import functools
import flask


def add_response_headers(headers: dict):
    """This decorator adds the headers passed in to the response"""

    def decorator(f):
        @functools.wraps(f)
        def decorated_function(*args, **kwargs):
            resp = flask.make_response(f(*args, **kwargs))
            h = resp.headers
            for header, value in headers.items():
                h[header] = value
            return resp

        return decorated_function

    return decorator


def vary_xhr():
    """View function decorator; adds HTTP header "Vary: X-Requested-With" to the response"""

    def decorator(f):
        header_adder = add_response_headers({'Vary': 'X-Requested-With'})
        return header_adder(f)

    return decorator