PiggyBank/piggybank/currencies.py

"""Dictionary of supported currencies as instances of a Currency class.

Face values are stored as decimals*.

* Decimal is used to avoid problems of rounding float numbers. So first two
digits to the right are used to store a fraction part. You can simply divide
this number by 100 to get a floating-point number.
"""

from __future__ import annotations
from operator import mul
from typing import Dict, List, TypedDict

__all__ = [ "Currency", "CURRENCIES", "BaseCurrencyError", 
            "CurrencyIsNotSupportedError", "CurrenciesCoinCountMismatchError",
            "CurrencyMismatchError"]


CURRENCIES: Dict[str, Currency] = dict()


class BaseCurrencyError(Exception):
    """Base class for all currency exeptions."""
    def __init__(self, message=None, *args, **kwargs) -> None:
        if message is None:
            message = self.__doc__
        super().__init__(message, *args, **kwargs)


class CurrencyIsNotSupportedError(BaseCurrencyError):
    """Currency is not supported."""
    pass


class CurrencyMismatchError(BaseCurrencyError):
    """Currencies doesn't match, but they must do so."""
    def __init__(self, extra=None):
        if not extra is None:
            super().__init__(f"{self.__doc__} {extra}")
        else:
            super().__init__(self.__doc__)


class CurrenciesCoinCountMismatchError(BaseCurrencyError):
    """Count of coins of a new currency and an old one should be equal."""
    pass


class Currency:
    """Currency's representation and methods to work with it.

    Arguments:
        iso_code    -- ISO code of a currency;
        name        -- full name of a currency;
        description -- description of a currency;
        coins_count -- number of face values of coins;
        coin_names  -- list of names of face values (e.g. 1c, 5c);
        face_values -- list of values for each face value in decimal
                       (e.g. $476.40 is 47640);
    """
    def __init__(self, iso_code: str, name: str, description: str,
                 coins_count: int, coin_names: List[str],
                 face_values: List[int]):
        self._iso = iso_code.upper()
        self._name = name
        self._description = description
        self._coins_count = coins_count
        self._coin_names = coin_names
        self._face_values = face_values

    @property
    def iso(self) -> str:
        """ISO code of a currency."""
        return self._iso

    @property
    def name(self) -> str:
        """Full name of a currency."""
        return self._name

    @property
    def description(self) -> str:
        """Description of a currency (e.g. country)."""
        return self._description

    @property
    def count(self):
        """Count of coins of a currency."""
        return self._coins_count

    @property
    def coin_names(self) -> List[str]:
        """Names of coins (usually face values, e.g. 25¢).
        From least to most."""
        return self._coin_names

    @property
    def face_values(self) -> List[int]:
        """Face values of coins. From least to most."""
        return self._face_values

    def multiply(self, lst: List[int]) -> List[float]:
        """Multiplies a list by face values. Length of list must match
        currency's coins count."""
        if len(lst) != len(self):
            raise CurrenciesCoinCountMismatchError
        return list(map(mul, lst, self.face_values))

    @staticmethod
    def from_string(currency: str) -> Currency:
        """Creates a Currency object from its string representation."""
        iso, name, desc, ccnt, fvn, fv = currency.split(";")
        return Currency(iso, name, desc, int(ccnt),
               fvn.split(","), list(map(int, fv.split(","))))

    def __mul__(self, lst: List[int]) -> List[float]:
        return self.multiply(lst)

    def __len__(self) -> int:
        return self.count

    def __str__(self):
        return f"{self.iso};{self.name};{self.description};" \
               f"{self.count};{','.join(self.coin_names)};" \
               f"{','.join(list(map(str, self.face_values)))}"