#!/usr/bin/env python3
import quick2wire.i2c as i2c
import array 
import sys
import time
import math 

R_CONST=8314.3
MW_CONST=18.016
AM2315_I2CADDR = 0x5c
AM2315_WAITTIME = 0.150
MAXTRYS=3
FUNCTION_CODE_READ = 0x03
readBytes = array.array ("B",[0x00,0x04])
class AM2315(object): 
    def __init__(self): 
        pass
    def __del__(self): 
        pass
    def values(self): 
        i=0
        errcode=0 
        hum = 999
        temp = 999
        while i <= MAXTRYS:
          with i2c.I2CMaster() as bus: 
            try:
               bus.transaction(i2c.writing_bytes(AM2315_I2CADDR, 
                   FUNCTION_CODE_READ,*readBytes )) 
               time.sleep(AM2315_WAITTIME)
               read_results = bus.transaction(i2c.reading(AM2315_I2CADDR, 8))
#               print(read_results)
               break
            except: 
               i = i+1 
        if i > MAXTRYS:
           errcode=1
        else:
           s=bytearray(read_results[0])
           crc = 256*s[7]+s[6]
           t = bytearray([s[0],s[1],s[2],s[3],s[4],s[5]])
           c = self.crc16(t) 
           if crc != c:
             errcode=2
           else:
             hum = (256*s[2]+s[3])/10
             temp = (256*s[4]+s[5])/10
        return hum,temp,errcode   
    def humidity(self): 
        x=self.values()
        return self.values()[0]

    def temperature(self): 
        return self.values()[1]

    def SDD(self,T,mode):
        return 6.1078 * math.pow(10,((self.a(mode)*T)/(self.b(mode)+T)))
    def DD(self,mode):
        r = self.humidity()
        T = self.temperature()
        return r/100 * self.SDD(T,mode)
    def a(self,mode):
        T = self.temperature()
        if T >= 0:
           return 7.5
        if T < 0 and mode == 0 :
           return 7.6
        if T < 0 and mode == 1 :
           return 9.5
    def b(self,mode):
        T = self.temperature()
        if T >= 0:
           return 237
        if T < 0 and mode == 0 :
           return 240.7
        if T < 0 and mode == 1 :
           return 265.5
    def TD(self,mode):
        v=math.log10(self.DD(mode)/6.1078)
        return (self.b(mode)*v)/(self.a(mode)-v)
    def RR(self,mode):
        T = self.temper,lature()
        return 100*self.SDD(self.TD(T),mode) / self.SDD(T,mode)
    def AFr(self,mode):
        T = self.temperature()
        return math.pow(10,5)*MW_CONST/R_CONST*self.DD(mode)/self.TK(T)
    def TK(self,T):
        return T+273.15
    def crc16(self, char):
         crc = 0xFFFF
         for l in char:
               crc = crc ^ l
               for i in range(1,9):
                   if (crc & 0x01):
                      crc = crc >> 1
                      crc = crc ^ 0xA001
                   else:
                      crc = crc >> 1
         return crc