Value after Firestore operation 0 || Swift

Question

I've began writing a Notification/Events app for my School as a Project. Im very new to Swift and Firebase. I used Storybaord.

I have a function that gets the Amount of Events/Posts in the Database:

func getPostCount() -> Int {
        var count = 0
        messageDB.collection("MainPosts").getDocuments()
        {
            (querySnapshot, err) in

            if let err = err
            {
                print("Error getting documents: \(err)");
            }
            else
            {
                for document in querySnapshot!.documents {
                    count += 1
                }
                print(count)    // => should be 10 is 10
            }
            print(count)    // => should be 10 is 10
        }
        print(count)    // => should be 10 is 0
        return count
    }

I'm getting all Documents from the DB and foreach I add 1 to the count. But when i try to return it after the

messageDB.collection("MainPosts").getDocuments(){}

the value is 0. If Im going to try returning the value inside of the Firestore operation I going to get the error:

Unexpected non-void return value in void function

What should i do?

Console:

0
10
10

I think i know why but Im not sure.

Is the function:

messageDB.collection("MainPosts").getDocuments(){}

Async? And if so is there a await keyword or something similar?