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 Foundation

// Include dataBridges client library package
import databridges_sio_swift_client

public class pubsubapp{
    // Initialize dataBridges client
    public var dbridge:databridges_sio_swift_client =  databridges_sio_swift_client()
    public var helloWorld:Subscribe?=nil;
    public var sessionID:String 

    public func randomString(of length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        var s = ""
        for _ in 0 ..< length {
            s.append(letters.randomElement()!)
        }
        return s
    }

    public func Execute() {

        // Replace your application key below, which you have received from dataBridges management portal.
        dbridge.appkey = "____appKey______";

        // Replace your authentication url below, which you have received from dataBridges management portal.
        // example https://endpoint01.databridges.io/client/v1/authenticate
        dbridge.auth_url = "_____URL_____"; 

        // lets create a sessionID
        self.sessionID = self.randomString(7); 
        print("sessionID is \(self.sessionID)")

        try? self.dbridge.connectionstate?.bind("connected", {  (event: Any) in
            print("Connected to dataBridges real-time network !!!") 

            do{
                // Subscribe to channel 'Hello-World'
                try self.helloWorld = (self.dbridge.channel?.subscribe("Hello-World"))!
            }catch {
                let db = error as?  dBError
                print("Channel subscription faced an exception: \(db?.source) \(db?.code) \(db?.message)")
            }

            if (self.helloWorld != nil){
                // We will bind to subscription success event. On success, we will publish event messages.
                try? self.helloWorld?.bind("dbridges:subscribe.success", {  (event: Any ,  metadata: MetaData) in
                    print("dbridges:subscribe.success \(metadata.ToString())")
                    // we can also check if the helloWorld subscription isOnline.
                    if(self.helloWorld.isOnline() != nil){
                        print("Publishing greetings ")
                        do{
                            // Subscribe to channel 'Hello-World'
                            try self.helloWorld?.publish("greetings", "Greetings from " + self.sessionID)
                        }catch {
                            let db = error as?  dBError
                            print("Publishing messages faced an exception:  \(db?.source) \(db?.code) \(db?.message)")
                        }
                     }
                });

                //Bind to the channel.event that you want to process. Here we will bind to 'greetings'
                try? self.helloWorld?.bind("greetings", {  (payload: Any ,  metadata: MetaData) in
                    print("received greeting message : \(payload as! String)")
                });

                // Bind to Subscription failure event, to get notified if subscription to channel has been rejected by dataBridges network
                try? self.helloWorld?.bind("dbridges:subscribe.fail", {  (event: Any ,  metadata: MetaData) in
                    let db = event as?  dBError
                    print("Channel subscription faced an exception: \(db?.source) \(db?.code) \(db?.message)");
                });
            }
        });

        //Bind to disconnected event, to get intimation about dataBridges network disconnection.
        try? self.dbridge.connectionstate?.bind("disconnected", {  (event: Any) in
            print("Disconnected from dataBridges real-time network")
        })

        // Connect to dataBridges. If any runtime error it will be caught in catch().
        do{
            try self.dbridge.connect()
        }catch {
            let db = error as?  dBError
            print("dataBridges Connection exception.. \(db?.source) \(db?.code) \(db?.message)")
        } 
    }
}