using Nonemm.Core;

namespace Nonemm.Core.Tests;

/// Where the sun stands, checked against what the calendar says it must be.
public class GraylineTests
{
    [Fact]
    public void TheSunIsOverTheTropicAtTheSolstice()
    {
        (double latitude, _) = Grayline.SubsolarPoint(new DateTime(2026, 6, 21, 12, 0, 0, DateTimeKind.Utc));

        Assert.Equal(23.4, latitude, 0.1);
    }

    [Fact]
    public void TheSunIsOverTheEquatorAtTheEquinox()
    {
        (double latitude, _) = Grayline.SubsolarPoint(new DateTime(2026, 3, 20, 14, 46, 0, DateTimeKind.Utc));

        Assert.Equal(0, latitude, 0.1);
    }

    /// At noon UTC the sun is over Greenwich, give or take the quarter of an
    /// hour the equation of time moves it by.
    [Fact]
    public void TheSunIsOverGreenwichAtNoon()
    {
        (_, double longitude) = Grayline.SubsolarPoint(new DateTime(2026, 6, 21, 12, 0, 0, DateTimeKind.Utc));

        Assert.Equal(0, longitude, 1.0);
    }

    /// The two ways of asking have to agree: at the moment `SunTimes` says the
    /// sun rises, it is on the horizon.
    [Fact]
    public void SunriseAgreesWithTheSunStandingOnTheHorizon()
    {
        (DateTime rise, DateTime set) =
            SunTimes.For(48.15, 17.11, new DateTime(2026, 8, 31, 0, 0, 0, DateTimeKind.Utc))!.Value;

        Assert.Equal(Grayline.Horizon, Grayline.Elevation(48.15, 17.11, rise), 0.3);
        Assert.Equal(Grayline.Horizon, Grayline.Elevation(48.15, 17.11, set), 0.3);
    }

    [Fact]
    public void MiddayIsDaylightAndMidnightIsNot()
    {
        DateTime noon = new(2026, 8, 31, 12, 0, 0, DateTimeKind.Utc);

        Assert.True(Grayline.IsDaylight(0, 0, noon));
        Assert.False(Grayline.IsDaylight(0, 180, noon));
    }

    /// The terminator crosses every meridian once between the poles while the
    /// sun is over the equator, and the polar day has no crossing at all.
    [Fact]
    public void TheTerminatorCrossesAMeridianWhereTheSunIsOnTheHorizon()
    {
        DateTime moment = new(2026, 8, 31, 12, 0, 0, DateTimeKind.Utc);

        double crossing = Grayline.LatitudeAt(30, moment)!.Value;

        Assert.Equal(Grayline.Horizon, Grayline.Elevation(crossing, 30, moment), 0.3);
    }

    [Fact]
    public void TheNorthPoleIsLitInJuneAndDarkInDecember()
    {
        Assert.True(Grayline.IsNorthPoleLit(new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc)));
        Assert.False(Grayline.IsNorthPoleLit(new DateTime(2026, 12, 21, 0, 0, 0, DateTimeKind.Utc)));
    }
}