Tau.Acuvim/portal/tests/Tau.Acuvim.Portal.Tests/CostCalculatorTests.cs

using Tau.Acuvim.Portal.Domain.Rates;
using Tau.Acuvim.Portal.Services;

namespace Tau.Acuvim.Portal.Tests;

public class CostCalculatorTests
{
    private static Tariff BuildTariff(
        decimal defaultRate = 2.50m,
        decimal fixedCharge = 100m,
        decimal vatPct = 15m,
        params TariffPeriod[] periods)
    {
        var t = new Tariff
        {
            Id = 1,
            Name = "Test",
            EffectiveFrom = new DateOnly(2026, 1, 1),
            DefaultRatePerKwh = defaultRate,
            FixedMonthlyCharge = fixedCharge,
            VatPercentage = vatPct,
            IsActive = true,
            Periods = periods.ToList()
        };
        return t;
    }

    private static TariffPeriod Period(string name, DayOfWeekFlag days, string start, string end, decimal rate) => new()
    {
        Name = name,
        DaysOfWeek = days,
        StartTime = TimeOnly.Parse(start),
        EndTime = TimeOnly.Parse(end),
        RatePerKwh = rate
    };

    [Fact]
    public void EmptySamples_ReturnsZeroBase_StillIncludesFixedAndVat()
    {
        var t = BuildTariff();
        var calc = new CostCalculator();

        var r = calc.Calculate(t, Array.Empty<ConsumptionSample>());

        Assert.Equal(0m, r.BaseCost);
        Assert.Equal(100m, r.FixedCharges);
        Assert.Equal(100m, r.Subtotal);
        Assert.Equal(15m, r.Vat);
        Assert.Equal(115m, r.TotalCost);
    }

    [Fact]
    public void NoPeriods_UsesDefaultRate()
    {
        var t = BuildTariff(defaultRate: 2m, fixedCharge: 0, vatPct: 0);
        var calc = new CostCalculator();
        var samples = new[] { new ConsumptionSample(new DateTime(2026, 5, 17, 10, 0, 0, DateTimeKind.Utc), 5m) };

        var r = calc.Calculate(t, samples);

        Assert.Equal(10m, r.BaseCost);
        Assert.Equal(10m, r.TotalCost);
    }

    [Fact]
    public void MatchingPeriod_UsesPeriodRate()
    {
        var peak = Period("Peak", DayOfWeekFlag.Weekdays, "17:00", "20:00", 5m);
        var t = BuildTariff(defaultRate: 2m, fixedCharge: 0, vatPct: 0, periods: peak);
        var calc = new CostCalculator();
        // Sunday 17:30 UTC — Sunday is NOT in Weekdays, expect default
        var sundaySample = new ConsumptionSample(new DateTime(2026, 5, 17, 17, 30, 0, DateTimeKind.Utc), 1m);
        // Monday 18:00 UTC — should hit peak
        var mondaySample = new ConsumptionSample(new DateTime(2026, 5, 18, 18, 0, 0, DateTimeKind.Utc), 1m);

        var r = calc.Calculate(t, new[] { sundaySample, mondaySample });

        Assert.Equal(2m + 5m, r.BaseCost);
    }

    [Fact]
    public void SampleOutsideAllPeriods_FallsBackToDefault()
    {
        var morning = Period("Morning", DayOfWeekFlag.All, "06:00", "09:00", 4m);
        var t = BuildTariff(defaultRate: 1m, fixedCharge: 0, vatPct: 0, periods: morning);
        var calc = new CostCalculator();
        var sample = new ConsumptionSample(new DateTime(2026, 5, 18, 12, 0, 0, DateTimeKind.Utc), 10m);

        var r = calc.Calculate(t, new[] { sample });

        Assert.Equal(10m, r.BaseCost);
    }

    [Fact]
    public void OverlappingPeriods_FirstByStartTimeWins()
    {
        var early = Period("Early", DayOfWeekFlag.All, "08:00", "18:00", 5m);
        var late = Period("Late", DayOfWeekFlag.All, "10:00", "14:00", 99m);
        var t = BuildTariff(0m, 0m, 0m, late, early);
        var calc = new CostCalculator();
        var noonSample = new ConsumptionSample(new DateTime(2026, 5, 18, 12, 0, 0, DateTimeKind.Utc), 1m);

        var r = calc.Calculate(t, new[] { noonSample });

        Assert.Equal(5m, r.BaseCost);
    }

    [Fact]
    public void TimezoneConversion_ShiftsSampleIntoLocalPeriod()
    {
        var sastEvening = Period("SAST evening", DayOfWeekFlag.All, "17:00", "20:00", 10m);
        var t = BuildTariff(defaultRate: 1m, fixedCharge: 0, vatPct: 0, periods: sastEvening);
        var calc = new CostCalculator();
        var jhb = TimeZoneInfo.CreateCustomTimeZone("SAST", TimeSpan.FromHours(2), "SAST", "SAST");

        // 16:00 UTC == 18:00 SAST → inside the period
        var inWindow = new ConsumptionSample(new DateTime(2026, 5, 18, 16, 0, 0, DateTimeKind.Utc), 1m);
        // 16:00 UTC default behaviour (UTC tz) is outside the period → default rate
        var defaultR = calc.Calculate(t, new[] { inWindow });
        Assert.Equal(1m, defaultR.BaseCost);

        // Now with SAST → in window
        var sastR = calc.Calculate(t, new[] { inWindow }, timeZone: jhb);
        Assert.Equal(10m, sastR.BaseCost);
    }

    [Fact]
    public void VatAndFixedCharge_AppliedToBase()
    {
        var t = BuildTariff(defaultRate: 2m, fixedCharge: 100m, vatPct: 15m);
        var calc = new CostCalculator();
        var samples = new[] { new ConsumptionSample(new DateTime(2026, 5, 18, 12, 0, 0, DateTimeKind.Utc), 100m) };

        var r = calc.Calculate(t, samples);

        Assert.Equal(200m, r.BaseCost);                  // 100 kWh * 2.00
        Assert.Equal(100m, r.FixedCharges);
        Assert.Equal(300m, r.Subtotal);
        Assert.Equal(45m, r.Vat);                        // 15% of 300
        Assert.Equal(345m, r.TotalCost);
    }

    [Fact]
    public void IncludeFixedMonthlyCharge_False_ExcludesFixed()
    {
        var t = BuildTariff(defaultRate: 2m, fixedCharge: 100m, vatPct: 10m);
        var calc = new CostCalculator();
        var samples = new[] { new ConsumptionSample(new DateTime(2026, 5, 18, 12, 0, 0, DateTimeKind.Utc), 10m) };

        var r = calc.Calculate(t, samples, includeFixedMonthlyCharge: false);

        Assert.Equal(20m, r.BaseCost);
        Assert.Equal(0m, r.FixedCharges);
        Assert.Equal(20m, r.Subtotal);
        Assert.Equal(2m, r.Vat);
        Assert.Equal(22m, r.TotalCost);
    }

    [Fact]
    public void DayOfWeekFiltering_HonoursWeekendOnlyPeriod()
    {
        var weekend = Period("Weekend special", DayOfWeekFlag.Weekends, "00:00", "23:59", 0.5m);
        var t = BuildTariff(defaultRate: 2m, fixedCharge: 0, vatPct: 0, periods: weekend);
        var calc = new CostCalculator();
        var monday = new ConsumptionSample(new DateTime(2026, 5, 18, 10, 0, 0, DateTimeKind.Utc), 10m); // Monday
        var saturday = new ConsumptionSample(new DateTime(2026, 5, 16, 10, 0, 0, DateTimeKind.Utc), 10m); // Saturday

        var r = calc.Calculate(t, new[] { monday, saturday });

        Assert.Equal(20m + 5m, r.BaseCost); // Mon at default 2.00 + Sat at 0.50
    }

    [Fact]
    public void NullTariff_Throws()
    {
        var calc = new CostCalculator();
        Assert.Throws<ArgumentNullException>(() =>
            calc.Calculate(null!, Array.Empty<ConsumptionSample>()));
    }
}