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 ApplyDiscount_99_90_with_10_percent_rounds_to_89_90()
    {
        // 99.90 * (1 - 10/100) = 89.91 → rounded to nearest 0.05 = 89.90
        Assert.Equal(89.90m, PriceCalculator.ApplyDiscount(99.90m, 10m));
    }

    [Fact]
    public void ApplyDiscount_10_with_33_percent_rounds_correctly()
    {
        // 10 * (1 - 33/100) = 6.70 → 6.70 is already a multiple of 0.05
        Assert.Equal(6.70m, PriceCalculator.ApplyDiscount(10m, 33m));
    }

    [Fact]
    public void ApplyDiscount_5_55_with_10_percent_rounds_to_5_00()
    {
        // 5.55 * 0.9 = 4.995 → rounded to nearest 0.05 = 5.00
        Assert.Equal(5.00m, PriceCalculator.ApplyDiscount(5.55m, 10m));
    }
}