#!/usr/bin/python

import struct
import array 
import time
import io
import fcntl

I2C_SLAVE = 0x0703					# 
HTU21D_ADDR = 0x40					#
CMD_READ_TEMP_HOLD = "\xE3"
CMD_READ_HUM_HOLD = "\xE5"
CMD_READ_TEMP_NOHOLD = "\xF3"
CMD_READ_HUM_NOHOLD = "\xF5"
CMD_WRITE_USER_REG = "\xE6"
CMD_READ_USER_REG = "\xE7"
CMD_SOFT_RESET= "\xFE"

class i2c(object):
   def __init__(self, device, bus):

      self.fr = io.open("/dev/i2c-"+str(bus), "rb", buffering=0)
      self.fw = io.open("/dev/i2c-"+str(bus), "wb", buffering=0)

      # set device address

      fcntl.ioctl(self.fr, I2C_SLAVE, device)
      fcntl.ioctl(self.fw, I2C_SLAVE, device)

   def write(self, bytes):
      self.fw.write(bytes)

   def read(self, bytes):
      return self.fr.read(bytes)

   def close(self):
      self.fw.close()
      self.fr.close()

class HTU21D(object):
   def __init__(self):
      self.dev = i2c(HTU21D_ADDR, 1)  #HTU21D 0x40, bus 1
      self.dev.write(CMD_SOFT_RESET)  #soft reset
      time.sleep(.1)

   def ctemp(self, sensorTemp):
      tSensorTemp = sensorTemp / 65536.0
      return -46.85 + (175.72 * tSensorTemp)

   def chumid(self, sensorHumid):
      tSensorHumid = sensorHumid / 65536.0
      return -6.0 + (125.0 * tSensorHumid)

   def crc8check(self, value):
      # Ported from Sparkfun Arduino HTU21D Library
      remainder = ( ( value[0] << 8 ) + value[1] ) << 8
      remainder |= value[2]
      
      # POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1
      # divsor = 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
      divsor = 0x988000
      
      for i in range(0, 16):
         if(remainder & 1 << (23 - i)):
            remainder ^= divsor
            divsor = divsor >> 1

      if remainder == 0:
         return True
      else:
         return False
   
   def read_tmperature(self):
      self.dev.write(CMD_READ_TEMP_NOHOLD)  #measure temp
      time.sleep(.1)

      data = self.dev.read(3)
      buf = array.array('B', data)

      #if self.crc8check(buf):
      temp = (buf[0] << 8 | buf[1]) & 0xFFFC
      return self.ctemp(temp)
      #else:
      #  return -255
         
   def read_humidity(self):
      self.dev.write(CMD_READ_HUM_NOHOLD) #measure humidity
      time.sleep(.1)

      data = self.dev.read(3)
      buf = array.array('B', data)
      
      #if self.crc8check(buf):
      humid = (buf[0] << 8 | buf[1]) & 0xFFFC
      return self.chumid(humid)
      #else:
      #  return -255
         
if __name__ == "__main__":
   obj = HTU21D()
   print (obj.read_tmperature())
   print (obj.read_humidity())