fileWriting.scala

/*Enumeratee to manage writing to the file writer. Mapping any errors to Left*/
type ErrorOrActivity = Either[Error,Activity]
    
def fileWriting: Enumeratee[Activity, ErrorOrActivity] = {        
    
    /* writeToFile returns a Promise, but the Enumeratee type constraint 
     * does not expect a Promise. flatMap will return an 
     * Enumeratee[Activity,ErrorOrActivity] given a function from Activity 
     * to Promise[ErrorOrActivity].
     */
    KloutEnumeratee.flatMap[ErrorOrActivity] { activity=>            
        writeToFile(activity.json).map{
            case e @ Failure(_)     => Left(e)
            case _                  => Right(activity) 
        }            
    }
}