Pub / Sub app

#    Code a Pub/Sub app to publish 'greetings ' message. The app will also receive the greetings message from other app instances. 
#    We can run 100's of these pub/sub app instances. Each of them will send a single greeting message and will receive greetings from all the other app instances. 

import asyncio 
import string
import random

# Include dataBridges client library package
from databridges_sio_client_lib import dBridges
from databridges_sio_client_lib.exceptions import dBError

class pubSubApp():
    def __init__(self):
        self.dbridge = None
        self.helloWorld = None
        self.sessionID = None 

    # Bind to disconnected event, to get intimation about dataBridges network disconnection.
    async def disconnected(self):
        print("Disconnected from dataBridges real-time network:")

    async def connected(self):
        print("Connected to dataBridges real-time network !!!");
        try:
            # Subscribe to channel 'Hello-World',
            self.helloWorld =  await self.dbridge.channel.subscribe("Hello-World")
        except Exception as dberror:
            print("Channel subscription faced an exception: ", dberror.source, dberror.code, dberror.message)

        if self.helloWorld != None:
            # We will bind to subscription success event. On success, we will publish event messages.
            async def subscribe_success(payload, metadata):
                # we can also check if the helloWorld subscription isOnline.
                if(self.helloWorld.isOnline()):
                    print("Publishing greetings ")
                    try:
                        await self.helloWorld.publish("greetings", "Greetings from " + self.sessionID)
                    except Exception as dberror:
                        print("Publishing messages faced an exception:  ", dberror.source, dberror.code, dberror.message) 

            self.helloWorld.bind("dbridges:subscribe.success", subscribe_success)

            async def subscribe_fail(payload, metadata):
                print("Channel subscription faced an exception:", payload.source, payload.code, payload.message)

            # Bind to Subscription failure event, to get notified if subscription to channel has been rejected by dataBridges network
            self.helloWorld.bind("dbridges:subscribe.fail", subscribe_fail)


            async def greetingEvent(payload, metadata):
                print("received greeting message : ", payload)

            # Bind to the channel.event that you want to process. Here we will bind to 'greetings'
            self.helloWorld.bind("greetings", greetingEvent)


    async def MainExecute(self): 
        #  Initialize dataBridges client
        self.dbridge = dBridges()

        #  Replace your application key below, which you have received from dataBridges management portal.
        #  use system variables for greater security of your keys
        self.dbridge.auth_url = "_____URL_____"

        #  Replace your authentication url below, which you have received from dataBridges management portal.
        #  example https://endpoint01.databridges.io/client/v1/authenticate
        #  use system variables for greater security of your keys
        self.dbridge.appkey = "____appKey______"

        # lets create a sessionID
        self.sessionID = ''.join(random.choices(string.ascii_lowercase + string.digits, k=7))
        print("sessionID is " + self.sessionID); 

        self.dbridge.connectionstate.bind("connected", self.connected) 
        self.dbridge.connectionstate.bind("disconnected", self.disconnected)

        #  Connect to dataBridges. If any runtime error it will be caught in catch().
        try:
            await self.dbridge.connect()
        except dBError as dberror:
            print("dataBridges Connection exception..", dberror.source, dberror.code, dberror.message) 

if __name__ == '__main__':
    try:
        pubSub = pubSubApp()
        asyncio.run(pubSub.MainExecute())
    except Exception as e:
        print(e)