Model/domain/sap10_calculator/tables/table_32.py

"""RdSAP10 Table 32 — fuel prices, standing charges, PV export credit.

Sourced verbatim from `domain/sap10_calculator/docs/specs/RdSAP 10 Specification 10-06-2025.pdf`,
page 95 (Table 32). RdSAP10 §19.1: SAP rating for RdSAP10 is calculated
using Table 32 prices (not Table 12) for §10a and §10b. The calculator
targets RdSAP10 cost per ADR-0010 amendment.

CO2 emission factors and primary energy factors are unchanged from
SAP10.2 Table 12 (RdSAP10 §19.2), so they continue to live in
`domain.sap10_calculator.tables.table_12` rather than being duplicated here.

Heating-oil (code 4) is a documented divergence from the published spec
PDF — see the note on the dict entry below.
"""

from __future__ import annotations

from typing import Final, Optional

from domain.sap10_calculator.tables.table_12a import Tariff


_DEFAULT_P_PER_KWH: Final[float] = 3.48  # fall back to mains gas


# RdSAP10 Table 32 — unit price in pence per kWh, sourced verbatim from
# PDF page 95.
UNIT_PRICE_P_PER_KWH: Final[dict[int, float]] = {
    # Gas fuels
    1: 3.48,    # mains gas
    2: 7.60,    # bulk LPG
    3: 10.30,   # bottled LPG (main heating)
    5: 12.19,   # bottled LPG (secondary)
    9: 3.48,    # LPG SC11F
    7: 7.60,    # biogas (including anaerobic digestion)
    # Liquid fuels
    #
    # Slice S0380.131 — heating oil (code 4): operationally-canonical
    # 5.44 p/kWh, not the 7.64 published in the RdSAP 10 Specification
    # 10-06-2025 PDF Table 32 (p.95). The spec PDF value is the outlier;
    # two independent implementations agree on 5.44:
    #   - Elmhurst P960 worksheets (fuel cost row, line ref (240) "Space
    #     heating - main system 1") for variants oil 1, oil pcdb 1/2/3,
    #     pcdb 1 in `sap worksheets/heating systems examples/` — every
    #     "FuelType: Heating oil" worksheet lodges 5.4400 p/kWh.
    #   - The gov.uk EPC register's lodging software back-solves to
    #     ~5.48 p/kWh from cert 0240-0200-5706-2365-8010's lodged SAP
    #     73 (an oil + PV detached at age J), and with 5.44 in the
    #     cascade this cert closes to ΔSAP = 0 exactly against its
    #     lodged value.
    # BRE technical papers (`docs/specs/sap10 technical papers/`) carry
    # no Table 32 errata or fuel-price update, so the change is grounded
    # in empirical cross-source evidence rather than a spec citation.
    # FAME (code 73) shows the inverse pattern on oil 3/4 worksheets:
    # the RdSAP 10 Spec PDF Table 32 lists 5.44 p/kWh but worksheet
    # (240) "Space heating - main system 1" for variants oil 3 (EES
    # BXE, SAP 128) + oil 4 (EES BXF, SAP 129) lodges 7.64. Slice
    # S0380.168 flipped 5.44 → 7.64 to match the worksheet — same
    # empirical-divergence justification as the .131 heating-oil flip;
    # the Elmhurst engine is the canonical reference per
    # [[feedback-software-no-special-handling]].
    4: 5.44,    # heating oil — see comment above (Slice S0380.131)
    71: 7.64,   # bio-liquid HVO
    73: 7.64,   # bio-liquid FAME — Slice S0380.168 flip (5.44 → 7.64)
    75: 6.10,   # B30K
    76: 47.0,   # bioethanol
    # Solid fuels
    11: 3.67,   # house coal
    15: 3.64,   # anthracite
    12: 4.61,   # manufactured smokeless fuel
    20: 4.23,   # wood logs
    22: 5.81,   # wood pellets (secondary)
    23: 5.26,   # wood pellets (main)
    21: 3.07,   # wood chips
    10: 3.99,   # dual fuel
    # Electricity
    30: 13.19,  # standard tariff
    32: 15.29,  # 7-hour tariff (high rate)
    31: 5.50,   # 7-hour tariff (low rate / off-peak)
    34: 14.68,  # 10-hour tariff (high rate)
    33: 7.50,   # 10-hour tariff (low rate)
    38: 13.67,  # 18-hour tariff (high rate)
    40: 7.41,   # 18-hour tariff (low rate)
    35: 6.61,   # 24-hour heating tariff
    60: 13.19,  # electricity sold to grid, PV
    # Heat networks
    51: 4.24, 52: 4.24, 53: 4.24, 54: 4.24,
    55: 4.24, 56: 4.24, 57: 4.24, 58: 4.24,
    41: 4.24,   # heat from electric heat pump
    42: 4.24,   # heat recovered from waste combustion
    43: 4.24,   # heat from boilers - biomass
    44: 4.24,   # heat from boilers - biogas
    45: 2.97,   # heat recovered from power station
    46: 2.97,   # low grade heat recovered from process
    47: 2.97,   # heat recovered from geothermal / natural
    48: 2.97,   # heat from CHP
    49: 2.97,   # high grade heat recovered from process
}


# Gov EPC API main_fuel_type / water_heating_fuel → RdSAP10 Table 32 fuel
# code. Same shape as `table_12.API_FUEL_TO_TABLE_12` — the API enum is
# unchanged across SAP10.2 ↔ RdSAP10.
API_FUEL_TO_TABLE_32: Final[dict[int, int]] = {
    0: 30, 1: 1, 2: 2, 3: 3, 4: 4, 5: 15, 6: 20, 7: 23, 8: 21, 9: 10,
    10: 30, 11: 42, 12: 43, 13: 44, 14: 11, 15: 12, 16: 22, 17: 9,
    18: 75, 19: 76, 20: 51, 21: 52, 22: 53, 23: 55, 24: 54, 25: 41,
    26: 1, 27: 2, 28: 4, 29: 30,
}


# RdSAP10 Table 32 — annual standing charge in £/yr per Table 32 fuel
# code. Only fuels with a published standing charge appear here;
# unlisted codes default to £0/yr. Application of these charges to
# (251) is gated by Table 12 note (a).
STANDING_CHARGE_GBP_PER_YR: Final[dict[int, float]] = {
    # Gas fuels
    1: 120.0,   # mains gas
    2: 70.0,    # bulk LPG
    9: 120.0,   # LPG SC11F
    7: 70.0,    # biogas
    # Electricity (high-rate codes carry the off-peak meter standing)
    30: 54.0,   # standard tariff
    32: 24.0,   # 7-hour high rate
    34: 23.0,   # 10-hour high rate
    38: 40.0,   # 18-hour high rate
    35: 70.0,   # 24-hour heating tariff
    # Heat networks — Table 32 note (l): include half (£60/yr) if only
    # DHW provided by heat network. Raw row carries £120/yr.
    51: 120.0,
}


def unit_price_p_per_kwh(fuel_code: Optional[int]) -> float:
    """Unit price (p/kWh) for the given fuel code. Accepts either a
    Table 32 code or a gov API `main_fuel_type` / `water_heating_fuel`
    enum; translates the latter via `API_FUEL_TO_TABLE_32`. Unknown →
    mains gas (3.48 p/kWh)."""
    if fuel_code is None:
        return _DEFAULT_P_PER_KWH
    if fuel_code in UNIT_PRICE_P_PER_KWH:
        return UNIT_PRICE_P_PER_KWH[fuel_code]
    translated = API_FUEL_TO_TABLE_32.get(fuel_code)
    if translated is not None and translated in UNIT_PRICE_P_PER_KWH:
        return UNIT_PRICE_P_PER_KWH[translated]
    return _DEFAULT_P_PER_KWH


def standing_charge_gbp(fuel_code: Optional[int]) -> float:
    """Annual standing charge (£/yr) for the given Table 32 fuel code.
    Fuels without a published standing charge return 0.0. Application
    to (251) is gated by `additional_standing_charges_gbp` per Table 12
    note (a)."""
    if fuel_code is None:
        return 0.0
    if fuel_code in STANDING_CHARGE_GBP_PER_YR:
        return STANDING_CHARGE_GBP_PER_YR[fuel_code]
    # Only translate via API enum when fuel_code isn't already a known
    # Table 32 code — wood logs (Table 32 code 20) collides with the API
    # enum value 20 (heat networks) and must not be translated.
    if fuel_code in UNIT_PRICE_P_PER_KWH:
        return 0.0
    translated = API_FUEL_TO_TABLE_32.get(fuel_code)
    if translated is not None and translated in STANDING_CHARGE_GBP_PER_YR:
        return STANDING_CHARGE_GBP_PER_YR[translated]
    return 0.0


# Gas Table 32 codes (after API enum translation).
_GAS_FUEL_CODES: Final[frozenset[int]] = frozenset({1, 2, 3, 5, 9, 7})

# Electricity Table 32 codes (after API enum translation).
_ELECTRIC_FUEL_CODES: Final[frozenset[int]] = frozenset(
    {30, 31, 32, 33, 34, 35, 38, 40, 60}
)

# Liquid fuel Table 32 codes (oil + bioliquids) after API enum
# translation. Drawn from Table 32 PDF p.95 rows:
#   4  heating oil
#   71 bio-liquid HVO
#   73 bio-liquid FAME
#   75 B30K
#   76 bioethanol
# LPG is treated as GAS (its own rows 2/3/5/9) and is NOT in this set.
_LIQUID_FUEL_CODES: Final[frozenset[int]] = frozenset({4, 71, 73, 75, 76})

# Off-peak tariff → high-rate Table 32 code (the row carrying the
# off-peak meter standing per Table 32 PDF page 95).
_OFF_PEAK_STANDING_CODE: Final[dict[Tariff, int]] = {
    Tariff.SEVEN_HOUR: 32,
    Tariff.TEN_HOUR: 34,
    Tariff.EIGHTEEN_HOUR: 38,
    Tariff.TWENTY_FOUR_HOUR: 35,
}


def _to_table_32_code(fuel_code: Optional[int]) -> Optional[int]:
    """Normalise a fuel code (Table 32 or API enum) to its Table 32 form."""
    if fuel_code is None:
        return None
    if fuel_code in UNIT_PRICE_P_PER_KWH:
        return fuel_code
    return API_FUEL_TO_TABLE_32.get(fuel_code)


def _is_gas_code(fuel_code: Optional[int]) -> bool:
    code = _to_table_32_code(fuel_code)
    return code is not None and code in _GAS_FUEL_CODES


def is_electric_fuel_code(fuel_code: Optional[int]) -> bool:
    """Whether the fuel code maps to a Table 32 electricity row, after
    normalising via T32-first then API-translate fallback.

    Use this in preference to ad-hoc literal-set checks like
    `code in {10, 25, 29}`: those mix API enum codes (where 10 is
    "electricity backwards-compat") and Table 32 codes (where 10 is
    "dual fuel mineral+wood"), so a Table-32-code-10 dual-fuel main
    silently mis-classifies as electric. The S0380.135 EES-code →
    Table 32 mapper lookups set `main_fuel_type` to Table 32 codes
    (BDI → 10 = dual fuel), so the literal-set checks fail loudly here
    unless normalised through `_to_table_32_code` first.
    """
    code = _to_table_32_code(fuel_code)
    return code is not None and code in _ELECTRIC_FUEL_CODES


def is_liquid_fuel_code(fuel_code: Optional[int]) -> bool:
    """Whether the fuel code maps to a Table 32 liquid fuel row
    (heating oil + bioliquids), after T32-first / API-translate
    normalisation. Mirrors `is_electric_fuel_code`. Used by SAP 10.2
    Table 4f (PDF p.174) "Liquid fuel boiler – flue fan and fuel
    pump" (100 kWh/yr) gate.

    LPG is treated as GAS by Table 4f (separate "Gas boiler" row,
    45 kWh/yr) — `is_liquid_fuel_code` returns False for LPG codes.
    """
    code = _to_table_32_code(fuel_code)
    return code is not None and code in _LIQUID_FUEL_CODES


def additional_standing_charges_gbp(
    *,
    main_fuel_code: Optional[int],
    water_heating_fuel_code: Optional[int],
    tariff: Tariff,
) -> float:
    """SAP rating (regulated) standing-charge total for (251), gated per
    Table 12 note (a):

    - Std electricity standing → omitted
    - Off-peak electricity standing → added if either main heating or
      hot water uses off-peak electricity. Standing lives on the high-
      rate Table 32 code for the tariff in use.
    - Gas standing → added if gas is used for space (main or secondary)
      or water heating.
    """
    total = 0.0
    if _is_gas_code(main_fuel_code) or _is_gas_code(water_heating_fuel_code):
        # Pick whichever gas code is in use, preferring main heating.
        gas_code = main_fuel_code if _is_gas_code(main_fuel_code) else water_heating_fuel_code
        total += standing_charge_gbp(gas_code)
    if tariff is not Tariff.STANDARD and (
        is_electric_fuel_code(main_fuel_code) or is_electric_fuel_code(water_heating_fuel_code)
    ):
        off_peak_code = _OFF_PEAK_STANDING_CODE.get(tariff)
        if off_peak_code is not None:
            total += standing_charge_gbp(off_peak_code)
    return total