using Xunit;

namespace Prices.Tests;

public sealed class PriceCalculatorTests
{
    [Fact]
    public void No_discount_keeps_the_price()
    {
        Assert.Equal(100m, PriceCalculator.ApplyDiscount(100m, 0m));
    }

    [Fact]
    public void A_full_discount_makes_it_free()
    {
        Assert.Equal(0m, PriceCalculator.ApplyDiscount(200m, 100m));
    }

    [Fact]
    public void A_quarter_off_200_is_150()
    {
        Assert.Equal(150m, PriceCalculator.ApplyDiscount(200m, 25m));
    }

    [Fact]
    public void Half_off_80_is_40()
    {
        Assert.Equal(40m, PriceCalculator.ApplyDiscount(80m, 50m));
    }

    [Fact]
    public void A_discount_above_100_percent_is_refused()
    {
        Assert.Throws<ArgumentOutOfRangeException>(() => PriceCalculator.ApplyDiscount(100m, 101m));
    }

    [Fact]
    public void Swiss_rappernrundung_rounds_to_nearest_0_05()
    {
        // 99.90 * 0.9 = 89.91 → 89.91 * 20 = 1798.2 → round to 1798 → 1798 / 20 = 89.90
        Assert.Equal(89.90m, PriceCalculator.ApplyDiscount(99.90m, 10m));
    }

    [Fact]
    public void Rounding_rounds_down_when_cent_remainder_is_below_0_05()
    {
        // 1.23 * 0.5 = 0.615 → 0.615 * 20 = 12.3 → round to 12 → 12 / 20 = 0.60
        Assert.Equal(0.60m, PriceCalculator.ApplyDiscount(1.23m, 50m));
    }

    [Fact]
    public void Rounding_rounds_up_when_cent_remainder_is_at_0_05()
    {
        // 3.37 * 0.5 = 1.685 → 1.685 * 20 = 33.7 → round to 34 → 34 / 20 = 1.70
        Assert.Equal(1.70m, PriceCalculator.ApplyDiscount(3.37m, 50m));
    }
}