from __future__ import annotations

from dataclasses import dataclass
from typing import Optional, TYPE_CHECKING, TypeVar

from datatypes.epc.domain.epc import Epc
from datatypes.epc.domain.epc_property_data import EpcPropertyData

if TYPE_CHECKING:
    from domain.sap10_calculator.calculator import SapResult

_T = TypeVar("_T")
_KG_PER_TONNE = 1000.0


@dataclass(frozen=True)
class Performance:
    """One half of a Baseline Performance — a single set of SAP10 figures.

    The four quantities a Property is rated on (CONTEXT.md: Lodged / Effective
    Performance): SAP score, EPC Band, carbon emissions, and Primary Energy
    Intensity. Used for both the Lodged half (off the gov register) and the
    Effective half (what the modelling pipeline scored against).
    """

    sap_score: int
    epc_band: Epc
    co2_emissions: float
    primary_energy_intensity: int

    @classmethod
    def from_sap_result(cls, result: "SapResult") -> "Performance":
        """The four rated quantities, read off a calculator `SapResult`
        (ADR-0013): band derived from the score, CO2 converted kg→tonnes, PEUI
        rounded to the lodged integer scale. The `from_*` factory mirrors
        `Epc.from_sap_score`; living on the target keeps the SAP calculator
        free of any `property_baseline` dependency."""
        return cls(
            sap_score=result.sap_score,
            epc_band=Epc.from_sap_score(result.sap_score),
            co2_emissions=result.co2_kg_per_yr / _KG_PER_TONNE,
            primary_energy_intensity=round(result.primary_energy_kwh_per_m2),
        )


def _require(value: Optional[_T], field: str) -> _T:
    if value is None:
        raise ValueError(
            f"EPC is missing recorded performance field {field!r}; "
            "cannot establish Lodged Performance"
        )
    return value


def lodged_performance(epc: EpcPropertyData) -> Performance:
    """The Lodged Performance recorded on an EPC — what the gov register says.

    Reads the four rated quantities straight off the EPC's recorded fields
    (CONTEXT.md: Primary Energy Intensity is recorded as `energy_consumption_current`).
    Unmodified by modelling.
    """
    return Performance(
        sap_score=_require(epc.energy_rating_current, "energy_rating_current"),
        epc_band=_require(
            epc.current_energy_efficiency_band, "current_energy_efficiency_band"
        ),
        co2_emissions=_require(epc.co2_emissions_current, "co2_emissions_current"),
        primary_energy_intensity=_require(
            epc.energy_consumption_current, "energy_consumption_current"
        ),
    )