#!/usr/bin/env python3

"""
Finding UHF RFID tags with a rubik/WYUAN RD905UW.
"""

import serial, crcmod, time

#BAUDRATE = 115200
#BAUDRATE = 9600
BAUDRATE = 57600


class UHF:
    def __init__(self):
        self.ser = serial.Serial('/dev/ttyUSB0', BAUDRATE)
    def crc16(self, s):
        crc16 = crcmod.predefined.Crc('crc-16-mcrf4xx')
        crc16.update(s)
        r = crc16.digest()
        r = r[::-1]
        #print(repr(r))
        #exit()
        #r = b'\xdb\x4b'
        return r
    def recv_with_crc16(self):
        count_byte = self.ser.read(1)
        count = ord(count_byte)
        s = self.ser.read(count)
        s, c = s[:-2], s[-2:]
        c2 = self.crc16(count_byte+s)
        #print('s', repr(s))
        #print('c0', repr(c))
        #print('c2', repr(c2))
        if (c != c2):
            print('Checksum MISMATCH')
        return s
        pass
    def send_with_crc16(self, s):
        print(repr(s))
        s = bytes([len(s)+2]) + s
        c = self.crc16(s)
        r = s + c
        #print(repr(r))
        #exit()
        self.ser.write(r)
        pass
    def get_info(self):
        #self.send_with_crc16(b'\xff\x21')
        self.send_with_crc16(b'\x00\x01')
        #r = self.ser.read(5)
        r = self.recv_with_crc16()
        print(repr(r))
        pass
    def get_info_loop(self):
        while True:
            self.get_info()
            time.sleep(0.05) # not really needed
        pass
    def run(self):
        #self.get_info()
        self.get_info_loop()

def mainfunc():
    uhf = UHF()
    uhf.run()

def mainfunc_loop():
    while True:
        try:
            mainfunc()
        except serial.serialutil.SerialException:
            pass

if (__name__ == '__main__'):
    #mainfunc()
    mainfunc_loop()