IoT – Using public dweet.io service, Raspberry Pi and some electronic components, to control Led lighting via mobile phone.

"""
Code taken from Gary Smart book , Practical Python Programming for IoT.
An excellent book for hobbist like me to combine Python with IoT devices/application - ******
"""

import signal
import json
import os
import sys
import logging
from gpiozero import Device, LED
from gpiozero.pins.pigpio import PiGPIOFactory
from time import sleep
from uuid import uuid1
import requests                                                                    # (1)


# Global Variables
LED_GPIO_PIN = 21                   # GPIO Pin 21 on Raspi 3B, pin number is 40(last pin on outer rail)
THING_NAME_FILE = 'thing_name.txt'  # name of file that stores out device ID
URL = 'https://dweet.io'            # Dweet.io service API
last_led_state = None               # Current state of LED ("on", "off", "blinking")
thing_name = None                   # Thing name (as persisted in THING_NAME_FILE)
led = None                          # GPIOZero LED instance


# Initialize Logging, set level to INFO
logging.basicConfig(level=logging.WARNING)  
logger = logging.getLogger('main')  # Using logger for this module
logger.setLevel(logging.INFO)                      


# Initialize GPIO
Device.pin_factory = PiGPIOFactory()


# Function Definitions
def init_led():                                 #Initial and assign led variable
    global led
    led = LED(LED_GPIO_PIN)
    led.off()


def resolve_thing_name(thing_file):
    if os.path.exists(thing_file):                          # if file contains ID, reuse ID for 'thing'(device - Raspi 3B)
        with open(thing_file, 'r') as file_handle:
            name = file_handle.read()
            logger.info('Thing name ' + name + ' loaded from ' + thing_file)
            return name.strip()
    else:
        name = str(uuid1())[:8]  # UUID object to string.    # Else produce a 8 digit ID and write to file,
        logger.info('Created new thing name ' + name)          # for future use(reuse)                              

        with open(thing_file, 'w') as f:                                           
            f.write(name)

    return name


def get_latest_dweet():
    resource = URL + '/get/latest/dweet/for/' + thing_name      # An API request to dweet.io for device latest state
    logger.debug('Getting last dweet from url %s', resource)    # dweet last for 24hrs (free version)

    r = requests.get(resource)                                                     

    if r.status_code == 200:                                 # if Status is ok, get data(json format)
        dweet = r.json()  
        logger.debug('Last dweet for thing was %s', dweet)

        dweet_content = None

        if dweet['this'] == 'succeeded':                        # if there is 'succeeded' text in ['this'],
            
            dweet_content = dweet['with'][0]['content']        # get the key-value pair in ['content']

        return dweet_content

    else:
        logger.error('Getting last dweet failed with http status %s', r.status_code)
        return {}



def poll_dweets_forever(delay_secs=2):
    while True:                              # to consistently ping for dweet for our device
        dweet = get_latest_dweet()                                                
        if dweet is not None:
            process_dweet(dweet)                                                  

            sleep(delay_secs)                                                      



def process_dweet(dweet):
    global last_led_state
                                      # to get the return from get_latest_dweet()and 
                                      # extract the ['state'] value. Can be 'on', 'off' or 'blink'.
    if not 'state' in dweet:
        return

    led_state = dweet['state']

    if led_state == last_led_state:                                               
        return                          # if LED is already in requested state.

    if led_state == 'on':                                                         
        led.on()
    elif led_state == 'blink':
        led.blink()
    else:                               # Off, including any unhandled state.
        led_state = 'off'
        led.off()

    if led_state != last_led_state:                                               
        last_led_state = led_state
        logger.info('LED ' + led_state)


def print_instructions():                                   # some info for user 
    """Print instructions to terminal."""
    print("LED Control URLs - Try them in your web browser:")
    print("  On    : " + URL + "/dweet/for/" + thing_name + "?state=on")
    print("  Off   : " + URL + "/dweet/for/" + thing_name + "?state=off")
    print("  Blink : " + URL + "/dweet/for/" + thing_name + "?state=blink\n")


def signal_handler(sig, frame):                     
    print('You pressed Control+C')          # to handle and capture when Ctrl C is pressed, 
    led.off                                 # which is to exit the application for Linux/Unix OS
    sys.exit(0)




# Initialise led variable and get or set device ID
thing_name = resolve_thing_name(THING_NAME_FILE)     # this thing_name will be use in get_latest_dweet().
init_led()


# Main entry point
if __name__ == '__main__':
    signal.signal(signal.SIGINT, signal_handler)    # Capture CTRL + C
    print_instructions()                                                           

    # Initialise LED from last dweet.
    last_dweet = get_latest_dweet()                                               
    if (last_dweet):
        process_dweet(last_dweet)

    print('Waiting for dweets. Press Control+C to exit.')
    
    poll_dweets_forever()       # Get dweets by polling a URL on a schedule
                                # by pinging dweet.io consistently using get_latest_dweet()