from __future__ import annotations

from typing import Final

from domain.fuel_rates.fuel import Fuel
from domain.sap10_calculator.exceptions import UnmappedSapCode

# SAP 10.2 / Table 32 fuel code -> canonical billing Fuel (ADR-0014). Bounded to
# the ~47 Table 32 fuel codes (the keys of `table_12.UNIT_PRICE_P_PER_KWH`) — the
# carrier, NOT the PCDB product, so a thousand PCDB heat pumps all share one code.
# Input is a normalised Table 32 fuel code (the calculator sets `main_fuel_type`
# to Table 32 codes); an unmapped code raises `UnmappedSapCode` rather than
# guessing — a bounded, self-surfacing backlog [[reference-unmapped-sap-code]].
_CODE_TO_FUEL: Final[dict[int, Fuel]] = {
    **dict.fromkeys([1, 7], Fuel.MAINS_GAS),  # mains gas, grid biogas
    **dict.fromkeys([2, 3, 5, 9], Fuel.LPG),
    **dict.fromkeys([4, 71, 73, 75, 76], Fuel.OIL),  # heating oil + bio-liquids
    **dict.fromkeys([11, 15], Fuel.COAL),  # house coal, anthracite
    **dict.fromkeys([12], Fuel.SMOKELESS),
    **dict.fromkeys([20, 21], Fuel.WOOD_LOGS),  # logs, chips
    **dict.fromkeys([22, 23], Fuel.WOOD_PELLETS),
    **dict.fromkeys([30], Fuel.ELECTRICITY),  # standard tariff
    # 7/10/18-hour off-peak tariffs + 24-hour heating tariff — priced once the
    # off-peak day/night slice lands; ELECTRICITY_OFF_PEAK is unpriced until then.
    **dict.fromkeys([31, 32, 33, 34, 35, 38, 40], Fuel.ELECTRICITY_OFF_PEAK),
    # "heat from ..." community/heat-network + distribution codes (41-58).
    **dict.fromkeys(range(41, 59), Fuel.HEAT_NETWORK),
}


def sap_code_to_fuel(code: int) -> Fuel:
    """Map a SAP 10.2 / Table 32 fuel code to its canonical billing Fuel.

    Raises ``UnmappedSapCode`` on a code with no single billing carrier — e.g.
    dual fuel (10) or the grid-export codes (36/60), which are not an end use's
    input fuel.
    """
    fuel = _CODE_TO_FUEL.get(code)
    if fuel is None:
        raise UnmappedSapCode("fuel_code", code)
    return fuel