from pathlib import Path
import sys

import pytest


SCRIPTS = Path(__file__).resolve().parents[1] / "scripts"
sys.path.insert(0, str(SCRIPTS))

from water_metrics import calculate_instantaneous_load_kg_day  # noqa: E402


def test_calculates_load_from_milligrams_per_litre_and_cubic_metres_per_second():
    load = calculate_instantaneous_load_kg_day(
        concentration=1.0,
        concentration_unit="mg/L",
        discharge=1.0,
        discharge_unit="m3/s",
    )

    assert load == pytest.approx(86.4)


def test_missing_discharge_is_not_treated_as_zero():
    with pytest.raises(ValueError, match="Missing discharge"):
        calculate_instantaneous_load_kg_day(
            concentration=0.1,
            concentration_unit="mg/L",
            discharge=None,
            discharge_unit="m3/s",
        )