"""
ams CCS811 Indoor Air Quality Sensor
Date:  April 2018
License: This code is public domain
Based on CCS811 datasheet. Inspired by Adafruit and Sparkfun libraries
Tested with Adafruit CCS811 Air quality breakout. Product ID: 3566
Tested on NodeMCU and Wemos D1 Mini (ESP8266) MicroPython v1.8.7-7-gb5a1a20a3
and MicroPython v1.9.3-8-g63826ac5c on 2017-11-01; ESP module with ESP8266
"""
"""Modified for BBC MicroBit
D Burrin Oct 2020"""
from microbit import *

class CCS811(object):

    
    """CCS811 gas sensor. Measures eCO2 in ppm and TVOC in ppb"""

    def __init__(self, addr=91):
        #self.devices = i2c.scan()
        #self.i2cb = i2cb
        self.addr = addr      # 0x5A = 90, 0x5B = 91
        self.tVOC = 0
        self.eCO2 = 0
        self.mode = 1       # Constant power mode; measurement every second
        self.error = False

        # Check if sensor is vailable at i2c bus address
        devices = i2c.scan()
        if self.addr not in devices:
            raise ValueError('CCS811 not found. Please check wiring. Pull nWake to ground.')
        # See figure 22 in datasheet: Bootloader Register Map
        #Check HW_ID register (0x20) - correct value 0x81
        i2c.write(0x5b,b'\x20')
        hardware_id = i2c.read(0x5b,1)
        print("HW",hardware_id)
        if (hardware_id[0] != 0x81):
            raise ValueError('Wrong Hardware ID.')
        # Check Status Register (0x00) to see if valid application present-
        i2c.write(0x5b,b'\x00')
        status = i2c.read(0x5b, 1)
        # See figure 12 in datasheet: Status register: Bit 4: App valid
        if not (status[0] >> 4) & 0x01:
           raise ValueError('Application not valid.')
        # Application start. Write with no data to App_Start (0xF4)
        i2c.write(0x5b, b'\xf4')
        # Set drive mode 1 - see Figure 13 in datasheet: Measure Mode Register (0x01)
        #self.i2c.writeto_mem(self.addr, 0x01, bytearray([0b00011000]))
        i2c.write(0x5b,b'\x01\x18')

    def __string__(self):
        return 'eCO2: %d ppm, TVOC: %d ppb' % (s.eCO2, s.tVOC)
        # doesn't seem to work

    def data_ready(self):
        """returns true if new data was downloaded. Values in .eCO2 and .tVOV"""
        i2c.write(0x5b,b'\x00')
        status = i2c.read(0x5b, 1)
        # bit 3 in the status register: data_ready
        if (status[0] >> 3) & 0x01:
            # datasheet Figure 14: Algorithm Register Byte Order (0x02)
            i2c.write(0x5b,b'\x02')
            register = i2c.read(0x5b, 4)
            co2HB = register[0]
            co2LB = register[1]
            tVOCHB = register[2]
            tVOCLB = register[3]
            self.eCO2 = ((co2HB << 8) | co2LB)
            self.tVOC = ((tVOCHB << 8) | tVOCLB)
            return True
        else:
            return False

    def get_baseline(self):
        i2c.write(0x5b,b'\x011')
        register = i2c.read(0x5b,2)
        HB = register[0]
        LB = register[1]
        #baseline = (HB << 8) | LB
        return HB, LB

    def put_baseline(self,HB,LB):
        register = bytearray([0x00,0x00])
        register[0] = HB
        register[1] = LB
        i2c.write(self.addr,0x11,register)
    
    def put_envdata(self,humidity,temp):
        envregister = bytearray([0x00,0x00,0x00,0x00])
        envregister[0] = int(humidity) << 1
        t = int(temp//1)
        tf = temp % 1
        t_H = (t+25) << 9
        t_L = int(tf*512)
        t_comb = t_H | t_L
        envregister[2] = t_comb >> 8
        envregister[3] = t_comb & 0xFF
        i2c.write(self.addr,0x05,envregister)
        #return envregister



def main():
    #from machine import Pin, I2C
    import time
    #i2c = I2C(scl=Pin(5), sda=Pin(4))
    s = CCS811()
    time.sleep(1)
    while True:
        if s.data_ready():
            print('eCO2: %d ppm, TVOC: %d ppb' % (s.eCO2, s.tVOC))
            time.sleep(1)

main()