Firestore - Creating a copy of a collection

Question

So I have a collection called "Drafts" which contains multiple documents each with an auto ID. Each document contains the fields "name" and "details". Each document is displayed in a tableViewCell under "nameLabel" and "detailsLabel". What I would like to do is when the user clicks on a button at the top of the screen of the First viewController, a copy of the collection "Drafts" is created and pasted under a new collection name called "Messages". This collection is then referencing the Second viewControllers tableViewCells just like on the First ViewController only this time its being referenced under the collection "Messages". Having done some research I have a vague inclination that the answer uses cloud functions to essentially create a copy of the collection and paste it with a new collection name. However being relatively new to coding and firebase, I have no idea how to do this and don't know if this is the correct solution. Please may someone help, any help is greatly appreciated!! Thanks!

First ViewController

func loadDrafts() {

    let userRef = db.collection("Users").document(user!)

    let draftsRef = userRef.collection("Drafts")

    exercisesRef.getDocuments { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            if let snapshot = querySnapshot {
                for document in snapshot.documents {
                    let data = document.data()
                    let name = data["name"] as? String ?? ""
                    let details = data["details"] as? String ?? ""
                    let newDrafts = DraftMessages(name: name, details: details)
                    self.array.append(newDrafts)
                }
                self.tableView.reloadData()
            }
        }
    }

}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! DraftsCell

    cell.nameLabel.text = array[indexPath.row].name
    cell.detailsLabel.text = array[indexPath.row].details

    return cell
}

@IBAction func goButton(_ sender: UIButton) {

\\ Add code here to create copy of previous collection "Drafts" and paste in new collection "Messages"

}

Second ViewController

func loadData() {

    let userRef = db.collection("Users").document(user!)

    userRef.collection("Messages").getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            for document in querySnapshot!.documents {
                let data = document.data()
                let name = data["name"] as? String ?? ""
                let details = data["details"] as? String ?? ""
                let newMessages = Messages(name: name, details: details)
                self.array.append(newMessages)
            }
            self.tableView.reloadData()
        }
    }
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! MessagesCell

    cell.nameLabel.text = array[indexPath.row].name
    cell.detailsLabel.text = array[indexPath.row].details

    return cell

}

Answer 1

Here is my working solution. Many thanks to Franks for the help!

@IBAction func goButton(_ sender: UIButton) {

    let userRef = db.collection("Users").document(user!)

    let draftsRef = userRef.collection("Drafts")

    draftsRef.getDocuments { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            if let snapshot = querySnapshot {
                for document in snapshot.documents {
                    let data = document.data()
                    let batch = self.db.batch()
                    let docset = querySnapshot

                    let messagesRef = userRef.collection("Messages").document()

                    docset?.documents.forEach {_ in batch.setData(data, forDocument: messagesRef)}

                    batch.commit(completion: { (error) in
                        if let error = error {
                            print("\(error)")
                        } else {
                            print("success")
                        }
                    })
                }
            }
        }
    }
}

Edit for Vaibhav Jhaveri:

This function (hopefully) both duplicates the fetched documents data and the data inside of that documents subcollection. (I have not tested this though)

func duplicate() {
    let userRef = db.collection("Users").document(userID)
    let batch = self.db.batch()

    let draftsRef = userRef.collection("Drafts")
    draftsRef.getDocuments { (snapshot, err) in
        if let err = err {
            print(err.localizedDescription)
            return
        }

        guard let snapshot = snapshot else { return }

        snapshot.documents.forEach({ (document) in
            let data = document.data()
            let messageID = UUID().uuidString

            let messagesRef = userRef.collection("Messages").document(messageID)
            batch.setData(data, forDocument: messagesRef, merge: true)

            let yourSubCollectionRef = draftsRef.document(document.documentID).collection("yourSubCollection")
            yourSubCollectionRef.getDocuments(completion: { (subSnapshot, subErr) in
                if let subErr = subErr {
                    print(subErr.localizedDescription)
                    return
                }

                guard let subSnapshot = subSnapshot else { return }

                subSnapshot.documents.forEach({ (subDocument) in
                    let subData = subDocument.data()
                    let subDocID = UUID().uuidString

                    let yourNewSubCollectionRef = userRef.collection("Messages").document(messageID).collection("yourSubCollection").document(subDocID)
                    batch.setData(subData, forDocument: yourNewSubCollectionRef, merge: true)
                })
            })
        })

        batch.commit()
    }
}