using MeterVault.Core.Domain;
using MeterVault.Core.Normalization;
using static MeterVault.Core.Tests.TestData;

namespace MeterVault.Core.Tests;

/// <summary>
/// instant_rate: the reading value is an instantaneous rate (e.g. kW) integrated over time into
/// consumption (kWh). Uses the trapezoidal rule between consecutive samples, attributed to the
/// interval's end reading — the first reading only seeds the integral.
/// </summary>
public sealed class InstantRateNormalizerTests
{
    private readonly INormalizationEngine _engine = NormalizationEngine.CreateDefault();

    private static DateTimeOffset At(int hour) => new(new DateTime(2024, 6, 1, 0, 0, 0, DateTimeKind.Utc).AddHours(hour));

    [Fact]
    public void Constant_rate_integrates_to_rate_times_hours()
    {
        // 2 kW held steady for 3 hours → 6 kWh, booked at the end of the interval.
        var ctx = new NormalizationContext
        {
            Meter = new MeterConfig { MeterId = 1, Mode = MeterMode.InstantRate, Unit = "kWh" },
            Readings = [Reading(1, At(0), 2), Reading(1, At(3), 2)],
        };

        var result = _engine.Normalize(ctx);

        var row = Assert.Single(result);
        Assert.Equal(6d, row.Amount, 6);
        Assert.Equal(At(3), row.Time);
        Assert.Equal(ConsumptionKind.Consumption, row.Kind);
    }

    [Fact]
    public void Linear_ramp_integrates_trapezoidally_per_interval()
    {
        // 0 kW → 2 kW → 4 kW at 1-hour steps. Intervals: (0+2)/2·1 = 1, (2+4)/2·1 = 3.
        var ctx = new NormalizationContext
        {
            Meter = new MeterConfig { MeterId = 1, Mode = MeterMode.InstantRate, Unit = "kWh" },
            Readings = [Reading(1, At(0), 0), Reading(1, At(1), 2), Reading(1, At(2), 4)],
        };

        var result = _engine.Normalize(ctx);

        // First reading only seeds the integral: N readings → N−1 rows.
        Assert.Equal([1d, 3d], result.Select(c => c.Amount));
        Assert.Equal([At(1), At(2)], result.Select(c => c.Time));
    }

    [Fact]
    public void Negative_rate_is_preserved_as_export()
    {
        // A bidirectional power sensor reading −4 kW for an hour → −4 kWh (net export), not clamped.
        var ctx = new NormalizationContext
        {
            Meter = new MeterConfig { MeterId = 1, Mode = MeterMode.InstantRate, Unit = "kWh" },
            Readings = [Reading(1, At(0), -4), Reading(1, At(1), -4)],
        };

        var result = _engine.Normalize(ctx);

        Assert.Equal(-4d, Assert.Single(result).Amount, 6);
    }

    [Fact]
    public void Single_reading_produces_no_consumption()
    {
        var ctx = new NormalizationContext
        {
            Meter = new MeterConfig { MeterId = 1, Mode = MeterMode.InstantRate, Unit = "kWh" },
            Readings = [Reading(1, At(0), 5)],
        };

        Assert.Empty(_engine.Normalize(ctx));
    }
}