FirebaseApp Client in Scala

How to properly load the FirebaseAuth Java client in Scala

While I was using the FirebaseAuth Java client, I was getting this error:

Execution exception[[IllegalStateException: FirebaseApp name [DEFAULT] already exists!]]

When my Play application reloaded itself, FirebaseApp.initializeApp() was getting called again from the application loader, which caused this error.

I made a simple wrapper to handle this:

import com.google.auth.oauth2.GoogleCredentials
import com.google.firebase.{ FirebaseOptions, FirebaseApp }

import scala.util.Try

object FirebaseAppLoader {
  def apply(credentials: GoogleCredentials): FirebaseApp = {
    Try(FirebaseApp.getInstance()).toEither match {
      // App hasn't been initialized yet, so we initialize it
      case Left(_: IllegalStateException) =>
        FirebaseApp.initializeApp(
          new FirebaseOptions.Builder()
            .setCredentials(credentials)
            .build
        )
      // Reuse the already-initialized app
      case Right(app) => app
      // Some other exception occurred
      case Left(e) => throw e
    }
  }
}

We simply just try to get the Firebase app instance (wrapped in a Try), and if it doesn't exist, we initialize it, which should happen just once.

Using this wrapper is as simple as val firebaseApp: FirebaseApp = FirebaseAppLoader(credentials). Or with macwire, val firebaseApp: FirebaseApp = wireWith(FirebaseAppLoader(_)).