integ_constraints.ru

service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{uid} {
      allow write: if request.resource.data.age >= 18
                    && request.resource.data.email.matches('.+@.+')
                    && request.resource.data.screenName is string
                    && get(/databases/$(database)/documents/screenNames/$(request.resource.data.screenName)).data.uid == uid
                    && exists(request.resource.data.company);
    }
  }
}