Swift push notification

https://firebase.google.com/docs/cloud-messaging/ios/client
    create project
    add required POD
    create apns key in apple developer portal
    upload that token in to firebase project
------------
push notfication in appDelegate method execution steps

didFinishLaunchingWithOptions
didReceiveRegistrationToken  -- this return the push token

        didRegisterForRemoteNotificationsWithDeviceToken  --  this will run when app kill and run again

send notification from firebase
app is in foreground - userNotificationCenter - willPresent
app in bg -
    notification shows in notification bar
    click on notification' - userNotificationCenter - didReceive

app kill and send notification  (same as above)
     notification shows in notification bar
    click on notification' - userNotificationCenter - didReceive

-------------
{
    "to": "PUSH_TOKEN_HERE",
    "notification": {
        "body": "You have authorized LKR 20.00 to test from your A/C *******0269 on 23-04-2018 at 11:10. TXN ID : 20857",
        "title": "Payment Successful !!",
        "icon": ""
    },
    "data": {
        "notificationType": "WEB_PAYMENT",
        "data": {
            "instrumentReference": "W000000000000631"
        }
    }
}

notification  - this part automatically handled by app when only app in background (both android and ios). it shows notification. we need to pass body and title

data - this part only trigger when app is in forground (in both ios & android). we can catch these values inside data object.