PiggyBank/piggybank/currency.py

"""Currency class and a set of exceptions.

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.

Currency string has following format:
    <ISO>;<CURRENCY NAME>;<COINS COUNT>;{}<FRACTION SYMBOL>,{}<CURRENCY SYMBOL>
    ;<FACE VALUES>

{} with currency symbol used as a placeholder for where to put digits.

Example:
    RUB;Russian ruble;8;{} коп.,{}₽;1,5,10,50,100,200,500,1000
    USD;US Dollar;6;{}¢,${};1,5,10,25,50,100
"""

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

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


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."""


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):
    """Length of list supplied doesn't corresponds coins count."""


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;
        coins_count     -- number of face values of coins;
        fraction_symbol -- a symbol or word for a fraction of currency (e.g. c, cent);
        currency_symbol -- a symbol or word for a currency (e.g. $);
        face_values     -- list of values for each face value in decimal;
    """
    def __init__(self, iso_code: str, name: str, coins_count: int,
                 fraction_symbol: str, currency_symbol: str,
                 face_values: List[int]):
        self._iso = iso_code.upper()
        self._name = name
        self._coins_count = coins_count
        self._fraction_symbol = fraction_symbol
        self._currency_symbol = currency_symbol
        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 count(self):
        """Count of coins of a currency."""
        return self._coins_count

    @property
    def fraction_symbol(self) -> str:
        """Returns a symbol or word for a fraction of a currency."""
        return self._fraction_symbol

    @property
    def currency_symbol(self) -> str:
        """Returns a symbol or word for a currency."""
        return self._currency_symbol

    @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, count, syms, fv = currency.split(';')
        frac_sym, cur_sym = syms.split(',')
        return Currency(iso, name, int(count), frac_sym, cur_sym,
                        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.count};" \
               f"{self.fraction_symbol},{self.currency_symbol};" \
               f"{','.join(list(map(str, self.face_values)))}"