observer

type Observer interface {
	RegisterCallback(id ulid.ULID, topicName string, callback func(data interface{}))
	RegisterChannel(id ulid.ULID, topicName string, channel chan interface{})

	UnregisterCallback(id ulid.ULID, topicName string)
	UnregisterChannel(id ulid.ULID, topicName string)

	Send(topicName string, data interface{})
	SendTo(topicName string, data interface{}, sendToIDs map[ulid.ULID]bool)
	SendExcept(topicName string, data interface{}, filterOutIDs map[ulid.ULID]bool)
}