from __future__ import annotations

from dataclasses import dataclass, field
from datetime import date, timedelta
from decimal import Decimal

from app.db.base import SessionLocal
from app.integrations.cbr import CNY_CODE, CbrClient, CbrDataError
from app.integrations.gateway import GatewayError
from app.repositories.exchange_rates import ExchangeRateRepository
from app.repositories.reference import ReferenceRepository
from app.services.request_log import save_request_log

CNY = "CNY"


@dataclass
class FxRatesUpdateResult:
    date_to: date
    date_from: date | None = None
    saved: int = 0
    error: str | None = None
    messages: list[str] = field(default_factory=list)

    @property
    def ok(self) -> bool:
        return self.error is None


@dataclass(frozen=True)
class FxRateRow:
    rate_date: date
    nominal: int
    rate: Decimal
    rate_per_unit: Decimal


async def _cny_currency_id() -> int:
    async with SessionLocal() as session:
        currency_id = await ReferenceRepository(session).get_currency_id(CNY)
    if currency_id is None:
        raise RuntimeError("В справочнике валют нет CNY — примените миграции.")
    return currency_id


async def update(
    up_to: date, user: str, *, cbr: CbrClient | None = None
) -> FxRatesUpdateResult:
    """Догружает курс CNY с дня после последнего сохранённого по up_to.

    Если курсов ещё нет — с 01.01 года даты up_to. Повторная загрузка тех же
    дат — upsert.
    """
    result = FxRatesUpdateResult(date_to=up_to)
    currency_id = await _cny_currency_id()

    async with SessionLocal() as session:
        last = await ExchangeRateRepository(session).last_rate_date(currency_id)
    date_from = last + timedelta(days=1) if last else date(up_to.year, 1, 1)
    if date_from > up_to:
        result.messages.append(
            f"Курс CNY уже загружен по {last:%d.%m.%Y} — обновлять нечего."
        )
        return result
    result.date_from = date_from

    cbr = cbr or CbrClient.from_settings()
    try:
        rates = cbr.get_rates(date_from, up_to, CNY_CODE)
    except (GatewayError, CbrDataError) as exc:
        result.error = f"Не удалось получить курс CNY от ЦБ: {exc}"
        result.messages.append(result.error)
        return result
    finally:
        await save_request_log(cbr.gateway, user)

    if not rates:
        result.messages.append(
            f"ЦБ не вернул курсов CNY за {date_from:%d.%m.%Y}–{up_to:%d.%m.%Y}."
        )
        return result

    async with SessionLocal() as session:
        await ExchangeRateRepository(session).upsert_many(currency_id, rates, user)
        await session.commit()
    result.saved = len(rates)
    last_rate = rates[-1]
    result.messages.append(
        f"Сохранено курсов CNY: {len(rates)} "
        f"({rates[0].rate_date:%d.%m.%Y}–{last_rate.rate_date:%d.%m.%Y}), "
        f"последний — {last_rate.rate_per_unit} за {last_rate.rate_date:%d.%m.%Y}."
    )
    return result


async def list_recent(limit: int = 10) -> list[FxRateRow]:
    currency_id = await _cny_currency_id()
    async with SessionLocal() as session:
        rows = await ExchangeRateRepository(session).list_recent(currency_id, limit)
    return [
        FxRateRow(
            rate_date=row.rate_date,
            nominal=row.nominal,
            rate=row.rate,
            rate_per_unit=row.rate / row.nominal,
        )
        for row in rows
    ]