from calc.parser import Num, BinOp, Unary, Node


class EvalError(Exception):
    pass


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

    Result type rule: if the result is mathematically an integer (no
    fractional part), return int; otherwise return float.
    """
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        val = evaluate(node.operand)
        if node.op == '-':
            return _coerce(-val)
        raise EvalError(f"unknown unary op {node.op!r}")
    if isinstance(node, BinOp):
        left = evaluate(node.left)
        right = evaluate(node.right)
        op = node.op
        if op == '+':
            return _coerce(left + right)
        if op == '-':
            return _coerce(left - right)
        if op == '*':
            return _coerce(left * right)
        if op == '/':
            if right == 0:
                raise EvalError("division by zero")
            return _coerce(left / right)
        raise EvalError(f"unknown binary op {op!r}")
    raise EvalError(f"unknown node type {type(node).__name__}")


def _coerce(value):
    if isinstance(value, float) and value == int(value):
        return int(value)
    return value