open class XModemPacket {

    var bytes = ByteArray(133)
        protected set

    init {
        bytes[0] = 1
        
        when(this) {
            is RequestPacket -> {
                bytes[1] = packetNumberSend.toByte()
                bytes[2] = packetNumberSend.inv().toByte()
                packetNumberSend++
            }
            is ResponsePacket -> packetNumberReceived++
        }

        bytes.fill(255.toByte(), 3, 131)
    }

    companion object {
        var packetNumberReceived = 0
        var packetNumberSend = 0

        fun resetPacketNumber() {
            packetNumberReceived = 0
            packetNumberSend = 0
        }
    }
}