import decimal
from functools import total_ordering
from numbers import Real

class Context(object):
    def __init__(self, **kwargs):
        self.context = decimal.Context(**kwargs)

    def __enter__(self):
        with decimal.localcontext(self.context) as c:
            return c

    def __exit__(self, *args):
        pass

MONEY_CONTEXT = Context(prec=3, rounding=decimal.ROUND_HALF_UP)

@total_ordering
class Money(object):
    def __init__(self, symbol, amount):
        self.symbol = symbol
        self.amount = amount

    @classmethod
    def fromstr(cls, money):
        symbol, amount = money[0], money[1:]
        return cls(
            symbol,
            decimal.Decimal(amount).quantize(
                decimal.Decimal('.01'),
                rounding=decimal.ROUND_DOWN
            )
        )

    def _raise_if_separate_types(self, other):
        if not isinstance(other, Money):
            raise TypeError("Can't use money and non-money together")

        if not self.symbol == other.symbol:
            # not true, but conversions are another matter
            raise TypeError("Can't compare across monetary types")

    def __eq__(self, other):
        self._raise_if_separate_types(other)
        return self.amount == other.amount

    def __lt__(self, other):
        self._raise_if_separate_types(other)
        return self.amount < other.amount

    def __add__(self, other):
        self._raise_if_separate_types(other)

        with decimal.localcontext(_MONEY_CONTEXT):
            amount = self.amount + other.amount

        return self.__class__(self.symbol, amount)

    def __neg__(self):
        amount = (-self.amount)
        return self.__class__(self.symbol, amount)

    def __sub__(self, other):
        self._raise_if_separate_types(other)
        return self + (-other)

    def __mul__(self, other):
        if not isinstance(other, Real):
            raise TypeError("Can only multiple money by real numbers")

        if isinstance(other, float):
            other = _MONEY_CONTEXT.create_decimal_from_float(other)

        with MONEY_CONTEXT:
            amount = (self.amount * other).quantize(decimal.Decimal('.01'))

        return self.__class__(self.symbol, amount)

    def __div__(self, other):
        if not isinstance(other, Real):
            raise TypeError("Can only divide money by real numbers")

        if isinstance(other, float):
            other = _MONEY_CONTEXT.create_decimal_from_float(other)

        with MONEY_CONTEXT:
            amount = (self.amount / other).quantize(decimal.Decimal('.01'))

        return self.__class__(self.symbol, amount)

    def __str__(self):
        return '{}{!s}'.format(self.symbol, self.amount)

    def __repr__(self):
        return 'Money(symbol={!r}, amount={!r})'.format(self.symbol, self.amount)