function auth(email, pass) {
  if (!email || !pass)
    throw new Error(
      "Missing credentials"
    );
  return firebase
    .auth()
    .signIn(email, pass)
    .then(user => {
      return db.collection(
        "users"
      ).doc(user.uid).get();
    })
    .then(snap => {
      if (!snap.exists) {
        return createProfile(
          user.uid
        );
      }
      return snap.data();
    });
}