from .math_rational_add_rational import add_rational
from .math_rational_divide_rational import divide_rational
from .math_rational_multiply_rational import multiply_rational
from .math_rational_subtract_rational import subtract_rational
from .math_rational_types import Rational, RationalOp


def calculate_rational(a: Rational, op: RationalOp, b: Rational) -> Rational:
    """Add, subtract, multiply or divide two fractions exactly.

    The result is always reduced with a positive denominator, so equal values
    have equal fields.
    """
    if op == "add":
        return add_rational(a, b)
    if op == "subtract":
        return subtract_rational(a, b)
    if op == "multiply":
        return multiply_rational(a, b)
    if op == "divide":
        return divide_rational(a, b)
    raise ValueError('unknown operation "%s"' % (op,))