Snippet of the Week: Rating Your App ⭐️

import Foundation

public enum UserSelection: Int {
    case noSelection  = 0
    case writeReview
    case giveFeedback
    case maybeLater
}

/// This helper keeps track of the actions that can trigger the 'Rate our app' dialog.
final public class RateOurAppHelper: NSObject {
    /// A notification with this name is posted
    public static let ShouldShowDialogNotification = "RateOurApp_ShouldShowDialogNotification"
    
    fileprivate let RateOurAppKeys_lastKnownAppVersion = "RateOurAppKeys_lastKnownAppVersion"
    fileprivate let RateOurAppKeys_actionCounter = "RateOurAppKeys_actionCounter"
    fileprivate let RateOurAppKeys_userSelection = "RateOurAppKeys_userSelection"
    
    fileprivate var userDefaults: UserDefaults
    fileprivate var bundle: NWABundle
    
    /// The number of actions needed before we should ask for a rating.
    public fileprivate(set) var actionThreshold: Int
    
    /// The last known app version the helper knows of. If this is the first time the helper is initialized, the current version will be used.
    public fileprivate(set) var lastKnownAppVersion: String {
        didSet {
            userDefaults.setValue(lastKnownAppVersion, forKey: RateOurAppKeys_lastKnownAppVersion)
        }
    }
    /// The action counter keeps track of any positive user actions, after which we _might_ ask for a rating.
    public fileprivate(set) var actionCounter: Int {
        didSet {
            userDefaults.set(actionCounter, forKey: RateOurAppKeys_actionCounter)
        }
    }
    /// The last user selection
    public fileprivate(set) var userSelection: UserSelection {
        didSet {
            userDefaults.set(userSelection.rawValue, forKey: RateOurAppKeys_userSelection)
        }
    }
    
    /// Creates a new helper. Added to make sure that `[RateOurAppHelper new]` doesn't crash the app. Less pretty though.
    convenience override init() {
        self.init(bundle: Bundle.main)
    }
    
    /// Creates a new helper.
    public required init(actionThreshold: Int = 2, userDefaults: UserDefaults = UserDefaults.standard, bundle: NWABundle = Bundle.main) {
        self.userDefaults = userDefaults
        self.bundle = bundle
        self.actionThreshold = actionThreshold
        
        if let appVersion = userDefaults.string(forKey: RateOurAppKeys_lastKnownAppVersion) {
            self.lastKnownAppVersion = appVersion
        }
        else {
            self.lastKnownAppVersion = try! bundle.appVersionNumber()
            // We forcibly ignore the thrown error, since an app can't actually be distributed without a version number.
        }
        
        if let userSelection = UserSelection(rawValue: userDefaults.integer(forKey: RateOurAppKeys_userSelection)) {
            self.userSelection = userSelection
        }
        else {
            self.userSelection = .noSelection
        }
        
        self.actionCounter = userDefaults.integer(forKey: RateOurAppKeys_actionCounter)
        
        super.init()
    }
    
    deinit {
        userDefaults.synchronize()
    }
}

extension RateOurAppHelper {
    /// Resets all values of the helper.
    public func reset() {
        lastKnownAppVersion = ""
        actionCounter = 0
        userSelection = .noSelection
        
        userDefaults.removeObject(forKey: RateOurAppKeys_lastKnownAppVersion)
        userDefaults.removeObject(forKey: RateOurAppKeys_actionCounter)
        userDefaults.removeObject(forKey: RateOurAppKeys_userSelection)
    }
    
    /// To be called every app launch, this performs the migrations that need to happen between app updates. Usually this means resetting any counters to ask for another rating.
    public func performMigration() {
        let currentAppVersion = try! bundle.appVersionNumber()
        
        if currentAppVersion != lastKnownAppVersion {
            lastKnownAppVersion = currentAppVersion
            
            actionCounter = 0
            
            if userSelection != .writeReview {
                userSelection = .noSelection
            }
        }
    }
    
    /// To be called after the user has completed a positive action. This increases the actionCounter by one.
    public func increaseActionCounter() {
        actionCounter += 1
    }
    
    /// To be called if the user is currently in a happy flow and is more likely to leave a positive review or to have some critique.
    /// This checks whether the user should be asked to rate the app. If so, sends out a notification and executes the optional handler. Either one should show the rating dialog.
    ///
    /// - parameters:
    ///   - center: The center which posts the notification. Defaults to `NSNotificationCenter.defaultCenter()`.
    ///   - handler: The handler that is executed to show the rating dialog.
    public func trigger(notificationCenter center: NotificationCenter? = NotificationCenter.default, handler: (() -> Void)? = nil) {
        if shouldAskUser() {
            center?.post(name: Notification.Name(rawValue: RateOurAppHelper.ShouldShowDialogNotification), object: nil)
            handler?()
        }
    }
    
    fileprivate func shouldAskUser() -> Bool {
        let thresholdReached = actionCounter >= actionThreshold
        
        switch userSelection {
        case .noSelection where thresholdReached:
            return true
        default:
            return false
        }
    }
    
    /// To be called after the user has made a selection. This saves the user's selection to refer to later.
    ///
    /// - parameters:
    ///   - selection: The option the user selected.
    public func saveUserSelection(_ selection: UserSelection) {
        userSelection = selection
    }
}

import Foundation

public enum NSBundleError: Error {
    case noAppVersionFound
}

public protocol NWABundle {
    func appVersionNumber() throws -> String
}

extension Bundle: NWABundle {
    fileprivate var NSBundle_AppVersionKey: String { return "CFBundleShortVersionString" }
    
    /// Returns the app's version number.
    ///
    /// - throws: A `NoAppVersionFound` error if the version number was not found.
    /// - returns: The app's version number (e.g. '2.1.0')
    public func appVersionNumber() throws -> String {
        guard let version = object(forInfoDictionaryKey: NSBundle_AppVersionKey) as? String else {
            throw NSBundleError.noAppVersionFound
        }
        return version
    }
}