Argument "direction" should be an enum, or a proper class

[maxalbert]

A bunch of metrics take a direction argument which can be one of the values {"in", "out", "both"}. There is a lot of duplicated logic that either checks the validity of these parameters or takes decisions based on one of the values. At the very least direction should be an enum to avoid these checks. It could possibly help to even promote it to a proper class so that other code doesn't need to take decisions on direction's behalf when the logic really belongs there.