from __future__ import annotations

from typing import Final

from domain.fuel_rates.fuel import Fuel
from domain.sap10_calculator.exceptions import UnmappedSapCode
from domain.sap10_calculator.tables.table_32 import to_table_32_code

# Table 32 fuel code -> canonical billing Fuel (ADR-0014). Bounded to the ~47
# Table 32 fuel codes (the keys of `UNIT_PRICE_P_PER_KWH`) — the carrier, NOT the
# PCDB product, so a thousand PCDB heat pumps all share one code. 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 one of the calculator's per-end-use fuel codes to its billing Fuel.

    The code may be a raw gov-API `main_fuel_type` enum or an already-Table-32
    code depending on the source mapper (until [[adr-0015]] normalizes the cert),
    so it is first run through the calculator's own ``to_table_32_code`` —
    T32-first, then API-translate — the **same** normalization the calculator's
    pricing/CO2 helpers use, so the bill's carrier matches what the calculator
    billed. The normalized Table-32 code is then dispatched to a 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.
    """
    # Normalize to a Table-32 code; fall back to the raw code for billing fuels
    # the price table does not carry (the 41-58 heat-network range — `to_table_32_
    # code` returns None there, but they still resolve to HEAT_NETWORK and so to
    # UnpricedFuel, which is stricter — and correct — than the calculator's
    # lossy default-to-mains-gas for an unpriced code).
    normalized = to_table_32_code(code)
    fuel = _CODE_TO_FUEL.get(normalized if normalized is not None else code)
    if fuel is None:
        raise UnmappedSapCode("fuel_code", code)
    return fuel