using Shouldly;
using Xunit;

namespace Just.PreciseMath.Tests;

public class PreciseMathTests
{
    [Fact]
    public void AbsPreservesBothComponentsAndCanonicalSpecialValues()
    {
        double[] scalars = [0.0, -0.0, 1.0, -1.0, double.Epsilon, -double.Epsilon,
            double.MaxValue, double.MinValue, double.PositiveInfinity, double.NegativeInfinity, double.NaN];
        foreach (double scalar in scalars)
        {
            // Binary64 is an independent reference when the input has no residual.
            DoubleDouble actual = DDMath.Abs(new DoubleDouble(scalar));
            AssertBits(actual, double.IsNaN(scalar) ? double.NaN : Math.Abs(scalar), 0.0);
            DoubleDouble.IsCanonical(actual).ShouldBeTrue();
        }

        foreach (double low in new[] { Math.ScaleB(1.0, -54), -Math.ScaleB(1.0, -54), double.Epsilon, -double.Epsilon })
        {
            DoubleDouble positive = DoubleDouble.FromComponents(1.0, low);
            DoubleDouble negative = DoubleDouble.FromComponents(-1.0, -low);
            AssertBits(DDMath.Abs(positive), 1.0, low);
            AssertBits(DDMath.Abs(negative), 1.0, low);
        }
    }

    private static void AssertBits(DoubleDouble actual, double high, double low)
    {
        BitConverter.DoubleToInt64Bits(actual.High).ShouldBe(BitConverter.DoubleToInt64Bits(high));
        BitConverter.DoubleToInt64Bits(actual.Low).ShouldBe(BitConverter.DoubleToInt64Bits(low));
    }
}