SolutionAggregationViewController.swift

//
//  Copyright (c) 2017 Google Inc.
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
//

import UIKit

import FirebaseCore
import FirebaseFirestore

class SolutionAggregationViewController: UIViewController {

  var db: Firestore!

  // [START restaurant_struct]
  struct Restaurant {

    let name: String
    let avgRating: Float
    let numRatings: Int

  }

  let arinell = Restaurant(name: "Arinell Pizza", avgRating: 4.65, numRatings: 683)
  // [END restaurant_struct]

  struct Rating {
    let rating: Float
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    db = Firestore.firestore()
  }

  func getRatingsSubcollection() async {
    // [START get_ratings_subcollection]
    do {
      let snapshot = try await db.collection("restaurants")
        .document("arinell-pizza")
        .collection("ratings")
        .getDocuments()
      print(snapshot)
    } catch {
      print(error)
    }
    // [END get_ratings_subcollection]
  }

  // [START add_rating_transaction]
  func addRatingTransaction(restaurantRef: DocumentReference, rating: Float) async {
    let ratingRef: DocumentReference = restaurantRef.collection("ratings").document()

    do {
      let _ = try await db.runTransaction({ (transaction, errorPointer) -> Any? in
        do {
          let restaurantDocument = try transaction.getDocument(restaurantRef).data()
          guard var restaurantData = restaurantDocument else { return nil }

          // Compute new number of ratings
          let numRatings = restaurantData["numRatings"] as! Int
          let newNumRatings = numRatings + 1

          // Compute new average rating
          let avgRating = restaurantData["avgRating"] as! Float
          let oldRatingTotal = avgRating * Float(numRatings)
          let newAvgRating = (oldRatingTotal + rating) / Float(newNumRatings)

          // Set new restaurant info
          restaurantData["numRatings"] = newNumRatings
          restaurantData["avgRating"] = newAvgRating

          // Commit to Firestore
          transaction.setData(restaurantData, forDocument: restaurantRef)
          transaction.setData(["rating": rating], forDocument: ratingRef)
        } catch {
          // Error getting restaurant data
          // ...
        }

        return nil
      })
    } catch {
      // ...
    }
  }
  // [END add_rating_transaction]

}