from sfatables.runtime import SFATablesRules

def fetch_context(slice_hrn, user_hrn, contexts):
    """
    Returns the request context required by sfatables. At some point, this
    mechanism should be changed to refer to "contexts", which is the
    information that sfatables is requesting. But for now, we just return
    the basic information needed in a dict.
    """
    base_context = {'sfa':{'user':{'hrn':user_hrn}, 'slice':{'hrn':slice_hrn}}}
    return base_context

def run_sfatables(chain, hrn, origin_hrn, rspec, context_callback = None ):
    """
    Run the rspec through sfatables
    @param chain Name of rule chain
    @param hrn Object's hrn
    @param origin_hrn Original caller's hrn
    @param rspec Incoming rspec
    @param context_callback Callback used to generate the request context  

    @return rspec
    """
    if not context_callback:
        context_callback = fetch_context

    chain = chain.upper()
    rules = SFATablesRules(chain)
    if rules.sorted_rule_list:
        contexts = rules.contexts
        request_context = context_callback(hrn, origin_hrn, contexts)
        rules.set_context(request_context)
        newrspec = rules.apply(rspec)
    else:
        newrspec = rspec
    return newrspec