from calc.parser import Num, BinOp, Unary


class EvalError(Exception):
    pass


def evaluate(node) -> int | float:
    """Walk an AST node and return the numeric result.

    Returns int for whole-valued results, float otherwise.
    Raises EvalError on division by zero.
    """
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        return -evaluate(node.operand)
    if isinstance(node, BinOp):
        left = evaluate(node.left)
        right = evaluate(node.right)
        if node.op == '+':
            result = left + right
        elif node.op == '-':
            result = left - right
        elif node.op == '*':
            result = left * right
        elif node.op == '/':
            if right == 0:
                raise EvalError("division by zero")
            result = left / right
        else:
            raise EvalError(f"unknown operator {node.op!r}")
        # Return int when the result is whole-valued
        if isinstance(result, float) and result.is_integer():
            return int(result)
        return result
    raise EvalError(f"unknown node type {type(node)!r}")