Subtract Int with firestore value in Swift - ios

Question

I'm trying to make a coupon system in my app.
When a user has typed in a textfield it should look for a coupon that matches the text.
I've managed to retrieve the correct document but i don't know how to subtract the document fieldvalue "percentOff" from my cart's subtotal.
Here is some code:
My code for getting the document:
func textFieldDidEndEditing(_ textField: UITextField) {
if textField == couponTxt {
let collectionRef = db.collection("coupons")
collectionRef.whereField("name", isEqualTo: couponTxt.text!).getDocuments { (snapshot, err) in
if let err = err {
print("Error getting document: \(err)")
} else {
for document in (snapshot?.documents)! {
if document == document {
let data = document.data()
let couponData = Coupon.init(data: data)
print(document.documentID)
}
}
}
}
}
}
This is my model for getting the data for the coupons:
init(data: [String: Any]) {
self.name = data["name"] as? String ?? ""
self.id = data["id"] as? String ?? ""
self.percentOff = data["percentOff"] as? Double ?? 0.0
self.kronerOff = data["kronerOff"] as? Double ?? 0.0
self.usageLeft = data["usageLeft"] as? Int ?? 0
}
Code from my PaymentCart class - the subtotal:
var subtotal: Int {
var amount = 0
for item in cartItem {
let priceOere = Int(item.price * 100)
amount += priceOere
}
return amount
}
So my question is - now that I can get the correct document how can I get the value from percentOff and minus my current subtotal with that.
Thank you!

Answer 1

When you get the coupon document and create the Coupon object, you must put it somewhere if you want to later access it. Right now, you don't do anything with couponData except initialize it. subtotal is a computed property that needs to access couponData so couponData must be within the scope of this computed property, so just make that happen. For example, if subtotal is in a view controller, then just make couponData an instance property in that same view controller. And then subtotal may look something like this:
var coupon: Coupon?
var subtotal: Int {
var amount = 0
for item in cartItem {
let priceOere = Int(item.price * 100)
amount += priceOere
}
if let coupon = coupon {
let discountRate = 1 - coupon.percentOff // assuming a 10% off coupon is 0.1 and not 10.0
return amount * discountRate
} else {
return amount
}
}
But before you get here, you must assign a value to coupon:
func textFieldDidEndEditing(_ textField: UITextField) {
if textField == couponTxt {
let collectionRef = db.collection("coupons")
collectionRef.whereField("name", isEqualTo: couponTxt.text!).getDocuments { (snapshot, err) in
if let err = err {
print("Error getting document: \(err)")
} else {
for document in (snapshot?.documents)! {
if document == document {
let data = document.data()
let couponData = Coupon(data: data)
self.coupon = couponData // assign it to the instance property
print(document.documentID)
}
}
}
}
}