"""Pydantic models for per-city cost-of-living data.

Every category figure is monthly GBP for a single person — the
denomination the simulator expects when scaling `spending_gbp`. The
source object retains the original currency, FX rate, and snapshot
date so we can re-validate or update a stale baseline.
"""
from __future__ import annotations

from datetime import date
from decimal import Decimal
from typing import Literal

from pydantic import BaseModel, ConfigDict, Field

SourceName = Literal["numbeo", "expatistan", "baseline", "manual"]


class ColSource(BaseModel):
    """Provenance for a CityCostIndex entry — where did the numbers come
    from and when. The simulator surfaces this in the SimulateResult so
    the user can audit which baseline was applied."""

    model_config = ConfigDict(frozen=True)

    name: SourceName
    url: str | None = None
    snapshot_date: date
    raw_currency: str = "GBP"
    gbp_per_unit: Decimal = Decimal("1")


class CategoryBreakdown(BaseModel):
    """Per-category monthly costs in GBP for a single person."""

    model_config = ConfigDict(frozen=True)

    rent_1bed_center: Decimal
    rent_1bed_outside: Decimal | None = None
    groceries: Decimal
    restaurants: Decimal
    transport: Decimal
    utilities: Decimal
    leisure: Decimal


class CityCostIndex(BaseModel):
    """One city's headline cost-of-living snapshot."""

    model_config = ConfigDict(frozen=True)

    city: str
    city_slug: str = Field(min_length=1)
    country: str
    total_single_no_rent_gbp: Decimal
    total_single_with_rent_gbp: Decimal
    breakdown: CategoryBreakdown
    source: ColSource

    @property
    def total_monthly_gbp(self) -> Decimal:
        """The number the simulator uses for ratios — `with rent` is the
        right anchor because moving location changes rent too."""
        return self.total_single_with_rent_gbp