from calc.parser import Num, BinOp, Unary


class EvalError(Exception):
    pass


def evaluate(node):
    """Walk the AST returned by parse() and return int | float."""
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        if node.op == '-':
            return -evaluate(node.operand)
        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 left + right
        if node.op == '-':
            return left - right
        if node.op == '*':
            return left * right
        if node.op == '/':
            if right == 0:
                raise EvalError("division by zero")
            return left / right
        raise EvalError(f"unknown binary op {node.op!r}")
    raise EvalError(f"unknown AST node type {type(node).__name__!r}")


def format_result(value) -> str:
    """Format a numeric result: whole-valued floats print without '.0', others as-is."""
    if isinstance(value, float) and value == int(value):
        return str(int(value))
    return str(value)