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test/Scry.Tests/PerceptualHashTests.cs

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+using Scry.Core.Imaging;
+using SkiaSharp;
+using Xunit;
+
+namespace Scry.Tests;
+
+public class PerceptualHashTests
+{
+    [Fact]
+    public void ComputeHash_ReturnsConsistentHash()
+    {
+        using var bitmap = CreateTestBitmap(32, 32, SKColors.Red);
+        
+        var hash1 = PerceptualHash.ComputeHash(bitmap);
+        var hash2 = PerceptualHash.ComputeHash(bitmap);
+        
+        Assert.Equal(hash1, hash2);
+    }
+    
+    [Fact]
+    public void ComputeColorHash_Returns24Bytes()
+    {
+        using var bitmap = CreateTestBitmap(32, 32, SKColors.Blue);
+        
+        var hash = PerceptualHash.ComputeColorHash(bitmap);
+        
+        Assert.Equal(24, hash.Length);
+    }
+    
+    [Fact]
+    public void HammingDistance_IdenticalHashes_ReturnsZero()
+    {
+        var hash = new byte[] { 0xFF, 0x00, 0xAB, 0xCD };
+        
+        var distance = PerceptualHash.HammingDistance(hash, hash);
+        
+        Assert.Equal(0, distance);
+    }
+    
+    [Fact]
+    public void HammingDistance_OppositeHashes_ReturnsMaxBits()
+    {
+        var hash1 = new byte[] { 0x00, 0x00 };
+        var hash2 = new byte[] { 0xFF, 0xFF };
+        
+        var distance = PerceptualHash.HammingDistance(hash1, hash2);
+        
+        Assert.Equal(16, distance);
+    }
+    
+    [Fact]
+    public void HammingDistance_SingleBitDifference()
+    {
+        var hash1 = new byte[] { 0b00000000 };
+        var hash2 = new byte[] { 0b00000001 };
+        
+        var distance = PerceptualHash.HammingDistance(hash1, hash2);
+        
+        Assert.Equal(1, distance);
+    }
+    
+    [Fact]
+    public void CalculateConfidence_ZeroDistance_ReturnsOne()
+    {
+        var confidence = PerceptualHash.CalculateConfidence(0, 192);
+        
+        Assert.Equal(1.0f, confidence);
+    }
+    
+    [Fact]
+    public void CalculateConfidence_HalfDistance_ReturnsHalf()
+    {
+        var confidence = PerceptualHash.CalculateConfidence(96, 192);
+        
+        Assert.Equal(0.5f, confidence);
+    }
+    
+    [Theory]
+    [InlineData("reference/brainstorm.png")]
+    [InlineData("reference/force_of_will.png")]
+    [InlineData("single_cards/llanowar_elves.jpg")]
+    public void ComputeColorHash_RealImages_ProducesValidHash(string imagePath)
+    {
+        var fullPath = Path.Combine("TestImages", imagePath);
+        if (!File.Exists(fullPath))
+        {
+            return;
+        }
+        
+        using var bitmap = SKBitmap.Decode(fullPath);
+        Assert.NotNull(bitmap);
+        
+        var hash = PerceptualHash.ComputeColorHash(bitmap);
+        
+        Assert.Equal(24, hash.Length);
+        Assert.True(hash.Any(b => b != 0), "Hash should not be all zeros");
+    }
+    
+    [Fact]
+    public void SimilarImages_HaveLowHammingDistance()
+    {
+        using var bitmap1 = CreateGradientBitmap(32, 32, SKColors.Red, SKColors.Blue);
+        using var bitmap2 = CreateGradientBitmap(32, 32, SKColors.Red, SKColors.Blue);
+        
+        var hash1 = PerceptualHash.ComputeColorHash(bitmap1);
+        var hash2 = PerceptualHash.ComputeColorHash(bitmap2);
+        
+        var distance = PerceptualHash.HammingDistance(hash1, hash2);
+        
+        Assert.Equal(0, distance);
+    }
+    
+    [Fact]
+    public void DifferentImages_HaveHighHammingDistance()
+    {
+        using var bitmap1 = CreateTestBitmap(32, 32, SKColors.Red);
+        using var bitmap2 = CreateTestBitmap(32, 32, SKColors.Blue);
+        
+        var hash1 = PerceptualHash.ComputeColorHash(bitmap1);
+        var hash2 = PerceptualHash.ComputeColorHash(bitmap2);
+        
+        var distance = PerceptualHash.HammingDistance(hash1, hash2);
+        
+        Assert.True(distance > 10, $"Expected distance > 10, got {distance}");
+    }
+    
+    private static SKBitmap CreateTestBitmap(int width, int height, SKColor color)
+    {
+        var bitmap = new SKBitmap(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
+        using var canvas = new SKCanvas(bitmap);
+        canvas.Clear(color);
+        return bitmap;
+    }
+    
+    private static SKBitmap CreateGradientBitmap(int width, int height, SKColor start, SKColor end)
+    {
+        var bitmap = new SKBitmap(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
+        using var canvas = new SKCanvas(bitmap);
+        using var paint = new SKPaint();
+        paint.Shader = SKShader.CreateLinearGradient(
+            new SKPoint(0, 0),
+            new SKPoint(width, height),
+            new[] { start, end },
+            SKShaderTileMode.Clamp);
+        canvas.DrawRect(0, 0, width, height, paint);
+        return bitmap;
+    }
+}