"""SAP 10.2 Table 13 — high-rate fraction for electric DHW heating.

Locks `electric_dhw_high_rate_fraction` against the published table grid
and the Note-2 clamp at
`domain/sap10_calculator/docs/specs/sap-10-2-full-specification-2025-03-14.pdf`,
page 197. Table 12a's "Immersion water heater" row (PDF p.191) routes
electric immersion DHW here.

The helper evaluates the Note-2 equations, which the spec offers as an
exact alternative to the rounded grid — the pins below check that the
equations reproduce the published 2-dp cells.
"""
from __future__ import annotations

from domain.sap10_calculator.tables.table_12a import Tariff
from domain.sap10_calculator.tables.table_13 import (
    electric_dhw_high_rate_fraction,
)

# Appendix J Table 1b occupancy N at a few total floor areas (m²) — the
# anchor for the V/N grid cells below. Computed from the same piecewise
# formula the §4 worksheet uses (water_heating.assumed_occupancy).
_N_AT_TFA_100 = 2.7395  # N(100 m²)
_N_AT_TFA_60 = 1.9816   # N(60 m²)

# Table 13 high-rate-fraction grid cells (PDF p.197), keyed by (floor
# area row, cylinder litres column, tariff, single?) → published value.
_GRID_TOL = 0.005  # the published grid is rounded to 2 dp


def test_table_13_dual_immersion_matches_published_grid() -> None:
    # Arrange — SAP 10.2 Table 13 (PDF p.197), 110 L cylinder, dual
    # immersion. Floor area 100 m² row: 7-hour = 0.18, 10-hour = 0.10.

    # Act
    seven = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=False, tariff=Tariff.SEVEN_HOUR,
    )
    ten = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=False, tariff=Tariff.TEN_HOUR,
    )

    # Assert
    assert abs(seven - 0.18) <= _GRID_TOL
    assert abs(ten - 0.10) <= _GRID_TOL


def test_table_13_single_immersion_matches_published_grid() -> None:
    # Arrange — SAP 10.2 Table 13 (PDF p.197), 110 L cylinder, single
    # immersion. Floor area 100 m² row: 7-hour = 0.61, 10-hour = 0.23.
    # Single immersion carries a much larger high-rate fraction than dual.

    # Act
    seven = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=True, tariff=Tariff.SEVEN_HOUR,
    )
    ten = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=True, tariff=Tariff.TEN_HOUR,
    )

    # Assert
    assert abs(seven - 0.61) <= _GRID_TOL
    assert abs(ten - 0.23) <= _GRID_TOL


def test_table_13_large_cylinder_single_immersion_clamps_to_zero() -> None:
    # Arrange — SAP 10.2 Table 13 Note 2 (PDF p.197): "If these formulae
    # give a value less than zero, set the high-rate fraction to zero." A
    # 210 L cylinder with single immersion on a 10-hour tariff falls below
    # zero (the published 210 L 10-hour column is 0), so the helper clamps.

    # Act
    fraction = electric_dhw_high_rate_fraction(
        cylinder_volume_l=210.0, occupancy_n=_N_AT_TFA_60,
        single_immersion=True, tariff=Tariff.TEN_HOUR,
    )

    # Assert
    assert fraction == 0.0


def test_table_13_eighteen_and_twenty_four_hour_bill_full_low_rate() -> None:
    # Arrange — SAP 10.2 Table 12a (PDF p.191) is titled "High-rate
    # fractions for systems using 7-hour and 10-hour tariffs"; its
    # "Immersion water heater" row lists the tariff as "7-hour or 10-hour"
    # only, routing to Table 13. An 18-hour / 24-hour tariff is OUTSIDE the
    # table's scope: it provides at least 18 hours/day at the low rate, more
    # than enough to heat any immersion cylinder off-peak, so the high-rate
    # fraction is 0 (100% billed at the low rate). The Elmhurst dr87
    # worksheet for solid fuel 5 (cert 001431: 18-hour meter, 110 L dual
    # immersion, WHC 903) bills HW (245) high-rate = 0.0 kWh, (246) low-rate
    # = 100% — confirming high_frac = 0 for an 18-hour immersion DHW.

    # Act
    eighteen = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=False, tariff=Tariff.EIGHTEEN_HOUR,
    )
    twenty_four = electric_dhw_high_rate_fraction(
        cylinder_volume_l=110.0, occupancy_n=_N_AT_TFA_100,
        single_immersion=False, tariff=Tariff.TWENTY_FOUR_HOUR,
    )

    # Assert
    assert eighteen == 0.0
    assert twenty_four == 0.0