from dataclasses import dataclass

CURRENCY_SYMBOLS = {
    "RUB": "₽",
    "USD": "$",
    "EUR": "€",
    "GBP": "£",
    "CNY": "¥",
    "JPY": "¥",
    "KZT": "₸",
    "UAH": "₴",
}


@dataclass
class ExchangeRate:
    from_currency: str = "USD"
    to_currency: str = "RUB"
    rate: float = 80.0

    def to_dict(self) -> dict:
        return {
            "from_currency": self.from_currency,
            "to_currency": self.to_currency,
            "rate": self.rate,
        }

    @classmethod
    def from_dict(cls, data: dict) -> "ExchangeRate":
        return cls(
            from_currency=data.get("from_currency", "USD"),
            to_currency=data.get("to_currency", "RUB"),
            rate=data.get("rate", 80.0),
        )


DEFAULT_RATES: list[ExchangeRate] = [
    ExchangeRate(from_currency="USD", to_currency="RUB", rate=80.0),
]


class CurrencyError(Exception):
    pass


class CurrencyConverter:
    def __init__(self, rates: list[ExchangeRate] | None = None):
        self._rates: dict[tuple[str, str], float] = {}
        if rates:
            for r in rates:
                self.set_rate(r.from_currency, r.to_currency, r.rate)

    def set_rate(self, from_currency: str, to_currency: str, rate: float) -> None:
        if rate <= 0:
            raise CurrencyError(f"Rate must be positive: {rate}")
        self._rates[(from_currency, to_currency)] = rate
        inverse = 1.0 / rate
        self._rates[(to_currency, from_currency)] = inverse

    def get_rate(self, from_currency: str, to_currency: str) -> float:
        if from_currency == to_currency:
            return 1.0
        try:
            return self._rates[(from_currency, to_currency)]
        except KeyError:
            raise CurrencyError(f"No exchange rate: {from_currency} → {to_currency}")

    def convert(self, amount: float, from_currency: str, to_currency: str) -> float:
        if from_currency == to_currency:
            return amount
        rate = self.get_rate(from_currency, to_currency)
        return round(amount * rate, 2)

    def get_symbol(self, currency: str) -> str:
        return CURRENCY_SYMBOLS.get(currency, currency)

    @classmethod
    def with_defaults(cls) -> "CurrencyConverter":
        return cls(DEFAULT_RATES)