"""The Wall U-Value Gate (ADR-0051).

A wall insulation Option is offered only when it would actually lower the main
wall's derived U-value: on a modern construction age band RdSAP's Table 6-10
cascade assigns an as-built wall its at-regs U-value, and the post-measure
state resolves to the *same* value — the measure costs thousands for +0.00 SAP
(property 711795, PRD #1435 WS2: timber frame at age band L, 0.280 → 0.280).

The comparison uses a deliberately thin `u_wall` parameter mapping (the
`envelope.py` style — construction, age band, insulation type/thickness,
documentary wall thickness), omitting the calculator's rich extras (surveyor
description, dry-lining, lodged `wall_u_value`). The omissions bias the gate
toward OFFERING — both sides are computed identically, so a genuine no-op still
compares equal — never toward suppressing a real measure.
"""

from typing import Any, Final, Optional

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

# Improvements below this are float noise, not a physical change. NOT a
# materiality threshold — how much improvement is worth the cost stays with the
# Optimiser (ADR-0016/0024).
_NOISE_FLOOR_W_PER_M2K: Final[float] = 0.01

# RdSAP `wall_insulation_type` 4 = as-built / assumed (no added insulation).
_WALL_INSULATION_NONE: Final[int] = 4


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 wall_insulation_lowers_u(
    main: SapBuildingPart,
    country_code: Optional[str],
    *,
    insulation_type: int,
    insulation_thickness_mm: Optional[int] = None,
) -> bool:
    """Whether insulating the main wall to ``insulation_type`` (+ optional
    thickness) lowers its derived U-value by more than float noise — the Wall
    U-Value Gate (ADR-0051)."""
    country: Country = Country.from_code(country_code)
    age_band = main.construction_age_band
    construction: Optional[int] = _int_or_none(main.wall_construction)
    if construction == WALL_UNKNOWN:
        construction = None
    wall_thickness_mm = main.wall_thickness_mm
    current_type: Optional[int] = _int_or_none(main.wall_insulation_type)
    current_u: float = u_wall(
        country,
        age_band,
        construction,
        _parse_thickness_mm(main.wall_insulation_thickness),
        insulation_present=(
            current_type is not None and current_type != _WALL_INSULATION_NONE
        ),
        wall_insulation_type=current_type,
        wall_thickness_mm=wall_thickness_mm,
    )
    post_u: float = u_wall(
        country,
        age_band,
        construction,
        insulation_thickness_mm,
        insulation_present=True,
        wall_insulation_type=insulation_type,
        wall_thickness_mm=wall_thickness_mm,
    )
    return current_u - post_u > _NOISE_FLOOR_W_PER_M2K