# -*- coding: utf-8 -*-
  
  """
  author  Benoit Dubois
  licence GPL v3+
  brief   Basic protocol communication with stm32 discovery board.
  """
  import pyb
  import uselect
  import ustruct
  
  
  class SerialCom(object):
  
      def __init__(self, id_=0):
          self.vcom = pyb.USB_VCP(id_)
          self.poller = uselect.poll()
          self.poller.register(self.vcom, uselect.POLLIN)
  
      def write_message(self, msg):
          header = ustruct.pack('<L', len(msg))
          self.vcom.write(header + msg.encode('utf-8'))
  
      def read_message(self):
          header = self.vcom.read(4)
          if header is None:
              print("Read error: no data readed")
              return ''
          if len(header) == 4:
              msg_len = ustruct.unpack('<L', header)[0]
              try:
                  data = self.vcom.read(msg_len).decode('utf-8')
              except:
                  print("Serial read error")
                  return
              # Check message validity
              if data is None:
                  print("Read error: data received but no message to read")
                  return
              if len(data) != msg_len:
                  print("Read error: bad message length")
              return data
  
      def write_message_simple(self, msg):
          self.vcom.write(msg.encode('utf-8'))
  
      def read_message_simple(self):
          data = self.vcom.readline().decode('utf-8')
          if data is None:
              print("Read error: data received but no message to read")
              return
          return data
  
  
  def test():
      scom = SerialCom()
      while True:
          scom.poller.poll(250)
          if scom.vcom.any():
              msg = scom.read_message_simple()
              if msg is not None:
                  scom.write_simple_message("Read: " + msg)
  
  
  #test()