Preprocessor Token for Firebase to avoid initialize Firebase multi-times.

FirebaseInstance.swift

public struct FirebasePreprocessorToken {
    public static let `default` = FirebasePreprocessorToken()

    private init() {
        #if RELEASE
        let googleServiceInfoPlist = "GoogleService-Info"
        #elseif STAGING
        let googleServiceInfoPlist = "GoogleService-Info-Stg"
        #else
        let googleServiceInfoPlist = "GoogleService-Info-Dev"
        #endif
        guard FirebaseApp.app() == nil else { return }
        let plist = Bundle.main.path(forResource: googleServiceInfoPlist, ofType: "plist")!
        let firebaseOptions = FirebaseOptions(contentsOfFile: plist)!
        FirebaseApp.configure(options: firebaseOptions)
    }
}

// ex: For FCM
public class NotificationReceiver: NSObject {

    public static let shared = NotificationReceiver()
    public let token = PublishSubject<FCMToken>()
    public let remoteMessage = PublishSubject<MessagingRemoteMessage>()
    public var apnsToken: Data? {
        return Messaging.messaging().apnsToken
    }
    let disposeBag = DisposeBag()

    var subscribedTopics: Set<FCMTopicModel>

    private init(instance: FirebasePreprocessorToken = .default) {
        subscribedTopics = []
        super.init()
        Messaging.messaging().delegate = self
    }
}

// ex: For Google Analytics for Firebase
public class FirebaseAnalyticsTracker {
    public static let shared = FirebaseAnalyticsTracker()
    private init(token: FirebasePreprocessorToken = .default) {}

    public func track(event: String, parameters: [String: Any] = [:]) {
        Analytics.logEvent(event, parameters: parameters)
    }
}