// firebase authentication works with firestore database to collect personal data
final CollectionReference _userCollection = FirebaseFirestore.instance.collection('users');
FirebaseAuth.instance.createUserWithEmailAndPassword(email: email, password: password).then((value) {
// set personal user data by user id
_userCollection.doc(FirebaseAuth.instance.currentUser!.uid).set({
"email": email,
"name": name,
"weight": weight,
"height": height,
"age": age,
"gender": gender
});
}