = chain[mipLevel].Height;

// ImageSharp Box sampler + Compand=false: no gamma correction,

// averages pixel values in sRGB space — matches MipMapper exactly.

using var imageSharp = ImageLoader.LoadTestImageSharp("../../../testImages/test_gradient_1_512.jpg");

using var reference = imageSharp.Clone(x => x.Resize(new ResizeOptions

{

Size = new Size(mipW, mipH),

Sampler = KnownResamplers.Box,

Compand = false

}));

var mipColors = TestHelper.GetSinglePixelArrayAsColors(chain[mipLevel]);

var refColors = TestHelper.GetSinglePixelArrayAsColors(reference);

var psnr = ImageQuality.PeakSignalToNoiseRatio(mipColors, refColors);

output.WriteLine($"Mip level {mipLevel} ({mipW}x{mipH}): PSNR vs ImageSharp Box = {psnr:F2} dB");

Assert.True(psnr > 40,

$"Mip level {mipLevel}: PSNR vs ImageSharp Box was {psnr:F2} dB (expected > 40)");

}

}

}