"""The Floor U-Value Gate — the ground-floor arm of ADR-0051.

A floor insulation Option is offered only when it would actually lower the
ground floor's derived U-value: on a modern construction age band RdSAP's
BS EN ISO 13370 / Table 19 cascade assigns an as-built floor its at-regs
U-value and the post-measure state resolves to the same value — the measure
costs thousands for +0.00 SAP (portfolio 796: solid_floor_insulation offered
at £3-4k on age-band-L dwellings 709782/709790).

Same thin-mapping philosophy as the Wall U-Value Gate (`wall_u_value_gate`):
the calculator's rich extras (surveyor description, lodged `floor_u_value`)
are deliberately omitted — both sides are computed identically, so a genuine
no-op still compares equal, and omissions only ever bias toward OFFERING.
"""

from typing import Any, Final, Optional

from datatypes.epc.domain.epc_property_data import SapBuildingPart
from domain.sap10_ml.rdsap_uvalues import Country, u_floor

# Improvements below this are float noise, not a physical change. NOT a
# materiality threshold — economics stay with the Optimiser (ADR-0016/0024).
_NOISE_FLOOR_W_PER_M2K: Final[float] = 0.01


def _int_or_none(value: Any) -> Optional[int]:
    return value if isinstance(value, int) else None


def _parse_thickness_mm(value: Any) -> Optional[int]:
    if value is None or isinstance(value, int):
        return value
    if isinstance(value, str) and value.strip().isdigit():
        return int(value.strip())
    return None  # "NI" / free text — thickness not known


def floor_insulation_lowers_u(
    main: SapBuildingPart,
    country_code: Optional[str],
    *,
    insulation_thickness_mm: int,
) -> bool:
    """Whether insulating the main part's ground floor to
    ``insulation_thickness_mm`` lowers its derived U-value by more than float
    noise — the Floor U-Value Gate (ADR-0051)."""
    country: Country = Country.from_code(country_code)
    age_band = main.construction_age_band
    ground = next(
        (fd for fd in main.sap_floor_dimensions if fd.floor == 0),
        main.sap_floor_dimensions[0] if main.sap_floor_dimensions else None,
    )
    construction: Optional[int] = (
        _int_or_none(ground.floor_construction) if ground is not None else None
    )
    area = ground.total_floor_area_m2 if ground is not None else None
    perimeter = ground.heat_loss_perimeter_m if ground is not None else None
    current_u: float = u_floor(
        country,
        age_band,
        construction,
        _parse_thickness_mm(main.floor_insulation_thickness),
        area,
        perimeter,
        main.wall_thickness_mm,
    )
    post_u: float = u_floor(
        country,
        age_band,
        construction,
        insulation_thickness_mm,
        area,
        perimeter,
        main.wall_thickness_mm,
    )
    return current_u - post_u > _NOISE_FLOOR_W_PER_M2K