// ScanForCensus calls c.Add for each occupant of g with the time
// provided by timeFn and census.Key provided by keyFn. This is
// used to populate a Census from a pre-existing Grid.
func ScanForCensus(c census.Census, g Grid, timeFn func(interface{}) interface{}, keyFn func(interface{}) *census.Key) {
var locs []Point
g.Locations(&locs)
for _, p := range locs {
if key := keyFn(p.V); key != nil {
c.Add(timeFn(p.V), *key)
}
}
}
// WatchForCensus monitors ch and invokes c.Add and c.Remove as
// appropriate with the time provided by timeFn and census.Key
// provided by keyFn. If keyFn returns nil, no event will be recorded.
func WatchForCensus(c census.Census, ch <-chan []Update, timeFn func(interface{}) interface{}, keyFn func(interface{}) *census.Key) {
for updates := range ch {
for _, u := range updates {
if u.IsAdd() || u.IsReplace() {
if key := keyFn(u.New.V); key != nil {
c.Add(timeFn(u.New.V), *key)
}
}
if u.IsRemove() || u.IsReplace() {
if key := keyFn(u.Old.V); key != nil {
c.Remove(timeFn(u.Old.V), *key)
}
}
}
}
}