meeting-assistant/MeetingAssistant.Tests/PngTestFixture.cs

namespace MeetingAssistant.Tests;

internal static class PngTestFixture
{
    private const string Solid2X2 =
        "iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAYAAABytg0kAAAAAXNSR0IArs4c6QAAADhlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAAqACAAQAAAABAAAAAqADAAQAAAABAAAAAgAAAADO0J6QAAAAEklEQVQIHWP8DwQMQMAEIkAAAD34BACALvQ5AAAAAElFTkSuQmCC";
    private const string Solid4X4 =
        "iVBORw0KGgoAAAANSUhEUgAAAAQAAAAECAYAAACp8Z5+AAAAAXNSR0IArs4c6QAAADhlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAAqACAAQAAAABAAAABKADAAQAAAABAAAABAAAAADmpNw4AAAAFUlEQVQIHWP8DwQMSIAJiQ1mEhYAAAZdBAQjjGwcAAAAAElFTkSuQmCC";
    private const string Solid8X6 =
        "iVBORw0KGgoAAAANSUhEUgAAAAgAAAAGCAYAAAD+Bd/7AAAAAXNSR0IArs4c6QAAADhlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAAqACAAQAAAABAAAACKADAAQAAAABAAAABgAAAAAJfOcJAAAAFklEQVQIHWP8DwQMeAATHjmw1GBQAAAQiQQIVmhjoQAAAABJRU5ErkJggg==";

    public static byte[] Solid(int width, int height)
    {
        var encoded = (width, height) switch
        {
            (2, 2) => Solid2X2,
            (4, 4) => Solid4X4,
            (8, 6) => Solid8X6,
            _ => throw new ArgumentOutOfRangeException(
                nameof(width),
                $"No deterministic PNG fixture exists for {width}x{height}.")
        };
        return Convert.FromBase64String(encoded);
    }

    public static (int Width, int Height) ReadDimensions(byte[] png)
    {
        if (!png.AsSpan(0, 8).SequenceEqual(
                new byte[] { 137, 80, 78, 71, 13, 10, 26, 10 }))
        {
            throw new InvalidDataException("The fixture is not a PNG.");
        }

        return (
            System.Buffers.Binary.BinaryPrimitives.ReadInt32BigEndian(png.AsSpan(16, 4)),
            System.Buffers.Binary.BinaryPrimitives.ReadInt32BigEndian(png.AsSpan(20, 4)));
    }
}