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14b45a1b3e
Slice 1 of Bill Derivation — the reference-data foundation that later slices price the calculator's per-end-use kWh against: - Fuel enum (canonical billing fuels; the join key between the calculator's SAP-code fuels and the rates snapshot). COAL + HEAT_NETWORK are members with no national rate. - FuelRates value object: unit_rate_p_per_kwh / standing_charge_p_per_day / seg_export_p_per_kwh; raises UnpricedFuel on a fuel it has no rate for rather than billing at a wrong default. - FuelRatesRepository port (ADR-0011 Repo-reads-stored-reference-data) + StaticFileFuelRatesRepository reading a committed JSON snapshot. - Snapshot fuel_rates_2026_q2.json: GB national, Apr-Jun 2026 Ofgem cap (gas/electricity) + DESNZ/NEP May 2026 (off-gas). Carries the full researched data; the value object exposes single-rate fuels this slice. Off-peak (day/night), house coal and heat network raise UnpricedFuel until later slices. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
43 lines
1.5 KiB
Python
43 lines
1.5 KiB
Python
from __future__ import annotations
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from enum import Enum
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class Fuel(Enum):
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"""A canonical billing fuel — the join key between the calculator's
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per-end-use fuel (mapped from SAP fuel codes) and the Fuel Rates snapshot
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(ADR-0014). Member names match the snapshot's keys.
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``COAL`` (traditional house coal) and ``HEAT_NETWORK`` are carried as
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members so a cert lodging them maps to a Fuel, but they have no national
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rate — pricing them raises ``UnpricedFuel`` (house coal's domestic sale is
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illegal in England; heat networks are scheme-specific).
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"""
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MAINS_GAS = "MAINS_GAS"
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ELECTRICITY = "ELECTRICITY"
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ELECTRICITY_OFF_PEAK = "ELECTRICITY_OFF_PEAK"
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OIL = "OIL"
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LPG = "LPG"
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COAL = "COAL"
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SMOKELESS = "SMOKELESS"
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WOOD_LOGS = "WOOD_LOGS"
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WOOD_PELLETS = "WOOD_PELLETS"
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HEAT_NETWORK = "HEAT_NETWORK"
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class UnpricedFuel(ValueError):
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"""Bill Derivation was asked for a rate on a fuel the current Fuel Rates
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snapshot does not price (ADR-0014).
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Raised rather than billing at a wrong default so the gap surfaces
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immediately — house coal and heat networks have no national rate, and
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off-peak electricity needs the day/night split that a later slice adds.
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"""
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def __init__(self, fuel: Fuel) -> None:
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super().__init__(
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f"no rate for fuel {fuel.name} in the current Fuel Rates snapshot; "
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f"add it to the snapshot or map this end use to a priced fuel"
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)
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self.fuel = fuel
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