var db: Firestore!

override func viewDidLoad() {

super.viewDidLoad()

db = Firestore.firestore()

}

// [START counter_structs]

// counters/${ID}

struct Counter {

let numShards: Int

init(numShards: Int) {

self.numShards = numShards

}

}

// counters/${ID}/shards/${NUM}

struct Shard {

let count: Int

init(count: Int) {

self.count = count

}

}

// [END counter_structs]

// [START create_counter]

func createCounter(ref: DocumentReference, numShards: Int) async {

do {

try await ref.setData(["numShards": numShards])

for i in 0...numShards {

try await ref.collection("shards").document(String(i)).setData(["count": 0])

}

} catch {

// ...

}

}

// [END create_counter]

// [START increment_counter]

func incrementCounter(ref: DocumentReference, numShards: Int) {

// Select a shard of the counter at random

let shardId = Int(arc4random_uniform(UInt32(numShards)))

let shardRef = ref.collection("shards").document(String(shardId))

shardRef.updateData([

"count": FieldValue.increment(Int64(1))

])

}

// [END increment_counter]

// [START get_count]

func getCount(ref: DocumentReference) async {

do {

let querySnapshot = try await ref.collection("shards").getDocuments()

var totalCount = 0

for document in querySnapshot.documents {

let count = document.data()["count"] as! Int

totalCount += count

}

print("Total count is \(totalCount)")

} catch {

// handle error

}

}

// [END get_count]