from calc.parser import Num, BinOp, Unary


class EvalError(Exception):
    pass


def evaluate(node):
    """Walk the AST and return int | float.

    Result type rule: if the mathematical value is a whole number, return int;
    otherwise return float.
    """
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        v = evaluate(node.operand)
        if node.op == '-':
            return _normalize(-v)
        raise EvalError(f"unknown unary op {node.op!r}")
    if isinstance(node, BinOp):
        left = evaluate(node.left)
        right = evaluate(node.right)
        if node.op == '+':
            return _normalize(left + right)
        if node.op == '-':
            return _normalize(left - right)
        if node.op == '*':
            return _normalize(left * right)
        if node.op == '/':
            if right == 0:
                raise EvalError("division by zero")
            return _normalize(left / right)
        raise EvalError(f"unknown binary op {node.op!r}")
    raise EvalError(f"unknown node type {type(node).__name__}")


def _normalize(v):
    if isinstance(v, float) and v == int(v):
        return int(v)
    return v