import datetime
from typing import Iterable, Union

from money.currency import Currency
from money.money import Money


class ExchangeRate:

    def __init__(
        self,
        from_currency: Currency,
        to_currency: Currency,
        rate: Money,
        rate_date: datetime.date,
    ) -> None:
        self.from_currency = from_currency
        self.to_currency = to_currency
        self.rate = rate
        self.rate_date = rate_date

    @property
    def descriptor(self) -> str:
        return (
            str(self.from_currency.value)
            + str(self.to_currency.value)
            + str(self.rate_date.strftime("%Y-%m-%d"))
        )


class ExchangeRates:

    def __init__(self, rates: Union[Iterable[ExchangeRate], None] = None):

        self._rate_index = {}

        if rates is not None:
            for rate in rates:
                if not isinstance(rate, ExchangeRate):
                    raise TypeError("ExchangeRates can only hold Rates.")
                self._rate_index[rate.descriptor] = rate

    def add_rate(self, new_rate: ExchangeRate) -> None:
        self._rate_index[new_rate.descriptor] = new_rate

    def __iter__(self):
        return iter(self._rate_index.values())