def dayIterator(start: DateTime, end: DateTime, period: String) = {
    period match {
      case "day"   => Iterator.iterate(start)((_ plusDays 1)) takeWhile (_ isBefore end)
      case "week"  => Iterator.iterate(start)(_ plusWeeks 1) takeWhile (_ isBefore end)
      case "month" => Iterator.iterate(start)(_ plusMonths 1) takeWhile (_ isBefore end)
    }
  }

scala> dayIterator(new DateTime("2017-09-13"), new DateTime("2017-09-27"), "week").foreach(println)
    2017-09-13T00:00:00.000+05:30
    2017-09-20T00:00:00.000+05:30

2017-09-13T00:00:00.000+05:30 (Wednesday) -- 2017-09-17T00:00:00.000+05:30 (Sunday)
2017-09-18T00:00:00.000+05:30 (Monday) -- 2017-09-24T00:00:00.000+05:30 (Sunday)
2017-09-25T00:00:00.000+05:30 (Monday) -- 2017-09-27T00:00:00.000+05:30 (Wednesday)