fetching data from firebase - swift

Question

I am new to using firebase, I am trying to fetch data from firebase. I have childIdArray, driverIdArray which I fetch from local database. I call method getLocationFromFirebase using the driverId and dateFormatForDriverLocation(20170505) I use for loop here because I have tableView where I show Estimate time arrival(eta) after calculating the etaArray. I have obseveEventType so that I can listen changes in location of Driver. Problem is I don't get the Index [i] of of Driver whose location is changed.
var etaArray : [String] = []
var childIDArray : [String] = []
var childDriverArray : [Int] = []
var latitudeArray : [Double] = []
var longitudeArray : [Double] = []
var dateFormatForDriverLocation : String?
override func viewDidLoad() {
super.viewDidLoad()
getCurrentLocationFromFirebase()
let date = NSDate()
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyyMMdd"
dateFormatForDriverLocation = dateFormatter.stringFromDate(date)
}
func getCurrentLocationFromFirebase()
{
let myGroup = dispatch_group_create()
for i in 0 ..< self.childDriverArray.count {
dispatch_group_enter(myGroup)
var latitudeDriver = ""
var longitudeDriver = ""
let rootReference = FIRDatabase.database().reference()
let DriverId = String(self.childDriverArray[i])
let pickLat = String(latitudeArray[i])
let pickLong = String(longitudeArray[i])
let driverPath = rootReference.child("gogoapp_driver/\(DriverId)")
driverPath.observeEventType(.Value, withBlock: { snapshot in
if snapshot.hasChild(self.dateFormatForDriverLocation!)
{
if let childSnapshot = snapshot.childSnapshotForPath("\(self.dateFormatForDriverLocation!)") as? FIRDataSnapshot
{
let currentDateData : FIRDataSnapshot = childSnapshot
print(i)
//for getting the last value of location
let child = currentDateData.children.reverse()[0]
if let latitude = child.value!!["latitude"] as? String
{
latitudeDriver = latitude
}
if let longitude = child.value!!["longitude"] as? String
{
longitudeDriver = longitude
}
self.GoogleDistanceMatrixApi(latitudeDriver, driverLong: longitudeDriver, pickUpLat: pickLat, pickUpLong: pickLong, completion: {(success) -> Void in
if success.isEmpty
{
}
else
{
self.etaArray[i] = success
}
})
}
}
})
dispatch_group_leave(myGroup)
}
}
func GoogleDistanceMatrixApi(driverLat : String, driverLong : String, pickUpLat : String, pickUpLong : String, completion:((sucess: String) -> Void)) {
var Text = "as"
completion(sucess: TEXT!)
}