private enum class Kind(val stringValue: String) {
    OUTGOING("outgoing"),
    INCOMING("incoming")
}

enum class Event(val stringValue: String) {
    CALL_INITIATED("call_initiated"),
    CALL_RECEIVED("call_received"),
    CALL_ANSWERED("call_answered"),
    CALL_CANCELLED("call_cancelled"),
    CALL_REJECTED("call_rejected"),
    CALL_ESTABLISHED("call_established"),
    CALL_ENDED("call_ended")
}