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_rounding_example()
    {
        // 99.90 * 90 / 100 = 89.91, gerundet auf 0.05 = 89.90
        Assert.Equal(89.90m, PriceCalculator.ApplyDiscount(99.90m, 10m));
    }

    [Fact]
    public void Swiss_rounding_exact()
    {
        // 100.00 * 85 / 100 = 85.00, exakt ein 0.05-Vielfaches
        Assert.Equal(85.00m, PriceCalculator.ApplyDiscount(100.00m, 15m));
    }

    [Fact]
    public void Swiss_rounding_midpoint_up()
    {
        // 10.00 * 95 / 100 = 9.50, exakt
        Assert.Equal(9.50m, PriceCalculator.ApplyDiscount(10.00m, 5m));
    }

    [Fact]
    public void Negative_price_throws()
    {
        Assert.Throws<ArgumentOutOfRangeException>(() => PriceCalculator.ApplyDiscount(-1m, 10m));
    }
}