"""Crude annual heat/hot-water/lighting demand approximations.

Used by `transform.py` to populate the `predicted_*_kwh` features (slice 16d).
These are deliberately coarse: they give the model a physics-shaped starting
point that it can adjust against the cert's real kWh labels.  See ADR-0008
for the "crude annual" rationale.

Formulas:

- predicted_space_heating_kwh
  ~= envelope_heat_loss_w_per_k * HDH_region / efficiency_main_heating
  where HDH_region is heating degree hours per year by SAP region.

- predicted_hot_water_kwh  (SAP10.2 Appendix J simplified)
  V_d ~= 25 * N_occupants + 36 (litres / day)
  Q_HW_useful ~= 4.18 * V_d * (55 - 12) * 365 * 1e-3 (kWh / yr)
  N_occupants defaulted from total_floor_area_m2 per SAP J Table 1b.

- predicted_lighting_kwh   (SAP10.2 Section L simplified)
  base ~= 9.3 * TFA * (1 - 0.5 * led_share - 0.4 * cfl_share)
"""

from __future__ import annotations

from math import exp
from typing import Final, Optional


# SAP10.2 Table 6 / U6 heating degree hours per year by SAP region (K * h).
# Coarse grouping: most regions cluster ~50-60k; using region_code if known.
_HDH_BY_REGION: Final[dict[int, float]] = {
    1: 51000,   # Thames
    2: 52000,   # SE England
    3: 50000,   # Southern
    4: 51000,   # SW England
    5: 53000,   # Severn (5E + 5W treated together)
    6: 54000,   # Midlands
    7: 55000,   # W Pennines / Lancashire
    8: 55000,   # NW England / SW Scotland
    9: 56000,   # Borders / North Tyne
    10: 56000,  # NE England
    11: 56000,  # E Pennines / Yorkshire
    12: 54000,  # E Anglia
    13: 56000,  # Wales (Mid)
    14: 58000,  # W Scotland
    15: 59000,  # E Scotland
    16: 60000,  # NE Scotland
    17: 62000,  # Highland
    18: 60000,  # Western Isles
    19: 60000,  # Orkney
    20: 62000,  # Shetland
    21: 54000,  # Northern Ireland
    22: 53000,  # Isle of Man
}

_HDH_UK_AVG: Final[float] = 53000.0


def _hdh_for_region(region_code: Optional[str]) -> float:
    if region_code is None:
        return _HDH_UK_AVG
    try:
        code = int(region_code)
    except (TypeError, ValueError):
        return _HDH_UK_AVG
    return _HDH_BY_REGION.get(code, _HDH_UK_AVG)


def predicted_space_heating_kwh(
    envelope_heat_loss_w_per_k: float,
    region_code: Optional[str],
    seasonal_efficiency_main: float,
    ventilation_heat_loss_w_per_k: float = 0.0,
) -> float:
    """Annual delivered space-heating kWh.

    delivered_kWh = HLC * HDH_region * 1e-3  / efficiency
    where HLC = envelope (conduction + bridging) + ventilation (infiltration),
    HDH is K*hours/year. SAP10.2 §5 routes both losses through the same demand
    pipeline. Ventilation defaults to 0 for back-compat with pre-slice-20a
    callers.
    """
    hlc = envelope_heat_loss_w_per_k + ventilation_heat_loss_w_per_k
    if hlc <= 0 or seasonal_efficiency_main <= 0:
        return 0.0
    hdh = _hdh_for_region(region_code)
    useful_kwh = hlc * hdh * 1e-3
    return useful_kwh / seasonal_efficiency_main


def _default_occupants_sap_j(total_floor_area_m2: float) -> float:
    """SAP10.2 Appendix J Table 1b default occupancy.

    N = 1 + 1.76 * (1 - exp(-0.000349 * (TFA - 13.9)^2)) + 0.0013 * (TFA - 13.9)
    for TFA > 13.9 m^2; otherwise N = 1.
    """
    if total_floor_area_m2 <= 13.9:
        return 1.0
    x = total_floor_area_m2 - 13.9
    return 1.0 + 1.76 * (1.0 - exp(-0.000349 * x * x)) + 0.0013 * x


def predicted_hot_water_kwh(
    total_floor_area_m2: Optional[float],
    seasonal_efficiency_water: float,
    *,
    cylinder_size: Optional[int] = None,
    cylinder_insulation_thickness_mm: Optional[int] = None,
    cylinder_insulation_type: Optional[int] = None,
    age_band: Optional[str] = None,
    has_wwhrs: bool = False,
    has_solar_water_heating: bool = False,
) -> float:
    """Annual delivered hot-water kWh per SAP10.2 Appendix J (slice 17b).

    Components (all kWh useful, sum then divided by efficiency for delivered):
      useful_demand = 4.18 * Vd * 43 * 365 / 3600  (Vd in litres/day)
      distribution_loss = useful_demand * 0.15
      storage_loss     = volume * insulation_factor * 365 * 0.6
      primary_loss(age) = 245 (A-J) or 60 (K-M)
      wwhrs_credit     = useful_demand * 0.12  if has_wwhrs
      solar_hw_credit  = 250                   if has_solar_water_heating

    Defaults follow RdSAP10 §11 / Table 29 for missing cylinder fields.
    """
    if total_floor_area_m2 is None or total_floor_area_m2 <= 0:
        return 0.0
    if seasonal_efficiency_water <= 0:
        return 0.0
    n = _default_occupants_sap_j(total_floor_area_m2)
    vd_litres = 25.0 * n + 36.0
    useful_kwh = 4.18 * vd_litres * (55.0 - 12.0) * 365.0 / 3600.0
    distribution_loss = useful_kwh * 0.15
    storage_loss = _cylinder_storage_loss_kwh(
        cylinder_size=cylinder_size,
        cylinder_insulation_thickness_mm=cylinder_insulation_thickness_mm,
        cylinder_insulation_type=cylinder_insulation_type,
        age_band=age_band,
    )
    primary_loss = _primary_circuit_loss_kwh(age_band)
    wwhrs_credit = useful_kwh * 0.12 if has_wwhrs else 0.0
    solar_credit = 250.0 if has_solar_water_heating else 0.0
    total_useful = max(
        0.0,
        useful_kwh + distribution_loss + storage_loss + primary_loss - wwhrs_credit - solar_credit,
    )
    return total_useful / seasonal_efficiency_water


# SAP10.2 cylinder volume by RdSAP10 size code (Table 28).
_CYLINDER_VOLUME_L: Final[dict[int, float]] = {1: 110.0, 2: 160.0, 3: 210.0}

# SAP10.2 Table 2 storage loss factor (kWh / litre / day) by insulation
# thickness in mm.  Lower number = better insulation.
_STORAGE_LOSS_FACTOR: Final[dict[int, float]] = {
    0: 0.0203,    # uninsulated -> high loss
    12: 0.0152,   # 12 mm jacket
    25: 0.0078,   # 25 mm foam
    38: 0.0056,
    50: 0.0043,
    80: 0.0025,
    100: 0.0022,
    150: 0.0014,
    200: 0.0011,
}

# RdSAP10 Table 29 cylinder-insulation default by age band when unknown:
# A-F -> 12 mm jacket, G-H -> 25 mm foam, I-M -> 38 mm foam.
_AGE_TO_DEFAULT_CYLINDER_INS_MM: Final[dict[str, int]] = {
    "A": 12, "B": 12, "C": 12, "D": 12, "E": 12, "F": 12,
    "G": 25, "H": 25,
    "I": 38, "J": 38, "K": 38, "L": 38, "M": 38,
}


def _cylinder_storage_loss_kwh(
    cylinder_size: Optional[int],
    cylinder_insulation_thickness_mm: Optional[int],
    cylinder_insulation_type: Optional[int],
    age_band: Optional[str],
) -> float:
    """Annual cylinder storage loss (kWh useful, before efficiency division).

    Returns 0 when no cylinder is described AND age_band is unknown (assume
    instantaneous / combi without storage).  Heated-space modifier 0.6.
    """
    if cylinder_size is None and age_band is None:
        return 0.0
    volume = _CYLINDER_VOLUME_L.get(cylinder_size or 1, 110.0)
    thickness = cylinder_insulation_thickness_mm
    if thickness is None and age_band is not None:
        thickness = _AGE_TO_DEFAULT_CYLINDER_INS_MM.get(age_band.upper())
    if thickness is None:
        thickness = 38
    factor = _nearest_storage_loss_factor(thickness)
    heated_space_modifier = 0.6
    return volume * factor * 365.0 * heated_space_modifier


def _nearest_storage_loss_factor(thickness_mm: int) -> float:
    """Pick the SAP10.2 Table 2 row with thickness closest <= the supplied
    value.  For thicknesses below 12 mm, uses the uninsulated 0-row."""
    candidates = sorted(_STORAGE_LOSS_FACTOR.keys())
    chosen = candidates[0]
    for t in candidates:
        if t <= thickness_mm:
            chosen = t
    return _STORAGE_LOSS_FACTOR[chosen]


def _primary_circuit_loss_kwh(age_band: Optional[str]) -> float:
    """Annual primary-pipework loss (kWh useful) by age band.

    RdSAP10 Table 29: pre-2007 (A-J) no primary insulation -> 245 kWh/yr;
    K, L, M -> full insulation -> 60 kWh/yr. Unknown -> 245.
    """
    if age_band is None:
        return 245.0
    return 60.0 if age_band.upper() in ("K", "L", "M") else 245.0


def predicted_lighting_kwh(
    total_floor_area_m2: Optional[float],
    cfl_count: Optional[int],
    led_count: Optional[int],
    incandescent_count: Optional[int],
) -> float:
    """Annual lighting kWh (SAP10.2 Section L simplified).

    Base demand ~ 9.3 * TFA kWh/yr; reduced by low-energy bulb share.  LED
    bulbs cut consumption by ~50%, CFL by ~40%, incandescent by 0%.
    Missing counts treated as zero.

    DEPRECATED for SAP rating use. The spec-faithful Appendix L L1-L11
    cascade is in `domain.sap10_calculator.worksheet.internal_gains.annual_lighting_kwh`
    and is what `cert_to_inputs` now plumbs into `inputs.lighting_kwh_per_yr`.
    This heuristic over-counts ~3× on the Elmhurst cohort (528 vs 140 kWh
    on 000474). Kept only for `domain.sap10_ml.ecf.energy_cost_factor` and
    `domain.sap10_ml.transform.transform_to_predictions` — legacy ML predictor
    callsites that pre-date the SAP rewrite. Rip when those migrate.
    See ADR-0010 amendment "Appendix L lighting (2026-05-22)".
    """
    if total_floor_area_m2 is None or total_floor_area_m2 <= 0:
        return 0.0
    cfl = cfl_count or 0
    led = led_count or 0
    inc = incandescent_count or 0
    total_bulbs = max(1, cfl + led + inc)
    led_share = led / total_bulbs
    cfl_share = cfl / total_bulbs
    reduction = 0.5 * led_share + 0.4 * cfl_share
    return 9.3 * total_floor_area_m2 * (1.0 - reduction)