using System;

namespace VirtualChemistry.Test;

public static class BIndexTest
{
    private static int BIndex(int index, int multi)
    {
        if (multi == 1)
            return 0;
        if (multi % 2 == 1)
        {
            int center = multi / 2 + 1;
            return center - index;
        }

        if (multi % 2 == 0)
        {
            double center = multi / 2 + 0.5;
            return (int)(center > index ? Math.Ceiling(center - index) : Math.Floor(center - index));
        }

        return 0;
    }
    [Test]
    public static void TestCase1()
    {
        Assert.That(BIndex(1, 1), Is.EqualTo(0));
        Assert.That(BIndex(1, 2), Is.EqualTo(1));
        Assert.That(BIndex(2,2), Is.EqualTo(-1));
        Assert.That(BIndex(1, 3), Is.EqualTo(1));
        Assert.That(BIndex(2, 3), Is.EqualTo(0));
        Assert.That(BIndex(3, 3), Is.EqualTo(-1));
        Assert.That(BIndex(1,4), Is.EqualTo(2));
        Assert.That(BIndex(2, 4), Is.EqualTo(1));
        Assert.That(BIndex(3, 4), Is.EqualTo(-1));
        Assert.That(BIndex(4, 4), Is.EqualTo(-2));
        Assert.That(BIndex(1, 5), Is.EqualTo(2));
        Assert.That(BIndex(2, 5), Is.EqualTo(1));
        Assert.That(BIndex(3, 5), Is.EqualTo(0));
        Assert.That(BIndex(4, 5), Is.EqualTo(-1));
        Assert.That(BIndex(5, 5), Is.EqualTo(-2));
        Assert.That(BIndex(1, 6), Is.EqualTo(3));
        Assert.That(BIndex(2, 6), Is.EqualTo(2));
        Assert.That(BIndex(3, 6),Is.EqualTo(1));
        Assert.That(BIndex(4, 6),Is.EqualTo(-1));
        Assert.That(BIndex(5, 6), Is.EqualTo(-2));
        Assert.That(BIndex(6,6), Is.EqualTo(-3));
    }
}