"""SAP 10.2 Table 4b (PDF p.168) — "Seasonal efficiency for gas and
liquid fuel boilers", winter / summer pair per Table 4b sub-row code
(`sap_main_heating_code` 101-141).

This table is the spec-canonical fallback when a gas / oil boiler is
NOT in the PCDB. Winter efficiency feeds (206)..(212) space heating;
summer efficiency feeds Appendix D §D2.1 (2) Equation D1 alongside
winter to derive the worksheet (217)m monthly water-heating efficiency.

Codes are grouped in Table 4b by boiler type:

  101-109   Gas boilers (mains, LPG, biogas) 1998 or later
  110-114   Gas pre-1998 with fan-assisted flue
  115-119   Gas pre-1998 with balanced / open flue
  120-123   Combined Primary Storage Units (CPSU)
  124-132   Liquid fuel boilers (oil, etc.)
  133-141   Range cooker boilers (gas + liquid fuel)

The winter column is duplicated in `domain.sap10_ml.sap_efficiencies.
_SPACE_EFF_BY_CODE` for backward-compat with that module's interim
ML cascade; the canonical source for new cascade work is here per
[[sap10_ml deprecation]] memory.
"""

from __future__ import annotations

from typing import Final, Optional


# Verbatim from SAP 10.2 spec PDF p.168 (the "Boiler ... Efficiency, %
# Winter / Summer" table). All values percent.
_TABLE_4B_SEASONAL_EFF_PCT_BY_CODE: Final[dict[int, tuple[float, float]]] = {
    # Gas boilers (including mains gas, LPG and biogas) 1998 or later
    101: (74.0, 64.0),   # Regular non-condensing with automatic ignition
    102: (84.0, 74.0),   # Regular condensing with automatic ignition
    103: (74.0, 65.0),   # Non-condensing combi with automatic ignition
    104: (84.0, 75.0),   # Condensing combi with automatic ignition
    105: (70.0, 60.0),   # Regular non-condensing with permanent pilot
    106: (80.0, 70.0),   # Regular condensing with permanent pilot
    107: (70.0, 61.0),   # Non-condensing combi with permanent pilot
    108: (80.0, 71.0),   # Condensing combi with permanent pilot
    109: (66.0, 56.0),   # Back boiler to radiators
    # Gas pre-1998 with fan-assisted flue
    110: (73.0, 63.0),   # Regular, low thermal capacity
    111: (69.0, 59.0),   # Regular, high or unknown thermal capacity
    112: (71.0, 62.0),   # Combi
    113: (84.0, 75.0),   # Condensing combi
    114: (84.0, 74.0),   # Regular, condensing
    # Gas pre-1998 with balanced or open flue
    115: (66.0, 56.0),   # Regular, wall mounted
    116: (56.0, 46.0),   # Regular, floor mounted, pre 1979
    117: (66.0, 56.0),   # Regular, floor mounted, 1979 to 1997
    118: (66.0, 57.0),   # Combi
    119: (66.0, 56.0),   # Back boiler to radiators
    # Combined Primary Storage Units (CPSU)
    120: (74.0, 72.0),   # With automatic ignition (non-condensing)
    121: (83.0, 81.0),   # With automatic ignition (condensing)
    122: (70.0, 68.0),   # With permanent pilot (non-condensing)
    123: (79.0, 77.0),   # With permanent pilot (condensing)
    # Liquid fuel boilers
    124: (66.0, 54.0),   # Standard oil boiler pre-1985
    125: (71.0, 59.0),   # Standard oil boiler 1985 to 1997
    126: (80.0, 68.0),   # Standard oil boiler, 1998 or later
    127: (84.0, 72.0),   # Condensing oil boiler
    128: (71.0, 62.0),   # Combi oil boiler, pre-1998
    129: (77.0, 68.0),   # Combi oil boiler, 1998 or later
    130: (82.0, 73.0),   # Condensing combi oil boiler
    131: (66.0, 54.0),   # Oil room heater with boiler to radiators, pre 2000
    132: (71.0, 59.0),   # Oil room heater with boiler to radiators, 2000 or later
    # Range cooker boilers (mains gas, LPG and biogas)
    133: (47.0, 37.0),   # Single burner with permanent pilot
    134: (51.0, 41.0),   # Single burner with automatic ignition
    135: (61.0, 51.0),   # Twin burner with permanent pilot (non-condensing) pre 1998
    136: (66.0, 56.0),   # Twin burner with automatic ignition (non-condensing) pre 1998
    137: (66.0, 56.0),   # Twin burner with permanent pilot (non-condensing) 1998 or later
    138: (71.0, 61.0),   # Twin burner with automatic ignition (non-condensing) 1998 or later
    # Range cooker boilers (liquid fuel)
    139: (61.0, 49.0),   # Single burner
    140: (71.0, 59.0),   # Twin burner (non-condensing) pre 1998
    141: (76.0, 64.0),   # Twin burner (non-condensing) 1998 or later
}


def table_4b_seasonal_efficiencies_pct(
    sap_main_heating_code: Optional[int],
) -> Optional[tuple[float, float]]:
    """Return the SAP 10.2 Table 4b `(winter, summer)` efficiency pair
    as percentages, or `None` when the lodged code is not a Table 4b
    boiler sub-row (e.g. Table 4a category code, no lodging).

    Total contract — never raises; non-Table-4b codes fall through to
    None so the caller can route to the scalar / category cascade.
    """
    if sap_main_heating_code is None:
        return None
    return _TABLE_4B_SEASONAL_EFF_PCT_BY_CODE.get(sap_main_heating_code)