Cannot save Firestore data into global struct - swift

Question

I'm new to Swift and I'm having trouble sending data in my Firestore database to my global data structure (array in a struct). I looked through many similar questions and tried their solutions for hours to no avail, so please help me. I am totally stuck.
I somewhat understand that the problem lies in the initializeDocs() section of my code being asynchronous. I've tried DispatchQueue.main.async as well as completion handlers (although I'm not sure if the way I did them was correct), but I'm still getting the same result- i.e. the Firestore data is not being saved in the struct and I am instead getting back an empty array when I try calling them in my init function. Any help is appreciated.
Here is my code:
struct booksStruc{
static var modelAry = [Model]()
static var titles: [String] = []
static var authors: [String] = []
static var years: [String] = []
static var emails: [String] = []
static var capacity = 0
static var counter = 0
}
init(logo:String, title:String, author:String, year:String, email:String, desc:String) {
let group = DispatchGroup()
ref = Database.database().reference()
super.init()
group.enter()
DispatchQueue.main.async{
self.initializeDocs()
group.leave()
}
self.logoTitle = logo
self.imageTitle = title
self.imageAuthor = author
self.imageYear = year
self.imageEmail = email
self.imageDesc = desc
print("end of init's titles are ", booksStruc.titles)
print("end of init's capacity is ", booksStruc.capacity)
}
func initializeDocs() {
db.collection("books").getDocuments() { (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
let downloadGroup = DispatchGroup()
downloadGroup.enter()
DispatchQueue.main.async{
for document in querySnapshot!.documents {
let dictionary = document.data()
booksStruc.capacity = document.data().capacity
//print("capacity is: ", capacity)
for(key, value) in dictionary{
if(key == "title"){
booksStruc.titles.append(value as! String)
} else if(key == "author"){
booksStruc.authors.append(value as! String)
} else if(key == "year"){
booksStruc.years.append(value as! String)
} else if(key == "email"){
booksStruc.emails.append(value as! String)
}
//print("\(key) : \(value)")
}
}
downloadGroup.leave()
}
}
}
print("titles are ", booksStruc.titles)
print("capacity is ", booksStruc.capacity)
}