anchor.diff:  %% @doc Body producing function for
   %% 	`GET /usageManagement/v1/usage'
   %% 	requests.
  -get_usage(_Query) ->
  +get_usage([] = _Query) ->
   	{ok, Directory} = application:get_env(ocs, ipdr_log_dir),
   	case file:list_dir(Directory) of
   		{ok, Files} ->
  
positive.code: 			{ok, Headers, Body};
  		{error, _Reason} ->
  			{error, 500}
  	end.
  
  -spec get_usage(Id, Query) -> Result
  
negative.code: usage_characteristics([], _Ipdr, Acc) ->
  	lists:reverse(Acc).
  
  %% @hidden
  usage_aaa_auth(Events) ->
  	UsageSpec = {{"id", "AAAAccessUsageSpec"},
  			{"href", "/usageManagement/v1/usageSpecification/AAAAccessUsageSpec"},
  			{name, "AAAAccessUsageSpec"}},
  	Type = "AAAAccessUsageSpec",
  	Status = "received",
  	F = fun({Milliseconds, N, P, Node, Server, Client,
  					Type, ReqAttrs, _RespAttrs},  Acc) ->
  				ID = "access-" ++ integer_to_list(Milliseconds)
  						++ integer_to_list(N),
  				Href = "/usageManagement/v1/usage/" ++ ID,
  				Date = ocs_log:iso8601(Milliseconds),
  				Protocol = case P of
  					radius ->
  						"RADIUS";
  					diameter ->
  						"DIAMETER"
  				end,
  				UsageChars = [{struct, [{name, "protocol"}, {"value", Protocol}]},
  						{struct, [{"name", ""}, {"value", ""}]}],
  				JsonObj = {struct, [{"id", ID}, {"href", Href},
  						{"date", Date}, {"type", Type}, {"status", Status},
  						{"usageSpecification", UsageSpec},
  						{"usageCharacteristic", {array, UsageChars}}]},
  				[JsonObj | Acc];
  		(_, Acc) ->
  				%% TODO support for DIAMETER
  				Acc
  	end,
  	lists:reverse(lists:foldl(F, [], Events)).
  
  %% @hidden
  spec_aaa_auth() ->
  