filesource.scala

case class Context(local: Boolean)

trait FileSource {
  def readFile(location: String): String
  def writeFile(location: String, content: String): Unit
}
object FileSource {
  def apply(context: Context): FileSource {
    if (context.local) new LocalFileSource(context) else new ExternalFileSource(context)
  }
}

class LocalFileSource(context: Context) extends FileSource {
  // implementation
}

class ExternalFileSource(context: Context) extends FileSource {
  // implementation
}