Nexus.Reader/tests/NexusReader.Application.Tests/Services/ValidateImageSignatureTests.cs

using FluentAssertions;
using Xunit;

namespace NexusReader.Application.Tests.Services;

public class ValidateImageSignatureTests
{
    [Fact]
    public void Validate_PNG_WithCorrectSignature_ReturnsTrue()
    {
        // Arrange
        byte[] pngBytes = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A];
        string fileName = "image.png";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(pngBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeTrue();
        contentType.Should().Be("image/png");
    }

    [Fact]
    public void Validate_JPEG_WithCorrectSignature_ReturnsTrue()
    {
        // Arrange
        byte[] jpegBytes = [0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 0x4A, 0x46];
        string fileName = "photo.jpg";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(jpegBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeTrue();
        contentType.Should().Be("image/jpeg");
    }

    [Fact]
    public void Validate_WEBP_WithCorrectSignature_ReturnsTrue()
    {
        // Arrange
        byte[] webpBytes = [
            0x52, 0x49, 0x46, 0x46, // RIFF
            0x00, 0x00, 0x00, 0x00, // length
            0x57, 0x45, 0x42, 0x50  // WEBP
        ];
        string fileName = "graphic.webp";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(webpBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeTrue();
        contentType.Should().Be("image/webp");
    }

    [Fact]
    public void Validate_GIF_WithCorrectSignature_ReturnsTrue()
    {
        // Arrange
        byte[] gifBytes = [
            0x47, 0x49, 0x46, 0x38, 0x39, 0x61, // GIF89a
            0x01, 0x00, 0x01, 0x00
        ];
        string fileName = "animation.gif";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(gifBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeTrue();
        contentType.Should().Be("image/gif");
    }

    [Fact]
    public void Validate_WithMismatchingExtension_ReturnsFalse()
    {
        // Arrange: Valid PNG bytes but JPEG extension
        byte[] pngBytes = [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A];
        string fileName = "spoofed.jpg";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(pngBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeFalse();
    }

    [Fact]
    public void Validate_WithInvalidSignature_ReturnsFalse()
    {
        // Arrange: Plain text bytes but PNG extension
        byte[] txtBytes = [0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x77, 0x6F]; // "Hello wo"
        string fileName = "not_a_png.png";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(txtBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeFalse();
        contentType.Should().BeEmpty();
    }

    [Fact]
    public void Validate_WithShortBytes_ReturnsFalse()
    {
        // Arrange
        byte[] shortBytes = [0x89, 0x50];
        string fileName = "short.png";

        // Act
        bool isValid = ImageValidator.ValidateImageSignature(shortBytes, fileName, out string contentType);

        // Assert
        isValid.Should().BeFalse();
        contentType.Should().BeEmpty();
    }
}