from __future__ import annotations

from collections.abc import Mapping, Sequence
from dataclasses import dataclass
from enum import Enum

from domain.fuel_rates.fuel import Fuel


class BillSection(Enum):
    """A user-meaningful slice of the annual energy bill — the calculator's raw
    end uses folded into the sections the UI shows (ADR-0014)."""

    HEATING = "HEATING"
    HOT_WATER = "HOT_WATER"
    LIGHTING = "LIGHTING"
    APPLIANCES = "APPLIANCES"
    COOKING = "COOKING"
    PUMPS_FANS = "PUMPS_FANS"


@dataclass(frozen=True)
class EnergyLine:
    """One section's delivered energy on one fuel. A section may have more than
    one line (e.g. gas main heating + electric secondary heating)."""

    section: BillSection
    fuel: Fuel
    kwh: float


@dataclass(frozen=True)
class EnergyBreakdown:
    """A Property's delivered energy per end use, the input to Bill Derivation —
    produced from SAP10 Calculation in a later slice. ``exported_kwh`` is PV
    generation exported to the grid, credited at the SEG rate."""

    lines: Sequence[EnergyLine]
    exported_kwh: float = 0.0


@dataclass(frozen=True)
class BillSectionCost:
    """One section's rolled-up delivered kWh and annual cost (£)."""

    kwh: float
    cost_gbp: float


@dataclass(frozen=True)
class Bill:
    """A Property's annual energy bill, composed per section plus the per-meter
    standing charges and the SEG export credit, and the total (ADR-0014)."""

    sections: Mapping[BillSection, BillSectionCost]
    standing_charges_gbp: float
    seg_credit_gbp: float
    total_gbp: float